120 lines
2.7 KiB
Go
120 lines
2.7 KiB
Go
/*
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Package rfc6979 is an implementation of RFC 6979's deterministic DSA.
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Such signatures are compatible with standard Digital Signature Algorithm
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(DSA) and Elliptic Curve Digital Signature Algorithm (ECDSA) digital
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signatures and can be processed with unmodified verifiers, which need not be
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aware of the procedure described therein. Deterministic signatures retain
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the cryptographic security features associated with digital signatures but
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can be more easily implemented in various environments, since they do not
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need access to a source of high-quality randomness.
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(https://tools.ietf.org/html/rfc6979)
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Provides functions similar to crypto/dsa and crypto/ecdsa.
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*/
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package rfc6979
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import (
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"bytes"
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"crypto/hmac"
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"hash"
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"math/big"
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)
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// mac returns an HMAC of the given key and message.
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func mac(alg func() hash.Hash, k, m, buf []byte) []byte {
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h := hmac.New(alg, k)
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h.Write(m)
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return h.Sum(buf[:0])
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}
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// https://tools.ietf.org/html/rfc6979#section-2.3.2
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func bits2int(in []byte, qlen int) *big.Int {
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vlen := len(in) * 8
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v := new(big.Int).SetBytes(in)
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if vlen > qlen {
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v = new(big.Int).Rsh(v, uint(vlen-qlen))
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}
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return v
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}
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// https://tools.ietf.org/html/rfc6979#section-2.3.3
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func int2octets(v *big.Int, rolen int) []byte {
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out := v.Bytes()
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// pad with zeros if it's too short
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if len(out) < rolen {
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out2 := make([]byte, rolen)
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copy(out2[rolen-len(out):], out)
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return out2
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}
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// drop most significant bytes if it's too long
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if len(out) > rolen {
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out2 := make([]byte, rolen)
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copy(out2, out[len(out)-rolen:])
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return out2
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}
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return out
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}
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// https://tools.ietf.org/html/rfc6979#section-2.3.4
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func bits2octets(in []byte, q *big.Int, qlen, rolen int) []byte {
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z1 := bits2int(in, qlen)
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z2 := new(big.Int).Sub(z1, q)
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if z2.Sign() < 0 {
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return int2octets(z1, rolen)
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}
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return int2octets(z2, rolen)
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}
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var one = big.NewInt(1)
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// https://tools.ietf.org/html/rfc6979#section-3.2
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func generateSecret(q, x *big.Int, alg func() hash.Hash, hash []byte, test func(*big.Int) bool) {
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qlen := q.BitLen()
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holen := alg().Size()
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rolen := (qlen + 7) >> 3
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bx := append(int2octets(x, rolen), bits2octets(hash, q, qlen, rolen)...)
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// Step B
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v := bytes.Repeat([]byte{0x01}, holen)
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// Step C
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k := bytes.Repeat([]byte{0x00}, holen)
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// Step D
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k = mac(alg, k, append(append(v, 0x00), bx...), k)
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// Step E
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v = mac(alg, k, v, v)
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// Step F
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k = mac(alg, k, append(append(v, 0x01), bx...), k)
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// Step G
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v = mac(alg, k, v, v)
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// Step H
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for {
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// Step H1
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var t []byte
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// Step H2
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for len(t) < qlen/8 {
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v = mac(alg, k, v, v)
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t = append(t, v...)
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}
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// Step H3
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secret := bits2int(t, qlen)
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if secret.Cmp(one) >= 0 && secret.Cmp(q) < 0 && test(secret) {
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return
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}
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k = mac(alg, k, append(v, 0x00), k)
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v = mac(alg, k, v, v)
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}
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}
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