aboutsummaryrefslogtreecommitdiff
path: root/doc/draft-ietf-acme-acme-03.txt
blob: b8f4d87974432a6ff9e3353f2a651d5678c31544 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416




Network Working Group                                          R. Barnes
Internet-Draft                                                   Mozilla
Intended status: Standards Track                      J. Hoffman-Andrews
Expires: January 9, 2017                                             EFF
                                                               J. Kasten
                                                  University of Michigan
                                                           July 08, 2016


          Automatic Certificate Management Environment (ACME)
                        draft-ietf-acme-acme-03

Abstract

   Certificates in the Web's X.509 PKI (PKIX) are used for a number of
   purposes, the most significant of which is the authentication of
   domain names.  Thus, certificate authorities in the Web PKI are
   trusted to verify that an applicant for a certificate legitimately
   represents the domain name(s) in the certificate.  Today, this
   verification is done through a collection of ad hoc mechanisms.  This
   document describes a protocol that a certificate authority (CA) and
   an applicant can use to automate the process of verification and
   certificate issuance.  The protocol also provides facilities for
   other certificate management functions, such as certificate
   revocation.

   DISCLAIMER: This is a work in progress draft of ACME and has not yet
   had a thorough security analysis.

   RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH: The source for
   this draft is maintained in GitHub.  Suggested changes should be
   submitted as pull requests at https://github.com/ietf-wg-acme/acme .
   Instructions are on that page as well.  Editorial changes can be
   managed in GitHub, but any substantive change should be discussed on
   the ACME mailing list (acme@ietf.org).

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any



Barnes, et al.           Expires January 9, 2017                [Page 1]

Internet-Draft                    ACME                         July 2016


   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 9, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Deployment Model and Operator Experience  . . . . . . . . . .   4
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Message Transport . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  HTTPS Requests  . . . . . . . . . . . . . . . . . . . . .   9
     5.2.  Request Authentication  . . . . . . . . . . . . . . . . .   9
     5.3.  Request URI Integrity . . . . . . . . . . . . . . . . . .  10
       5.3.1.  "url" (URL) JWS header parameter  . . . . . . . . . .  10
     5.4.  Replay protection . . . . . . . . . . . . . . . . . . . .  11
       5.4.1.  Replay-Nonce  . . . . . . . . . . . . . . . . . . . .  11
       5.4.2.  "nonce" (Nonce) JWS header parameter  . . . . . . . .  12
     5.5.  Rate limits . . . . . . . . . . . . . . . . . . . . . . .  12
     5.6.  Errors  . . . . . . . . . . . . . . . . . . . . . . . . .  12
   6.  Certificate Management  . . . . . . . . . . . . . . . . . . .  14
     6.1.  Resources . . . . . . . . . . . . . . . . . . . . . . . .  14
       6.1.1.  Directory . . . . . . . . . . . . . . . . . . . . . .  16
       6.1.2.  Registration Objects  . . . . . . . . . . . . . . . .  17
       6.1.3.  Application Objects . . . . . . . . . . . . . . . . .  19
       6.1.4.  Authorization Objects . . . . . . . . . . . . . . . .  21
     6.2.  Registration  . . . . . . . . . . . . . . . . . . . . . .  23
       6.2.1.  Account Key Roll-over . . . . . . . . . . . . . . . .  25
       6.2.2.  Account deactivation  . . . . . . . . . . . . . . . .  27
     6.3.  Applying for Certificate Issuance . . . . . . . . . . . .  28
       6.3.1.  Downloading the Certificate . . . . . . . . . . . . .  30
     6.4.  Identifier Authorization  . . . . . . . . . . . . . . . .  31



Barnes, et al.           Expires January 9, 2017                [Page 2]

Internet-Draft                    ACME                         July 2016


       6.4.1.  Responding to Challenges  . . . . . . . . . . . . . .  33
       6.4.2.  Deactivating an Authorization . . . . . . . . . . . .  35
     6.5.  Certificate Revocation  . . . . . . . . . . . . . . . . .  36
   7.  Identifier Validation Challenges  . . . . . . . . . . . . . .  38
     7.1.  Key Authorizations  . . . . . . . . . . . . . . . . . . .  39
     7.2.  HTTP  . . . . . . . . . . . . . . . . . . . . . . . . . .  40
     7.3.  TLS with Server Name Indication (TLS SNI) . . . . . . . .  42
     7.4.  DNS . . . . . . . . . . . . . . . . . . . . . . . . . . .  44
     7.5.  Out-of-Band . . . . . . . . . . . . . . . . . . . . . . .  45
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  46
     8.1.  Well-Known URI for the HTTP Challenge . . . . . . . . . .  46
     8.2.  Replay-Nonce HTTP Header  . . . . . . . . . . . . . . . .  47
     8.3.  "url" JWS Header Parameter  . . . . . . . . . . . . . . .  47
     8.4.  "nonce" JWS Header Parameter  . . . . . . . . . . . . . .  47
     8.5.  URN Sub-namespace for ACME (urn:ietf:params:acme) . . . .  48
     8.6.  New Registries  . . . . . . . . . . . . . . . . . . . . .  48
       8.6.1.  Error Codes . . . . . . . . . . . . . . . . . . . . .  48
       8.6.2.  Resource Types  . . . . . . . . . . . . . . . . . . .  49
       8.6.3.  Identifier Types  . . . . . . . . . . . . . . . . . .  49
       8.6.4.  Challenge Types . . . . . . . . . . . . . . . . . . .  50
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  50
     9.1.  Threat model  . . . . . . . . . . . . . . . . . . . . . .  51
     9.2.  Integrity of Authorizations . . . . . . . . . . . . . . .  52
     9.3.  Denial-of-Service Considerations  . . . . . . . . . . . .  54
     9.4.  Server-Side Request Forgery . . . . . . . . . . . . . . .  55
     9.5.  CA Policy Considerations  . . . . . . . . . . . . . . . .  55
   10. Operational Considerations  . . . . . . . . . . . . . . . . .  56
     10.1.  DNS over TCP . . . . . . . . . . . . . . . . . . . . . .  56
     10.2.  Default Virtual Hosts  . . . . . . . . . . . . . . . . .  56
     10.3.  Use of DNSSEC Resolvers  . . . . . . . . . . . . . . . .  57
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  57
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  58
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  58
     12.2.  Informative References . . . . . . . . . . . . . . . . .  60
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  61

1.  Introduction

   Certificates in the Web PKI [RFC5280] are most commonly used to
   authenticate domain names.  Thus, certificate authorities in the Web
   PKI are trusted to verify that an applicant for a certificate
   legitimately represents the domain name(s) in the certificate.

   Existing Web PKI certificate authorities tend to run on a set of ad
   hoc protocols for certificate issuance and identity verification.  A
   typical user experience is something like:

   o  Generate a PKCS#10 [RFC2986] Certificate Signing Request (CSR).



Barnes, et al.           Expires January 9, 2017                [Page 3]

Internet-Draft                    ACME                         July 2016


   o  Cut-and-paste the CSR into a CA web page.

   o  Prove ownership of the domain by one of the following methods:

      *  Put a CA-provided challenge at a specific place on the web
         server.

      *  Put a CA-provided challenge at a DNS location corresponding to
         the target domain.

      *  Receive CA challenge at a (hopefully) administrator-controlled
         e-mail address corresponding to the domain and then respond to
         it on the CA's web page.

   o  Download the issued certificate and install it on their Web
      Server.

   With the exception of the CSR itself and the certificates that are
   issued, these are all completely ad hoc procedures and are
   accomplished by getting the human user to follow interactive natural-
   language instructions from the CA rather than by machine-implemented
   published protocols.  In many cases, the instructions are difficult
   to follow and cause significant confusion.  Informal usability tests
   by the authors indicate that webmasters often need 1-3 hours to
   obtain and install a certificate for a domain.  Even in the best
   case, the lack of published, standardized mechanisms presents an
   obstacle to the wide deployment of HTTPS and other PKIX-dependent
   systems because it inhibits mechanization of tasks related to
   certificate issuance, deployment, and revocation.

   This document describes an extensible framework for automating the
   issuance and domain validation procedure, thereby allowing servers
   and infrastructural software to obtain certificates without user
   interaction.  Use of this protocol should radically simplify the
   deployment of HTTPS and the practicality of PKIX authentication for
   other protocols based on TLS [RFC5246].

2.  Deployment Model and Operator Experience

   The major guiding use case for ACME is obtaining certificates for Web
   sites (HTTPS [RFC2818]).  In that case, the server is intended to
   speak for one or more domains, and the process of certificate
   issuance is intended to verify that the server actually speaks for
   the domain(s).

   Different types of certificates reflect different kinds of CA
   verification of information about the certificate subject.  "Domain
   Validation" (DV) certificates are by far the most common type.  For



Barnes, et al.           Expires January 9, 2017                [Page 4]

Internet-Draft                    ACME                         July 2016


   DV validation, the CA merely verifies that the requester has
   effective control of the web server and/or DNS server for the domain,
   but does not explicitly attempt to verify their real-world identity.
   (This is as opposed to "Organization Validation" (OV) and "Extended
   Validation" (EV) certificates, where the process is intended to also
   verify the real-world identity of the requester.)

   DV certificate validation commonly checks claims about properties
   related to control of a domain name - properties that can be observed
   by the issuing authority in an interactive process that can be
   conducted purely online.  That means that under typical
   circumstances, all steps in the request, verification, and issuance
   process can be represented and performed by Internet protocols with
   no out-of-band human intervention.

   When deploying a current HTTPS server, an operator generally gets a
   prompt to generate a self-signed certificate.  When an operator
   deploys an ACME-compatible web server, the experience would be
   something like this:

   o  The ACME client prompts the operator for the intended domain
      name(s) that the web server is to stand for.

   o  The ACME client presents the operator with a list of CAs from
      which it could get a certificate.  (This list will change over
      time based on the capabilities of CAs and updates to ACME
      configuration.)  The ACME client might prompt the operator for
      payment information at this point.

   o  The operator selects a CA.

   o  In the background, the ACME client contacts the CA and requests
      that a certificate be issued for the intended domain name(s).

   o  Once the CA is satisfied, the certificate is issued and the ACME
      client automatically downloads and installs it, potentially
      notifying the operator via e-mail, SMS, etc.

   o  The ACME client periodically contacts the CA to get updated
      certificates, stapled OCSP responses, or whatever else would be
      required to keep the server functional and its credentials up-to-
      date.

   The overall idea is that it's nearly as easy to deploy with a CA-
   issued certificate as a self-signed certificate, and that once the
   operator has done so, the process is self-sustaining with minimal
   manual intervention.  Close integration of ACME with HTTPS servers,
   for example, can allow the immediate and automated deployment of



Barnes, et al.           Expires January 9, 2017                [Page 5]

Internet-Draft                    ACME                         July 2016


   certificates as they are issued, optionally sparing the human
   administrator from additional configuration work.

3.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   The two main roles in ACME are "client" and "server".  The ACME
   client uses the protocol to request certificate management actions,
   such as issuance or revocation.  An ACME client therefore typically
   runs on a web server, mail server, or some other server system which
   requires valid TLS certificates.  The ACME server runs at a
   certificate authority, and responds to client requests, performing
   the requested actions if the client is authorized.

   An ACME client is represented by an "account key pair".  The client
   uses the private key of this key pair to sign all messages sent to
   the server.  The server uses the public key to verify the
   authenticity and integrity of messages from the client.

4.  Protocol Overview

   ACME allows a client to request certificate management actions using
   a set of JSON messages carried over HTTPS.  In some ways, ACME
   functions much like a traditional CA, in which a user creates an
   account, adds identifiers to that account (proving control of the
   domains), and requests certificate issuance for those domains while
   logged in to the account.

   In ACME, the account is represented by an account key pair.  The "add
   a domain" function is accomplished by authorizing the key pair for a
   given domain.  Certificate issuance and revocation are authorized by
   a signature with the key pair.

   The first phase of ACME is for the client to register with the ACME
   server.  The client generates an asymmetric key pair and associates
   this key pair with a set of contact information by signing the
   contact information.  The server acknowledges the registration by
   replying with a registration object echoing the client's input.  The
   server can also provide terms of service at this stage, which the
   client can present to a human user.








Barnes, et al.           Expires January 9, 2017                [Page 6]

Internet-Draft                    ACME                         July 2016


         Client                                                  Server

         Contact Information
         Signature                     ------->

                                       <-------            Registration
                                                       Terms of Service

   Once the client is registered, there are three major steps it needs
   to take to get a certificate:

   1.  Apply for a certificate to be issued

   2.  Fulfill the server's requirements for issuance

   3.  Finalize the application and request issuance

   The client's application for a certificate describes the desired
   certificate using a PKCS#10 Certificate Signing Request (CSR) plus a
   few additional fields that capture semantics that are not supported
   in the CSR format.  If the server is willing to consider issuing such
   a certificate, it responds with a list of requirements that the
   client must satisfy before the certificate will be issued.

