crypto/elliptic: refactor package structure

Not quite golang.org/wiki/TargetSpecific compliant, but almost.

The only substantial code change is in randFieldElement: it used to use
Params().BitSize instead of Params().N.BitLen(), which is semantically
incorrect, even if the two values are the same for all named curves.

For #52182

Change-Id: Ibc47450552afe23ea74fcf55d1d799d5d7e5487c
Reviewed-on: https://go-review.googlesource.com/c/go/+/315273
Run-TryBot: Filippo Valsorda <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>
Reviewed-by: Roland Shoemaker <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Russ Cox <[email protected]>

Author: FiloSottile

src/crypto/ecdsa/ecdsa.go

@@ -128,7 +128,7 @@ func randFieldElement(c elliptic.Curve, rand io.Reader) (k *big.Int, err error)
 	params := c.Params()
 	// Note that for P-521 this will actually be 63 bits more than the order, as
 	// division rounds down, but the extra bit is inconsequential.
-	b := make([]byte, params.BitSize/8+8) // TODO: use params.N.BitLen()
+	b := make([]byte, params.N.BitLen()/8+8)
 	_, err = io.ReadFull(rand, b)
 	if err != nil {
 		return
@@ -228,13 +228,13 @@ func Sign(rand io.Reader, priv *PrivateKey, hash []byte) (r, s *big.Int, err err
 
 	// Create a CSPRNG that xors a stream of zeros with
 	// the output of the AES-CTR instance.
-	csprng := cipher.StreamReader{
+	csprng := &cipher.StreamReader{
 		R: zeroReader,
 		S: cipher.NewCTR(block, []byte(aesIV)),
 	}
 
 	c := priv.PublicKey.Curve
-	return sign(priv, &csprng, c, hash)
+	return sign(priv, csprng, c, hash)
 }
 
 func signGeneric(priv *PrivateKey, csprng *cipher.StreamReader, c elliptic.Curve, hash []byte) (r, s *big.Int, err error) {
@@ -353,16 +353,14 @@ func VerifyASN1(pub *PublicKey, hash, sig []byte) bool {
 	return Verify(pub, hash, r, s)
 }
 
-type zr struct {
-	io.Reader
-}
+type zr struct{}
 
-// Read replaces the contents of dst with zeros.
-func (z *zr) Read(dst []byte) (n int, err error) {
+// Read replaces the contents of dst with zeros. It is safe for concurrent use.
+func (zr) Read(dst []byte) (n int, err error) {
 	for i := range dst {
 		dst[i] = 0
 	}
 	return len(dst), nil
 }
 
-var zeroReader = &zr{}
+var zeroReader = zr{}

src/crypto/elliptic/elliptic.go

@@ -36,295 +36,6 @@ type Curve interface {
 	ScalarBaseMult(k []byte) (x, y *big.Int)
 }
 
