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plonk: moved the initialisation of the array of expected hash values …
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…to the transcript hasher constructor (cf. #61 (comment)); added exception handling in case the buffer length is invalid (cf. #61 (comment))
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Vesselin Velichkov committed Aug 17, 2022
1 parent 78dd119 commit 47b9272
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Showing 3 changed files with 55 additions and 37 deletions.
3 changes: 3 additions & 0 deletions libsnark/zk_proof_systems/plonk/srs.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -244,6 +244,9 @@ template<typename ppT> class transcript_hasher
private:
// buffer accumulating data to be hashed
std::vector<uint8_t> buffer;
// array containing the hash values of the communication transcript
// i.e. the six challenges (in this order): beta, gamma, alpha, zeta, nu, u
std::array<libff::Fr<ppT>, 6> hash_values;

public:
void add_element(const libff::Fr<ppT> &element);
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88 changes: 52 additions & 36 deletions libsnark/zk_proof_systems/plonk/srs.tcc
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Original file line number Diff line number Diff line change
Expand Up @@ -75,6 +75,25 @@ template<typename ppT>
transcript_hasher<ppT>::transcript_hasher(std::vector<uint8_t> &buffer)
: buffer(std::move(buffer))
{
// test array containing the expected hash values of the communication
// transcript i.e. the communication challenges (in this order): beta,
// gamma, alpha, zeta, nu, u WARNING! specific to curve BLS12-381
this->hash_values = {
libff::Fr<ppT>("3710899868510394644410941212967766116886736137326022751"
"891187938298987182388"), // beta
libff::Fr<ppT>("110379303840831945879077096653321168432672740458288022"
"49545114995763715746939"), // gamma
libff::Fr<ppT>("379799789992747238930717819864848384921111623418803600"
"22719385400306128734648"), // alpha
libff::Fr<ppT>("4327197228921839935583364394550235027071910395980312641"
"5018065799136107272465"), // zeta
libff::Fr<ppT>(
"275158598338697752421507265080923414294782807831923791651"
"55175653098691426347"), // nu
libff::Fr<ppT>(
"1781751143954696684632449211212056577828855388109883650570"
"6049265393896966778"), // u
};
}

/// clear the buffer (for now only for testing)
Expand Down Expand Up @@ -156,35 +175,45 @@ void transcript_hasher<ppT>::add_element(const libff::G2<ppT> &element)
/// BLAKE, etc.
template<typename ppT> libff::Fr<ppT> transcript_hasher<ppT>::get_hash()
{
using Field = libff::Fr<ppT>;

size_t buffer_len = this->buffer.size();
// DEBUG
printf("[%s:%d] len %7d\n", __FILE__, __LINE__, (int)buffer_len);

// vector of valid lengths (\attention specific to BLS12-381)
std::vector<size_t> length{288, 320, 416, 704, 896, 1120};
const std::vector<size_t> length{288, 320, 416, 704, 896, 1120};

// If we are here, then the hasher buffer has invalid length so throw an
// exception
bool b_valid_length =
((buffer_len == length[0]) || (buffer_len == length[1]) ||
(buffer_len == length[2]) || (buffer_len == length[3]) ||
(buffer_len == length[4]) || (buffer_len == length[5]));
try {
if (!b_valid_length) {
throw std::logic_error(
"Error: invalid length of transcript hasher buffer");
}
} catch (const std::logic_error &e) {
std::cout << "Error: " << e.what() << "\n";
}
if (!b_valid_length) {
printf(
"[%s:%d] Error: invalid length of transcript hasher buffer\n",
__FILE__,
__LINE__);
}
assert(b_valid_length);

libff::Fr<ppT> challenge = 0;

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");
// beta
if (buffer_len == length[0]) {
printf(
"[%s:%d] buffer_len %d: beta\n",
__FILE__,
__LINE__,
(int)buffer_len);
return beta;
challenge = this->hash_values[0]; // beta
}
// gamma
if (buffer_len == length[1]) {
Expand All @@ -193,7 +222,7 @@ template<typename ppT> libff::Fr<ppT> transcript_hasher<ppT>::get_hash()
__FILE__,
__LINE__,
(int)buffer_len);
return gamma;
challenge = this->hash_values[1]; // gamma
}
// alpha
if (buffer_len == length[2]) {
Expand All @@ -202,7 +231,7 @@ template<typename ppT> libff::Fr<ppT> transcript_hasher<ppT>::get_hash()
__FILE__,
__LINE__,
(int)buffer_len);
return alpha;
challenge = this->hash_values[2]; // alpha
}
// zeta
if (buffer_len == length[3]) {
Expand All @@ -211,13 +240,13 @@ template<typename ppT> libff::Fr<ppT> transcript_hasher<ppT>::get_hash()
__FILE__,
__LINE__,
(int)buffer_len);
return zeta;
challenge = this->hash_values[3]; // zeta
}
// nu
if (buffer_len == length[4]) {
printf(
"[%s:%d] buffer_len %d: nu\n", __FILE__, __LINE__, (int)buffer_len);
return nu;
challenge = this->hash_values[4]; // nu
}
// u
if (buffer_len == length[5]) {
Expand All @@ -228,23 +257,10 @@ template<typename ppT> libff::Fr<ppT> transcript_hasher<ppT>::get_hash()
__LINE__,
(int)buffer_len);
this->buffer.clear();
return u;
}
bool b_valid_length =
((buffer_len == length[0]) || (buffer_len == length[1]) ||
(buffer_len == length[2]) || (buffer_len == length[3]) ||
(buffer_len == length[4]) || (buffer_len == length[5]));
try {
if (!b_valid_length) {
throw std::logic_error(
"Error: invalid length of transcript hasher buffer");
}
} catch (const std::logic_error &e) {
std::cout << "Error: " << e.what() << "\n";
challenge = this->hash_values[5]; // u
}
assert(b_valid_length);
// If we are here, then the hasher buffer has invalid length so return error
return 0;

return challenge;
}

/// Compute a universal srs (usrs). It is composed *only* of encoded
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1 change: 0 additions & 1 deletion libsnark/zk_proof_systems/plonk/tests/test_plonk.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,6 @@

namespace libsnark
{

#define PLONK_MAX_DEGREE 245

// Manipulate elements of a valid proof to assert that proof
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