   For example, in most cases, the server will require the client to
   demonstrate that it controls the identifiers in the requested
   certificate.  Because there are many different ways to validate
   possession of different types of identifiers, the server will choose
   from an extensible set of challenges that are appropriate for the
   identifier being claimed.  The client responds with a set of
   responses that tell the server which challenges the client has
   completed.  The server then validates the challenges to check that
   the client has accomplished the challenge.

   Once the validation process is complete and the server is satisfied
   that the client has met its requirements, the server can either
   proactively issue the requested certificate or wait for the client to
   request that the application be "finalized", at which point the
   certificate will be issued and provided to the client.












Barnes, et al.           Expires January 9, 2017                [Page 7]

Internet-Draft                    ACME                         July 2016


         Application
         Signature                     ------->
                                       <-------            Requirements
                                                     (e.g., Challenges)

         Responses
         Signature                     ------->

                             <~~~~~~~~Validation~~~~~~~~>

         Finalize application
         Signature                     ------->
                                       <-------             Certificate

   To revoke a certificate, the client simply sends a revocation request
   indicating the certificate to be revoked, signed with an authorized
   key pair.  The server indicates whether the request has succeeded.

         Client                                                 Server

         Revocation request
         Signature                    -------->

                                      <--------                 Result

   Note that while ACME is defined with enough flexibility to handle
   different types of identifiers in principle, the primary use case
   addressed by this document is the case where domain names are used as
   identifiers.  For example, all of the identifier validation
   challenges described in Section 7 below address validation of domain
   names.  The use of ACME for other protocols will require further
   specification, in order to describe how these identifiers are encoded
   in the protocol, and what types of validation challenges the server
   might require.

5.  Message Transport

   Communications between an ACME client and an ACME server are done
   over HTTPS, using JWS to provide some additional security properties
   for messages sent from the client to the server.  HTTPS provides
   server authentication and confidentiality.  With some ACME-specific
   extensions, JWS provides authentication of the client's request
   payloads, anti-replay protection, and integrity for the HTTPS request
   URI.







Barnes, et al.           Expires January 9, 2017                [Page 8]

Internet-Draft                    ACME                         July 2016


5.1.  HTTPS Requests

   Each ACME function is accomplished by the client sending a sequence
   of HTTPS requests to the server, carrying JSON messages
   [RFC2818][RFC7159].  Use of HTTPS is REQUIRED.  Clients SHOULD
   support HTTP public key pinning [RFC7469], and servers SHOULD emit
   pinning headers.  Each subsection of Section 6 below describes the
   message formats used by the function, and the order in which messages
   are sent.

   In all HTTPS transactions used by ACME, the ACME client is the HTTPS
   client and the ACME server is the HTTPS server.

   ACME servers that are intended to be generally accessible need to use
   Cross-Origin Resource Sharing (CORS) in order to be accessible from
   browser-based clients [W3C.CR-cors-20130129].  Such servers SHOULD
   set the Access-Control-Allow-Origin header field to the value "*".

   Binary fields in the JSON objects used by ACME are encoded using
   base64url encoding described in [RFC4648] Section 5, according to the
   profile specified in JSON Web Signature [RFC7515] Section 2.  This
   encoding uses a URL safe character set.  Trailing '=' characters MUST
   be stripped.

5.2.  Request Authentication

   All ACME requests with a non-empty body MUST encapsulate the body in
   a JWS object, signed using the account key pair.  The server MUST
   verify the JWS before processing the request.  (For readability,
   however, the examples below omit this encapsulation.)  Encapsulating
   request bodies in JWS provides a simple authentication of requests by
   way of key continuity.

   JWS objects sent in ACME requests MUST meet the following additional
   criteria:

   o  The JWS MUST be encoded using UTF-8

   o  The JWS MUST NOT have the value "none" in its "alg" field

   o  The JWS Protected Header MUST include the following fields:

      *  "alg"

      *  "jwk"

      *  "nonce" (defined below)




Barnes, et al.           Expires January 9, 2017                [Page 9]

Internet-Draft                    ACME                         July 2016


      *  "url" (defined below)

   Note that this implies that GET requests are not authenticated.
   Servers MUST NOT respond to GET requests for resources that might be
   considered sensitive.

   In the examples below, JWS objects are shown in the JSON or flattened
   JSON serialization, with the protected header and payload expressed
   as base64url(content) instead of the actual base64-encoded value, so
   that the content is readable.  Some fields are omitted for brevity,
   marked with "...".

5.3.  Request URI Integrity

   It is common in deployment the entity terminating TLS for HTTPS to be
   different from the entity operating the logical HTTPS server, with a
   "request routing" layer in the middle.  For example, an ACME CA might
   have a content delivery network terminate TLS connections from
   clients so that it can inspect client requests for denial-of-service
   protection.

   These intermediaries can also change values in the request that are
   not signed in the HTTPS request, e.g., the request URI and headers.
   ACME uses JWS to provide a limited integrity mechanism, which
   protects against an intermediary changing the request URI to another
   ACME URI of a different type.  (It does not protect against changing
   between URIs of the same type, e.g., from one authorization URI to
   another).

   As noted above, all ACME request object carry a "url" parameter in
   their protected header.  This header parameter encodes the URL to
   which the client is directing the request.  On receiving such an
   object in an HTTP request, the server MUST compare the "url"
   parameter to the request URI.  If the two do not match, then the
   server MUST reject the request as unauthorized.

   Except for the directory resource, all ACME resources are addressed
   with URLs provided to the client by the server.  In such cases, the
   client MUST set the "url" field to the exact string provided by the
   server (rather than performing any re-encoding on the URL).

5.3.1.  "url" (URL) JWS header parameter

   The "url" header parameter specifies the URL to which this JWS object
   is directed [RFC3986].  The "url" parameter MUST be carried in the
   protected header of the JWS.  The value of the "nonce" header MUST be
   a JSON string representing the URL.




Barnes, et al.           Expires January 9, 2017               [Page 10]

Internet-Draft                    ACME                         July 2016


5.4.  Replay protection

   In order to protect ACME resources from any possible replay attacks,
   ACME requests have a mandatory anti-replay mechanism.  This mechanism
   is based on the server maintaining a list of nonces that it has
   issued to clients, and requiring any signed request from the client
   to carry such a nonce.

   An ACME server MUST include a Replay-Nonce header field in each
   successful response it provides to a client, with contents as
   specified below.  In particular, the ACME server MUST provide a
   Replay-Nonce header field in response to a HEAD request for any valid
   resource.  (This allows clients to easily obtain a fresh nonce.)  It
   MAY also provide nonces in error responses.

   Every JWS sent by an ACME client MUST include, in its protected
   header, the "nonce" header parameter, with contents as defined below.
   As part of JWS verification, the ACME server MUST verify that the
   value of the "nonce" header is a value that the server previously
   provided in a Replay-Nonce header field.  Once a nonce value has
   appeared in an ACME request, the server MUST consider it invalid, in
   the same way as a value it had never issued.

   When a server rejects a request because its nonce value was
   unacceptable (or not present), it SHOULD provide HTTP status code 400
   (Bad Request), and indicate the ACME error code
   "urn:ietf:params:acme:error:badNonce".

   The precise method used to generate and track nonces is up to the
   server.  For example, the server could generate a random 128-bit
   value for each response, keep a list of issued nonces, and strike
   nonces from this list as they are used.

5.4.1.  Replay-Nonce

   The "Replay-Nonce" header field includes a server-generated value
   that the server can use to detect unauthorized replay in future
   client requests.  The server should generate the value provided in
   Replay-Nonce in such a way that they are unique to each message, with
   high probability.

   The value of the Replay-Nonce field MUST be an octet string encoded
   according to the base64url encoding described in Section 2 of
   [RFC7515].  Clients MUST ignore invalid Replay-Nonce values.

     base64url = [A-Z] / [a-z] / [0-9] / "-" / "_"

     Replay-Nonce = *base64url



Barnes, et al.           Expires January 9, 2017               [Page 11]

Internet-Draft                    ACME                         July 2016


   The Replay-Nonce header field SHOULD NOT be included in HTTP request
   messages.

5.4.2.  "nonce" (Nonce) JWS header parameter

   The "nonce" header parameter provides a unique value that enables the
   verifier of a JWS to recognize when replay has occurred.  The "nonce"
   header parameter MUST be carried in the protected header of the JWS.

   The value of the "nonce" header parameter MUST be an octet string,
   encoded according to the base64url encoding described in Section 2 of
   [RFC7515].  If the value of a "nonce" header parameter is not valid
   according to this encoding, then the verifier MUST reject the JWS as
   malformed.

5.5.  Rate limits

   Creation of resources can be rate limited to ensure fair usage and
   prevent abuse.  Once the rate limit is exceeded, the server MUST
   respond with an error with the code "rateLimited".  Additionally, the
   server SHOULD send a "Retry-After" header indicating when the current
   request may succeed again.  If multiple rate limits are in place,
   that is the time where all rate limits allow access again for the
   current request with exactly the same parameters.

   In addition to the human readable "detail" field of the error
   response, the server MAY send one or multiple tokens in the "Link"
   header pointing to documentation about the specific hit rate limits
   using the "rate-limit" relation.

5.6.  Errors

   Errors can be reported in ACME both at the HTTP layer and within ACME
   payloads.  ACME servers can return responses with an HTTP error
   response code (4XX or 5XX).  For example: If the client submits a
   request using a method not allowed in this document, then the server
   MAY return status code 405 (Method Not Allowed).

   When the server responds with an error status, it SHOULD provide
   additional information using problem document [RFC7807].  To
   facilitate automatic response to errors, this document defines the
   following standard tokens for use in the "type" field (within the
   "urn:ietf:params:acme:error:" namespace):








Barnes, et al.           Expires January 9, 2017               [Page 12]

Internet-Draft                    ACME                         July 2016


   +-----------------------+-------------------------------------------+
   | Code                  | Description                               |
   +-----------------------+-------------------------------------------+
   | badCSR                | The CSR is unacceptable (e.g., due to a   |
   |                       | short key)                                |
   |                       |                                           |
   | badNonce              | The client sent an unacceptable anti-     |
   |                       | replay nonce                              |
   |                       |                                           |
   | connection            | The server could not connect to           |
   |                       | validation target                         |
   |                       |                                           |
   | dnssec                | DNSSEC validation failed                  |
   |                       |                                           |
   | caa                   | CAA records forbid the CA from issuing    |
   |                       |                                           |
   | malformed             | The request message was malformed         |
   |                       |                                           |
   | serverInternal        | The server experienced an internal error  |
   |                       |                                           |
   | tls                   | The server received a TLS error during    |
   |                       | validation                                |
   |                       |                                           |
   | unauthorized          | The client lacks sufficient authorization |
   |                       |                                           |
   | unknownHost           | The server could not resolve a domain     |
   |                       | name                                      |
   |                       |                                           |
   | rateLimited           | The request exceeds a rate limit          |
   |                       |                                           |
   | invalidContact        | The contact URI for a registration was    |
   |                       | invalid                                   |
   |                       |                                           |
   | rejectedIdentifier    | The server will not issue for the         |
   |                       | identifier                                |
   |                       |                                           |
   | unsupportedIdentifier | Identifier is not supported, but may be   |
   |                       | in future                                 |
   +-----------------------+-------------------------------------------+

   This list is not exhaustive.  The server MAY return errors whose
   "type" field is set to a URI other than those defined above.  Servers
   MUST NOT use the ACME URN namespace for errors other than the
   standard types.  Clients SHOULD display the "detail" field of such
   errors.






Barnes, et al.           Expires January 9, 2017               [Page 13]

Internet-Draft                    ACME                         July 2016


   Authorization and challenge objects can also contain error
   information to indicate why the server was unable to validate
   authorization.

6.  Certificate Management

   In this section, we describe the certificate management functions
   that ACME enables:

   o  Account Key Registration

   o  Application for a Certificate

   o  Account Key Authorization

   o  Certificate Issuance

   o  Certificate Revocation

6.1.  Resources

   ACME is structured as a REST application with a few types of
   resources:

   o  Registration resources, representing information about an account

   o  Application resources, represnting an account's requests to issue
      certificates

   o  Authorization resources, representing an account's authorization
      to act for an identifier

   o  Challenge resources, representing a challenge to prove control of
      an identifier

   o  Certificate resources, representing issued certificates

   o  A "directory" resource

   o  A "new-registration" resource

   o  A "new-application" resource

   o  A "revoke-certificate" resource

   o  A "key-change" resource





Barnes, et al.           Expires January 9, 2017               [Page 14]

Internet-Draft                    ACME                         July 2016


   For the "new-X" resources above, the server MUST have exactly one
   resource for each function.  This resource may be addressed by
   multiple URIs, but all must provide equivalent functionality.

