kyber_algos.h

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/*
 * Crystals Kyber Internal Algorithms
 * Based on the public domain reference implementation by the
 * designers (https://github.com/pq-crystals/kyber)
 *
 * Further changes
 * (C) 2021-2024 Jack Lloyd
 * (C) 2021-2022 Manuel Glaser and Michael Boric, Rohde & Schwarz Cybersecurity
 * (C) 2021-2022 René Meusel and Hannes Rantzsch, neXenio GmbH
 * (C) 2024 René Meusel, Rohde & Schwarz Cybersecurity
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 */
 
#ifndef BOTAN_KYBER_ALGOS_H_
#define BOTAN_KYBER_ALGOS_H_
 
#include <botan/internal/kyber_symmetric_primitives.h>
#include <botan/internal/kyber_types.h>
 
namespace Botan::Kyber_Algos {
 
void encode_polynomial_vector(std::span<uint8_t> out, const KyberPolyVecNTT& p);
 
KyberPolyVecNTT decode_polynomial_vector(std::span<const uint8_t> a, const KyberConstants& mode);
 
KyberPoly polynomial_from_message(StrongSpan<const KyberMessage> msg);
 
KyberMessage polynomial_to_message(const KyberPoly& p);
 
KyberInternalKeypair expand_keypair(KyberPrivateKeySeed seed, KyberConstants mode);
 
void compress_ciphertext(StrongSpan<KyberCompressedCiphertext> out,
                         const KyberPolyVec& u,
                         const KyberPoly& v,
                         const KyberConstants& m_mode);
 
std::pair<KyberPolyVec, KyberPoly> decompress_ciphertext(StrongSpan<const KyberCompressedCiphertext> ct,
                                                         const KyberConstants& mode);
 
KyberPolyMat sample_matrix(StrongSpan<const KyberSeedRho> seed, bool transposed, const KyberConstants& mode);
 
void sample_polynomial_from_cbd(KyberPoly& poly,
                                KyberConstants::KyberEta eta,
                                const KyberSamplingRandomness& randomness);
 
template <concepts::resizable_byte_buffer T = secure_vector<uint8_t>>
T encode_polynomial_vector(const KyberPolyVecNTT& vec, const KyberConstants& mode) {
   T r(mode.polynomial_vector_bytes());
   encode_polynomial_vector(r, vec);
   return r;
}
 
/**
 * Allows sampling multiple polynomials from a single seed via a XOF.
 *
 * Used in Algorithms 13 (K-PKE.KeyGen) and 14 (K-PKE.Encrypt), and takes care
 * of the continuous nonce value internally.
 */
template <typename SeedT>
   requires std::same_as<KyberSeedSigma, SeedT> || std::same_as<KyberEncryptionRandomness, SeedT>
class PolynomialSampler {
   public:
      PolynomialSampler(StrongSpan<const SeedT> seed, const KyberConstants& mode) :
            m_seed(seed), m_mode(mode), m_nonce(0) {}
 
      KyberPolyVec sample_polynomial_vector_cbd_eta1() {
         KyberPolyVec vec(m_mode.k());
         for(auto& poly : vec) {
            sample_poly_cbd(poly, m_mode.eta1());
         }
         return vec;
      }
 
      KyberPoly sample_polynomial_cbd_eta2()
         requires std::same_as<KyberEncryptionRandomness, SeedT>
      {
         KyberPoly poly;
         sample_poly_cbd(poly, m_mode.eta2());
         return poly;
      }
 
      KyberPolyVec sample_polynomial_vector_cbd_eta2()
         requires std::same_as<KyberEncryptionRandomness, SeedT>
      {
         KyberPolyVec vec(m_mode.k());
         for(auto& poly : vec) {
            sample_poly_cbd(poly, m_mode.eta2());
         }
         return vec;
      }
 
   private:
      KyberSamplingRandomness prf(size_t bytes) {
         const auto& sym = m_mode.symmetric_primitives();
         auto seed_span = m_seed.get();
         sym.setup_PRF(m_prf_xof, seed_span, m_nonce++);
         return m_prf_xof->output<KyberSamplingRandomness>(bytes);
      }
 
      void sample_poly_cbd(KyberPoly& poly, KyberConstants::KyberEta eta) {
         const auto randomness = [&] {
            switch(eta) {
               case KyberConstants::KyberEta::_2:
                  return prf(2 * poly.size() / 4);
               case KyberConstants::KyberEta::_3:
                  return prf(3 * poly.size() / 4);
            }
 
            BOTAN_ASSERT_UNREACHABLE();
         }();
 
         sample_polynomial_from_cbd(poly, eta, randomness);
      }
 
   private:
      StrongSpan<const SeedT> m_seed;
      const KyberConstants& m_mode;
      uint8_t m_nonce;
      std::unique_ptr<Botan::XOF> m_prf_xof;
};
 
template <typename T>
PolynomialSampler(T, const KyberConstants&) -> PolynomialSampler<T>;
 
}  // namespace Botan::Kyber_Algos
 
#endif