1package kzgceremony
 2
 3import (
 4	"math/big"
 5
 6	"github.com/ethereum/go-ethereum/crypto/bls12381"
 7)
 8
 9type Contribution struct {
10	SRS *SRS
11}
12
13type SRS struct {
14	G1s []*bls12381.PointG1
15	G2s []*bls12381.PointG2
16}
17
18type toxicWaste struct {
19	tau   *big.Int
20	TauG2 *bls12381.PointG2
21}
22
23// newEmptySRS creates an empty SRS
24func newEmptySRS(nG1, nG2 int) *SRS {
25	g1s := make([]*bls12381.PointG1, nG1)
26	g2s := make([]*bls12381.PointG2, nG2)
27	g1 := bls12381.NewG1()
28	g2 := bls12381.NewG2()
29	// one_G1 := g1.One()
30	// one_G2 := g2.One()
31	for i := 0; i < nG1; i++ {
32		g1s[i] = g1.One()
33		// g1.MulScalar(g1s[i], one_G1, big.NewInt(int64(i)))
34	}
35	for i := 0; i < nG2; i++ {
36		g2s[i] = g2.One()
37		// g2.MulScalar(g2s[i], one_G2, big.NewInt(int64(i)))
38	}
39	return &SRS{g1s, g2s}
40}
41
42func tau(randomness []byte) *toxicWaste {
43	g2 := bls12381.NewG2()
44	tau := new(big.Int).Mod(
45		new(big.Int).SetBytes(randomness),
46		g2.Q())
47	TauG2 := g2.New()
48	g2.MulScalar(TauG2, g2.One(), tau)
49
50	return &toxicWaste{tau, TauG2}
51}
52
53func computeContribution(t *toxicWaste, prevSRS *SRS) *SRS {
54	srs := newEmptySRS(len(prevSRS.G1s), len(prevSRS.G2s))
55	g1 := bls12381.NewG1()
56	g2 := bls12381.NewG2()
57	Q := g1.Q() // Q = |G1| == |G2|
58
59	for i := 0; i < len(prevSRS.G1s); i++ {
60		tau_i := new(big.Int).Exp(t.tau, big.NewInt(int64(i)), Q)
61		g1.MulScalar(srs.G1s[i], prevSRS.G1s[i], tau_i)
62	}
63	for i := 0; i < len(prevSRS.G2s); i++ {
64		tau_i := new(big.Int).Exp(t.tau, big.NewInt(int64(i)), Q)
65		g2.MulScalar(srs.G2s[i], prevSRS.G2s[i], tau_i)
66	}
67
68	return srs
69}
70
71// Contribute
72func Contribute(prevSRS *SRS, randomness []byte) (Contribution, error) {
73	// set tau from randomness
74	tw := tau(randomness)
75
76	newSRS := computeContribution(tw, prevSRS)
77
78	return Contribution{SRS: newSRS}, nil
79}