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plonk: replaced structure transcript_hash_t with class transcript_has…
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…her that makes a call to hash function. for the moment it directly returns the expected hash values for the purposes of testing. addresses issue #56.
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Vesselin Velichkov committed Jul 29, 2022
1 parent ae9d145 commit ef3297b
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13 changes: 3 additions & 10 deletions libsnark/zk_proof_systems/plonk/prover.hpp
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Expand Up @@ -461,23 +461,16 @@ template<typename ppT> class plonk_prover
/// \param[in] blind_scalars: random blinding scalars b1, b2, ..., b9
/// used in prover rounds 1 and 2 (see Sect. 8.3, roumds
/// 1,2 [GWC19])
/// \param[in] transcript_hash: hashes of the communication transcript
/// after prover rounds 1,2,3,4,5. TODO: \attention
/// currently the structure is used as an input initialized
/// with hard-coded example values for debug purposes. In
/// the long run it should be modified to be used as an
/// output. More specifically, the hard-coded values should
/// be overwritten with the actual transcript hashes
/// produced after the respective rounds within \ref
/// compute_proof
/// \param[in] transcript_hasher: hashes of the communication
/// transcript after prover rounds 1,2,3,4,5.
///
/// OUTPUT
/// \param[out] proof: SNARK proof Pi (see above)
static plonk_proof<ppT> compute_proof(
const srs<ppT> &srs,
const std::vector<Field> &witness,
const std::vector<libff::Fr<ppT>> &blind_scalars,
transcript_hash_t<ppT> &transcript_hash);
transcript_hasher<ppT> &hasher);
};

} // namespace libsnark
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33 changes: 16 additions & 17 deletions libsnark/zk_proof_systems/plonk/prover.tcc
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Expand Up @@ -994,15 +994,8 @@ plonk_proof<ppT>::plonk_proof(
/// \param[in] blind_scalars: random blinding scalars b1, b2, ..., b9
/// used in prover rounds 1 and 2 (see Sect. 8.3, roumds
/// 1,2 [GWC19])
/// \param[in] transcript_hash: hashes of the communication transcript
/// after prover rounds 1,2,3,4,5. TODO: \attention
/// currently the structure is used as an input initialized
/// with hard-coded example values for debug purposes. In
/// the long run it should be modified to be used as an
/// output. More specifically, the hard-coded values should
/// be overwritten with the actual transcript hashes
/// produced after the respective rounds within \ref
/// compute_proof
/// \param[in] transcript_hasher: hashes of the communication
/// transcript after prover rounds 1,2,3,4,5.
///
/// OUTPUT
/// \param[out] proof: SNARK proof Pi (see above)
Expand All @@ -1011,7 +1004,7 @@ plonk_proof<ppT> plonk_prover<ppT>::compute_proof(
const srs<ppT> &srs,
const std::vector<Field> &witness,
const std::vector<libff::Fr<ppT>> &blind_scalars,
transcript_hash_t<ppT> &transcript_hash)
transcript_hasher<ppT> &hasher)
{
// Prover Round 0 (initialization)
printf("[%s:%d] Prover Round 0...\n", __FILE__, __LINE__);
Expand All @@ -1024,27 +1017,28 @@ plonk_proof<ppT> plonk_prover<ppT>::compute_proof(

printf("[%s:%d] Prover Round 2...\n", __FILE__, __LINE__);
// - beta, gamma: permutation challenges - hashes of transcript of round 1
const libff::Fr<ppT> beta = transcript_hash.beta;
const libff::Fr<ppT> gamma = transcript_hash.gamma;
const libff::Fr<ppT> beta = hasher.get_hash();
const libff::Fr<ppT> gamma = hasher.get_hash();

round_two_out_t<ppT> round_two_out = plonk_prover::round_two(
beta, gamma, round_zero_out, blind_scalars, witness, srs);

printf("[%s:%d] Prover Round 3...\n", __FILE__, __LINE__);
// - alpha: quotient challenge - hash of transcript of rounds 1,2
libff::Fr<ppT> alpha = transcript_hash.alpha;
const libff::Fr<ppT> alpha = hasher.get_hash();
round_three_out_t<ppT> round_three_out = plonk_prover::round_three(
alpha, beta, gamma, round_zero_out, round_one_out, round_two_out, srs);

printf("[%s:%d] Prover Round 4...\n", __FILE__, __LINE__);
// - zeta: evaluation challenge - hash of transcriptof rounds 1,2,3
libff::Fr<ppT> zeta = transcript_hash.zeta;
const libff::Fr<ppT> zeta = hasher.get_hash();
round_four_out_t<ppT> round_four_out =
plonk_prover::round_four(zeta, round_one_out, round_three_out, srs);

printf("[%s:%d] Prover Round 5...\n", __FILE__, __LINE__);
/// - nu: opening challenge -- hash of transcript (denoted by v in
/// [GWC19])
libff::Fr<ppT> nu = transcript_hash.nu;
const libff::Fr<ppT> nu = hasher.get_hash();
round_five_out_t<ppT> round_five_out = plonk_prover::round_five(
alpha,
beta,
Expand All @@ -1060,10 +1054,15 @@ plonk_proof<ppT> plonk_prover<ppT>::compute_proof(