-func matchesSpecificCurve(params *CurveParams, available ...Curve) (Curve, bool) {
-	for _, c := range available {
-		if params == c.Params() {
-			return c, true
-		}
-	}
-	return nil, false
-}
-
-// CurveParams contains the parameters of an elliptic curve and also provides
-// a generic, non-constant time implementation of Curve.
-type CurveParams struct {
-	P       *big.Int // the order of the underlying field
-	N       *big.Int // the order of the base point
-	B       *big.Int // the constant of the curve equation
-	Gx, Gy  *big.Int // (x,y) of the base point
-	BitSize int      // the size of the underlying field
-	Name    string   // the canonical name of the curve
-}
-
-func (curve *CurveParams) Params() *CurveParams {
-	return curve
-}
-
-// CurveParams operates, internally, on Jacobian coordinates. For a given
-// (x, y) position on the curve, the Jacobian coordinates are (x1, y1, z1)
-// where x = x1/z1² and y = y1/z1³. The greatest speedups come when the whole
-// calculation can be performed within the transform (as in ScalarMult and
-// ScalarBaseMult). But even for Add and Double, it's faster to apply and
-// reverse the transform than to operate in affine coordinates.
-
-// polynomial returns x³ - 3x + b.
-func (curve *CurveParams) polynomial(x *big.Int) *big.Int {
-	x3 := new(big.Int).Mul(x, x)
-	x3.Mul(x3, x)
-
-	threeX := new(big.Int).Lsh(x, 1)
-	threeX.Add(threeX, x)
-
-	x3.Sub(x3, threeX)
-	x3.Add(x3, curve.B)
-	x3.Mod(x3, curve.P)
-
-	return x3
-}
-
-func (curve *CurveParams) IsOnCurve(x, y *big.Int) bool {
-	// If there is a dedicated constant-time implementation for this curve operation,
-	// use that instead of the generic one.
-	if specific, ok := matchesSpecificCurve(curve, p224, p384, p521); ok {
-		return specific.IsOnCurve(x, y)
-	}
-
-	if x.Sign() < 0 || x.Cmp(curve.P) >= 0 ||
-		y.Sign() < 0 || y.Cmp(curve.P) >= 0 {
-		return false
-	}
-
-	// y² = x³ - 3x + b
-	y2 := new(big.Int).Mul(y, y)
-	y2.Mod(y2, curve.P)
-
-	return curve.polynomial(x).Cmp(y2) == 0
-}
-
-// zForAffine returns a Jacobian Z value for the affine point (x, y). If x and
-// y are zero, it assumes that they represent the point at infinity because (0,
-// 0) is not on the any of the curves handled here.
-func zForAffine(x, y *big.Int) *big.Int {
-	z := new(big.Int)
-	if x.Sign() != 0 || y.Sign() != 0 {
-		z.SetInt64(1)
-	}
-	return z
-}
-
-// affineFromJacobian reverses the Jacobian transform. See the comment at the
-// top of the file. If the point is ∞ it returns 0, 0.
-func (curve *CurveParams) affineFromJacobian(x, y, z *big.Int) (xOut, yOut *big.Int) {
-	if z.Sign() == 0 {
-		return new(big.Int), new(big.Int)
-	}
-
-	zinv := new(big.Int).ModInverse(z, curve.P)
-	zinvsq := new(big.Int).Mul(zinv, zinv)
-
-	xOut = new(big.Int).Mul(x, zinvsq)
-	xOut.Mod(xOut, curve.P)
-	zinvsq.Mul(zinvsq, zinv)
-	yOut = new(big.Int).Mul(y, zinvsq)
-	yOut.Mod(yOut, curve.P)
-	return
-}
-
-func (curve *CurveParams) Add(x1, y1, x2, y2 *big.Int) (*big.Int, *big.Int) {
-	// If there is a dedicated constant-time implementation for this curve operation,
-	// use that instead of the generic one.
-	if specific, ok := matchesSpecificCurve(curve, p224, p384, p521); ok {
-		return specific.Add(x1, y1, x2, y2)
-	}
-
-	z1 := zForAffine(x1, y1)
-	z2 := zForAffine(x2, y2)
-	return curve.affineFromJacobian(curve.addJacobian(x1, y1, z1, x2, y2, z2))
-}
-
-// addJacobian takes two points in Jacobian coordinates, (x1, y1, z1) and
-// (x2, y2, z2) and returns their sum, also in Jacobian form.
-func (curve *CurveParams) addJacobian(x1, y1, z1, x2, y2, z2 *big.Int) (*big.Int, *big.Int, *big.Int) {
-	// See https://hyperelliptic.org/EFD/g1p/auto-shortw-jacobian-3.html#addition-add-2007-bl
-	x3, y3, z3 := new(big.Int), new(big.Int), new(big.Int)
-	if z1.Sign() == 0 {
-		x3.Set(x2)
-		y3.Set(y2)
-		z3.Set(z2)
-		return x3, y3, z3
-	}
-	if z2.Sign() == 0 {
-		x3.Set(x1)
-		y3.Set(y1)
-		z3.Set(z1)
-		return x3, y3, z3
-	}
-
-	z1z1 := new(big.Int).Mul(z1, z1)
-	z1z1.Mod(z1z1, curve.P)
-	z2z2 := new(big.Int).Mul(z2, z2)
-	z2z2.Mod(z2z2, curve.P)
-
