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-rw-r--r--key/key.go148
1 files changed, 148 insertions, 0 deletions
diff --git a/key/key.go b/key/key.go
new file mode 100644
index 0000000..57978e0
--- /dev/null
+++ b/key/key.go
@@ -0,0 +1,148 @@
+package key
+
+import (
+ "bytes"
+ "crypto/rand"
+ "crypto/sha512"
+ "encoding/binary"
+ "errors"
+
+ "dim13.org/signify/bhash"
+
+ "golang.org/x/crypto/ed25519"
+)
+
+const DefaultRounds = 42
+
+var (
+ ErrInvalidPK = errors.New("unsupported format")
+ ErrInvalidKDF = errors.New("unsupported KDF")
+ ErrPassphrase = errors.New("incorrect passphrase")
+ ErrInvalidKey = errors.New("invalid key")
+ ErrKeyNum = errors.New("verification failed: checked against wrong key")
+ ErrInvalidSig = errors.New("signature verfication failed")
+)
+
+var (
+ pkAlg = [2]byte{'E', 'd'}
+ kdfAlg = [2]byte{'B', 'K'}
+)
+
+type Sig struct {
+ PKAlg [2]byte
+ KeyNum [8]byte
+ Sig [ed25519.SignatureSize]byte
+}
+
+type Pub struct {
+ PKAlg [2]byte
+ KeyNum [8]byte
+ Key [ed25519.PublicKeySize]byte
+}
+
+type Enc struct {
+ PKAlg [2]byte
+ KDFAlg [2]byte
+ KDFRounds uint32
+ Salt [16]byte
+ Checksum [8]byte
+ KeyNum [8]byte
+ Key [ed25519.PrivateKeySize]byte
+}
+
+func (v *Sig) Check() error {
+ if v.PKAlg != pkAlg {
+ return ErrInvalidPK
+ }
+ return nil
+}
+
+func (v *Pub) Check() error {
+ if v.PKAlg != pkAlg {
+ return ErrInvalidPK
+ }
+ return nil
+}
+
+func (v *Pub) Verify(message []byte, sig *Sig) error {
+ if v.KeyNum != sig.KeyNum {
+ return ErrKeyNum
+ }
+ if !ed25519.Verify(ed25519.PublicKey(v.Key[:]), message, sig.Sig[:]) {
+ return ErrInvalidSig
+ }
+ return nil
+}
+
+func (v *Enc) Sign(message []byte) *Sig {
+ sig := &Sig{PKAlg: v.PKAlg, KeyNum: v.KeyNum}
+ copy(sig.Sig[:], ed25519.Sign(ed25519.PrivateKey(v.Key[:]), message))
+ return sig
+}
+
+func (v *Enc) Check() error {
+ if v.PKAlg != pkAlg {
+ return ErrInvalidPK
+ }
+ if v.KDFAlg != kdfAlg {
+ return ErrInvalidKDF
+ }
+ sum := sha512.Sum512(v.Key[:])
+ if !bytes.Equal(sum[:len(v.Checksum)], v.Checksum[:]) {
+ return ErrInvalidKey
+ }
+ return nil
+}
+
+func (e *Enc) Kdf(ask func() (string, error)) error {
+ if e.KDFRounds == 0 {
+ return nil
+ }
+ pass, err := ask()
+ if err != nil {
+ return err
+ }
+ xor := bhash.Pbkdf([]byte(pass), e.Salt[:], int(e.KDFRounds), len(e.Key))
+ for i := range xor {
+ e.Key[i] ^= xor[i]
+ }
+ return e.Check()
+}
+
+func Unmarshal(b []byte, v interface{}) error {
+ buf := bytes.NewReader(b)
+ if err := binary.Read(buf, binary.BigEndian, v); err != nil {
+ return err
+ }
+ return nil
+}
+
+func Marshal(v interface{}) ([]byte, error) {
+ buf := new(bytes.Buffer)
+ if err := binary.Write(buf, binary.BigEndian, v); err != nil {
+ return nil, err
+ }
+ return buf.Bytes(), nil
+}
+
+func NewKey() (Pub, Enc, error) {
+ pub, sec, err := ed25519.GenerateKey(rand.Reader)
+ if err != nil {
+ return Pub{}, Enc{}, err
+ }
+
+ pubKey := Pub{PKAlg: pkAlg}
+ encKey := Enc{PKAlg: pkAlg, KDFAlg: kdfAlg, KDFRounds: DefaultRounds}
+
+ copy(pubKey.Key[:], pub)
+ copy(encKey.Key[:], sec)
+
+ checkSum := sha512.Sum512(sec)
+ copy(encKey.Checksum[:], checkSum[:len(encKey.Checksum)])
+
+ rand.Read(encKey.Salt[:])
+ rand.Read(encKey.KeyNum[:])
+ pubKey.KeyNum = encKey.KeyNum
+
+ return pubKey, encKey, nil
+}