e9d1b1884c
- use elliptic.MarshalCompressed - use elliptic.UnmarshalCompressed - for older go versions use old methods - update dependencies - github.com/mr-tron/base58 v1.2.0 - github.com/pkg/errors v0.9.1 - github.com/stretchr/testify v1.7.0 Signed-off-by: Evgeniy Kulikov <kim@nspcc.ru>
79 lines
1.5 KiB
Go
79 lines
1.5 KiB
Go
// +build !go1.15
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package crypto
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import "math/big"
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// decompressPoints using formula y² = x³ - 3x + b
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// crypto/elliptic/elliptic.go:55
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func decompressPoints(x *big.Int, yBit uint) (*big.Int, *big.Int) {
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params := curve.Params()
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x3 := new(big.Int).Mul(x, x)
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x3.Mul(x3, x)
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threeX := new(big.Int).Lsh(x, 1)
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threeX.Add(threeX, x)
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x3.Sub(x3, threeX)
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x3.Add(x3, params.B)
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x3.Mod(x3, params.P)
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// y = √(x³ - 3x + b) mod p
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y := new(big.Int).ModSqrt(x3, params.P)
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// big.Int.Jacobi(a, b) can return nil
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if y == nil {
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return nil, nil
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}
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if y.Bit(0) != (yBit & 0x1) {
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y.Neg(y)
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y.Mod(y, params.P)
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}
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return x, y
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}
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func encodePoint(x, y *big.Int) []byte {
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data := make([]byte, PublicKeyCompressedSize)
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i := PublicKeyCompressedSize - len(x.Bytes())
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copy(data[i:], x.Bytes())
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if y.Bit(0) == 0x1 {
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data[0] = 0x3
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} else {
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data[0] = 0x2
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}
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return data
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}
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func decodePoint(data []byte) (x *big.Int, y *big.Int) {
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// empty data
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if len(data) == 0 {
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return
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}
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switch prefix := data[0]; prefix {
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case 0x02, 0x03: // compressed key
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// Incorrect length for compressed encoding
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if len(data) != PublicKeyCompressedSize {
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return nil, nil
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}
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x, y = decompressPoints(new(big.Int).SetBytes(data[1:]), uint(prefix))
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case 0x04: // uncompressed key
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// To get the public key, besides getting it from the data and checking,
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// we also must to check that the points are on an elliptic curve
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x, y = unmarshalXY(data)
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default: // unknown type
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return
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}
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if x == nil || y == nil || !curve.IsOnCurve(x, y) {
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x, y = nil, nil
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}
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return
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}
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