1 files changed, 188 insertions, 0 deletions
diff --git a/src/crypto/ecdsa/ecdsa_legacy.go b/src/crypto/ecdsa/ecdsa_legacy.go
new file mode 100644
index 0000000..12a40e4
--- /dev/null
+++ b/src/crypto/ecdsa/ecdsa_legacy.go
@@ -0,0 +1,188 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ecdsa
+
+import (
+	"crypto/elliptic"
+	"errors"
+	"io"
+	"math/big"
+
+	"golang.org/x/crypto/cryptobyte"
+	"golang.org/x/crypto/cryptobyte/asn1"
+)
+
+// This file contains a math/big implementation of ECDSA that is only used for
+// deprecated custom curves.
+
+func generateLegacy(c elliptic.Curve, rand io.Reader) (*PrivateKey, error) {
+	k, err := randFieldElement(c, rand)
+	if err != nil {
+		return nil, err
+	}
+
+	priv := new(PrivateKey)
+	priv.PublicKey.Curve = c
+	priv.D = k
+	priv.PublicKey.X, priv.PublicKey.Y = c.ScalarBaseMult(k.Bytes())
+	return priv, nil
+}
+
+// hashToInt converts a hash value to an integer. Per FIPS 186-4, Section 6.4,
+// we use the left-most bits of the hash to match the bit-length of the order of
+// the curve. This also performs Step 5 of SEC 1, Version 2.0, Section 4.1.3.
+func hashToInt(hash []byte, c elliptic.Curve) *big.Int {
+	orderBits := c.Params().N.BitLen()
+	orderBytes := (orderBits + 7) / 8
+	if len(hash) > orderBytes {
+		hash = hash[:orderBytes]
+	}
+
+	ret := new(big.Int).SetBytes(hash)
+	excess := len(hash)*8 - orderBits
+	if excess > 0 {
+		ret.Rsh(ret, uint(excess))
+	}
+	return ret
+}
+
+var errZeroParam = errors.New("zero parameter")
+
+// Sign signs a hash (which should be the result of hashing a larger message)
+// using the private key, priv. If the hash is longer than the bit-length of the
+// private key's curve order, the hash will be truncated to that length. It
+// returns the signature as a pair of integers. Most applications should use
+// SignASN1 instead of dealing directly with r, s.
+func Sign(rand io.Reader, priv *PrivateKey, hash []byte) (r, s *big.Int, err error) {
+	sig, err := SignASN1(rand, priv, hash)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	r, s = new(big.Int), new(big.Int)
+	var inner cryptobyte.String
+	input := cryptobyte.String(sig)
+	if !input.ReadASN1(&inner, asn1.SEQUENCE) ||
+		!input.Empty() ||
+		!inner.ReadASN1Integer(r) ||
+		!inner.ReadASN1Integer(s) ||
+		!inner.Empty() {
+		return nil, nil, errors.New("invalid ASN.1 from SignASN1")
+	}
+	return r, s, nil
+}
+
+func signLegacy(priv *PrivateKey, csprng io.Reader, hash []byte) (sig []byte, err error) {
+	c := priv.Curve
+
+	// SEC 1, Version 2.0, Section 4.1.3
+	N := c.Params().N
+	if N.Sign() == 0 {
+		return nil, errZeroParam
+	}
+	var k, kInv, r, s *big.Int
+	for {
+		for {
+			k, err = randFieldElement(c, csprng)
+			if err != nil {
+				return nil, err
+			}
+
+			kInv = new(big.Int).ModInverse(k, N)
+
+			r, _ = c.ScalarBaseMult(k.Bytes())
+			r.Mod(r, N)
+			if r.Sign() != 0 {
+				break
+			}
+		}
+
+		e := hashToInt(hash, c)
+		s = new(big.Int).Mul(priv.D, r)
+		s.Add(s, e)
+		s.Mul(s, kInv)
+		s.Mod(s, N) // N != 0
+		if s.Sign() != 0 {
+			break
+		}
+	}
+
+	return encodeSignature(r.Bytes(), s.Bytes())
+}
+
+// Verify verifies the signature in r, s of hash using the public key, pub. Its
+// return value records whether the signature is valid. Most applications should
+// use VerifyASN1 instead of dealing directly with r, s.
+func Verify(pub *PublicKey, hash []byte, r, s *big.Int) bool {
+	if r.Sign() <= 0 || s.Sign() <= 0 {
+		return false
+	}
+	sig, err := encodeSignature(r.Bytes(), s.Bytes())
+	if err != nil {
+		return false
+	}
+	return VerifyASN1(pub, hash, sig)
+}
+
+func verifyLegacy(pub *PublicKey, hash []byte, sig []byte) bool {
+	rBytes, sBytes, err := parseSignature(sig)
+	if err != nil {
+		return false
+	}
+	r, s := new(big.Int).SetBytes(rBytes), new(big.Int).SetBytes(sBytes)
+
+	c := pub.Curve
+	N := c.Params().N
+
+	if r.Sign() <= 0 || s.Sign() <= 0 {
+		return false
+	}
+	if r.Cmp(N) >= 0 || s.Cmp(N) >= 0 {
+		return false
+	}
+
+	// SEC 1, Version 2.0, Section 4.1.4
+	e := hashToInt(hash, c)
+	w := new(big.Int).ModInverse(s, N)
+
+	u1 := e.Mul(e, w)
+	u1.Mod(u1, N)
+	u2 := w.Mul(r, w)
+	u2.Mod(u2, N)
+
+	x1, y1 := c.ScalarBaseMult(u1.Bytes())
+	x2, y2 := c.ScalarMult(pub.X, pub.Y, u2.Bytes())
+	x, y := c.Add(x1, y1, x2, y2)
+
+	if x.Sign() == 0 && y.Sign() == 0 {
+		return false
+	}
+	x.Mod(x, N)
+	return x.Cmp(r) == 0
+}
+
+var one = new(big.Int).SetInt64(1)
+
+// randFieldElement returns a random element of the order of the given
+// curve using the procedure given in FIPS 186-4, Appendix B.5.2.
+func randFieldElement(c elliptic.Curve, rand io.Reader) (k *big.Int, err error) {
+	// See randomPoint for notes on the algorithm. This has to match, or s390x
+	// signatures will come out different from other architectures, which will
+	// break TLS recorded tests.
+	for {
+		N := c.Params().N
+		b := make([]byte, (N.BitLen()+7)/8)
+		if _, err = io.ReadFull(rand, b); err != nil {
+			return
+		}
+		if excess := len(b)*8 - N.BitLen(); excess > 0 {
+			b[0] >>= excess
+		}
+		k = new(big.Int).SetBytes(b)
+		if k.Sign() != 0 && k.Cmp(N) < 0 {
+			return
+		}
+	}
+}