   ACME uses different URIs for different management functions.  Each
   function is listed in a directory along with its corresponding URI,
   so clients only need to be configured with the directory URI.  These
   URIs are connected by a few different link relations [RFC5988].

   The "up" link relation is used with challenge resources to indicate
   the authorization resource to which a challenge belongs.  It is also
   used from certificate resources to indicate a resource from which the
   client may fetch a chain of CA certificates that could be used to
   validate the certificate in the original resource.

   The "directory" link relation is present on all resources other than
   the directory and indicates the directory URL.

   The following diagram illustrates the relations between resources on
   an ACME server.  For the most part, these relations are expressed by
   URLs provided as strings in the resources' JSON representations.
   Lines with labels in quotes indicate HTTP link relations

                                  directory
                                      |
                                      |
          ----------------------------------------------------
          |                  |                               |
          |                  |                               |
          V                  V                               V
       new-reg            new-app                       revoke-cert
          |                  |                               ^
          |                  |                               | "revoke"
          V                  V                               |
         reg -------------> app -------------> cert ---------+
                            | ^                  |
                            | | "up"             | "up"
                            V |                  V
                           authz             cert-chain
                            | ^
                            | | "up"
                            V |
                          challenge

   The following table illustrates a typical sequence of requests
   required to establish a new account with the server, prove control of
   an identifier, issue a certificate, and fetch an updated certificate




Barnes, et al.           Expires January 9, 2017               [Page 15]

Internet-Draft                    ACME                         July 2016


   some time after issuance.  The "->" is a mnemonic for a Location
   header pointing to a created resource.

           +--------------------+----------------+------------+
           | Action             | Request        | Response   |
           +--------------------+----------------+------------+
           | Register           | POST new-reg   | 201 -> reg |
           |                    |                |            |
           | Apply for a cert   | POST new-app   | 201 -> app |
           |                    |                |            |
           | Fetch challenges   | GET  authz     | 200        |
           |                    |                |            |
           | Answer challenges  | POST challenge | 200        |
           |                    |                |            |
           | Poll for status    | GET  authz     | 200        |
           |                    |                |            |
           | Request issuance   | POST app       | 200        |
           |                    |                |            |
           | Check for new cert | GET  cert      | 200        |
           +--------------------+----------------+------------+

   The remainder of this section provides the details of how these
   resources are structured and how the ACME protocol makes use of them.

6.1.1.  Directory

   In order to help clients configure themselves with the right URIs for
   each ACME operation, ACME servers provide a directory object.  This
   should be the only URL needed to configure clients.  It is a JSON
   dictionary, whose keys are drawn from the following table and whose
   values are the corresponding URLs.

                   +-------------+--------------------+
                   | Key         | URL in value       |
                   +-------------+--------------------+
                   | new-reg     | New registration   |
                   |             |                    |
                   | new-app     | New application    |
                   |             |                    |
                   | revoke-cert | Revoke certificate |
                   |             |                    |
                   | key-change  | Key change         |
                   +-------------+--------------------+

   There is no constraint on the actual URI of the directory except that
   it should be different from the other ACME server resources' URIs,
   and that it should not clash with other services.  For instance:




Barnes, et al.           Expires January 9, 2017               [Page 16]

Internet-Draft                    ACME                         July 2016


   o  a host which function as both an ACME and Web server may want to
      keep the root path "/" for an HTML "front page", and and place the
      ACME directory under path "/acme".

   o  a host which only functions as an ACME server could place the
      directory under path "/".

   The dictionary MAY additionally contain a key "meta".  If present, it
   MUST be a JSON dictionary; each item in the dictionary is an item of
   metadata relating to the service provided by the ACME server.

   The following metadata items are defined, all of which are OPTIONAL:

   "terms-of-service" (optional, string):  A URI identifying the current
      terms of service.

   "website" (optional, string)):  An HTTP or HTTPS URL locating a
      website providing more information about the ACME server.

   "caa-identities" (optional, array of string):  Each string MUST be a
      lowercase hostname which the ACME server recognises as referring
      to itself for the purposes of CAA record validation as defined in
      [RFC6844].  This allows clients to determine the correct issuer
      domain name to use when configuring CAA record.

   Clients access the directory by sending a GET request to the
   directory URI.

   HTTP/1.1 200 OK
   Content-Type: application/json

   {
     "new-reg": "https://example.com/acme/new-reg",
     "new-app": "https://example.com/acme/new-app",
     "revoke-cert": "https://example.com/acme/revoke-cert",
     "key-change": "https://example.com/acme/key-change",
     "meta": {
       "terms-of-service": "https://example.com/acme/terms",
       "website": "https://www.example.com/",
       "caa-identities": ["example.com"]
     }
   }

6.1.2.  Registration Objects

   An ACME registration resource represents a set of metadata associated
   to an account key pair.  Registration resources have the following
   structure:



Barnes, et al.           Expires January 9, 2017               [Page 17]

Internet-Draft                    ACME                         July 2016


   key (required, dictionary):  The public key of the account key pair,
      encoded as a JSON Web Key object [RFC7517].

   status (required, string):  "good" or "deactivated"

   contact (optional, array of string):  An array of URIs that the
      server can use to contact the client for issues related to this
      authorization.  For example, the server may wish to notify the
      client about server-initiated revocation.

   agreement (optional, string):  A URI referring to a subscriber
      agreement or terms of service provided by the server (see below).
      Including this field indicates the client's agreement with the
      referenced terms.

   applications (required, string):  A URI from which a list of
      authorizations submitted by this account can be fetched via a GET
      request.  The result of the GET request MUST be a JSON object
      whose "applications" field is an array of strings, where each
      string is the URI of an authorization belonging to this
      registration.  The server SHOULD include pending applications, and
      SHOULD NOT include applications that are invalid.  The server MAY
      return an incomplete list, along with a Link header with link
      relation "next" indicating a URL to retrieve further entries.

   certificates (required, string):  A URI from which a list of
      certificates issued for this account can be fetched via a GET
      request.  The result of the GET request MUST be a JSON object
      whose "certificates" field is an array of strings, where each
      string is the URI of a certificate.  The server SHOULD NOT include
      expired or revoked certificates.  The server MAY return an
      incomplete list, along with a Link header with link relation
      "next" indicating a URL to retrieve further entries.

   {
     "contact": [
       "mailto:cert-admin@example.com",
       "tel:+12025551212"
     ],
     "agreement": "https://example.com/acme/terms",
     "authorizations": "https://example.com/acme/reg/1/authz",
     "certificates": "https://example.com/acme/reg/1/cert"
   }








Barnes, et al.           Expires January 9, 2017               [Page 18]

Internet-Draft                    ACME                         July 2016


6.1.3.  Application Objects

   An ACME registration resource represents a client's request for a
   certificate, and is used to track the progress of that application
   through to issuance.  Thus, the object contains information about the
   requested certificate, the server's requirements, and any
   certificates that have resulted from this application.

   status (required, string):  The status of this authorization.
      Possible values are: "unknown", "pending", "processing", "valid",
      and "invalid".

   expires (optional, string):  The timestamp after which the server
      will consider this application invalid, encoded in the format
      specified in RFC 3339 [RFC3339].  This field is REQUIRED for
      objects with "pending" or "valid" in the status field.

   csr (required, string):  A CSR encoding the parameters for the
      certificate being requested [RFC2986].  The CSR is sent in the
      Base64url-encoded version of the DER format.  (Note: This field
      uses the same modified Base64 encoding rules used elsewhere in
      this document, so it is different from PEM.)

   notBefore (optional, string):  The requested value of the notBefore
      field in the certificate, in the date format defined in [RFC3339]

   notAfter (optional, string):  The requested value of the notAfter
      field in the certificate, in the date format defined in [RFC3339]

   requirements (required, array):  The requirements that the client
      needs to fulfill before the requested certificate can be granted
      (for pending applications).  For final applications, the
      requirements that were met.  Each entry is a dictionary with
      parameters describing the requirement (see below).

   certificate (optional, string):  A URL for the certificate that has
      been issued in response to this application.














Barnes, et al.           Expires January 9, 2017               [Page 19]

Internet-Draft                    ACME                         July 2016


   {
     "status": "pending",
     "expires": "2015-03-01T14:09:00Z",

     "csr": "jcRf4uXra7FGYW5ZMewvV...rhlnznwy8YbpMGqwidEXfE",
     "notBefore": "2016-01-01T00:00:00Z",
     "notAfter": "2016-01-08T00:00:00Z",

     "requirements": [
       {
         "type": "authorization",
         "status": "valid",
         "url": "https://example.com/acme/authz/1234"
       },
       {
         "type": "out-of-band",
         "status": "pending",
         "url": "https://example.com/acme/payment/1234"
       }
     ]

     "certificate": "https://example.com/acme/cert/1234"
   }

   [[ Open issue: There are two possible behaviors for the CA here.
   Either (a) the CA automatically issues once all the requirements are
   fulfilled, or (b) the CA waits for confirmation from the client that
   it should issue.  If we allow both, we will need a signal in the
   application object of whether confirmation is required.  I would
   prefer that auto-issue be the default, which would imply a syntax
   like "confirm": true ]]

   [[ Open issue: Should this syntax allow multiple certificates?  That
   would support reissuance / renewal in a straightforward way,
   especially if the CSR / notBefore / notAfter could be updated. ]]

   The elements of the "requirements" array are immutable once set,
   except for their "status" fields.  If any other part of the object
   changes after the object is created, the client MUST consider the
   application invalid.

   The "requirements" array in the challenge SHOULD reflect everything
   that the CA required the client to do before issuance, even if some
   requirements were fulfilled in earlier applications.  For example, if
   a CA allows multiple applications to be fufilled based on a single
   authorization transaction, then it must reflect that authorization in
   all of the applications.




Barnes, et al.           Expires January 9, 2017               [Page 20]

Internet-Draft                    ACME                         July 2016


   Each entry in the "requirements" array expresses a requirement from
   the CA for the client to takek a particular action.  All requirements
   objects have the following basic fields:

   type (required, string):  The type of requirement (see below for
      defined types)

   status (required, string):  The status of this requirement.  Possible
      values are: "pending", "valid", and "invalid".

   All additional fields are specified by the requirement type.

6.1.3.1.  Authorization Requirement

   A requirement with type "authorization" requests that the ACME client
   complete an authorization transaction.  The server specifies the
   authorization by pre-provisioning a pending authorization resource
   and providing the URI for this resource in the requirement.

   url (required, string):  The URL for the authorization resource

   To fulfill this requirement, the ACME client should fetch the
   authorization object from the indicated URL, then follow the process
   for obtaining authorization as specified in Section 6.4.

6.1.3.2.  Out-of-Band Requirement

   A requirement with type "out-of-band" requests that the ACME client
   have a human user visit a web page in order to receive further
   instructions for how to fulfill the requirement.  The requirement
   object provides a URI for the web page to be visited.

   url (required, string):  The URL to be visited.  The scheme of this
      URL MUST be "http" or "https"

   To fulfill this requirement, the ACME client should direct the user
   to the indicated web page.

6.1.4.  Authorization Objects

   An ACME authorization object represents server's authorization for an
   account to represent an identifier.  In addition to the identifier,
   an authorization includes several metadata fields, such as the status
   of the authorization (e.g., "pending", "valid", or "revoked") and
   which challenges were used to validate possession of the identifier.

   The structure of an ACME authorization resource is as follows:




Barnes, et al.           Expires January 9, 2017               [Page 21]

Internet-Draft                    ACME                         July 2016


   identifier (required, dictionary of string):  The identifier that the
      account is authorized to represent

      type (required, string):  The type of identifier.

      value (required, string):  The identifier itself.

   status (required, string):  The status of this authorization.
      Possible values are: "unknown", "pending", "processing", "valid",
      "invalid" and "revoked".  If this field is missing, then the
      default value is "pending".

   expires (optional, string):  The timestamp after which the server
      will consider this authorization invalid, encoded in the format
      specified in RFC 3339 [RFC3339].  This field is REQUIRED for
      objects with "valid" in the "status field.

   scope (optional, string):  If this field is present, then it MUST
      contain a URI for an application resource, such that this
      authorization is only valid for that resource.  If this field is
      absent, then the CA MUST consider this authorization valid for all
      applications until the authorization expires. [[ Open issue: More
      flexible scoping? ]]

   challenges (required, array):  The challenges that the client needs
      to fulfill in order to prove possession of the identifier (for
      pending authorizations).  For final authorizations, the challenges
      that were used.  Each array entry is a dictionary with parameters
      required to validate the challenge, as specified in Section 7.

   combinations (optional, array of arrays of integers):  A collection
      of sets of challenges, each of which would be sufficient to prove
      possession of the identifier.  Clients complete a set of
      challenges that covers at least one set in this array.  Challenges
      are identified by their indices in the challenges array.  If no
      "combinations" element is included in an authorization object, the
      client completes all challenges.

