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| 1 | +// Copyright 2022 The Go Authors. All rights reserved. |
| 2 | +// Use of this source code is governed by a BSD-style |
| 3 | +// license that can be found in the LICENSE file. |
| 4 | + |
| 5 | +package ecdsa |
| 6 | + |
| 7 | +import ( |
| 8 | + "crypto/elliptic" |
| 9 | + "errors" |
| 10 | + "io" |
| 11 | + "math/big" |
| 12 | + |
| 13 | + "golang.org/x/crypto/cryptobyte" |
| 14 | + "golang.org/x/crypto/cryptobyte/asn1" |
| 15 | +) |
| 16 | + |
| 17 | +// This file contains a math/big implementation of ECDSA that is only used for |
| 18 | +// deprecated custom curves. |
| 19 | + |
| 20 | +func generateLegacy(c elliptic.Curve, rand io.Reader) (*PrivateKey, error) { |
| 21 | + k, err := randFieldElement(c, rand) |
| 22 | + if err != nil { |
| 23 | + return nil, err |
| 24 | + } |
| 25 | + |
| 26 | + priv := new(PrivateKey) |
| 27 | + priv.PublicKey.Curve = c |
| 28 | + priv.D = k |
| 29 | + priv.PublicKey.X, priv.PublicKey.Y = c.ScalarBaseMult(k.Bytes()) |
| 30 | + return priv, nil |
| 31 | +} |
| 32 | + |
| 33 | +// hashToInt converts a hash value to an integer. Per FIPS 186-4, Section 6.4, |
| 34 | +// we use the left-most bits of the hash to match the bit-length of the order of |
| 35 | +// the curve. This also performs Step 5 of SEC 1, Version 2.0, Section 4.1.3. |
| 36 | +func hashToInt(hash []byte, c elliptic.Curve) *big.Int { |
| 37 | + orderBits := c.Params().N.BitLen() |
| 38 | + orderBytes := (orderBits + 7) / 8 |
| 39 | + if len(hash) > orderBytes { |
| 40 | + hash = hash[:orderBytes] |
| 41 | + } |
| 42 | + |
| 43 | + ret := new(big.Int).SetBytes(hash) |
| 44 | + excess := len(hash)*8 - orderBits |
| 45 | + if excess > 0 { |
| 46 | + ret.Rsh(ret, uint(excess)) |
| 47 | + } |
| 48 | + return ret |
| 49 | +} |
| 50 | + |
| 51 | +var errZeroParam = errors.New("zero parameter") |
| 52 | + |
| 53 | +// Sign signs a hash (which should be the result of hashing a larger message) |
| 54 | +// using the private key, priv. If the hash is longer than the bit-length of the |
| 55 | +// private key's curve order, the hash will be truncated to that length. It |
| 56 | +// returns the signature as a pair of integers. Most applications should use |
| 57 | +// SignASN1 instead of dealing directly with r, s. |
| 58 | +func Sign(rand io.Reader, priv *PrivateKey, hash []byte) (r, s *big.Int, err error) { |
| 59 | + sig, err := SignASN1(rand, priv, hash) |
| 60 | + if err != nil { |
| 61 | + return nil, nil, err |
| 62 | + } |
| 63 | + |
| 64 | + r, s = new(big.Int), new(big.Int) |
| 65 | + var inner cryptobyte.String |
| 66 | + input := cryptobyte.String(sig) |
| 67 | + if !input.ReadASN1(&inner, asn1.SEQUENCE) || |
| 68 | + !input.Empty() || |
| 69 | + !inner.ReadASN1Integer(r) || |
| 70 | + !inner.ReadASN1Integer(s) || |
| 71 | + !inner.Empty() { |
| 72 | + return nil, nil, errors.New("invalid ASN.1 from SignASN1") |
| 73 | + } |
| 74 | + return r, s, nil |
| 75 | +} |
| 76 | + |
| 77 | +func signLegacy(priv *PrivateKey, csprng io.Reader, hash []byte) (sig []byte, err error) { |
| 78 | + c := priv.Curve |
| 79 | + |
| 80 | + // SEC 1, Version 2.0, Section 4.1.3 |
| 81 | + N := c.Params().N |
| 82 | + if N.Sign() == 0 { |
| 83 | + return nil, errZeroParam |
| 84 | + } |
| 85 | + var k, kInv, r, s *big.Int |
| 86 | + for { |
| 87 | + for { |
