Imported Upstream version 1.4upstream/1.4

1 files changed, 189 insertions, 0 deletions

diff --git a/src/crypto/ecdsa/ecdsa.go b/src/crypto/ecdsa/ecdsa.go
new file mode 100644
index 000000000..d6135531b
--- /dev/null
+++ b/src/crypto/ecdsa/ecdsa.go
@@ -0,0 +1,189 @@
+// Copyright 2011 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 implements the Elliptic Curve Digital Signature Algorithm, as
+// defined in FIPS 186-3.
+package ecdsa
+
+// References:
+//   [NSA]: Suite B implementer's guide to FIPS 186-3,
+//     http://www.nsa.gov/ia/_files/ecdsa.pdf
+//   [SECG]: SECG, SEC1
+//     http://www.secg.org/download/aid-780/sec1-v2.pdf
+
+import (
+	"crypto"
+	"crypto/elliptic"
+	"encoding/asn1"
+	"io"
+	"math/big"
+)
+
+// PublicKey represents an ECDSA public key.
+type PublicKey struct {
+	elliptic.Curve
+	X, Y *big.Int
+}
+
+// PrivateKey represents a ECDSA private key.
+type PrivateKey struct {
+	PublicKey
+	D *big.Int
+}
+
+type ecdsaSignature struct {
+	R, S *big.Int
+}
+
+// Public returns the public key corresponding to priv.
+func (priv *PrivateKey) Public() crypto.PublicKey {
+	return &priv.PublicKey
+}
+
+// Sign signs msg with priv, reading randomness from rand. This method is
+// intended to support keys where the private part is kept in, for example, a
+// hardware module. Common uses should use the Sign function in this package
+// directly.
+func (priv *PrivateKey) Sign(rand io.Reader, msg []byte, opts crypto.SignerOpts) ([]byte, error) {
+	r, s, err := Sign(rand, priv, msg)
+	if err != nil {
+		return nil, err
+	}
+
+	return asn1.Marshal(ecdsaSignature{r, s})
+}
+
+var one = new(big.Int).SetInt64(1)
+
+// randFieldElement returns a random element of the field underlying the given
+// curve using the procedure given in [NSA] A.2.1.
+func randFieldElement(c elliptic.Curve, rand io.Reader) (k *big.Int, err error) {
+	params := c.Params()
+	b := make([]byte, params.BitSize/8+8)
+	_, err = io.ReadFull(rand, b)
+	if err != nil {
+		return
+	}
+
+	k = new(big.Int).SetBytes(b)
+	n := new(big.Int).Sub(params.N, one)
+	k.Mod(k, n)
+	k.Add(k, one)
+	return
+}
+
+// GenerateKey generates a public and private key pair.
+func GenerateKey(c elliptic.Curve, rand io.Reader) (priv *PrivateKey, err error) {
+	k, err := randFieldElement(c, rand)
+	if err != nil {
+		return
+	}
+
+	priv = new(PrivateKey)
+	priv.PublicKey.Curve = c
+	priv.D = k
+	priv.PublicKey.X, priv.PublicKey.Y = c.ScalarBaseMult(k.Bytes())
+	return
+}
+
+// hashToInt converts a hash value to an integer. There is some disagreement
+// about how this is done. [NSA] suggests that this is done in the obvious
+// manner, but [SECG] truncates the hash to the bit-length of the curve order
+// first. We follow [SECG] because that's what OpenSSL does. Additionally,
+// OpenSSL right shifts excess bits from the number if the hash is too large
+// and we mirror that too.
+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
+}
+
+// fermatInverse calculates the inverse of k in GF(P) using Fermat's method.
+// This has better constant-time properties than Euclid's method (implemented
+// in math/big.Int.ModInverse) although math/big itself isn't strictly
+// constant-time so it's not perfect.
+func fermatInverse(k, N *big.Int) *big.Int {
+	two := big.NewInt(2)
+	nMinus2 := new(big.Int).Sub(N, two)
+	return new(big.Int).Exp(k, nMinus2, N)
+}
+
+// Sign signs an arbitrary length hash (which should be the result of hashing a
+// larger message) using the private key, priv. It returns the signature as a
+// pair of integers. The security of the private key depends on the entropy of
+// rand.
+func Sign(rand io.Reader, priv *PrivateKey, hash []byte) (r, s *big.Int, err error) {
+	// See [NSA] 3.4.1
+	c := priv.PublicKey.Curve
+	N := c.Params().N
+
+	var k, kInv *big.Int
+	for {
+		for {
+			k, err = randFieldElement(c, rand)
+			if err != nil {
+				r = nil
+				return
+			}
+
+			kInv = fermatInverse(k, N)
+			r, _ = priv.Curve.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)
+		if s.Sign() != 0 {
+			break
+		}
+	}
+
+	return
+}
+
+// Verify verifies the signature in r, s of hash using the public key, pub. Its
+// return value records whether the signature is valid.
+func Verify(pub *PublicKey, hash []byte, r, s *big.Int) bool {
+	// See [NSA] 3.4.2
+	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
+	}
+	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
+}