TrueCloudLab/frostfs-crypto
13
0
Fork 4
Code Issues 2 Pull requests Projects Releases 1 Activity

Refactor decompress Y point

Browse source
This commit is contained in:
Evgeniy Kulikov 2019-10-23 14:03:11 +03:00
parent c21ef9ef81
commit e60428333c
No known key found for this signature in database
GPG key ID: BF6AEE0A2A699BF2
1 changed files with 8 additions and 12 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

20
ecdsa.go
View file

@ -70,26 +70,22 @@ func unmarshalXY(data []byte) (x *big.Int, y *big.Int) {
return return
} }
// decompressPoints using formula y^2 = x^3 + ax + b mod p // decompressPoints using formula y² = x³ - 3x + b
// crypto/elliptic/elliptic.go:55
func decompressPoints(x *big.Int, yBit uint) (*big.Int, *big.Int) { func decompressPoints(x *big.Int, yBit uint) (*big.Int, *big.Int) {
params := curve.Params() params := curve.Params()
// x^3 mod P x3 := new(big.Int).Mul(x, x)
x3 := new(big.Int).Exp(x, new(big.Int).SetInt64(3), params.P) x3.Mul(x3, x)
// a * x mod P threeX := new(big.Int).Lsh(x, 1)
ax := new(big.Int).Mul(x, new(big.Int).SetInt64(-3)) threeX.Add(threeX, x)
ax.Mod(ax, params.P)
// x^3 + a * x mod P x3.Sub(x3, threeX)
x3.Add(x3, ax)
x3.Mod(x3, params.P)
// x^3 + a * x + b mod P
x3.Add(x3, params.B) x3.Add(x3, params.B)
x3.Mod(x3, params.P) x3.Mod(x3, params.P)
// y = sqrt(x^3 + ax + b mod p) mod P // y = √(x³ - 3x + b) mod p
y := new(big.Int).ModSqrt(x3, params.P) y := new(big.Int).ModSqrt(x3, params.P)
// big.Int.Jacobi(a, b) can return nil // big.Int.Jacobi(a, b) can return nil