-	u1 := new(big.Int).Mul(x1, z2z2)
-	u1.Mod(u1, curve.P)
-	u2 := new(big.Int).Mul(x2, z1z1)
-	u2.Mod(u2, curve.P)
-	h := new(big.Int).Sub(u2, u1)
-	xEqual := h.Sign() == 0
-	if h.Sign() == -1 {
-		h.Add(h, curve.P)
-	}
-	i := new(big.Int).Lsh(h, 1)
-	i.Mul(i, i)
-	j := new(big.Int).Mul(h, i)
-
-	s1 := new(big.Int).Mul(y1, z2)
-	s1.Mul(s1, z2z2)
-	s1.Mod(s1, curve.P)
-	s2 := new(big.Int).Mul(y2, z1)
-	s2.Mul(s2, z1z1)
-	s2.Mod(s2, curve.P)
-	r := new(big.Int).Sub(s2, s1)
-	if r.Sign() == -1 {
-		r.Add(r, curve.P)
-	}
-	yEqual := r.Sign() == 0
-	if xEqual && yEqual {
-		return curve.doubleJacobian(x1, y1, z1)
-	}
-	r.Lsh(r, 1)
-	v := new(big.Int).Mul(u1, i)
-
-	x3.Set(r)
-	x3.Mul(x3, x3)
-	x3.Sub(x3, j)
-	x3.Sub(x3, v)
-	x3.Sub(x3, v)
-	x3.Mod(x3, curve.P)
-
-	y3.Set(r)
-	v.Sub(v, x3)
-	y3.Mul(y3, v)
-	s1.Mul(s1, j)
-	s1.Lsh(s1, 1)
-	y3.Sub(y3, s1)
-	y3.Mod(y3, curve.P)
-
-	z3.Add(z1, z2)
-	z3.Mul(z3, z3)
-	z3.Sub(z3, z1z1)
-	z3.Sub(z3, z2z2)
-	z3.Mul(z3, h)
-	z3.Mod(z3, curve.P)
-
-	return x3, y3, z3
-}
-
-func (curve *CurveParams) Double(x1, y1 *big.Int) (*big.Int, *big.Int) {
-	// If there is a dedicated constant-time implementation for this curve operation,
-	// use that instead of the generic one.
-	if specific, ok := matchesSpecificCurve(curve, p224, p384, p521); ok {
-		return specific.Double(x1, y1)
-	}
-
-	z1 := zForAffine(x1, y1)
-	return curve.affineFromJacobian(curve.doubleJacobian(x1, y1, z1))
-}
-
-// doubleJacobian takes a point in Jacobian coordinates, (x, y, z), and
-// returns its double, also in Jacobian form.
-func (curve *CurveParams) doubleJacobian(x, y, z *big.Int) (*big.Int, *big.Int, *big.Int) {
-	// See https://hyperelliptic.org/EFD/g1p/auto-shortw-jacobian-3.html#doubling-dbl-2001-b
-	delta := new(big.Int).Mul(z, z)
-	delta.Mod(delta, curve.P)
-	gamma := new(big.Int).Mul(y, y)
-	gamma.Mod(gamma, curve.P)
-	alpha := new(big.Int).Sub(x, delta)
-	if alpha.Sign() == -1 {
-		alpha.Add(alpha, curve.P)
-	}
-	alpha2 := new(big.Int).Add(x, delta)
-	alpha.Mul(alpha, alpha2)
-	alpha2.Set(alpha)
-	alpha.Lsh(alpha, 1)
-	alpha.Add(alpha, alpha2)
-
-	beta := alpha2.Mul(x, gamma)
-
-	x3 := new(big.Int).Mul(alpha, alpha)
-	beta8 := new(big.Int).Lsh(beta, 3)
-	beta8.Mod(beta8, curve.P)
-	x3.Sub(x3, beta8)
-	if x3.Sign() == -1 {
-		x3.Add(x3, curve.P)
-	}
-	x3.Mod(x3, curve.P)
-
-	z3 := new(big.Int).Add(y, z)
-	z3.Mul(z3, z3)
-	z3.Sub(z3, gamma)
-	if z3.Sign() == -1 {
-		z3.Add(z3, curve.P)
-	}
-	z3.Sub(z3, delta)
-	if z3.Sign() == -1 {
-		z3.Add(z3, curve.P)
-	}
-	z3.Mod(z3, curve.P)
-
-	beta.Lsh(beta, 2)
-	beta.Sub(beta, x3)
-	if beta.Sign() == -1 {
-		beta.Add(beta, curve.P)
-	}
-	y3 := alpha.Mul(alpha, beta)
-
-	gamma.Mul(gamma, gamma)
-	gamma.Lsh(gamma, 3)
-	gamma.Mod(gamma, curve.P)
-
-	y3.Sub(y3, gamma)
-	if y3.Sign() == -1 {
-		y3.Add(y3, curve.P)
-	}
-	y3.Mod(y3, curve.P)
-
-	return x3, y3, z3
-}
-
-func (curve *CurveParams) ScalarMult(Bx, By *big.Int, k []byte) (*big.Int, *big.Int) {
-	// If there is a dedicated constant-time implementation for this curve operation,
-	// use that instead of the generic one.
-	if specific, ok := matchesSpecificCurve(curve, p224, p256, p384, p521); ok {
-		return specific.ScalarMult(Bx, By, k)
-	}
-
-	Bz := new(big.Int).SetInt64(1)
-	x, y, z := new(big.Int), new(big.Int), new(big.Int)
-
-	for _, byte := range k {
-		for bitNum := 0; bitNum < 8; bitNum++ {
-			x, y, z = curve.doubleJacobian(x, y, z)
-			if byte&0x80 == 0x80 {
-				x, y, z = curve.addJacobian(Bx, By, Bz, x, y, z)
-			}
-			byte <<= 1
-		}
-	}
-
-	return curve.affineFromJacobian(x, y, z)
-}
-
-func (curve *CurveParams) ScalarBaseMult(k []byte) (*big.Int, *big.Int) {
-	// If there is a dedicated constant-time implementation for this curve operation,
-	// use that instead of the generic one.
-	if specific, ok := matchesSpecificCurve(curve, p224, p256, p384, p521); ok {
-		return specific.ScalarBaseMult(k)
-	}
-
-	return curve.ScalarMult(curve.Gx, curve.Gy, k)
-}
-
 var mask = []byte{0xff, 0x1, 0x3, 0x7, 0xf, 0x1f, 0x3f, 0x7f}
 
 // GenerateKey returns a public/private key pair. The private key is