| 88 | + k, err = randFieldElement(c, csprng) |
| 89 | + if err != nil { |
| 90 | + return nil, err |
| 91 | + } |
| 92 | + |
| 93 | + kInv = new(big.Int).ModInverse(k, N) |
| 94 | + |
| 95 | + r, _ = c.ScalarBaseMult(k.Bytes()) |
| 96 | + r.Mod(r, N) |
| 97 | + if r.Sign() != 0 { |
| 98 | + break |
| 99 | + } |
| 100 | + } |
| 101 | + |
| 102 | + e := hashToInt(hash, c) |
| 103 | + s = new(big.Int).Mul(priv.D, r) |
| 104 | + s.Add(s, e) |
| 105 | + s.Mul(s, kInv) |
| 106 | + s.Mod(s, N) // N != 0 |
| 107 | + if s.Sign() != 0 { |
| 108 | + break |
| 109 | + } |
| 110 | + } |
| 111 | + |
| 112 | + return encodeSignature(r.Bytes(), s.Bytes()) |
| 113 | +} |
| 114 | + |
| 115 | +// Verify verifies the signature in r, s of hash using the public key, pub. Its |
| 116 | +// return value records whether the signature is valid. Most applications should |
| 117 | +// use VerifyASN1 instead of dealing directly with r, s. |
| 118 | +func Verify(pub *PublicKey, hash []byte, r, s *big.Int) bool { |
| 119 | + sig, err := encodeSignature(r.Bytes(), s.Bytes()) |
| 120 | + if err != nil { |
| 121 | + return false |
| 122 | + } |
| 123 | + return VerifyASN1(pub, hash, sig) |
| 124 | +} |
| 125 | + |
| 126 | +func verifyLegacy(pub *PublicKey, hash []byte, sig []byte) bool { |
| 127 | + rBytes, sBytes, err := parseSignature(sig) |
| 128 | + if err != nil { |
| 129 | + return false |
| 130 | + } |
| 131 | + r, s := new(big.Int).SetBytes(rBytes), new(big.Int).SetBytes(sBytes) |
| 132 | + |
| 133 | + c := pub.Curve |
| 134 | + N := c.Params().N |
| 135 | + |
| 136 | + if r.Sign() <= 0 || s.Sign() <= 0 { |
| 137 | + return false |
| 138 | + } |
| 139 | + if r.Cmp(N) >= 0 || s.Cmp(N) >= 0 { |
| 140 | + return false |
| 141 | + } |
| 142 | + |
| 143 | + // SEC 1, Version 2.0, Section 4.1.4 |
| 144 | + e := hashToInt(hash, c) |
| 145 | + w := new(big.Int).ModInverse(s, N) |
| 146 | + |
| 147 | + u1 := e.Mul(e, w) |
| 148 | + u1.Mod(u1, N) |
| 149 | + u2 := w.Mul(r, w) |
| 150 | + u2.Mod(u2, N) |
| 151 | + |
| 152 | + x1, y1 := c.ScalarBaseMult(u1.Bytes()) |
| 153 | + x2, y2 := c.ScalarMult(pub.X, pub.Y, u2.Bytes()) |
| 154 | + x, y := c.Add(x1, y1, x2, y2) |
| 155 | + |
| 156 | + if x.Sign() == 0 && y.Sign() == 0 { |
| 157 | + return false |
| 158 | + } |
| 159 | + x.Mod(x, N) |
| 160 | + return x.Cmp(r) == 0 |
| 161 | +} |
| 162 | + |
| 163 | +var one = new(big.Int).SetInt64(1) |
| 164 | + |
| 165 | +// randFieldElement returns a random element of the order of the given |
| 166 | +// curve using the procedure given in FIPS 186-4, Appendix B.5.2. |
| 167 | +func randFieldElement(c elliptic.Curve, rand io.Reader) (k *big.Int, err error) { |
| 168 | + // See randomPoint for notes on the algorithm. This has to match, or s390x |
| 169 | + // signatures will come out different from other architectures, which will |
| 170 | + // break TLS recorded tests. |
| 171 | + for { |
| 172 | + N := c.Params().N |
| 173 | + b := make([]byte, (N.BitLen()+7)/8) |
| 174 | + if _, err = io.ReadFull(rand, b); err != nil { |
| 175 | + return |
| 176 | + } |
| 177 | + if excess := len(b)*8 - N.BitLen(); excess > 0 { |
| 178 | + b[0] >>= excess |
| 179 | + } |
| 180 | + k = new(big.Int).SetBytes(b) |
| 181 | + if k.Sign() != 0 && k.Cmp(N) < 0 { |
| 182 | + return |
| 183 | + } |
| 184 | + } |
| 185 | +} |
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