hybrid_public_key.h

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/**
* Composite key pair that exposes the Public/Private key API but combines
* multiple key agreement schemes into a hybrid algorithm.
*
* (C) 2023 Jack Lloyd
*     2023 Fabian Albert, René Meusel - Rohde & Schwarz Cybersecurity
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#ifndef BOTAN_TLS_13_HYBRID_KEM_PUBLIC_KEY_H_
#define BOTAN_TLS_13_HYBRID_KEM_PUBLIC_KEY_H_
 
#include <botan/pubkey.h>
 
#include <botan/tls_algos.h>
 
#include <memory>
#include <vector>
 
namespace Botan::TLS {
 
/**
 * Composes a number of public keys as defined in this IETF draft:
 * https://datatracker.ietf.org/doc/html/draft-ietf-tls-hybrid-design-04
 *
 * To an upstream user, this composite key pair is presented as a KEM. Each
 * individual key pair must either work as a KEX or as a KEM. Currently, the
 * class can deal with ECC keys and Kyber.
 *
 * The typical use case provides exactly two keys (one traditional KEX and one
 * post-quantum secure KEM). However, this class technically allows composing
 * any number of such keys. Composing more than two keys simply generates a
 * shared secret based on more algorithms.
 *
 * Note that this class is not generic enough for arbitrary use cases but
 * serializes and parses keys and ciphertexts as described in the
 * above-mentioned IETF draft for a post-quantum TLS 1.3.
 */
class BOTAN_TEST_API Hybrid_KEM_PublicKey : public virtual Public_Key {
   public:
      static std::unique_ptr<Hybrid_KEM_PublicKey> load_for_group(Group_Params group,
                                                                  std::span<const uint8_t> concatenated_public_values);
 
   public:
      explicit Hybrid_KEM_PublicKey(std::vector<std::unique_ptr<Public_Key>> pks);
 
      Hybrid_KEM_PublicKey(Hybrid_KEM_PublicKey&&) = default;
      Hybrid_KEM_PublicKey(const Hybrid_KEM_PublicKey&) = delete;
      Hybrid_KEM_PublicKey& operator=(Hybrid_KEM_PublicKey&&) = default;
      Hybrid_KEM_PublicKey& operator=(const Hybrid_KEM_PublicKey&) = delete;
      ~Hybrid_KEM_PublicKey() = default;
 
      std::string algo_name() const override;
      size_t estimated_strength() const override;
      size_t key_length() const override;
      bool check_key(RandomNumberGenerator& rng, bool strong) const override;
      AlgorithmIdentifier algorithm_identifier() const override;
      std::vector<uint8_t> raw_public_key_bits() const override;
      std::vector<uint8_t> public_key_bits() const override;
      std::unique_ptr<Private_Key> generate_another(RandomNumberGenerator& rng) const final;
 
      bool supports_operation(PublicKeyOperation op) const override;
 
      std::unique_ptr<PK_Ops::KEM_Encryption> create_kem_encryption_op(
         std::string_view kdf, std::string_view provider = "base") const override;
 
      const auto& public_keys() const { return m_public_keys; }
 
   protected:
      std::vector<std::unique_ptr<Public_Key>> m_public_keys;
 
   private:
      size_t m_key_length;
      size_t m_estimated_strength;
};
 
BOTAN_DIAGNOSTIC_PUSH
BOTAN_DIAGNOSTIC_IGNORE_INHERITED_VIA_DOMINANCE
 
/**
 * Composes a number of private keys for hybrid key agreement as defined in this
 * IETF draft: https://datatracker.ietf.org/doc/html/draft-ietf-tls-hybrid-design-04
 */
class BOTAN_TEST_API Hybrid_KEM_PrivateKey final : public Private_Key,
                                                   public Hybrid_KEM_PublicKey {
   public:
      /**
       * Generate a hybrid private key for the given TLS code point.
       */
      static std::unique_ptr<Hybrid_KEM_PrivateKey> generate_from_group(Group_Params group, RandomNumberGenerator& rng);
 
   public:
      Hybrid_KEM_PrivateKey(std::vector<std::unique_ptr<Private_Key>> private_keys);
 
      secure_vector<uint8_t> private_key_bits() const override;
 
      std::unique_ptr<Public_Key> public_key() const override;
 
      bool check_key(RandomNumberGenerator& rng, bool strong) const override;
 
      std::unique_ptr<PK_Ops::KEM_Decryption> create_kem_decryption_op(
         RandomNumberGenerator& rng, std::string_view kdf, std::string_view provider = "base") const override;
 
      const auto& private_keys() const { return m_private_keys; }
 
   private:
      std::vector<std::unique_ptr<Private_Key>> m_private_keys;
};
 
BOTAN_DIAGNOSTIC_POP
 
}  // namespace Botan::TLS
 
#endif