2 * @file AccumulatorProofOfKnowledge.cpp
4 * @brief AccumulatorProofOfKnowledge class for the Zerocoin library.
6 * @author Ian Miers, Christina Garman and Matthew Green
9 * @copyright Copyright 2013 Ian Miers, Christina Garman and Matthew Green
10 * @license This project is released under the MIT license.
15 namespace libzerocoin {
17 AccumulatorProofOfKnowledge::AccumulatorProofOfKnowledge(const AccumulatorAndProofParams* p): params(p) {}
19 AccumulatorProofOfKnowledge::AccumulatorProofOfKnowledge(const AccumulatorAndProofParams* p,
20 const Commitment& commitmentToCoin, const AccumulatorWitness& witness,
21 Accumulator& a): params(p) {
23 Bignum sg = params->accumulatorPoKCommitmentGroup.g;
24 Bignum sh = params->accumulatorPoKCommitmentGroup.h;
26 Bignum g_n = params->accumulatorQRNCommitmentGroup.g;
27 Bignum h_n = params->accumulatorQRNCommitmentGroup.h;
29 Bignum e = commitmentToCoin.getContents();
30 Bignum r = commitmentToCoin.getRandomness();
32 Bignum r_1 = Bignum::randBignum(params->accumulatorModulus/4);
33 Bignum r_2 = Bignum::randBignum(params->accumulatorModulus/4);
34 Bignum r_3 = Bignum::randBignum(params->accumulatorModulus/4);
36 this->C_e = g_n.pow_mod(e, params->accumulatorModulus) * h_n.pow_mod(r_1, params->accumulatorModulus);
37 this->C_u = witness.getValue() * h_n.pow_mod(r_2, params->accumulatorModulus);
38 this->C_r = g_n.pow_mod(r_2, params->accumulatorModulus) * h_n.pow_mod(r_3, params->accumulatorModulus);
40 Bignum r_alpha = Bignum::randBignum(params->maxCoinValue * Bignum(2).pow(params->k_prime + params->k_dprime));
41 if(!(Bignum::randBignum(Bignum(3)) % 2)) {
45 Bignum r_gamma = Bignum::randBignum(params->accumulatorPoKCommitmentGroup.modulus);
46 Bignum r_phi = Bignum::randBignum(params->accumulatorPoKCommitmentGroup.modulus);
47 Bignum r_psi = Bignum::randBignum(params->accumulatorPoKCommitmentGroup.modulus);
48 Bignum r_sigma = Bignum::randBignum(params->accumulatorPoKCommitmentGroup.modulus);
49 Bignum r_xi = Bignum::randBignum(params->accumulatorPoKCommitmentGroup.modulus);
51 Bignum r_epsilon = Bignum::randBignum((params->accumulatorModulus/4) * Bignum(2).pow(params->k_prime + params->k_dprime));
52 if(!(Bignum::randBignum(Bignum(3)) % 2)) {
53 r_epsilon = 0-r_epsilon;
55 Bignum r_eta = Bignum::randBignum((params->accumulatorModulus/4) * Bignum(2).pow(params->k_prime + params->k_dprime));
56 if(!(Bignum::randBignum(Bignum(3)) % 2)) {
59 Bignum r_zeta = Bignum::randBignum((params->accumulatorModulus/4) * Bignum(2).pow(params->k_prime + params->k_dprime));
60 if(!(Bignum::randBignum(Bignum(3)) % 2)) {
64 Bignum r_beta = Bignum::randBignum((params->accumulatorModulus/4) * params->accumulatorPoKCommitmentGroup.modulus * Bignum(2).pow(params->k_prime + params->k_dprime));
65 if(!(Bignum::randBignum(Bignum(3)) % 2)) {
68 Bignum r_delta = Bignum::randBignum((params->accumulatorModulus/4) * params->accumulatorPoKCommitmentGroup.modulus * Bignum(2).pow(params->k_prime + params->k_dprime));
69 if(!(Bignum::randBignum(Bignum(3)) % 2)) {
