mirror of https://go.googlesource.com/go
192 lines
4.8 KiB
Go
192 lines
4.8 KiB
Go
// Copyright 2022 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package ecdsa
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import (
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"crypto/elliptic"
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"errors"
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"io"
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"math/big"
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"golang.org/x/crypto/cryptobyte"
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"golang.org/x/crypto/cryptobyte/asn1"
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)
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// This file contains a math/big implementation of ECDSA that is only used for
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// deprecated custom curves.
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func generateLegacy(c elliptic.Curve, rand io.Reader) (*PrivateKey, error) {
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k, err := randFieldElement(c, rand)
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if err != nil {
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return nil, err
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}
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priv := new(PrivateKey)
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priv.PublicKey.Curve = c
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priv.D = k
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priv.PublicKey.X, priv.PublicKey.Y = c.ScalarBaseMult(k.Bytes())
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return priv, nil
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}
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// hashToInt converts a hash value to an integer. Per FIPS 186-4, Section 6.4,
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// we use the left-most bits of the hash to match the bit-length of the order of
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// the curve. This also performs Step 5 of SEC 1, Version 2.0, Section 4.1.3.
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func hashToInt(hash []byte, c elliptic.Curve) *big.Int {
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orderBits := c.Params().N.BitLen()
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orderBytes := (orderBits + 7) / 8
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if len(hash) > orderBytes {
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hash = hash[:orderBytes]
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}
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ret := new(big.Int).SetBytes(hash)
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excess := len(hash)*8 - orderBits
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if excess > 0 {
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ret.Rsh(ret, uint(excess))
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}
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return ret
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}
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var errZeroParam = errors.New("zero parameter")
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// Sign signs a hash (which should be the result of hashing a larger message)
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// using the private key, priv. If the hash is longer than the bit-length of the
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// private key's curve order, the hash will be truncated to that length. It
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// returns the signature as a pair of integers. Most applications should use
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// [SignASN1] instead of dealing directly with r, s.
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func Sign(rand io.Reader, priv *PrivateKey, hash []byte) (r, s *big.Int, err error) {
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sig, err := SignASN1(rand, priv, hash)
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if err != nil {
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return nil, nil, err
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}
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r, s = new(big.Int), new(big.Int)
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var inner cryptobyte.String
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input := cryptobyte.String(sig)
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if !input.ReadASN1(&inner, asn1.SEQUENCE) ||
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!input.Empty() ||
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!inner.ReadASN1Integer(r) ||
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!inner.ReadASN1Integer(s) ||
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!inner.Empty() {
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return nil, nil, errors.New("invalid ASN.1 from SignASN1")
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}
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return r, s, nil
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}
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func signLegacy(priv *PrivateKey, csprng io.Reader, hash []byte) (sig []byte, err error) {
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c := priv.Curve
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// SEC 1, Version 2.0, Section 4.1.3
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N := c.Params().N
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if N.Sign() == 0 {
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return nil, errZeroParam
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}
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var k, kInv, r, s *big.Int
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for {
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for {
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k, err = randFieldElement(c, csprng)
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if err != nil {
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return nil, err
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}
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kInv = new(big.Int).ModInverse(k, N)
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r, _ = c.ScalarBaseMult(k.Bytes())
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r.Mod(r, N)
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if r.Sign() != 0 {
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break
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}
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}
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e := hashToInt(hash, c)
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s = new(big.Int).Mul(priv.D, r)
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s.Add(s, e)
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s.Mul(s, kInv)
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s.Mod(s, N) // N != 0
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if s.Sign() != 0 {
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break
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}
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}
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return encodeSignature(r.Bytes(), s.Bytes())
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}
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// Verify verifies the signature in r, s of hash using the public key, pub. Its
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// return value records whether the signature is valid. Most applications should
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// use VerifyASN1 instead of dealing directly with r, s.
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//
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// The inputs are not considered confidential, and may leak through timing side
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// channels, or if an attacker has control of part of the inputs.
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func Verify(pub *PublicKey, hash []byte, r, s *big.Int) bool {
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if r.Sign() <= 0 || s.Sign() <= 0 {
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return false
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}
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sig, err := encodeSignature(r.Bytes(), s.Bytes())
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if err != nil {
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return false
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}
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return VerifyASN1(pub, hash, sig)
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}
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func verifyLegacy(pub *PublicKey, hash []byte, sig []byte) bool {
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rBytes, sBytes, err := parseSignature(sig)
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if err != nil {
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return false
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}
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r, s := new(big.Int).SetBytes(rBytes), new(big.Int).SetBytes(sBytes)
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c := pub.Curve
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N := c.Params().N
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if r.Sign() <= 0 || s.Sign() <= 0 {
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return false
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}
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if r.Cmp(N) >= 0 || s.Cmp(N) >= 0 {
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return false
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}
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// SEC 1, Version 2.0, Section 4.1.4
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e := hashToInt(hash, c)
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w := new(big.Int).ModInverse(s, N)
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u1 := e.Mul(e, w)
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u1.Mod(u1, N)
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u2 := w.Mul(r, w)
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u2.Mod(u2, N)
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x1, y1 := c.ScalarBaseMult(u1.Bytes())
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x2, y2 := c.ScalarMult(pub.X, pub.Y, u2.Bytes())
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x, y := c.Add(x1, y1, x2, y2)
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if x.Sign() == 0 && y.Sign() == 0 {
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return false
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}
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x.Mod(x, N)
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return x.Cmp(r) == 0
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}
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var one = new(big.Int).SetInt64(1)
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// randFieldElement returns a random element of the order of the given
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// curve using the procedure given in FIPS 186-4, Appendix B.5.2.
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func randFieldElement(c elliptic.Curve, rand io.Reader) (k *big.Int, err error) {
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// See randomPoint for notes on the algorithm. This has to match, or s390x
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// signatures will come out different from other architectures, which will
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// break TLS recorded tests.
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for {
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N := c.Params().N
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b := make([]byte, (N.BitLen()+7)/8)
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if _, err = io.ReadFull(rand, b); err != nil {
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return
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}
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if excess := len(b)*8 - N.BitLen(); excess > 0 {
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b[0] >>= excess
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}
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k = new(big.Int).SetBytes(b)
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if k.Sign() != 0 && k.Cmp(N) < 0 {
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return
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}
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}
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}
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