mimc_permutation.hpp

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// DISCLAIMER:
// Content taken and adapted from:
// https://github.com/HarryR/ethsnarks/blob/master/src/gadgets/mimc.hpp
 
#ifndef __ZETH_CIRCUITS_MIMC_PERMUTATION_HPP__
#define __ZETH_CIRCUITS_MIMC_PERMUTATION_HPP__
 
#include "libzeth/circuits/mimc/mimc_round.hpp"
 
namespace libzeth
{
 
template<typename FieldT, size_t Exponent, size_t NumRounds>
class MiMC_permutation_gadget : public libsnark::gadget<FieldT>
{
private:
    // Round constants only available up to some maximum number of rounds. Note
    // that the instantiations used in this library do not use all 93 round
    // constants, but other instantiations may (in particular, see
    // instantiations for other curves in
    // https://github.com/clearmatics/zecale).
    static const size_t MaxRounds = 93;
    static_assert(
        NumRounds <= MaxRounds, "NumRounds must be less than MaxRounds");
 
    // Instantiate round gadget with exponent = Exponent
    using RoundT = MiMC_round_gadget<FieldT, Exponent>;
 
    // Vector of round constants
    static std::vector<FieldT> round_constants;
    static bool round_constants_initialized;
 
    // Vector of intermediate result values
    std::array<libsnark::pb_variable<FieldT>, NumRounds> round_results;
 
    // Vector of MiMC round_gadgets
    std::vector<RoundT> round_gadgets;
 
    // Common initialization
    MiMC_permutation_gadget(
        libsnark::protoboard<FieldT> &pb,
        const libsnark::pb_linear_combination<FieldT> &msg,
        const libsnark::pb_linear_combination<FieldT> &key,
        const libsnark::pb_variable<FieldT> &result,
        const libsnark::pb_linear_combination<FieldT> &add_to_result,
        const bool add_to_result_is_valid,
        const std::string &annotation_prefix);
 
public:
    MiMC_permutation_gadget(
        libsnark::protoboard<FieldT> &pb,
        const libsnark::pb_linear_combination<FieldT> &msg,
        const libsnark::pb_linear_combination<FieldT> &key,
        const libsnark::pb_variable<FieldT> &result,
        const std::string &annotation_prefix = "MiMC_permutation_gadget");
 
    MiMC_permutation_gadget(
        libsnark::protoboard<FieldT> &pb,
        const libsnark::pb_linear_combination<FieldT> &msg,
        const libsnark::pb_linear_combination<FieldT> &key,
        const libsnark::pb_variable<FieldT> &result,
        const libsnark::pb_linear_combination<FieldT> &add_to_result,
        const std::string &annotation_prefix = "MiMC_permutation_gadget");
 
    void generate_r1cs_constraints();
    void generate_r1cs_witness() const;
 
    // Constants vector initialization
    void setup_sha3_constants();
};
 
} // namespace libzeth
 
#include "libzeth/circuits/mimc/mimc_permutation.tcc"
 
#endif // __ZETH_CIRCUITS_MIMC_PERMUTATION_HPP__