1package kzgceremony
  2
  3import (
  4	"fmt"
  5	"math/big"
  6
  7	"github.com/ethereum/go-ethereum/crypto/bls12381"
  8)
  9
 10type Contribution struct {
 11	SRS   *SRS
 12	Proof *Proof
 13}
 14
 15type SRS struct {
 16	G1s []*bls12381.PointG1
 17	G2s []*bls12381.PointG2
 18}
 19
 20type toxicWaste struct {
 21	tau   *big.Int
 22	TauG2 *bls12381.PointG2
 23}
 24
 25type Proof struct {
 26	G2P    *bls12381.PointG2 // g₂ᵖ
 27	G1PTau *bls12381.PointG1 // g₂^τ' = g₂^{p ⋅ τ}
 28}
 29
 30// newEmptySRS creates an empty SRS
 31func newEmptySRS(nG1, nG2 int) *SRS {
 32	g1s := make([]*bls12381.PointG1, nG1)
 33	g2s := make([]*bls12381.PointG2, nG2)
 34	g1 := bls12381.NewG1()
 35	g2 := bls12381.NewG2()
 36	// one_G1 := g1.One()
 37	// one_G2 := g2.One()
 38	for i := 0; i < nG1; i++ {
 39		g1s[i] = g1.One()
 40		// g1.MulScalar(g1s[i], one_G1, big.NewInt(int64(i)))
 41	}
 42	for i := 0; i < nG2; i++ {
 43		g2s[i] = g2.One()
 44		// g2.MulScalar(g2s[i], one_G2, big.NewInt(int64(i)))
 45	}
 46	return &SRS{g1s, g2s}
 47}
 48
 49func tau(randomness []byte) *toxicWaste {
 50	g2 := bls12381.NewG2()
 51	tau := new(big.Int).Mod(
 52		new(big.Int).SetBytes(randomness),
 53		g2.Q())
 54	TauG2 := g2.New()
 55	g2.MulScalar(TauG2, g2.One(), tau)
 56
 57	return &toxicWaste{tau, TauG2}
 58}
 59
 60func computeContribution(t *toxicWaste, prevSRS *SRS) *SRS {
 61	srs := newEmptySRS(len(prevSRS.G1s), len(prevSRS.G2s))
 62	g1 := bls12381.NewG1()
 63	g2 := bls12381.NewG2()
 64	Q := g1.Q() // Q = |G1| == |G2|
 65
 66	fmt.Println("Computing [τ'⁰]₁, [τ'¹]₁, [τ'²]₁, ..., [τ'ⁿ⁻¹]₁, for n =", len(prevSRS.G1s))
 67	for i := 0; i < len(prevSRS.G1s); i++ {
 68		tau_i := new(big.Int).Exp(t.tau, big.NewInt(int64(i)), Q)
 69		g1.MulScalar(srs.G1s[i], prevSRS.G1s[i], tau_i)
 70	}
 71	fmt.Println("Computing [τ'⁰]₂, [τ'¹]₂, [τ'²]₂, ..., [τ'ⁿ⁻¹]₂, for n =", len(prevSRS.G2s))
 72	for i := 0; i < len(prevSRS.G2s); i++ {
 73		tau_i := new(big.Int).Exp(t.tau, big.NewInt(int64(i)), Q)
 74		g2.MulScalar(srs.G2s[i], prevSRS.G2s[i], tau_i)
 75	}
 76
 77	return srs
 78}
 79
 80func genProof(toxicWaste *toxicWaste, prevSRS, newSRS *SRS) *Proof {
 81	g1 := bls12381.NewG1()
 82	G1_p := g1.New()
 83	g1.MulScalar(G1_p, prevSRS.G1s[1], toxicWaste.tau) // g_1^{tau'} = g_1^{p * tau}, where p=toxicWaste.tau
 84
 85	return &Proof{toxicWaste.TauG2, G1_p}
 86}
 87
 88// Contribute
 89func Contribute(prevSRS *SRS, randomness []byte) (Contribution, error) {
 90	// set tau from randomness
 91	tw := tau(randomness)
 92
 93	newSRS := computeContribution(tw, prevSRS)
 94
 95	proof := genProof(tw, prevSRS, newSRS)
 96
 97	return Contribution{SRS: newSRS, Proof: proof}, nil
 98}
 99
100func Verify(prevSRS, newSRS *SRS, proof *Proof) bool {
101	g1 := bls12381.NewG1()
102
103	// check proof.G1PTau == newSRS.G1s[1]
104	if !g1.Equal(proof.G1PTau, newSRS.G1s[1]) {
105		return false
106	}
107
108	// WIP!
109	return true
110}