73 this->st_1 = (sg.pow_mod(r_alpha, params->accumulatorPoKCommitmentGroup.modulus) * sh.pow_mod(r_phi, params->accumulatorPoKCommitmentGroup.modulus)) % params->accumulatorPoKCommitmentGroup.modulus;
74 this->st_2 = (((commitmentToCoin.getCommitmentValue() * sg.inverse(params->accumulatorPoKCommitmentGroup.modulus)).pow_mod(r_gamma, params->accumulatorPoKCommitmentGroup.modulus)) * sh.pow_mod(r_psi, params->accumulatorPoKCommitmentGroup.modulus)) % params->accumulatorPoKCommitmentGroup.modulus;
75 this->st_3 = ((sg * commitmentToCoin.getCommitmentValue()).pow_mod(r_sigma, params->accumulatorPoKCommitmentGroup.modulus) * sh.pow_mod(r_xi, params->accumulatorPoKCommitmentGroup.modulus)) % params->accumulatorPoKCommitmentGroup.modulus;
77 this->t_1 = (h_n.pow_mod(r_zeta, params->accumulatorModulus) * g_n.pow_mod(r_epsilon, params->accumulatorModulus)) % params->accumulatorModulus;
78 this->t_2 = (h_n.pow_mod(r_eta, params->accumulatorModulus) * g_n.pow_mod(r_alpha, params->accumulatorModulus)) % params->accumulatorModulus;
79 this->t_3 = (C_u.pow_mod(r_alpha, params->accumulatorModulus) * ((h_n.inverse(params->accumulatorModulus)).pow_mod(r_beta, params->accumulatorModulus))) % params->accumulatorModulus;
80 this->t_4 = (C_r.pow_mod(r_alpha, params->accumulatorModulus) * ((h_n.inverse(params->accumulatorModulus)).pow_mod(r_delta, params->accumulatorModulus)) * ((g_n.inverse(params->accumulatorModulus)).pow_mod(r_beta, params->accumulatorModulus))) % params->accumulatorModulus;
82 CHashWriter hasher(0,0);
83 hasher << *params << sg << sh << g_n << h_n << commitmentToCoin.getCommitmentValue() << C_e << C_u << C_r << st_1 << st_2 << st_3 << t_1 << t_2 << t_3 << t_4;
85 //According to the proof, this hash should be of length k_prime bits. It is currently greater than that, which should not be a problem, but we should check this.
86 Bignum c = Bignum(hasher.GetHash());
88 this->s_alpha = r_alpha - c*e;
89 this->s_beta = r_beta - c*r_2*e;
90 this->s_zeta = r_zeta - c*r_3;
91 this->s_sigma = r_sigma - c*((e+1).inverse(params->accumulatorPoKCommitmentGroup.groupOrder));
92 this->s_eta = r_eta - c*r_1;
93 this->s_epsilon = r_epsilon - c*r_2;
94 this->s_delta = r_delta - c*r_3*e;
95 this->s_xi = r_xi + c*r*((e+1).inverse(params->accumulatorPoKCommitmentGroup.groupOrder));
96 this->s_phi = (r_phi - c*r) % params->accumulatorPoKCommitmentGroup.groupOrder;
97 this->s_gamma = r_gamma - c*((e-1).inverse(params->accumulatorPoKCommitmentGroup.groupOrder));
98 this->s_psi = r_psi + c*r*((e-1).inverse(params->accumulatorPoKCommitmentGroup.groupOrder));
101 /** Verifies that a commitment c is accumulated in accumulator a
103 bool AccumulatorProofOfKnowledge:: Verify(const Accumulator& a, const Bignum& valueOfCommitmentToCoin) const {
104 Bignum sg = params->accumulatorPoKCommitmentGroup.g;
105 Bignum sh = params->accumulatorPoKCommitmentGroup.h;
107 Bignum g_n = params->accumulatorQRNCommitmentGroup.g;
108 Bignum h_n = params->accumulatorQRNCommitmentGroup.h;
110 //According to the proof, this hash should be of length k_prime bits. It is currently greater than that, which should not be a problem, but we should check this.