   The only type of identifier defined by this specification is a fully-
   qualified domain name (type: "dns").  The value of the identifier
   MUST be the ASCII representation of the domain name.  Wildcard domain
   names (with "*" as the first label) MUST NOT be included in
   authorization requests.








Barnes, et al.           Expires January 9, 2017               [Page 22]

Internet-Draft                    ACME                         July 2016


   {
     "status": "valid",
     "expires": "2015-03-01T14:09:00Z",

     "identifier": {
       "type": "dns",
       "value": "example.org"
     },

     "challenges": [
       {
         "type": "http-01",
         "status": "valid",
         "validated": "2014-12-01T12:05:00Z",
         "keyAuthorization": "SXQe-2XODaDxNR...vb29HhjjLPSggwiE"
       }
     ]
   }

6.2.  Registration

   A client creates a new account with the server by sending a POST
   request to the server's new-registration URI.  The body of the
   request is a stub registration object containing only the "contact"
   field.

   POST /acme/new-reg HTTP/1.1
   Host: example.com
   Content-Type: application/jose+json

   {
     "protected": base64url({
       "alg": "ES256",
       "jwk": {...},
       "nonce": "6S8IqOGY7eL2lsGoTZYifg",
       "url": "https://example.com/acme/new-reg"
     })
     "payload": base64url({
       "contact": [
         "mailto:cert-admin@example.com",
         "tel:+12025551212"
       ]
     }),
     "signature": "RZPOnYoPs1PhjszF...-nh6X1qtOFPB519I"
   }

   The server MUST ignore any values provided in the "key",
   "authorizations", and "certificates" fields in registration bodies



Barnes, et al.           Expires January 9, 2017               [Page 23]

Internet-Draft                    ACME                         July 2016


   sent by the client, as well as any other fields that it does not
   recognize.  If new fields are specified in the future, the
   specification of those fields MUST describe whether they may be
   provided by the client.

   The server creates a registration object with the included contact
   information.  The "key" element of the registration is set to the
   public key used to verify the JWS (i.e., the "jwk" element of the JWS
   header).  The server returns this registration object in a 201
   (Created) response, with the registration URI in a Location header
   field.

   If the server already has a registration object with the provided
   account key, then it MUST return a 409 (Conflict) response and
   provide the URI of that registration in a Location header field.
   This allows a client that has an account key but not the
   corresponding registration URI to recover the registration URI.

   If the server wishes to present the client with terms under which the
   ACME service is to be used, it MUST indicate the URI where such terms
   can be accessed in a Link header with link relation "terms-of-
   service".  As noted above, the client may indicate its agreement with
   these terms by updating its registration to include the "agreement"
   field, with the terms URI as its value.  When these terms change in a
   way that requires an agreement update, the server MUST use a
   different URI in the Link header.

   HTTP/1.1 201 Created
   Content-Type: application/json
   Location: https://example.com/acme/reg/asdf
   Link: <https://example.com/acme/terms>;rel="terms-of-service"
   Link: <https://example.com/acme/some-directory>;rel="directory"

   {
     "key": { /* JWK from JWS header */ },
     "status": "good",

     "contact": [
       "mailto:cert-admin@example.com",
       "tel:+12025551212"
     ]
   }

   If the client wishes to update this information in the future, it
   sends a POST request with updated information to the registration
   URI.  The server MUST ignore any updates to the "key",
   "authorizations, or "certificates" fields, and MUST verify that the




Barnes, et al.           Expires January 9, 2017               [Page 24]

Internet-Draft                    ACME                         July 2016


   request is signed with the private key corresponding to the "key"
   field of the request before updating the registration.

   For example, to update the contact information in the above
   registration, the client could send the following request:

   POST /acme/reg/asdf HTTP/1.1
   Host: example.com
   Content-Type: application/jose+json

   {
     "protected": base64url({
       "alg": "ES256",
       "jwk": {...},
       "nonce": "ax5RnthDqp_Yf4_HZnFLmA",
       "url": "https://example.com/acme/reg/asdf"
     })
     "payload": base64url({
       "contact": [
         "mailto:certificates@example.com",
         "tel:+12125551212"
       ]
     }),
     "signature": "hDXzvcj8T6fbFbmn...rDzXzzvzpRy64N0o"
   }

   Servers SHOULD NOT respond to GET requests for registration resources
   as these requests are not authenticated.  If a client wishes to query
   the server for information about its account (e.g., to examine the
   "contact" or "certificates" fields), then it SHOULD do so by sending
   a POST request with an empty update.  That is, it should send a JWS
   whose payload is trivial ({}).

6.2.1.  Account Key Roll-over

   A client may wish to change the public key that is associated with a
   registration in order to recover from a key compromise or proactively
   mitigate the impact of an unnoticed key compromise.

   To change the key associate with an account, the client sends a POST
   request containing a key-change object with the following fields:

   oldKey (required, JWK):  The JWK representation of the original key
      (i.e., the client's current account key)

   newKey (requrired, JWK):  The JWK representation of the new key





Barnes, et al.           Expires January 9, 2017               [Page 25]

Internet-Draft                    ACME                         July 2016


   The JWS of this POST must have two signatures: one signature from the
   existing key on the account, and one signature from the new key that
   the client proposes to use.  This demonstrates that the client
   actually has control of the private key corresponding to the new
   public key.  The protected header must contain a JWK field containing
   the current account key.

   POST /acme/key-change HTTP/1.1
   Host: example.com
   Content-Type: application/jose+json

   {
     "payload": base64url({
       "oldKey": /* Old key in JWK form */
       "newKey": /* New key in JWK form */
     }),
     "signatures": [{
       "protected": base64url({
         "alg": "ES256",
         "jwk": /* old key */,
         "nonce": "pq00v-D1KB0sReG4jFfqVg",
         "url": "https://example.com/acme/key-change"
       }),
       "signature": "XFvVbo9diBlIBvhE...UI62sNT6MZsCJpQo"
     }, {
       "protected": base64url({
         "alg": "ES256",
         "jwk": /* new key */,
         "nonce": "vYjyueEYhMjpVQHe_unw4g",
         "url": "https://example.com/acme/key-change"
       }),
       "signature": "q20gG1f1r9cD6tBM...a48h0CkP11tl5Doo"
     }]
   }

   On receiving key-change request, the server MUST perform the
   following steps in addition to the typical JWS validation:

   1.  Check that the JWS protected header container a "jwk" field
       containing a key that matches a currently active account.

   2.  Check that there are exactly two signatures on the JWS.

   3.  Check that one of the signatures validates using the account key
       from (1).

   4.  Check that the "key" field contains a well-formed JWK that meets
       key strength requirements.



Barnes, et al.           Expires January 9, 2017               [Page 26]

Internet-Draft                    ACME                         July 2016


   5.  Check that the "key" field is not equivalent to the current
       account key or any other currently active account key.

   6.  Check that one of the two signatures on the JWS validates using
       the JWK from the "key" field.

   If all of these checks pass, then the server updates the
   corresponding registration by replacing the old account key with the
   new public key and returns status code 200.  Otherwise, the server
   responds with an error status code and a problem document describing
   the error.

6.2.2.  Account deactivation

   A client may deactivate an account by posting a signed update to the
   server with a status field of "deactivated."  Clients may wish to do
   this when the account key is compromised.

   POST /acme/reg/asdf HTTP/1.1
   Host: example.com
   Content-Type: application/jose+json

   {
     "protected": base64url({
       "alg": "ES256",
       "jwk": {...},
       "nonce": "ntuJWWSic4WVNSqeUmshgg",
       "url": "https://example.com/acme/reg/asdf"
     })
     "payload": base64url({
       "status": "deactivated"
     }),
     "signature": "earzVLd3m5M4xJzR...bVTqn7R08AKOVf3Y"
   }

   The server MUST verify that the request is signed by the account key.
   If the server accepts the deactivation request, it should reply with
   a 200 (OK) status code and the current contents of the registration
   object.

   Once an account is deactivated, the server MUST NOT accept further
   requests authorized by that account's key.  It is up to server policy
   how long to retain data related to that account, whether to revoke
   certificates issued by that account, and whether to send email to
   that account's contacts.  ACME does not provide a way to reactivate a
   deactivated account.





Barnes, et al.           Expires January 9, 2017               [Page 27]

Internet-Draft                    ACME                         July 2016


6.3.  Applying for Certificate Issuance

   The holder of an account key pair may use ACME to submit an
   application for a certificate to be issued.  The client makes this
   request by sending a POST request to the server's new-application
   resource.  The body of the POST is a JWS object whose JSON payload is
   a subset of the application object defined in Section 6.1.3,
   containing the fields that describe the certificate to be issued:

   csr (required, string):  A CSR encoding the parameters for the
      certificate being requested [RFC2986].  The CSR is sent in the
      Base64url-encoded version of the DER format.  (Note: This field
      uses the same modified Base64 encoding rules used elsewhere in
      this document, so it is different from PEM.)

   notBefore (optional, string):  The requested value of the notBefore
      field in the certificate, in the date format defined in [RFC3339]

   notAfter (optional, string):  The requested value of the notAfter
      field in the certificate, in the date format defined in [RFC3339]

   POST /acme/new-app HTTP/1.1
   Host: example.com
   Content-Type: application/jose+json

   {
     "protected": base64url({
       "alg": "ES256",
       "jwk": {...},
       "nonce": "5XJ1L3lEkMG7tR6pA00clA",
       "url": "https://example.com/acme/new-app"
     })
     "payload": base64url({
       "csr": "5jNudRx6Ye4HzKEqT5...FS6aKdZeGsysoCo4H9P",
       "notBefore": "2016-01-01T00:00:00Z",
       "notAfter": "2016-01-08T00:00:00Z"
     }),
     "signature": "H6ZXtGjTZyUnPeKn...wEA4TklBdh3e454g"
   }

   The CSR encodes the client's requests with regard to the content of
   the certificate to be issued.  The CSR MUST indicate the requested
   identifiers, either in the commonName portion of the requested
   subject name, or in an extensionRequest attribute [RFC2985]
   requesting a subjectAltName extension.

   The server MUST return an error if it cannot fulfil the request as
   specified, and MUST NOT issue a certificate with contents other than



Barnes, et al.           Expires January 9, 2017               [Page 28]

Internet-Draft                    ACME                         July 2016


   those requested.  If the server requires the request to be modified
   in a certain way, it should indicate the required changes using an
   appropriate error code and description.

   If the server is willing to issue the requested certificate, it
   responds with a 201 (Created) response.  The body of this response is
   an application object reflecting the client's request and any
   requirements the client must fulfill before the certificate will be
   issued.

   HTTP/1.1 201 Created
   Location: https://example.com/acme/app/asdf

   {
     "status": "pending",
     "expires": "2015-03-01T14:09:00Z",

     "csr": "jcRf4uXra7FGYW5ZMewvV...rhlnznwy8YbpMGqwidEXfE",
     "notBefore": "2016-01-01T00:00:00Z",
     "notAfter": "2016-01-08T00:00:00Z",

     "requirements": [
       {
         "type": "authorization",
         "status": "valid",
         "url": "https://example.com/acme/authz/1234"
       },
       {
         "type": "out-of-band",
         "status": "pending",
         "url": "https://example.com/acme/payment/1234"
       }
     ]
   }

   The application object returned by the server represents a promise
   that if the client fulfills the server's requirements before the
   "expires" time, then the server will issue the requested certificate.
   In the application object, any object in the "requirements" array
   whose status is "pending" represents an action that the client must
   perform before the server will issue the certificate.  If the client
   fails to complete the required actions before the "expires" time,
   then the server SHOULD change the status of the application to
   "invalid" and MAY delete the application resource.

   The server SHOULD issue the requested certificate and update the
   application resource with a URL for the certificate as soon as the
   client has fulfilled the server's requirements.  If the client has



Barnes, et al.           Expires January 9, 2017               [Page 29]

Internet-Draft                    ACME                         July 2016


   already satisfied the server's requirements at the time of this
   request (e.g., by obtaining authorization for all of the identifiers
   in the certificate in previous transactions), then the server MAY
   proactively issue the requested certificate and provide a URL for it
   in the "certificate" field of the application.  The server MUST,
   however, still list the satisfied requirements in the "requirements"
   array, with the state "valid".

