symmetric_key.h

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// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the Apache 2.0 License.
#pragma once
 
#include "ccf/crypto/entropy.h"
 
#include <span>
#include <vector>
 
namespace ccf::crypto
{
  constexpr size_t GCM_DEFAULT_KEY_SIZE = 32;
 
  constexpr size_t GCM_SIZE_TAG = 16;
 
  struct GcmHeader
  {
    uint8_t tag[GCM_SIZE_TAG] = {};
 
    // Size does not change after construction
    std::vector<uint8_t> iv;
 
    GcmHeader(size_t iv_size);
 
    void set_iv(const uint8_t* data, size_t size);
    [[nodiscard]] std::span<const uint8_t> get_iv() const;
 
    [[nodiscard]] size_t serialised_size() const;
    std::vector<uint8_t> serialise();
 
    void deserialise(const std::vector<uint8_t>& ser);
    void deserialise(const uint8_t*& data, size_t& size);
  };
 
  template <size_t IV_BYTES>
  struct FixedSizeGcmHeader : public GcmHeader
  {
    static constexpr size_t IV_SIZE = IV_BYTES;
 
    FixedSizeGcmHeader() : GcmHeader(IV_SIZE) {}
 
    static size_t serialised_size()
    {
      return GCM_SIZE_TAG + IV_SIZE;
    }
 
    void set_random_iv(EntropyPtr entropy = ccf::crypto::get_entropy())
    {
      iv = entropy->random(IV_SIZE);
    }
  };
 
  // GcmHeader with 12-byte (96-bit) IV
  constexpr size_t iv_size = 12;
  using StandardGcmHeader = FixedSizeGcmHeader<iv_size>;
 
  struct GcmCipher
  {
    StandardGcmHeader hdr;
    std::vector<uint8_t> cipher;
 
    GcmCipher();
    GcmCipher(size_t size);
 
    std::vector<uint8_t> serialise();
 
    void deserialise(const std::vector<uint8_t>& serial);
  };
 
  class KeyAesGcm
  {
  public:
    KeyAesGcm() = default;
    virtual ~KeyAesGcm() = default;
 
    // AES-GCM encryption
    virtual void encrypt(
      std::span<const uint8_t> iv,
      std::span<const uint8_t> plain,
      std::span<const uint8_t> aad,
      std::vector<uint8_t>& cipher,
      uint8_t tag[GCM_SIZE_TAG]) const = 0;
 
    // AES-GCM decryption
    virtual bool decrypt(
      std::span<const uint8_t> iv,
      const uint8_t tag[GCM_SIZE_TAG],
      std::span<const uint8_t> cipher,
      std::span<const uint8_t> aad,
      std::vector<uint8_t>& plain) const = 0;
 
    // Key size in bits
    [[nodiscard]] virtual size_t key_size() const = 0;
  };
 
  std::unique_ptr<KeyAesGcm> make_key_aes_gcm(std::span<const uint8_t> rawKey);
 
  inline void check_supported_aes_key_size(size_t num_bits)
  {
    // NOLINTNEXTLINE(cppcoreguidelines-avoid-magic-numbers,readability-magic-numbers)
    if (num_bits != 128 && num_bits != 192 && num_bits != 256)
    {
      throw std::runtime_error("Unsupported key size");
    }
  }
}