group.hpp

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// === AUDIT STATUS ===
// internal:    { status: Planned, auditors: [], commit: }
// external_1:  { status: not started, auditors: [], commit: }
// external_2:  { status: not started, auditors: [], commit: }
// =====================
 
#pragma once
 
#include "../../common/assert.hpp"
#include "./affine_element.hpp"
#include "./element.hpp"
#include "./wnaf.hpp"
#include "barretenberg/common/constexpr_utils.hpp"
#include "barretenberg/crypto/blake3s/blake3s.hpp"
#include <array>
#include <cinttypes>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
 
namespace bb {
 
template <typename Fq_, typename Fr_, typename Params> class group {
  public:
    // Allow using group::Fq and group::Fr
    using Fq = Fq_;
    using Fr = Fr_;
    using element = group_elements::element<Fq, Fr, Params>;
    using affine_element = group_elements::affine_element<Fq, Fr, Params>;
    static constexpr bool USE_ENDOMORPHISM = Params::USE_ENDOMORPHISM;
    static constexpr bool has_a = Params::has_a;
 
    static constexpr element one{ Params::one_x, Params::one_y, Fq::one() };
    static constexpr element point_at_infinity = one.set_infinity();
    static constexpr affine_element affine_one{ Params::one_x, Params::one_y };
    static constexpr affine_element affine_point_at_infinity = affine_one.set_infinity();
    static constexpr Fq curve_a = Params::a;
    static constexpr Fq curve_b = Params::b;
 
    inline static std::vector<affine_element> derive_generators(const std::vector<uint8_t>& domain_separator_bytes,
                                                                const size_t num_generators,
                                                                const size_t starting_index = 0)
    {
        // Safety: domain_separator_bytes is indexed via &domain_separator_bytes[0] below.
        // An empty domain separator would be UB and also defeats domain separation.
        BB_ASSERT(!domain_separator_bytes.empty(), "derive_generators: domain_separator_bytes must be non-empty");
 
        // We serialize the generator index into 4 bytes (uint32_t). Ensure we never silently truncate.
        if (num_generators > 0) {
            BB_ASSERT(starting_index <= static_cast<size_t>(UINT32_MAX),
                      "derive_generators: starting_index exceeds uint32 range");
            BB_ASSERT(num_generators - 1 <= static_cast<size_t>(UINT32_MAX) - starting_index,
                      "derive_generators: starting_index + num_generators exceeds uint32 range");
        }
 
        std::vector<affine_element> result;
        const auto domain_hash = blake3::blake3s_constexpr(&domain_separator_bytes[0], domain_separator_bytes.size());
        std::vector<uint8_t> generator_preimage;
        generator_preimage.reserve(64);
        std::copy(domain_hash.begin(), domain_hash.end(), std::back_inserter(generator_preimage));
        for (size_t i = 0; i < 32; ++i) {
            generator_preimage.emplace_back(0);
        }
        for (size_t i = starting_index; i < starting_index + num_generators; ++i) {
            auto generator_index = static_cast<uint32_t>(i);
            uint32_t mask = 0xff;
            generator_preimage[32] = static_cast<uint8_t>(generator_index >> 24);
            generator_preimage[33] = static_cast<uint8_t>((generator_index >> 16) & mask);
            generator_preimage[34] = static_cast<uint8_t>((generator_index >> 8) & mask);
            generator_preimage[35] = static_cast<uint8_t>(generator_index & mask);
            result.push_back(affine_element::hash_to_curve(generator_preimage));
        }
        return result;
    }
 
    inline static std::vector<affine_element> derive_generators(const std::string_view& domain_separator,
                                                                const size_t num_generators,
                                                                const size_t starting_index = 0)
    {
        std::vector<uint8_t> domain_bytes;
        for (char i : domain_separator) {
            domain_bytes.emplace_back(static_cast<unsigned char>(i));
        }
        return derive_generators(domain_bytes, num_generators, starting_index);
    }
};
 
} // namespace bb