   Once the client believes it has fulfilled the server's requirements,
   it should send a GET request to the application resource to obtain
   its current state.  The status of the application will indicate what
   action the client should take:

   o  "invalid": The certificate will not be issued.  Consider this
      application process abandoned.

   o  "pending": The server does not believe that the client has
      fulfilled the requirements.  Check the "requirements" array for
      requirements that are still pending.

   o  "processing": The server agrees that the requirements have been
      fulfilled, and is in the process of generating the certificate.
      Retry after the time given in the "Retry-After" header field of
      the response, if any.

   o  "valid": The server has issued the certificate and provisioned its
      URL to the "certificate" field of the application.  Download the
      certificate.

6.3.1.  Downloading the Certificate

   To download the issued certificate, the client simply sends a GET
   request to the certificate URL.

   The default format of the certificate is DER (application/pkix-cert).
   The client may request other formats by including an Accept header in
   its request.  For example, the client may use the media type
   application/x-pem-file to request the certificate in PEM format.

   The server provides metadata about the certificate in HTTP headers.
   In particular, the server MUST send one or more link relation header
   fields [RFC5988] with relation "up", each indicating a single
   certificate resource for the issuer of this certificate.  The server
   MAY also include the "up" links from these resources to enable the
   client to build a full certificate chain.






Barnes, et al.           Expires January 9, 2017               [Page 30]

Internet-Draft                    ACME                         July 2016


   The server MUST also provide a link relation header field with
   relation "author" to indicate the application under which this
   certificate was issued.

   If the CA participates in Certificate Transparency (CT) [RFC6962],
   then they may want to provide the client with a Signed Certificate
   Timestamp (SCT) that can be used to prove that a certificate was
   submitted to a CT log.  An SCT can be included as an extension in the
   certificate or as an extension to OCSP responses for the certificate.
   The server can also provide the client with direct access to an SCT
   for a certificate using a Link relation header field with relation
   "ct-sct".

   GET /acme/cert/asdf HTTP/1.1
   Host: example.com
   Accept: application/pkix-cert

   HTTP/1.1 200 OK
   Content-Type: application/pkix-cert
   Link: <https://example.com/acme/ca-cert>;rel="up";title="issuer"
   Link: <https://example.com/acme/revoke-cert>;rel="revoke"
   Link: <https://example.com/acme/app/asdf>;rel="author"
   Link: <https://example.com/acme/sct/asdf>;rel="ct-sct"
   Link: <https://example.com/acme/some-directory>;rel="directory"

   [DER-encoded certificate]

   A certificate resource represents a single, immutable certificate.
   If the client wishes to obtain a renewed certificate, the client
   initiates a new application process to request one.

   Because certificate resources are immutable once issuance is
   complete, the server MAY enable the caching of the resource by adding
   Expires and Cache-Control headers specifying a point in time in the
   distant future.  These headers have no relation to the certificate's
   period of validity.

6.4.  Identifier Authorization

   The identifier authorization process establishes the authorization of
   an account to manage certificates for a given identifier.  This
   process must assure the server of two things: First, that the client
   controls the private key of the account key pair, and second, that
   the client holds the identifier in question.  This process may be
   repeated to associate multiple identifiers to a key pair (e.g., to
   request certificates with multiple identifiers), or to associate
   multiple accounts with an identifier (e.g., to allow multiple
   entities to manage certificates).  The server may declare that an



Barnes, et al.           Expires January 9, 2017               [Page 31]

Internet-Draft                    ACME                         July 2016


   authorization is only valid for a specific application by setting the
   "scope" field of the authorization to the URI for that application.

   Authorization resources are created by the server in response to
   certificate applications submitted by an account key holder; their
   URLs are provided to the client in "authorization" requirement
   objects.  The authorization object is implicitly tied to the account
   key used to sign the new-application request.

   When a client receives an application from the server with an
   "authorization" requirement, it downloads the authorization resource
   by sending a GET request to the indicated URL.

   GET /acme/authz/1234 HTTP/1.1
   Host: example.com

   HTTP/1.1 200 OK
   Content-Type: application/json
   Link: <https://example.com/acme/some-directory>;rel="directory"

   {
     "status": "pending",

     "identifier": {
       "type": "dns",
       "value": "example.org"
     },

     "challenges": [
       {
         "type": "http-01",
         "uri": "https://example.com/authz/asdf/0",
         "token": "IlirfxKKXAsHtmzK29Pj8A"
       },
       {
         "type": "dns-01",
         "uri": "https://example.com/authz/asdf/1",
         "token": "DGyRejmCefe7v4NfDGDKfA"
       }
     ],

     "combinations": [[0], [1]]
   }








Barnes, et al.           Expires January 9, 2017               [Page 32]

Internet-Draft                    ACME                         July 2016


6.4.1.  Responding to Challenges

   To prove control of the identifier and receive authorization, the
   client needs to respond with information to complete the challenges.
   To do this, the client updates the authorization object received from
   the server by filling in any required information in the elements of
   the "challenges" dictionary.  (This is also the stage where the
   client should perform any actions required by the challenge.)

   The client sends these updates back to the server in the form of a
   JSON object with the response fields required by the challenge type,
   carried in a POST request to the challenge URI (not authorization
   URI).  This allows the client to send information only for challenges
   it is responding to.

   For example, if the client were to respond to the "http-01" challenge
   in the above authorization, it would send the following request:

   POST /acme/authz/asdf/0 HTTP/1.1
   Host: example.com
   Content-Type: application/jose+json

   {
     "protected": base64url({
       "alg": "ES256",
       "jwk": {...},
       "nonce": "Q_s3MWoqT05TrdkM2MTDcw",
       "url": "https://example.com/acme/authz/asdf/0"
     })
     "payload": base64url({
       "type": "http-01",
       "keyAuthorization": "IlirfxKKXA...vb29HhjjLPSggwiE"
     }),
     "signature": "9cbg5JO1Gf5YLjjz...SpkUfcdPai9uVYYQ"
   }

   The server updates the authorization document by updating its
   representation of the challenge with the response fields provided by
   the client.  The server MUST ignore any fields in the response object
   that are not specified as response fields for this type of challenge.
   The server provides a 200 (OK) response with the updated challenge
   object as its body.

   If the client's response is invalid for some reason, or does not
   provide the server with appropriate information to validate the
   challenge, then the server MUST return an HTTP error.  On receiving
   such an error, the client SHOULD undo any actions that have been




Barnes, et al.           Expires January 9, 2017               [Page 33]

Internet-Draft                    ACME                         July 2016


   taken to fulfill the challenge, e.g., removing files that have been
   provisioned to a web server.

   Presumably, the client's responses provide the server with enough
   information to validate one or more challenges.  The server is said
   to "finalize" the authorization when it has completed all the
   validations it is going to complete, and assigns the authorization a
   status of "valid" or "invalid", corresponding to whether it considers
   the account authorized for the identifier.  If the final state is
   "valid", the server MUST add an "expires" field to the authorization.
   When finalizing an authorization, the server MAY remove the
   "combinations" field (if present) or remove any challenges still
   pending.  The server SHOULD NOT remove challenges with status
   "invalid".

   Usually, the validation process will take some time, so the client
   will need to poll the authorization resource to see when it is
   finalized.  For challenges where the client can tell when the server
   has validated the challenge (e.g., by seeing an HTTP or DNS request
   from the server), the client SHOULD NOT begin polling until it has
   seen the validation request from the server.

   To check on the status of an authorization, the client sends a GET
   request to the authorization URI, and the server responds with the
   current authorization object.  In responding to poll requests while
   the validation is still in progress, the server MUST return a 202
   (Accepted) response, and MAY include a Retry-After header field to
   suggest a polling interval to the client.























Barnes, et al.           Expires January 9, 2017               [Page 34]

Internet-Draft                    ACME                         July 2016


   GET /acme/authz/asdf HTTP/1.1
   Host: example.com

   HTTP/1.1 200 OK

   {
     "status": "valid",
     "expires": "2015-03-01T14:09:00Z",

     "identifier": {
       "type": "dns",
       "value": "example.org"
     },

     "challenges": [
       {
         "type": "http-01"
         "status": "valid",
         "validated": "2014-12-01T12:05:00Z",
         "token": "IlirfxKKXAsHtmzK29Pj8A",
         "keyAuthorization": "IlirfxKKXA...vb29HhjjLPSggwiE"
       }
     ]
   }

6.4.2.  Deactivating an Authorization

   If a client wishes to relinquish its authorization to issue
   certificates for an identifier, then it may request that the server
   deactivate each authorization associated with that identifier by
   sending a POST request with the static object {"status":
   "deactivated"}.



















Barnes, et al.           Expires January 9, 2017               [Page 35]

Internet-Draft                    ACME                         July 2016


   POST /acme/authz/asdf HTTP/1.1
   Host: example.com
   Content-Type: application/jose+json

   {
     "protected": base64url({
       "alg": "ES256",
       "jwk": {...},
       "nonce": "xWCM9lGbIyCgue8di6ueWQ",
       "url": "https://example.com/acme/authz/asdf"
     })
     "payload": base64url({
       "status": "deactivated"
     }),
     "signature": "srX9Ji7Le9bjszhu...WTFdtujObzMtZcx4"
   }

   The server MUST verify that the request is signed by the account key
   corresponding to the account that owns the authorization.  If the
   server accepts the deactivation, it should reply with a 200 (OK)
   status code and the current contents of the registration object.

   The server MUST NOT treat deactivated authorization objects as
   sufficient for issuing certificates.

6.5.  Certificate Revocation

   To request that a certificate be revoked, the client sends a POST
   request to the ACME server's revoke-cert URI.  The body of the POST
   is a JWS object whose JSON payload contains the certificate to be
   revoked:

   certificate (required, string):  The certificate to be revoked, in
      the base64url-encoded version of the DER format.  (Note: This
      field uses the same modified Base64 encoding rules used elsewhere
      in this document, so it is different from PEM.)

   reason (optional, int):  One of the revocation reasonCodes defined in
      RFC 5280 [RFC5280] Section 5.3.1 to be used when generating OCSP
      responses and CRLs.  If this field is not set the server SHOULD
      use the unspecified (0) reasonCode value when generating OCSP
      responses and CRLs.  The server MAY disallow a subset of
      reasonCodes from being used by the user.








Barnes, et al.           Expires January 9, 2017               [Page 36]

Internet-Draft                    ACME                         July 2016


   POST /acme/revoke-cert HTTP/1.1
   Host: example.com
   Content-Type: application/jose+json

   {
     "protected": base64url({
       "alg": "ES256",
       "jwk": {...},
       "nonce": "JHb54aT_KTXBWQOzGYkt9A",
       "url": "https://example.com/acme/revoke-cert"
     })
     "payload": base64url({
       "certificate": "MIIEDTCCAvegAwIBAgIRAP8...",
       "reason": 1
     }),
     "signature": "Q1bURgJoEslbD1c5...3pYdSMLio57mQNN4"
   }

   Revocation requests are different from other ACME request in that
   they can be signed either with an account key pair or the key pair in
   the certificate.  Before revoking a certificate, the server MUST
   verify that the key used to sign the request is authorized to revoke
   the certificate.  The server SHOULD consider at least the following
   keys authorized for a given certificate:

   o  the public key in the certificate.

   o  an account key that is authorized to act for all of the
      identifier(s) in the certificate.

   If the revocation succeeds, the server responds with status code 200
   (OK).  If the revocation fails, the server returns an error.

   HTTP/1.1 200 OK
   Content-Length: 0

   --- or ---

   HTTP/1.1 403 Forbidden
   Content-Type: application/problem+json
   Content-Language: en

   {
     "type": "urn:ietf:params:acme:error:unauthorized"
     "detail": "No authorization provided for name example.net"
     "instance": "http://example.com/doc/unauthorized"
   }




Barnes, et al.           Expires January 9, 2017               [Page 37]

Internet-Draft                    ACME                         July 2016


7.  Identifier Validation Challenges

   There are few types of identifiers in the world for which there is a
   standardized mechanism to prove possession of a given identifier.  In
   all practical cases, CAs rely on a variety of means to test whether
   an entity applying for a certificate with a given identifier actually
   controls that identifier.

   Challenges provide the server with assurance that an account key
   holder is also the entity that controls an identifier.  For each type
   of challenge, it must be the case that in order for an entity to
   successfully complete the challenge the entity must both:

   o  Hold the private key of the account key pair used to respond to
      the challenge

   o  Control the identifier in question

   Section 9 documents how the challenges defined in this document meet
   these requirements.  New challenges will need to document how they
   do.