111 CHashWriter hasher(0,0);
112 hasher << *params << sg << sh << g_n << h_n << valueOfCommitmentToCoin << C_e << C_u << C_r << st_1 << st_2 << st_3 << t_1 << t_2 << t_3 << t_4;
114 Bignum c = Bignum(hasher.GetHash()); //this hash should be of length k_prime bits
116 Bignum st_1_prime = (valueOfCommitmentToCoin.pow_mod(c, params->accumulatorPoKCommitmentGroup.modulus) * sg.pow_mod(s_alpha, params->accumulatorPoKCommitmentGroup.modulus) * sh.pow_mod(s_phi, params->accumulatorPoKCommitmentGroup.modulus)) % params->accumulatorPoKCommitmentGroup.modulus;
117 Bignum st_2_prime = (sg.pow_mod(c, params->accumulatorPoKCommitmentGroup.modulus) * ((valueOfCommitmentToCoin * sg.inverse(params->accumulatorPoKCommitmentGroup.modulus)).pow_mod(s_gamma, params->accumulatorPoKCommitmentGroup.modulus)) * sh.pow_mod(s_psi, params->accumulatorPoKCommitmentGroup.modulus)) % params->accumulatorPoKCommitmentGroup.modulus;
118 Bignum st_3_prime = (sg.pow_mod(c, params->accumulatorPoKCommitmentGroup.modulus) * (sg * valueOfCommitmentToCoin).pow_mod(s_sigma, params->accumulatorPoKCommitmentGroup.modulus) * sh.pow_mod(s_xi, params->accumulatorPoKCommitmentGroup.modulus)) % params->accumulatorPoKCommitmentGroup.modulus;
120 Bignum t_1_prime = (C_r.pow_mod(c, params->accumulatorModulus) * h_n.pow_mod(s_zeta, params->accumulatorModulus) * g_n.pow_mod(s_epsilon, params->accumulatorModulus)) % params->accumulatorModulus;
121 Bignum t_2_prime = (C_e.pow_mod(c, params->accumulatorModulus) * h_n.pow_mod(s_eta, params->accumulatorModulus) * g_n.pow_mod(s_alpha, params->accumulatorModulus)) % params->accumulatorModulus;
122 Bignum t_3_prime = ((a.getValue()).pow_mod(c, params->accumulatorModulus) * C_u.pow_mod(s_alpha, params->accumulatorModulus) * ((h_n.inverse(params->accumulatorModulus)).pow_mod(s_beta, params->accumulatorModulus))) % params->accumulatorModulus;
123 Bignum t_4_prime = (C_r.pow_mod(s_alpha, params->accumulatorModulus) * ((h_n.inverse(params->accumulatorModulus)).pow_mod(s_delta, params->accumulatorModulus)) * ((g_n.inverse(params->accumulatorModulus)).pow_mod(s_beta, params->accumulatorModulus))) % params->accumulatorModulus;
127 bool result_st1 = (st_1 == st_1_prime);
128 bool result_st2 = (st_2 == st_2_prime);
129 bool result_st3 = (st_3 == st_3_prime);
131 bool result_t1 = (t_1 == t_1_prime);
132 bool result_t2 = (t_2 == t_2_prime);
133 bool result_t3 = (t_3 == t_3_prime);
134 bool result_t4 = (t_4 == t_4_prime);
136 bool result_range = ((s_alpha >= -(params->maxCoinValue * Bignum(2).pow(params->k_prime + params->k_dprime + 1))) && (s_alpha <= (params->maxCoinValue * Bignum(2).pow(params->k_prime + params->k_dprime + 1))));
138 result = result_st1 && result_st2 && result_st3 && result_t1 && result_t2 && result_t3 && result_t4 && result_range;
143 } /* namespace libzerocoin */