1 files changed, 165 insertions, 0 deletions
diff --git a/src/crypto/elliptic/p521.go b/src/crypto/elliptic/p521.go
new file mode 100644
index 0000000..6a3ade3
--- /dev/null
+++ b/src/crypto/elliptic/p521.go
@@ -0,0 +1,165 @@
+// Copyright 2013 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 elliptic
+
+import (
+	"crypto/elliptic/internal/nistec"
+	"crypto/rand"
+	"math/big"
+)
+
+// p521Curve is a Curve implementation based on nistec.P521Point.
+//
+// It's a wrapper that exposes the big.Int-based Curve interface and encodes the
+// legacy idiosyncrasies it requires, such as invalid and infinity point
+// handling.
+//
+// To interact with the nistec package, points are encoded into and decoded from
+// properly formatted byte slices. All big.Int use is limited to this package.
+// Encoding and decoding is 1/1000th of the runtime of a scalar multiplication,
+// so the overhead is acceptable.
+type p521Curve struct {
+	params *CurveParams
+}
+
+var p521 p521Curve
+var _ Curve = p521
+
+func initP521() {
+	p521.params = &CurveParams{
+		Name:    "P-521",
+		BitSize: 521,
+		// FIPS 186-4, section D.1.2.5
+		P: bigFromDecimal("68647976601306097149819007990813932172694353001433" +
+			"0540939446345918554318339765605212255964066145455497729631139148" +
+			"0858037121987999716643812574028291115057151"),
+		N: bigFromDecimal("68647976601306097149819007990813932172694353001433" +
+			"0540939446345918554318339765539424505774633321719753296399637136" +
+			"3321113864768612440380340372808892707005449"),
+		B: bigFromHex("0051953eb9618e1c9a1f929a21a0b68540eea2da725b99b315f3b8" +
+			"b489918ef109e156193951ec7e937b1652c0bd3bb1bf073573df883d2c34f1ef" +
+			"451fd46b503f00"),
+		Gx: bigFromHex("00c6858e06b70404e9cd9e3ecb662395b4429c648139053fb521f8" +
+			"28af606b4d3dbaa14b5e77efe75928fe1dc127a2ffa8de3348b3c1856a429bf9" +
+			"7e7e31c2e5bd66"),
+		Gy: bigFromHex("011839296a789a3bc0045c8a5fb42c7d1bd998f54449579b446817" +
+			"afbd17273e662c97ee72995ef42640c550b9013fad0761353c7086a272c24088" +
+			"be94769fd16650"),
+	}
+}
+
+func (curve p521Curve) Params() *CurveParams {
+	return curve.params
+}
+
+func (curve p521Curve) IsOnCurve(x, y *big.Int) bool {
+	// IsOnCurve is documented to reject (0, 0), the conventional point at
+	// infinity, which however is accepted by p521PointFromAffine.
+	if x.Sign() == 0 && y.Sign() == 0 {
+		return false
+	}
+	_, ok := p521PointFromAffine(x, y)
+	return ok
+}
+
+func p521PointFromAffine(x, y *big.Int) (p *nistec.P521Point, ok bool) {
+	// (0, 0) is by convention the point at infinity, which can't be represented
+	// in affine coordinates. Marshal incorrectly encodes it as an uncompressed
+	// point, which SetBytes would correctly reject. See Issue 37294.
+	if x.Sign() == 0 && y.Sign() == 0 {
+		return nistec.NewP521Point(), true
+	}
+	if x.Sign() < 0 || y.Sign() < 0 {
+		return nil, false
+	}
+	if x.BitLen() > 521 || y.BitLen() > 521 {
+		return nil, false
+	}
+	p, err := nistec.NewP521Point().SetBytes(Marshal(P521(), x, y))
+	if err != nil {
+		return nil, false
+	}
+	return p, true
+}
+
+func p521PointToAffine(p *nistec.P521Point) (x, y *big.Int) {
+	out := p.Bytes()
+	if len(out) == 1 && out[0] == 0 {
+		// This is the correct encoding of the point at infinity, which
+		// Unmarshal does not support. See Issue 37294.
+		return new(big.Int), new(big.Int)
+	}
+	x, y = Unmarshal(P521(), out)
+	if x == nil {
+		panic("crypto/elliptic: internal error: Unmarshal rejected a valid point encoding")
+	}
+	return x, y
+}
+
+// p521RandomPoint returns a random point on the curve. It's used when Add,
+// Double, or ScalarMult are fed a point not on the curve, which is undefined
+// behavior. Originally, we used to do the math on it anyway (which allows
+// invalid curve attacks) and relied on the caller and Unmarshal to avoid this
+// happening in the first place. Now, we just can't construct a nistec.P521Point
+// for an invalid pair of coordinates, because that API is safer. If we panic,
+// we risk introducing a DoS. If we return nil, we risk a panic. If we return
+// the input, ecdsa.Verify might fail open. The safest course seems to be to
+// return a valid, random point, which hopefully won't help the attacker.
+func p521RandomPoint() (x, y *big.Int) {
+	_, x, y, err := GenerateKey(P521(), rand.Reader)
+	if err != nil {
+		panic("crypto/elliptic: failed to generate random point")
+	}
+	return x, y
+}
+
+func (p521Curve) Add(x1, y1, x2, y2 *big.Int) (*big.Int, *big.Int) {
+	p1, ok := p521PointFromAffine(x1, y1)
+	if !ok {
+		return p521RandomPoint()
+	}
+	p2, ok := p521PointFromAffine(x2, y2)
+	if !ok {
+		return p521RandomPoint()
+	}
+	return p521PointToAffine(p1.Add(p1, p2))
+}
+
+func (p521Curve) Double(x1, y1 *big.Int) (*big.Int, *big.Int) {
+	p, ok := p521PointFromAffine(x1, y1)
+	if !ok {
+		return p521RandomPoint()
+	}
+	return p521PointToAffine(p.Double(p))
+}
+
+func (p521Curve) ScalarMult(Bx, By *big.Int, scalar []byte) (*big.Int, *big.Int) {
+	p, ok := p521PointFromAffine(Bx, By)
+	if !ok {
+		return p521RandomPoint()
+	}
+	return p521PointToAffine(p.ScalarMult(p, scalar))
+}
+
+func (p521Curve) ScalarBaseMult(scalar []byte) (*big.Int, *big.Int) {
+	p := nistec.NewP521Generator()
+	return p521PointToAffine(p.ScalarMult(p, scalar))
+}
+
+func bigFromDecimal(s string) *big.Int {
+	b, ok := new(big.Int).SetString(s, 10)
+	if !ok {
+		panic("invalid encoding")
+	}
+	return b
+}
+
+func bigFromHex(s string) *big.Int {
+	b, ok := new(big.Int).SetString(s, 16)
+	if !ok {
+		panic("invalid encoding")
+	}
+	return b
+}