   ACME uses an extensible challenge/response framework for identifier
   validation.  The server presents a set of challenges in the
   authorization object it sends to a client (as objects in the
   "challenges" array), and the client responds by sending a response
   object in a POST request to a challenge URI.

   This section describes an initial set of challenge types.  Each
   challenge must describe:

   1.  Content of challenge objects

   2.  Content of response objects

   3.  How the server uses the challenge and response to verify control
       of an identifier

   Challenge objects all contain the following basic fields:

   type (required, string):  The type of challenge encoded in the
      object.

   uri (required, string):  The URI to which a response can be posted.

   status (required, string):  The status of this authorization.
      Possible values are: "pending", "valid", and "invalid".




Barnes, et al.           Expires January 9, 2017               [Page 38]

Internet-Draft                    ACME                         July 2016


   validated (optional, string):  The time at which this challenge was
      completed by the server, encoded in the format specified in RFC
      3339 [RFC3339].  This field is REQUIRED if the "status" field is
      "valid".

   error (optional, dictionary of string):  The error that occurred
      while the server was validating the challenge, if any.  This field
      is structured as a problem document [RFC7807].

   All additional fields are specified by the challenge type.  If the
   server sets a challenge's "status" to "invalid", it SHOULD also
   include the "error" field to help the client diagnose why they failed
   the challenge.

   Different challenges allow the server to obtain proof of different
   aspects of control over an identifier.  In some challenges, like HTTP
   and TLS SNI, the client directly proves its ability to do certain
   things related to the identifier.  The choice of which challenges to
   offer to a client under which circumstances is a matter of server
   policy.

   The identifier validation challenges described in this section all
   relate to validation of domain names.  If ACME is extended in the
   future to support other types of identifier, there will need to be
   new challenge types, and they will need to specify which types of
   identifier they apply to.

   [[ Editor's Note: In pre-RFC versions of this specification,
   challenges are labeled by type, and with the version of the draft in
   which they were introduced.  For example, if an HTTP challenge were
   introduced in version -03 and a breaking change made in version -05,
   then there would be a challenge labeled "http-03" and one labeled
   "http-05" - but not one labeled "http-04", since challenge in version
   -04 was compatible with one in version -04. ]]

   [[ Editor's Note: Operators SHOULD NOT issue "combinations" arrays in
   authorization objects that require the client to perform multiple
   challenges over the same type, e.g., ["http-03", "http-05"].
   Challenges within a type are testing the same capability of the
   domain owner, and it may not be possible to satisfy both at once. ]]

7.1.  Key Authorizations

   Several of the challenges in this document makes use of a key
   authorization string.  A key authorization is a string that expresses
   a domain holder's authorization for a specified key to satisfy a
   specified challenge, by concatenating the token for the challenge
   with a key fingerprint, separated by a "." character:



Barnes, et al.           Expires January 9, 2017               [Page 39]

Internet-Draft                    ACME                         July 2016


   key-authz = token || '.' || base64url(JWK\_Thumbprint(accountKey))

   The "JWK_Thumbprint" step indicates the computation specified in
   [RFC7638], using the SHA-256 digest.  As specified in the individual
   challenges below, the token for a challenge is a JSON string
   comprised entirely of characters in the URL-safe Base64 alphabet.
   The "||" operator indicates concatenation of strings.

   In computations involving key authorizations, such as the digest
   computations required for the DNS and TLS SNI challenges, the key
   authorization string MUST be represented in UTF-8 form (or,
   equivalently, ASCII).

   An example of how to compute a JWK thumbprint can be found in
   Section 3.1 of [RFC7638].  Note that some cryptographic libraries
   prepend a zero octet to the representation of the RSA public key
   parameters N and E, in order to avoid ambiguity with regard to the
   sign of the number.  As noted in JWA [RFC7518], a JWK object MUST NOT
   include this zero octet.  That is, any initial zero octets MUST be
   stripped before the values are base64url-encoded.

7.2.  HTTP

   With HTTP validation, the client in an ACME transaction proves its
   control over a domain name by proving that it can provision resources
   on an HTTP server that responds for that domain name.  The ACME
   server challenges the client to provision a file at a specific path,
   with a specific string as its content.

   As a domain may resolve to multiple IPv4 and IPv6 addresses, the
   server will connect to at least one of the hosts found in A and AAAA
   records, at its discretion.  Because many webservers allocate a
   default HTTPS virtual host to a particular low-privilege tenant user
   in a subtle and non-intuitive manner, the challenge must be completed
   over HTTP, not HTTPS.

   type (required, string):  The string "http-01"

   token (required, string):  A random value that uniquely identifies
      the challenge.  This value MUST have at least 128 bits of entropy,
      in order to prevent an attacker from guessing it.  It MUST NOT
      contain any characters outside the URL-safe Base64 alphabet and
      MUST NOT contain any padding characters ("=").

   {
     "type": "http-01",
     "token": "evaGxfADs6pSRb2LAv9IZf17Dt3juxGJ-PCt92wr-oA"
   }



Barnes, et al.           Expires January 9, 2017               [Page 40]

Internet-Draft                    ACME                         July 2016


   A client responds to this challenge by constructing a key
   authorization from the "token" value provided in the challenge and
   the client's account key.  The client then provisions the key
   authorization as a resource on the HTTP server for the domain in
   question.

   The path at which the resource is provisioned is comprised of the
   fixed prefix ".well-known/acme-challenge/", followed by the "token"
   value in the challenge.  The value of the resource MUST be the ASCII
   representation of the key authorization.

  .well-known/acme-challenge/evaGxfADs6pSRb2LAv9IZf17Dt3juxGJ-PCt92wr-oA

   The client's response to this challenge indicates its agreement to
   this challenge by sending the server the key authorization covering
   the challenge's token and the client's account key.  In addition, the
   client MAY advise the server at which IP the challenge is
   provisioned.

   keyAuthorization (required, string):  The key authorization for this
      challenge.  This value MUST match the token from the challenge and
      the client's account key.

   /* BEGIN JWS-signed content */
   {
     "keyAuthorization": "evaGxfADs...62jcerQ"
   }
   /* END JWS-signed content */

   On receiving a response, the server MUST verify that the key
   authorization in the response matches the "token" value in the
   challenge and the client's account key.  If they do not match, then
   the server MUST return an HTTP error in response to the POST request
   in which the client sent the challenge.

   Given a challenge/response pair, the server verifies the client's
   control of the domain by verifying that the resource was provisioned
   as expected.

   1.  Form a URI by populating the URI template [RFC6570]
       "http://{domain}/.well-known/acme-challenge/{token}", where:

       *  the domain field is set to the domain name being verified; and

       *  the token field is set to the token in the challenge.

   2.  Verify that the resulting URI is well-formed.




Barnes, et al.           Expires January 9, 2017               [Page 41]

Internet-Draft                    ACME                         July 2016


   3.  Dereference the URI using an HTTP GET request.

   4.  Verify that the body of the response is well-formed key
       authorization.  The server SHOULD ignore whitespace characters at
       the end of the body.

   5.  Verify that key authorization provided by the server matches the
       token for this challenge and the client's account key.

   If all of the above verifications succeed, then the validation is
   successful.  If the request fails, or the body does not pass these
   checks, then it has failed.

7.3.  TLS with Server Name Indication (TLS SNI)

   The TLS with Server Name Indication (TLS SNI) validation method
   proves control over a domain name by requiring the client to
   configure a TLS server referenced by an A/AAAA record under the
   domain name to respond to specific connection attempts utilizing the
   Server Name Indication extension [RFC6066].  The server verifies the
   client's challenge by accessing the reconfigured server and verifying
   a particular challenge certificate is presented.

   type (required, string):  The string "tls-sni-02"

   token (required, string):  A random value that uniquely identifies
      the challenge.  This value MUST have at least 128 bits of entropy,
      in order to prevent an attacker from guessing it.  It MUST NOT
      contain any characters outside the URL-safe Base64 alphabet and
      MUST NOT contain any padding characters ("=").

   {
     "type": "tls-sni-02",
     "token": "evaGxfADs6pSRb2LAv9IZf17Dt3juxGJ-PCt92wr-oA"
   }

   A client responds to this challenge by constructing a self-signed
   certificate which the client MUST provision at the domain name
   concerned in order to pass the challenge.

   The certificate may be constructed arbitrarily, except that each
   certificate MUST have exactly two subjectAlternativeNames, SAN A and
   SAN B.  Both MUST be dNSNames.

   SAN A MUST be constructed as follows: compute the SHA-256 digest of
   the UTF-8-encoded challenge token and encode it in lowercase
   hexadecimal form.  The dNSName is "x.y.token.acme.invalid", where x




Barnes, et al.           Expires January 9, 2017               [Page 42]

Internet-Draft                    ACME                         July 2016


   is the first half of the hexadecimal representation and y is the
   second half.

   SAN B MUST be constructed as follows: compute the SHA-256 digest of
   the UTF-8 encoded key authorization and encode it in lowercase
   hexadecimal form.  The dNSName is "x.y.ka.acme.invalid" where x is
   the first half of the hexadecimal representation and y is the second
   half.

   The client MUST ensure that the certificate is served to TLS
   connections specifying a Server Name Indication (SNI) value of SAN A.

   The response to the TLS-SNI challenge simply acknowledges that the
   client is ready to fulfill this challenge.

   keyAuthorization (required, string):  The key authorization for this
      challenge.  This value MUST match the token from the challenge and
      the client's account key.

   /* BEGIN JWS-signed content */
   {
     "keyAuthorization": "evaGxfADs...62jcerQ"
   }
   /* END JWS-signed content */

   On receiving a response, the server MUST verify that the key
   authorization in the response matches the "token" value in the
   challenge and the client's account key.  If they do not match, then
   the server MUST return an HTTP error in response to the POST request
   in which the client sent the challenge.

   Given a challenge/response pair, the ACME server verifies the
   client's control of the domain by verifying that the TLS server was
   configured appropriately, using these steps:

   1.  Compute SAN A and SAN B in the same way as the client.

   2.  Open a TLS connection to the domain name being validated on the
       requested port, presenting SAN A in the SNI field.  In the
       ClientHello initiating the TLS handshake, the server MUST include
       a server_name extension (i.e., SNI) containing SAN A.  The server
       SHOULD ensure that it does not reveal SAN B in any way when
       making the TLS connection, such that the presentation of SAN B in
       the returned certificate proves association with the client.

   3.  Verify that the certificate contains a subjectAltName extension
       containing dNSName entries of SAN A and SAN B and no other




Barnes, et al.           Expires January 9, 2017               [Page 43]

Internet-Draft                    ACME                         July 2016


       entries.  The comparison MUST be insensitive to case and ordering
       of names.

   It is RECOMMENDED that the ACME server validation TLS connections
   from multiple vantage points to reduce the risk of DNS hijacking
   attacks.

   If all of the above verifications succeed, then the validation is
   successful.  Otherwise, the validation fails.

7.4.  DNS

   When the identifier being validated is a domain name, the client can
   prove control of that domain by provisioning a resource record under
   it.  The DNS challenge requires the client to provision a TXT record
   containing a designated value under a specific validation domain
   name.

   type (required, string):  The string "dns-01"

   token (required, string):  A random value that uniquely identifies
      the challenge.  This value MUST have at least 128 bits of entropy,
      in order to prevent an attacker from guessing it.  It MUST NOT
      contain any characters outside the URL-safe Base64 alphabet and
      MUST NOT contain any padding characters ("=").

   {
     "type": "dns-01",
     "token": "evaGxfADs6pSRb2LAv9IZf17Dt3juxGJ-PCt92wr-oA"
   }

   A client responds to this challenge by constructing a key
   authorization from the "token" value provided in the challenge and
   the client's account key.  The client then computes the SHA-256
   digest of the key authorization.

   The record provisioned to the DNS is the base64url encoding of this
   digest.  The client constructs the validation domain name by
   prepending the label "_acme-challenge" to the domain name being
   validated, then provisions a TXT record with the digest value under
   that name.  For example, if the domain name being validated is
   "example.com", then the client would provision the following DNS
   record:

   _acme-challenge.example.com. 300 IN TXT "gfj9Xq...Rg85nM"






Barnes, et al.           Expires January 9, 2017               [Page 44]

Internet-Draft                    ACME                         July 2016


   The response to the DNS challenge provides the computed key
   authorization to acknowledge that the client is ready to fulfill this
   challenge.

   keyAuthorization (required, string):  The key authorization for this
      challenge.  This value MUST match the token from the challenge and
      the client's account key.

   /* BEGIN JWS-signed content */
   {
     "keyAuthorization": "evaGxfADs...62jcerQ"
   }
   /* END JWS-signed content */

   On receiving a response, the server MUST verify that the key
   authorization in the response matches the "token" value in the
   challenge and the client's account key.  If they do not match, then
   the server MUST return an HTTP error in response to the POST request
   in which the client sent the challenge.

