ml_kem_impl.h

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/*
 * Module-Lattice Key Encapsulation Mechanism (ML-KEM)
 *
 * (C) 2024 Jack Lloyd
 * (C) 2024 René Meusel, Rohde & Schwarz Cybersecurity
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 */
 
#ifndef BOTAN_ML_KEM_IMPL_H_
#define BOTAN_ML_KEM_IMPL_H_
 
#include <botan/hash.h>
#include <botan/rng.h>
#include <botan/xof.h>
 
#include <botan/internal/kyber_encaps_base.h>
#include <botan/internal/kyber_keys.h>
#include <botan/internal/kyber_symmetric_primitives.h>
#include <botan/internal/kyber_types.h>
 
namespace Botan {
 
class ML_KEM_Encryptor final : public Kyber_KEM_Encryptor_Base {
   public:
      ML_KEM_Encryptor(std::shared_ptr<const Kyber_PublicKeyInternal> key, std::string_view kdf) :
            Kyber_KEM_Encryptor_Base(kdf, *key), m_public_key(std::move(key)) {}
 
   protected:
      void encapsulate(StrongSpan<KyberCompressedCiphertext> out_encapsulated_key,
                       StrongSpan<KyberSharedSecret> out_shared_key,
                       RandomNumberGenerator& rng) override;
 
      const KyberConstants& mode() const override { return m_public_key->mode(); }
 
   private:
      std::shared_ptr<const Kyber_PublicKeyInternal> m_public_key;
};
 
class ML_KEM_Decryptor final : public Kyber_KEM_Decryptor_Base {
   public:
      ML_KEM_Decryptor(std::shared_ptr<const Kyber_PrivateKeyInternal> private_key,
                       std::shared_ptr<const Kyber_PublicKeyInternal> public_key,
                       std::string_view kdf) :
            Kyber_KEM_Decryptor_Base(kdf, *public_key),
            m_public_key(std::move(public_key)),
            m_private_key(std::move(private_key)) {}
 
   protected:
      void decapsulate(StrongSpan<KyberSharedSecret> out_shared_key,
                       StrongSpan<const KyberCompressedCiphertext> encapsulated_key) override;
 
      const KyberConstants& mode() const override { return m_private_key->mode(); }
 
   private:
      std::shared_ptr<const Kyber_PublicKeyInternal> m_public_key;
      std::shared_ptr<const Kyber_PrivateKeyInternal> m_private_key;
};
 
class ML_KEM_Symmetric_Primitives final : public Kyber_Symmetric_Primitives {
   public:
      ML_KEM_Symmetric_Primitives() :
            m_sha3_512(HashFunction::create_or_throw("SHA-3(512)")),
            m_sha3_256(HashFunction::create_or_throw("SHA-3(256)")),
            m_shake256_256(HashFunction::create_or_throw("SHAKE-256(256)")),
            m_shake128(Botan::XOF::create_or_throw("SHAKE-128")),
            m_shake256(Botan::XOF::create_or_throw("SHAKE-256")) {}
 
   protected:
      std::optional<std::array<uint8_t, 1>> seed_expansion_domain_separator(const KyberConstants& mode) const override {
         // NIST FIPS 203, Algorithm 13 (K-PKE.KeyGen)
         //    Byte 33 of the input to G is the module dimension k from {2,3,4}.
         //    This is included to establish domain separation between the three
         //    parameter sets
         return std::array{mode.k()};
      }
 
      HashFunction& get_G() const override { return *m_sha3_512; }
 
      HashFunction& get_H() const override { return *m_sha3_256; }
 
      HashFunction& get_J() const override { return *m_shake256_256; }
 
      HashFunction& get_KDF() const override { throw Invalid_State("ML-KEM does not support KDF()"); }
 
      Botan::XOF& get_PRF(std::span<const uint8_t> seed, const uint8_t nonce) const override {
         m_shake256->clear();
         m_shake256->update(seed);
         m_shake256->update(store_be(nonce));
         return *m_shake256;
      }
 
      Botan::XOF& get_XOF(std::span<const uint8_t> seed, std::tuple<uint8_t, uint8_t> matrix_position) const override {
         m_shake128->clear();
         m_shake128->update(seed);
         m_shake128->update(store_be(make_uint16(std::get<0>(matrix_position), std::get<1>(matrix_position))));
         return *m_shake128;
      }
 
   private:
      std::unique_ptr<HashFunction> m_sha3_512;
      std::unique_ptr<HashFunction> m_sha3_256;
      std::unique_ptr<HashFunction> m_shake256_256;
      std::unique_ptr<Botan::XOF> m_shake128;
      std::unique_ptr<Botan::XOF> m_shake256;
};
 
class ML_KEM_Expanding_Keypair_Codec final : public Kyber_Keypair_Codec {
   public:
      KyberInternalKeypair decode_keypair(std::span<const uint8_t> buffer, KyberConstants mode) const override;
      secure_vector<uint8_t> encode_keypair(KyberInternalKeypair keypair) const override;
};
 
}  // namespace Botan
 
#endif