83 lines
1.5 KiB
Go
83 lines
1.5 KiB
Go
package bn256
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import (
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"errors"
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"fmt"
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)
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type gfP [4]uint64
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func newGFp(x int64) (out *gfP) {
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if x >= 0 {
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out = &gfP{uint64(x)}
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} else {
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out = &gfP{uint64(-x)}
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gfpNeg(out, out)
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}
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montEncode(out, out)
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return out
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}
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func (e *gfP) String() string {
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return fmt.Sprintf("%16.16x%16.16x%16.16x%16.16x", e[3], e[2], e[1], e[0])
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}
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func (e *gfP) Set(f *gfP) {
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e[0] = f[0]
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e[1] = f[1]
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e[2] = f[2]
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e[3] = f[3]
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}
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func (e *gfP) Invert(f *gfP) {
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bits := [4]uint64{0x3c208c16d87cfd45, 0x97816a916871ca8d, 0xb85045b68181585d, 0x30644e72e131a029}
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sum, power := &gfP{}, &gfP{}
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sum.Set(rN1)
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power.Set(f)
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for word := 0; word < 4; word++ {
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for bit := uint(0); bit < 64; bit++ {
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if (bits[word]>>bit)&1 == 1 {
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gfpMul(sum, sum, power)
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}
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gfpMul(power, power, power)
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}
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}
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gfpMul(sum, sum, r3)
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e.Set(sum)
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}
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func (e *gfP) Marshal(out []byte) {
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for w := uint(0); w < 4; w++ {
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for b := uint(0); b < 8; b++ {
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out[8*w+b] = byte(e[3-w] >> (56 - 8*b))
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}
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}
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}
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func (e *gfP) Unmarshal(in []byte) error {
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// Unmarshal the bytes into little endian form
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for w := uint(0); w < 4; w++ {
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e[3-w] = 0
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for b := uint(0); b < 8; b++ {
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e[3-w] += uint64(in[8*w+b]) << (56 - 8*b)
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}
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}
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// Ensure the point respects the curve modulus
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for i := 3; i >= 0; i-- {
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if e[i] < p2[i] {
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return nil
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}
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if e[i] > p2[i] {
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return errors.New("bn256: coordinate exceeds modulus")
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}
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}
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return errors.New("bn256: coordinate equals modulus")
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}
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func montEncode(c, a *gfP) { gfpMul(c, a, r2) }
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func montDecode(c, a *gfP) { gfpMul(c, a, &gfP{1}) }
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