   To validate a DNS challenge, the server performs the following steps:

   1.  Compute the SHA-256 digest of the key authorization

   2.  Query for TXT records under the validation domain name

   3.  Verify that the contents of one of the TXT records matches the
       digest value

   If all of the above verifications succeed, then the validation is
   successful.  If no DNS record is found, or DNS record and response
   payload do not pass these checks, then the validation fails.

7.5.  Out-of-Band

   There may be cases where a server cannot perform automated validation
   of an identifier, for example if validation requires some manual
   steps.  In such cases, the server may provide an "out of band" (OOB)
   challenge to request that the client perform some action outside of
   ACME in order to validate possession of the identifier.

   The OOB challenge requests that the client have a human user visit a
   web page to receive instructions on how to validate possession of the
   identifier, by providing a URL for that web page.

   type (required, string):  The string "oob-01"





Barnes, et al.           Expires January 9, 2017               [Page 45]

Internet-Draft                    ACME                         July 2016


   url (required, string):  The URL to be visited.  The scheme of this
      URL MUST be "http" or "https"

   {
     "type": "oob-01",
     "url": "https://example.com/validate/evaGxfADs6pSRb2LAv9IZ"
   }

   A client responds to this challenge by presenting the indicated URL
   for a human user to navigate to.  If the user choses to complete this
   challege (by vising the website and completing its instructions), the
   client indicates this by sending a simple acknowledgement response to
   the server.

   type (required, string):  The string "oob-01"

   /* BEGIN JWS-signed content */
   {
     "type": "oob-01"
   }
   /* END JWS-signed content */

   On receiving a response, the server MUST verify that the value of the
   "type" field is as required.  Otherwise, the steps the server takes
   to validate identifier possession are determined by the server's
   local policy.

8.  IANA Considerations

   [[ Editor's Note: Should we create a registry for tokens that go into
   the various JSON objects used by this protocol, i.e., the field names
   in the JSON objects? ]]

8.1.  Well-Known URI for the HTTP Challenge

   The "Well-Known URIs" registry should be updated with the following
   additional value (using the template from [RFC5785]):

   URI suffix: acme-challenge

   Change controller: IETF

   Specification document(s): This document, Section Section 7.2

   Related information: N/A






Barnes, et al.           Expires January 9, 2017               [Page 46]

Internet-Draft                    ACME                         July 2016


8.2.  Replay-Nonce HTTP Header

   The "Message Headers" registry should be updated with the following
   additional value:

   | Header Field Name | Protocol | Status | Reference |
   +:------------+:------+:------+:-----------+ | Replay-Nonce | http |
   standard | Section 5.4.1 |

8.3.  "url" JWS Header Parameter

   The "JSON Web Signature and Encryption Header Parameters" registry
   should be updated with the following additional value:

   o  Header Parameter Name: "url"

   o  Header Parameter Description: URL

   o  Header Parameter Usage Location(s): JWE, JWS

   o  Change Controller: IESG

   o  Specification Document(s): Section 5.3.1 of RFC XXXX

   [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned
   to this document ]]

8.4.  "nonce" JWS Header Parameter

   The "JSON Web Signature and Encryption Header Parameters" registry
   should be updated with the following additional value:

   o  Header Parameter Name: "nonce"

   o  Header Parameter Description: Nonce

   o  Header Parameter Usage Location(s): JWE, JWS

   o  Change Controller: IESG

   o  Specification Document(s): Section 5.4.2 of RFC XXXX

   [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned
   to this document ]]







Barnes, et al.           Expires January 9, 2017               [Page 47]

Internet-Draft                    ACME                         July 2016


8.5.  URN Sub-namespace for ACME (urn:ietf:params:acme)

   The "IETF URN Sub-namespace for Registered Protocol Parameter
   Identifiers" registry should be updated with the following additional
   value, following the template in [RFC3553]:

   Registry name:  acme

   Specification:  RFC XXXX

   Repository:  URL-TBD

   Index value:  No transformation needed.  The

   [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned
   to this document, and replace URL-TBD with the URL assigned by IANA
   for registries of ACME parameters. ]]

8.6.  New Registries

   This document requests that IANA create the following new registries:

   1.  ACME Error Codes

   2.  ACME Resource Types

   3.  ACME Identifier Types

   4.  ACME Challenge Types

   All of these registries should be administered under a Specification
   Required policy [RFC5226].

8.6.1.  Error Codes

   This registry lists values that are used within URN values that are
   provided in the "type" field of problem documents in ACME.

   Template:

   o  Code: The label to be included in the URN for this error,
      following "urn:ietf:params:acme:"

   o  Description: A human-readable description of the error

   o  Reference: Where the error is defined





Barnes, et al.           Expires January 9, 2017               [Page 48]

Internet-Draft                    ACME                         July 2016


   Initial contents: The codes and descriptions in the table in
   Section 5.6 above, with the Reference field set to point to this
   specification.

8.6.2.  Resource Types

   This registry lists the types of resources that ACME servers may list
   in their directory objects.

   Template:

   o  Key: The value to be used as a dictionary key in the directory
      object

   o  Resource type: The type of resource labeled by the key

   o  Reference: Where the identifier type is defined

   Initial contents:

             +-------------+--------------------+-----------+
             | Key         | Resource type      | Reference |
             +-------------+--------------------+-----------+
             | new-reg     | New registration   | RFC XXXX  |
             |             |                    |           |
             | new-app     | New application    | RFC XXXX  |
             |             |                    |           |
             | revoke-cert | Revoke certificate | RFC XXXX  |
             |             |                    |           |
             | key-change  | Key change         | RFC XXXX  |
             +-------------+--------------------+-----------+

   [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned
   to this document ]]

8.6.3.  Identifier Types

   This registry lists the types of identifiers that ACME clients may
   request authorization to issue in certificates.

   Template:

   o  Label: The value to be put in the "type" field of the identifier
      object

   o  Reference: Where the identifier type is defined

   Initial contents:



Barnes, et al.           Expires January 9, 2017               [Page 49]

Internet-Draft                    ACME                         July 2016


                           +-------+-----------+
                           | Label | Reference |
                           +-------+-----------+
                           | dns   | RFC XXXX  |
                           +-------+-----------+

   [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned
   to this document ]]

8.6.4.  Challenge Types

   This registry lists the ways that ACME servers can offer to validate
   control of an identifier.  The "Identifier Type" field in template
   MUST be contained in the Label column of the ACME Identifier Types
   registry.

   Template:

   o  Label: The value to be put in the "type" field of challenge
      objects using this validation mechanism

   o  Identifier Type: The type of identifier that this mechanism
      applies to

   o  Reference: Where the challenge type is defined

   Initial Contents

                 +---------+-----------------+-----------+
                 | Label   | Identifier Type | Reference |
                 +---------+-----------------+-----------+
                 | http    | dns             | RFC XXXX  |
                 |         |                 |           |
                 | tls-sni | dns             | RFC XXXX  |
                 |         |                 |           |
                 | dns     | dns             | RFC XXXX  |
                 +---------+-----------------+-----------+

   [[ RFC EDITOR: Please replace XXXX above with the RFC number assigned
   to this document ]]

9.  Security Considerations

   ACME is a protocol for managing certificates that attest to
   identifier/key bindings.  Thus the foremost security goal of ACME is
   to ensure the integrity of this process, i.e., to ensure that the
   bindings attested by certificates are correct, and that only
   authorized entities can manage certificates.  ACME identifies clients



Barnes, et al.           Expires January 9, 2017               [Page 50]

Internet-Draft                    ACME                         July 2016


   by their account keys, so this overall goal breaks down into two more
   precise goals:

   1.  Only an entity that controls an identifier can get an account key
       authorized for that identifier

   2.  Once authorized, an account key's authorizations cannot be
       improperly transferred to another account key

   In this section, we discuss the threat model that underlies ACME and
   the ways that ACME achieves these security goals within that threat
   model.  We also discuss the denial-of-service risks that ACME servers
   face, and a few other miscellaneous considerations.

9.1.  Threat model

   As a service on the Internet, ACME broadly exists within the Internet
   threat model [RFC3552].  In analyzing ACME, it is useful to think of
   an ACME server interacting with other Internet hosts along three
   "channels":

   o  An ACME channel, over which the ACME HTTPS requests are exchanged

   o  A validation channel, over which the ACME server performs
      additional requests to validate a client's control of an
      identifier

   o  A contact channel, over which the ACME server sends messages to
      the registered contacts for ACME clients

   +------------+
   |    ACME    |     ACME Channel
   |   Client   |--------------------+
   +------------+                    |
          ^                          V
          |   Contact Channel  +------------+
          +--------------------|    ACME    |
                               |   Server   |
                               +------------+
   +------------+                    |
   | Validation |<-------------------+
   |   Server   |  Validation Channel
   +------------+

   In practice, the risks to these channels are not entirely separate,
   but they are different in most cases.  Each of the three channels,
   for example, uses a different communications pattern: the ACME
   channel will comprise inbound HTTPS connections to the ACME server,



Barnes, et al.           Expires January 9, 2017               [Page 51]

Internet-Draft                    ACME                         July 2016


   the validation channel outbound HTTP or DNS requests, and the contact
   channel will use channels such as email and PSTN.

   Broadly speaking, ACME aims to be secure against active and passive
   attackers on any individual channel.  Some vulnerabilities arise
   (noted below), when an attacker can exploit both the ACME channel and
   one of the others.

   On the ACME channel, in addition to network-layer attackers, we also
   need to account for application-layer man in the middle attacks, and
   for abusive use of the protocol itself.  Protection against
   application-layer MitM addresses potential attackers such as Content
   Distribution Networks (CDNs) and middleboxes with a TLS MitM
   function.  Preventing abusive use of ACME means ensuring that an
   attacker with access to the validation or contact channels can't
   obtain illegitimate authorization by acting as an ACME client
   (legitimately, in terms of the protocol).

9.2.  Integrity of Authorizations

   ACME allows anyone to request challenges for an identifier by
   registering an account key and sending a new-application request
   under that account key.  The integrity of the authorization process
   thus depends on the identifier validation challenges to ensure that
   the challenge can only be completed by someone who both (1) holds the
   private key of the account key pair, and (2) controls the identifier
   in question.

   Validation responses need to be bound to an account key pair in order
   to avoid situations where an ACME MitM can switch out a legitimate
   domain holder's account key for one of his choosing, e.g.:

   o  Legitimate domain holder registers account key pair A

   o  MitM registers account key pair B

   o  Legitimate domain holder sends a new-application request signed
      under account key A

   o  MitM suppresses the legitimate request, but sends the same request
      signed under account key B

   o  ACME server issues challenges and MitM forwards them to the
      legitimate domain holder

   o  Legitimate domain holder provisions the validation response





Barnes, et al.           Expires January 9, 2017               [Page 52]

Internet-Draft                    ACME                         July 2016


   o  ACME server performs validation query and sees the response
      provisioned by the legitimate domain holder

   o  Because the challenges were issued in response to a message signed
      account key B, the ACME server grants authorization to account key
      B (the MitM) instead of account key A (the legitimate domain
      holder)

   All of the challenges above have a binding between the account
   private key and the validation query made by the server, via the key
   authorization.  The key authorization is signed by the account
   private key, reflects the corresponding public key, and is provided
   to the server in the validation response.

   The association of challenges to identifiers is typically done by
   requiring the client to perform some action that only someone who
   effectively controls the identifier can perform.  For the challenges
   in this document, the actions are:

   o  HTTP: Provision files under .well-known on a web server for the
      domain

   o  TLS SNI: Configure a TLS server for the domain

   o  DNS: Provision DNS resource records for the domain

   There are several ways that these assumptions can be violated, both
   by misconfiguration and by attack.  For example, on a web server that
   allows non-administrative users to write to .well-known, any user can
   claim to own the server's hostname by responding to an HTTP
   challenge, and likewise for TLS configuration and TLS SNI.

   The use of hosting providers is a particular risk for ACME
   validation.  If the owner of the domain has outsourced operation of
   DNS or web services to a hosting provider, there is nothing that can
   be done against tampering by the hosting provider.  As far as the
   outside world is concerned, the zone or web site provided by the
   hosting provider is the real thing.

   More limited forms of delegation can also lead to an unintended party
   gaining the ability to successfully complete a validation
   transaction.  For example, suppose an ACME server follows HTTP
   redirects in HTTP validation and a web site operator provisions a
   catch-all redirect rule that redirects requests for unknown resources
   to a different domain.  Then the target of the redirect could use
   that to get a certificate through HTTP validation, since the
   validation path will not be known to the primary server.