// TODO: activate this part when we implement actual hashing of
// communication transcripts
#if 0
#if 0
// u: multipoint evaluation challenge -- hash of transcript from
// rounds 1,2,3,4,5
libff::Fr<ppT> u = transcript_hash.u;
const libff::Fr<ppT> u = hasher.get_hash();
#else
// do the hash anyway in order to keep the correct count of the
// hasher istep member (which resets to 0 only after the last hash
// is performed which is hash of u)
hasher.get_hash();
#endif

// construct proof
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42 changes: 16 additions & 26 deletions libsnark/zk_proof_systems/plonk/srs.hpp
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Expand Up @@ -179,32 +179,22 @@ template<typename ppT> class plonk_keypair
plonk_keypair(plonk_keypair<ppT> &&other) = default;
};

/// Hashes of transcript after prover rounds 1,2,3,4,5
template<typename ppT> struct transcript_hash_t {

/// - beta: permutation challenge - hashes of transcript after round 1
libff::Fr<ppT> beta;
/// - gamma: permutation challenge - hashes of transcript after round 1
libff::Fr<ppT> gamma;
/// - alpha: quotient challenge - hash of transcript after rounds 1,2
libff::Fr<ppT> alpha;
/// - zeta: evaluation challenge - hash of transcriptafter rounds 1,2,3
libff::Fr<ppT> zeta;
/// - nu: opening challenge - hash of transcript after rounds 1,2,3,4
/// (denoted by v in [GWC19])
libff::Fr<ppT> nu;
/// - u: multipoint evaluation challenge -- hash of transcript after rounds
/// 1,2,3,4,5
libff::Fr<ppT> u;

/// struct constructor
transcript_hash_t(
libff::Fr<ppT> &beta,
libff::Fr<ppT> &gamma,
libff::Fr<ppT> &alpha,
libff::Fr<ppT> &zeta,
libff::Fr<ppT> &nu,
libff::Fr<ppT> &u);
/// transcript hasher interface
template<typename ppT> class transcript_hasher
{
private:
// the current step of the hasher
size_t istep;

public:
void add_element(const libff::Fr<ppT> &element);
void add_element(const libff::G1<ppT> &element);
void add_element(const libff::G2<ppT> &element);

libff::Fr<ppT> get_hash();

// constructor
transcript_hasher(size_t &istep);
};

} // namespace libsnark
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67 changes: 58 additions & 9 deletions libsnark/zk_proof_systems/plonk/srs.tcc
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Expand Up @@ -70,19 +70,68 @@ plonk_keypair<ppT>::plonk_keypair(
{
}

/// struct transcript_hash_t constructor
/// transcript_hasher constructor
template<typename ppT>
transcript_hash_t<ppT>::transcript_hash_t(
libff::Fr<ppT> &beta,
libff::Fr<ppT> &gamma,
libff::Fr<ppT> &alpha,
libff::Fr<ppT> &zeta,
libff::Fr<ppT> &nu,
libff::Fr<ppT> &u)
: beta(beta), gamma(gamma), alpha(alpha), zeta(zeta), nu(nu), u(u)
transcript_hasher<ppT>::transcript_hasher(size_t &istep) : istep(istep)
{
}

/// dummy implementation of get_hash that directly returns the
/// expected hard-coded hashes for the purposes of unit testing TODO
/// to be replaced by a call to a proper hash function e.g. SHA2,
/// BLAKE, etc.
template<typename ppT> libff::Fr<ppT> transcript_hasher<ppT>::get_hash()
{
assert((this->istep >= 0) && (this->istep <= 5));
using Field = libff::Fr<ppT>;

Field beta = Field("3710899868510394644410941212967766116886736137326022751"
"891187938298987182388");
Field gamma = Field("110379303840831945879077096653321168432672740458288022"
"49545114995763715746939");
Field alpha = Field("379799789992747238930717819864848384921111623418803600"
"22719385400306128734648");
Field zeta = Field("4327197228921839935583364394550235027071910395980312641"
"5018065799136107272465");
Field nu = Field("275158598338697752421507265080923414294782807831923791651"
"55175653098691426347");
Field u = Field("1781751143954696684632449211212056577828855388109883650570"
"6049265393896966778");
if (this->istep == 0) {
printf("[%s:%d] istep %d\n", __FILE__, __LINE__, (int)istep);
this->istep++;
return beta;
}
if (this->istep == 1) {
printf("[%s:%d] istep %d\n", __FILE__, __LINE__, (int)istep);
this->istep++;
return gamma;
}
if (this->istep == 2) {
printf("[%s:%d] istep %d\n", __FILE__, __LINE__, (int)istep);
this->istep++;
return alpha;
}
if (this->istep == 3) {
printf("[%s:%d] istep %d\n", __FILE__, __LINE__, (int)istep);
this->istep++;
return zeta;
}
if (this->istep == 4) {
printf("[%s:%d] istep %d\n", __FILE__, __LINE__, (int)istep);
this->istep++;
return nu;
}
if (this->istep == 5) {
// reset step to 0
printf("[%s:%d] istep %d\n", __FILE__, __LINE__, (int)istep);
this->istep = 0;
return u;
}
// error
return 0;
}

/// Compute a universal srs (usrs). It is composed *only* of encoded
/// powers of the secret value in the group generator. Therefore a usrs
/// is independent of any particular circuit.
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