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crypto, crypto/secp256k1: add CompressPubkey (#15626)

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This adds the inverse to DecompressPubkey and improves a few minor
details in crypto/secp256k1.
This commit is contained in:
Felix Lange
2017-12-15 10:40:09 +01:00
committed by GitHub
parent 1f2176dedc
commit c6069a627c
6 changed files with 118 additions and 52 deletions
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46
crypto/secp256k1/curve.go
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@ -34,7 +34,6 @@ package secp256k1
import (
"crypto/elliptic"
"math/big"
"sync"
"unsafe"
"github.com/ethereum/go-ethereum/common/math"
@ -42,7 +41,7 @@ import (
/*
#include "libsecp256k1/include/secp256k1.h"
extern int secp256k1_pubkey_scalar_mul(const secp256k1_context* ctx, const unsigned char *point, const unsigned char *scalar);
extern int secp256k1_ext_scalar_mul(const secp256k1_context* ctx, const unsigned char *point, const unsigned char *scalar);
*/
import "C"
@ -236,7 +235,7 @@ func (BitCurve *BitCurve) ScalarMult(Bx, By *big.Int, scalar []byte) (*big.Int,
math.ReadBits(By, point[32:])
pointPtr := (*C.uchar)(unsafe.Pointer(&point[0]))
scalarPtr := (*C.uchar)(unsafe.Pointer(&scalar[0]))
res := C.secp256k1_pubkey_scalar_mul(context, pointPtr, scalarPtr)
res := C.secp256k1_ext_scalar_mul(context, pointPtr, scalarPtr)
// Unpack the result and clear temporaries.
x := new(big.Int).SetBytes(point[:32])
@ -263,14 +262,10 @@ func (BitCurve *BitCurve) ScalarBaseMult(k []byte) (*big.Int, *big.Int) {
// X9.62.
func (BitCurve *BitCurve) Marshal(x, y *big.Int) []byte {
byteLen := (BitCurve.BitSize + 7) >> 3
ret := make([]byte, 1+2*byteLen)
ret[0] = 4 // uncompressed point
xBytes := x.Bytes()
copy(ret[1+byteLen-len(xBytes):], xBytes)
yBytes := y.Bytes()
copy(ret[1+2*byteLen-len(yBytes):], yBytes)
ret[0] = 4 // uncompressed point flag
math.ReadBits(x, ret[1:1+byteLen])
math.ReadBits(y, ret[1+byteLen:])
return ret
}
@ -289,24 +284,21 @@ func (BitCurve *BitCurve) Unmarshal(data []byte) (x, y *big.Int) {
return
}
var (
initonce sync.Once
theCurve *BitCurve
)
var theCurve = new(BitCurve)
// S256 returns a BitCurve which implements secp256k1 (see SEC 2 section 2.7.1)
func init() {
// See SEC 2 section 2.7.1
// curve parameters taken from:
// http://www.secg.org/collateral/sec2_final.pdf
theCurve.P, _ = new(big.Int).SetString("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F", 16)
theCurve.N, _ = new(big.Int).SetString("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141", 16)
theCurve.B, _ = new(big.Int).SetString("0000000000000000000000000000000000000000000000000000000000000007", 16)
theCurve.Gx, _ = new(big.Int).SetString("79BE667EF9DCBBAC55A06295CE870B07029BFCDB2DCE28D959F2815B16F81798", 16)
theCurve.Gy, _ = new(big.Int).SetString("483ADA7726A3C4655DA4FBFC0E1108A8FD17B448A68554199C47D08FFB10D4B8", 16)
theCurve.BitSize = 256
}
// S256 returns a BitCurve which implements secp256k1.
func S256() *BitCurve {
initonce.Do(func() {
// See SEC 2 section 2.7.1
// curve parameters taken from:
// http://www.secg.org/collateral/sec2_final.pdf
theCurve = new(BitCurve)
theCurve.P, _ = new(big.Int).SetString("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F", 16)
theCurve.N, _ = new(big.Int).SetString("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141", 16)
theCurve.B, _ = new(big.Int).SetString("0000000000000000000000000000000000000000000000000000000000000007", 16)
theCurve.Gx, _ = new(big.Int).SetString("79BE667EF9DCBBAC55A06295CE870B07029BFCDB2DCE28D959F2815B16F81798", 16)
theCurve.Gy, _ = new(big.Int).SetString("483ADA7726A3C4655DA4FBFC0E1108A8FD17B448A68554199C47D08FFB10D4B8", 16)
theCurve.BitSize = 256
})
return theCurve
}