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package main

import (
	"errors"
	"flag"
	"fmt"
	"io/ioutil"
	"os"

	"dim13.org/signify/ask"
	"dim13.org/signify/bhash"
	"dim13.org/signify/file"
	"dim13.org/signify/key"
)

/*
	signify -C [-q] -p pubkey -x sigfile [file ...]
	signify -G [-n] [-c comment] -p pubkey -s seckey
	signify -S [-ez] [-x sigfile] -s seckey -m message
	signify -V [-eqz] [-p pubkey] [-t keytype] [-x sigfile] -m message
*/

const safePath = "/etc/signify"

var (
	ErrEZ = errors.New("can't combine -e and -z options")
)

var (
	checksum = flag.Bool("C", false, "Verify a signed checksum list")
	generate = flag.Bool("G", false, "Generate a new key pair")
	sign     = flag.Bool("S", false, "Sign the specfied message")
	verify   = flag.Bool("V", false, "Verify the message")
	comment  = flag.String("c", "signify", "Comment")
	embedded = flag.Bool("e", false, "Embed the message")
	msg      = flag.String("m", "", "Message file")
	nopass   = flag.Bool("n", false, "No key passphrase")
	pub      = flag.String("p", "", "Public key file")
	quiet    = flag.Bool("q", false, "Quiet mode")
	sec      = flag.String("s", "", "Secret key file")
	sig      = flag.String("x", "", "Signature file")
	gzip     = flag.Bool("z", false, "Sign and verify gzip archives")
)

type Mode int

const (
	ModeNone Mode = iota
	ModeCheck
	ModeGenerate
	ModeSign
	ModeVerify
)

func usage() {
	flag.Usage()
	os.Exit(1)
}

func fatal(err error) {
	fmt.Println(err)
	os.Exit(1)
}

func main() {
	flag.Parse()

	var mode Mode

	if *embedded && *gzip {
		fatal(ErrEZ)
	}

	if *generate {
		if mode != ModeNone {
			usage()
		}
		mode = ModeGenerate
	}

	if *checksum {
		if mode != ModeNone {
			usage()
		}
		mode = ModeCheck
	}

	if *sign {
		if mode != ModeNone {
			usage()
		}
		mode = ModeSign
	}

	if *verify {
		if mode != ModeNone {
			flag.Usage()
			os.Exit(2)
		}
		mode = ModeVerify
	}

	switch mode {
	case ModeGenerate:
		if err := Generate(*pub, *sec, *comment, *nopass); err != nil {
			fatal(err)
		}
	case ModeSign:
		if err := Sign(*msg, *sec, *embedded); err != nil {
			fatal(err)
		}
	case ModeVerify:
		if err := Verify(*msg, *pub, *quiet); err != nil {
			fatal(err)
		}
	default:
		usage()
	}
}

func Generate(pubFile, encFile, comment string, nopass bool) error {
	if err := file.Names(pubFile, encFile); err != nil {
		return err
	}

	pubKey, encKey, err := key.NewKey()
	if err != nil {
		return err
	}

	if nopass {
		encKey.KDFRounds = 0
	}
	if err := Kdf(encKey, ask.Confirmed); err != nil {
		return err
	}

	encRaw, err := key.Marshal(encKey)
	if err != nil {
		return err
	}

	block := &file.Block{
		Comment: fmt.Sprintf("%s secret key", comment),
		Bytes:   encRaw,
	}
	if err := file.EncodeFile(encFile, file.EncMode, block); err != nil {
		return err
	}

	pubRaw, err := key.Marshal(pubKey)
	if err != nil {
		return err
	}
	block = &file.Block{
		Comment: fmt.Sprintf("%s public key", comment),
		Bytes:   pubRaw,
	}
	if err := file.EncodeFile(pubFile, file.PubMode, block); err != nil {
		return err
	}

	return nil
}

func OpenEnc(fname string) (*key.Enc, error) {
	block, err := file.DecodeFile(fname)
	if err != nil {
		return nil, err
	}
	encKey := new(key.Enc)
	if err := key.Unmarshal(block.Bytes, encKey); err != nil {
		return nil, err
	}
	if err := Kdf(encKey, ask.Password); err != nil {
		return nil, err
	}
	if err := encKey.Check(); err != nil {
		return nil, err
	}
	return encKey, nil
}

func OpenPub(fname string) (*key.Pub, error) {
	block, err := file.DecodeFile(fname)
	if err != nil {
		return nil, err
	}
	pubKey := new(key.Pub)
	if err := key.Unmarshal(block.Bytes, pubKey); err != nil {
		return nil, err
	}
	if err := pubKey.Check(); err != nil {
		return nil, err
	}
	return pubKey, nil
}

func OpenSig(fname string) (*key.Sig, []byte, error) {
	block, err := file.DecodeFile(fname + ".sig")
	if err != nil {
		return nil, nil, err
	}
	sig := new(key.Sig)
	if err := key.Unmarshal(block.Bytes, sig); err != nil {
		return nil, nil, err
	}
	if err := sig.Check(); err != nil {
		return nil, nil, err
	}
	if len(block.Message) > 0 {
		return sig, block.Message, nil
	}
	msg, err := ioutil.ReadFile(fname)
	if err != nil {
		return nil, nil, err
	}
	return sig, msg, nil
}

func Sign(msgFile, encFile string, embed bool) error {
	encKey, err := OpenEnc(encFile)
	if err != nil {
		return err
	}
	body, err := ioutil.ReadFile(msgFile)
	if err != nil {
		return err
	}
	sig := encKey.Sign(body)
	sigRaw, err := key.Marshal(sig)
	if err != nil {
		return err
	}
	block := &file.Block{
		Comment: fmt.Sprintf("verify with %s", file.PubName(encFile)),
		Bytes:   sigRaw,
	}
	if embed {
		block.Message = body
	}
	if err := file.EncodeFile(msgFile+".sig", file.SigMode, block); err != nil {
		return err
	}
	return nil
}

func Verify(msgFile, pubFile string, quiet bool) error {
	pubKey, err := OpenPub(pubFile)
	if err != nil {
		return err
	}
	sig, body, err := OpenSig(msgFile)
	if err != nil {
		return err
	}
	if err := pubKey.Verify(body, sig); err != nil {
		return err
	}
	if !quiet {
		fmt.Println("Signature Verfied")
	}
	return nil
}

func Kdf(enc *key.Enc, ask func() (string, error)) error {
	if enc.KDFRounds == 0 {
		return nil
	}
	pass, err := ask()
	if err != nil {
		return err
	}
	xor := bhash.Pbkdf([]byte(pass), enc.Salt[:], int(enc.KDFRounds), len(enc.Key))
	for i := range xor {
		enc.Key[i] ^= xor[i]
	}
	return nil
}