ml-kem/tests/test_serialize.cpp

#include "ml_kem/internals/poly/serialize.hpp"
#include "randomshake/randomshake.hpp"
#include <gtest/gtest.h>

// Ensure that degree-255 polynomial serialization to byte array ( of length 32*l -bytes ) and deserialization of
// that byte array to degree-255 polynomial works as expected for parameterizable values of l | l ∈ [1, 12].
//
// `l` denotes significant bit width ( from LSB side ) for each coefficient of polynomial.
template<size_t l>
void
test_serialize_deserialize()
{
  constexpr size_t blen = (ml_kem_ntt::N * l) / 8;
  constexpr uint32_t mask = (1u << l) - 1u;

  std::vector<ml_kem_field::zq_t> src(ml_kem_ntt::N);
  std::vector<ml_kem_field::zq_t> dst(ml_kem_ntt::N);
  std::vector<uint8_t> bytes(blen);

  randomshake::randomshake_t<256> csprng{};

  for (size_t i = 0; i < ml_kem_ntt::N; i++) {
    src[i] = ml_kem_field::zq_t::random(csprng);
  }

  using poly_t = std::span<ml_kem_field::zq_t, ml_kem_ntt::N>;
  using serialized_t = std::span<uint8_t, blen>;

  ml_kem_utils::encode<l>(poly_t(src), serialized_t(bytes));
  ml_kem_utils::decode<l>(serialized_t(bytes), poly_t(dst));

  for (size_t i = 0; i < ml_kem_ntt::N; i++) {
    EXPECT_EQ((src[i].raw() & mask), (dst[i].raw() & mask));
  }
}

TEST(ML_KEM, PolynomialSerialization)
{
  test_serialize_deserialize<12>();
  test_serialize_deserialize<11>();
  test_serialize_deserialize<10>();
  test_serialize_deserialize<5>();
  test_serialize_deserialize<4>();
  test_serialize_deserialize<1>();
}