Barnes, et al.           Expires January 9, 2017               [Page 53]

Internet-Draft                    ACME                         July 2016


   The DNS is a common point of vulnerability for all of these
   challenges.  An entity that can provision false DNS records for a
   domain can attack the DNS challenge directly, and can provision false
   A/AAAA records to direct the ACME server to send its TLS SNI or HTTP
   validation query to a server of the attacker's choosing.  There are a
   few different mitigations that ACME servers can apply:

   o  Always querying the DNS using a DNSSEC-validating resolver
      (enhancing security for zones that are DNSSEC-enabled)

   o  Querying the DNS from multiple vantage points to address local
      attackers

   o  Applying mitigations against DNS off-path attackers, e.g., adding
      entropy to requests [I-D.vixie-dnsext-dns0x20] or only using TCP

   Given these considerations, the ACME validation process makes it
   impossible for any attacker on the ACME channel, or a passive
   attacker on the validation channel to hijack the authorization
   process to authorize a key of the attacker's choice.

   An attacker that can only see the ACME channel would need to convince
   the validation server to provide a response that would authorize the
   attacker's account key, but this is prevented by binding the
   validation response to the account key used to request challenges.  A
   passive attacker on the validation channel can observe the correct
   validation response and even replay it, but that response can only be
   used with the account key for which it was generated.

   An active attacker on the validation channel can subvert the ACME
   process, by performing normal ACME transactions and providing a
   validation response for his own account key.  The risks due to
   hosting providers noted above are a particular case.  For identifiers
   where the server already has some public key associated with the
   domain this attack can be prevented by requiring the client to prove
   control of the corresponding private key.

9.3.  Denial-of-Service Considerations

   As a protocol run over HTTPS, standard considerations for TCP-based
   and HTTP-based DoS mitigation also apply to ACME.

   At the application layer, ACME requires the server to perform a few
   potentially expensive operations.  Identifier validation transactions
   require the ACME server to make outbound connections to potentially
   attacker-controlled servers, and certificate issuance can require
   interactions with cryptographic hardware.




Barnes, et al.           Expires January 9, 2017               [Page 54]

Internet-Draft                    ACME                         July 2016


   In addition, an attacker can also cause the ACME server to send
   validation requests to a domain of its choosing by submitting
   authorization requests for the victim domain.

   All of these attacks can be mitigated by the application of
   appropriate rate limits.  Issues closer to the front end, like POST
   body validation, can be addressed using HTTP request limiting.  For
   validation and certificate requests, there are other identifiers on
   which rate limits can be keyed.  For example, the server might limit
   the rate at which any individual account key can issue certificates,
   or the rate at which validation can be requested within a given
   subtree of the DNS.

9.4.  Server-Side Request Forgery

   Server-Side Request Forgery (SSRF) attacks can arise when an attacker
   can cause a server to perform HTTP requests to an attacker-chosen
   URL.  In the ACME HTTP challenge validation process, the ACME server
   performs an HTTP GET request to a URL in which the attacker can
   choose the domain.  This request is made before the server has
   verified that the client controls the domain, so any client can cause
   a query to any domain.

   Some server implementations include information from the validation
   server's response (in order to facilitate debugging).  Such
   implementations enable an attacker to extract this information from
   any web server that is accessible to the ACME server, even if it is
   not accessible to the ACME client.

   It might seem that the risk of SSRF through this channel is limited
   by the fact that the attacker can only control the domain of the URL,
   not the path.  However, if the attacker first sets the domain to one
   they control, then they can send the server an HTTP redirect (e.g., a
   302 response) which will cause the server to query an arbitrary URI.

   In order to further limit the SSRF risk, ACME server operators should
   ensure that validation queries can only be sent to servers on the
   public Internet, and not, say, web services within the server
   operator's internal network.  Since the attacker could make requests
   to these public servers himself, he can't gain anything extra through
   an SSRF attack on ACME aside from a layer of anonymization.

9.5.  CA Policy Considerations

   The controls on issuance enabled by ACME are focused on validating
   that a certificate applicant controls the identifier he claims.
   Before issuing a certificate, however, there are many other checks
   that a CA might need to perform, for example:



Barnes, et al.           Expires January 9, 2017               [Page 55]

Internet-Draft                    ACME                         July 2016


   o  Has the client agreed to a subscriber agreement?

   o  Is the claimed identifier syntactically valid?

   o  For domain names:

      *  If the leftmost label is a '*', then have the appropriate
         checks been applied?

      *  Is the name on the Public Suffix List?

      *  Is the name a high-value name?

      *  Is the name a known phishing domain?

   o  Is the key in the CSR sufficiently strong?

   o  Is the CSR signed with an acceptable algorithm?

   CAs that use ACME to automate issuance will need to ensure that their
   servers perform all necessary checks before issuing.

10.  Operational Considerations

   There are certain factors that arise in operational reality that
   operators of ACME-based CAs will need to keep in mind when
   configuring their services.  For example:

10.1.  DNS over TCP

   As noted above, DNS forgery attacks against the ACME server can
   result in the server making incorrect decisions about domain control
   and thus mis-issuing certificates.  Servers SHOULD verify DNSSEC when
   it is available for a domain.  When DNSSEC is not available, servers
   SHOULD perform DNS queries over TCP, which provides better resistance
   to some forgery attacks than DNS over UDP.

10.2.  Default Virtual Hosts

   In many cases, TLS-based services are deployed on hosted platforms
   that use the Server Name Indication (SNI) TLS extension to
   distinguish between different hosted services or "virtual hosts".
   When a client initiates a TLS connection with an SNI value indicating
   a provisioned host, the hosting platform routes the connection to
   that host.

   When a connection comes in with an unknown SNI value, one might
   expect the hosting platform to terminate the TLS connection.



Barnes, et al.           Expires January 9, 2017               [Page 56]

Internet-Draft                    ACME                         July 2016


   However, some hosting platforms will choose a virtual host to be the
   "default", and route connections with unknown SNI values to that
   host.

   In such cases, the owner of the default virtual host can complete a
   TLS-based challenge (e.g., "tls-sni-02") for any domain with an A
   record that points to the hosting platform.  This could result in
   mis-issuance in cases where there are multiple hosts with different
   owners resident on the hosting platform.

   A CA that accepts TLS-based proof of domain control should attempt to
   check whether a domain is hosted on a domain with a default virtual
   host before allowing an authorization request for this host to use a
   TLS-based challenge.  A default virtual host can be detected by
   initiating TLS connections to the host with random SNI values within
   the namespace used for the TLS-based challenge (the "acme.invalid"
   namespace for "tls-sni-02").

10.3.  Use of DNSSEC Resolvers

   An ACME-based CA will often need to make DNS queries, e.g., to
   validate control of DNS names.  Because the security of such
   validations ultimately depends on the authenticity of DNS data, every
   possible precaution should be taken to secure DNS queries done by the
   CA.  It is therefore RECOMMENDED that ACME-based CAs make all DNS
   queries via DNSSEC-validating stub or recursive resolvers.  This
   provides additional protection to domains which choose to make use of
   DNSSEC.

   An ACME-based CA must use only a resolver if it trusts the resolver
   and every component of the network route by which it is accessed.  It
   is therefore RECOMMENDED that ACME-based CAs operate their own
   DNSSEC-validating resolvers within their trusted network and use
   these resolvers both for both CAA record lookups and all record
   lookups in furtherance of a challenge scheme (A, AAAA, TXT, etc.).

11.  Acknowledgements

   In addition to the editors listed on the front page, this document
   has benefited from contributions from a broad set of contributors,
   all the way back to its inception.

   o  Peter Eckersley, EFF

   o  Eric Rescorla, Mozilla

   o  Seth Schoen, EFF




Barnes, et al.           Expires January 9, 2017               [Page 57]

Internet-Draft                    ACME                         July 2016


   o  Alex Halderman, University of Michigan

   o  Martin Thomson, Mozilla

   o  Jakub Warmuz, University of Oxford

   This document draws on many concepts established by Eric Rescorla's
   "Automated Certificate Issuance Protocol" draft.  Martin Thomson
   provided helpful guidance in the use of HTTP.

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,
              <http://www.rfc-editor.org/info/rfc2818>.

   [RFC2985]  Nystrom, M. and B. Kaliski, "PKCS #9: Selected Object
              Classes and Attribute Types Version 2.0", RFC 2985,
              DOI 10.17487/RFC2985, November 2000,
              <http://www.rfc-editor.org/info/rfc2985>.

   [RFC2986]  Nystrom, M. and B. Kaliski, "PKCS #10: Certification
              Request Syntax Specification Version 1.7", RFC 2986,
              DOI 10.17487/RFC2986, November 2000,
              <http://www.rfc-editor.org/info/rfc2986>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <http://www.rfc-editor.org/info/rfc3339>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <http://www.rfc-editor.org/info/rfc4648>.






Barnes, et al.           Expires January 9, 2017               [Page 58]

Internet-Draft                    ACME                         July 2016


   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <http://www.rfc-editor.org/info/rfc5246>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <http://www.rfc-editor.org/info/rfc5280>.

   [RFC5988]  Nottingham, M., "Web Linking", RFC 5988,
              DOI 10.17487/RFC5988, October 2010,
              <http://www.rfc-editor.org/info/rfc5988>.

   [RFC6066]  Eastlake 3rd, D., "Transport Layer Security (TLS)
              Extensions: Extension Definitions", RFC 6066,
              DOI 10.17487/RFC6066, January 2011,
              <http://www.rfc-editor.org/info/rfc6066>.

   [RFC6570]  Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
              and D. Orchard, "URI Template", RFC 6570,
              DOI 10.17487/RFC6570, March 2012,
              <http://www.rfc-editor.org/info/rfc6570>.

   [RFC6844]  Hallam-Baker, P. and R. Stradling, "DNS Certification
              Authority Authorization (CAA) Resource Record", RFC 6844,
              DOI 10.17487/RFC6844, January 2013,
              <http://www.rfc-editor.org/info/rfc6844>.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <http://www.rfc-editor.org/info/rfc7159>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <http://www.rfc-editor.org/info/rfc7515>.

   [RFC7517]  Jones, M., "JSON Web Key (JWK)", RFC 7517,
              DOI 10.17487/RFC7517, May 2015,
              <http://www.rfc-editor.org/info/rfc7517>.

   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <http://www.rfc-editor.org/info/rfc7518>.






Barnes, et al.           Expires January 9, 2017               [Page 59]

Internet-Draft                    ACME                         July 2016


   [RFC7638]  Jones, M. and N. Sakimura, "JSON Web Key (JWK)
              Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September
              2015, <http://www.rfc-editor.org/info/rfc7638>.

   [RFC7807]  Nottingham, M. and E. Wilde, "Problem Details for HTTP
              APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016,
              <http://www.rfc-editor.org/info/rfc7807>.

12.2.  Informative References

   [I-D.vixie-dnsext-dns0x20]
              Vixie, P. and D. Dagon, "Use of Bit 0x20 in DNS Labels to
              Improve Transaction Identity", draft-vixie-dnsext-
              dns0x20-00 (work in progress), March 2008.

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              DOI 10.17487/RFC3552, July 2003,
              <http://www.rfc-editor.org/info/rfc3552>.

   [RFC3553]  Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An
              IETF URN Sub-namespace for Registered Protocol
              Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553, June
              2003, <http://www.rfc-editor.org/info/rfc3553>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC5785]  Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
              Uniform Resource Identifiers (URIs)", RFC 5785,
              DOI 10.17487/RFC5785, April 2010,
              <http://www.rfc-editor.org/info/rfc5785>.

   [RFC6962]  Laurie, B., Langley, A., and E. Kasper, "Certificate
              Transparency", RFC 6962, DOI 10.17487/RFC6962, June 2013,
              <http://www.rfc-editor.org/info/rfc6962>.

   [RFC7469]  Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning
              Extension for HTTP", RFC 7469, DOI 10.17487/RFC7469, April
              2015, <http://www.rfc-editor.org/info/rfc7469>.

   [W3C.CR-cors-20130129]
              Kesteren, A., "Cross-Origin Resource Sharing", World Wide
              Web Consortium CR CR-cors-20130129, January 2013,
              <http://www.w3.org/TR/2013/CR-cors-20130129>.




Barnes, et al.           Expires January 9, 2017               [Page 60]

Internet-Draft                    ACME                         July 2016


Authors' Addresses

   Richard Barnes
   Mozilla

   Email: rlb@ipv.sx


   Jacob Hoffman-Andrews
   EFF

   Email: jsha@eff.org


   James Kasten
   University of Michigan

   Email: jdkasten@umich.edu

































Barnes, et al.           Expires January 9, 2017               [Page 61]