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79 lines
1.7 KiB
79 lines
1.7 KiB
package kzgceremony
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import (
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"math/big"
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"github.com/ethereum/go-ethereum/crypto/bls12381"
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)
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type Contribution struct {
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SRS *SRS
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}
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type SRS struct {
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G1s []*bls12381.PointG1
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G2s []*bls12381.PointG2
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}
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type toxicWaste struct {
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tau *big.Int
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TauG2 *bls12381.PointG2
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}
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// newEmptySRS creates an empty SRS
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func newEmptySRS(nG1, nG2 int) *SRS {
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g1s := make([]*bls12381.PointG1, nG1)
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g2s := make([]*bls12381.PointG2, nG2)
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g1 := bls12381.NewG1()
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g2 := bls12381.NewG2()
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// one_G1 := g1.One()
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// one_G2 := g2.One()
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for i := 0; i < nG1; i++ {
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g1s[i] = g1.One()
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// g1.MulScalar(g1s[i], one_G1, big.NewInt(int64(i)))
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}
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for i := 0; i < nG2; i++ {
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g2s[i] = g2.One()
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// g2.MulScalar(g2s[i], one_G2, big.NewInt(int64(i)))
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}
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return &SRS{g1s, g2s}
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}
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func tau(randomness []byte) *toxicWaste {
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g2 := bls12381.NewG2()
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tau := new(big.Int).Mod(
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new(big.Int).SetBytes(randomness),
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g2.Q())
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TauG2 := g2.New()
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g2.MulScalar(TauG2, g2.One(), tau)
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return &toxicWaste{tau, TauG2}
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}
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func computeContribution(t *toxicWaste, prevSRS *SRS) *SRS {
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srs := newEmptySRS(len(prevSRS.G1s), len(prevSRS.G2s))
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g1 := bls12381.NewG1()
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g2 := bls12381.NewG2()
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Q := g1.Q() // Q = |G1| == |G2|
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for i := 0; i < len(prevSRS.G1s); i++ {
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tau_i := new(big.Int).Exp(t.tau, big.NewInt(int64(i)), Q)
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g1.MulScalar(srs.G1s[i], prevSRS.G1s[i], tau_i)
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}
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for i := 0; i < len(prevSRS.G2s); i++ {
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tau_i := new(big.Int).Exp(t.tau, big.NewInt(int64(i)), Q)
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g2.MulScalar(srs.G2s[i], prevSRS.G2s[i], tau_i)
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}
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return srs
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}
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// Contribute
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func Contribute(prevSRS *SRS, randomness []byte) (Contribution, error) {
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// set tau from randomness
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tw := tau(randomness)
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newSRS := computeContribution(tw, prevSRS)
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return Contribution{SRS: newSRS}, nil
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}
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