gcm.h

Go to the documentation of this file.

/*
* GCM Mode
* (C) 2013 Jack Lloyd
* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#ifndef BOTAN_AEAD_GCM_H_
#define BOTAN_AEAD_GCM_H_

#include <botan/aead.h>
#include <botan/sym_algo.h>

namespace Botan {

class BlockCipher;
class StreamCipher;
class GHASH;

/**
* GCM Mode
*/
class BOTAN_PUBLIC_API(2,0) GCM_Mode : public AEAD_Mode
   {
   public:
      void set_associated_data(const uint8_t ad[], size_t ad_len) override;

      std::string name() const override;

      size_t update_granularity() const override;

      Key_Length_Specification key_spec() const override;

      bool valid_nonce_length(size_t len) const override;

      size_t tag_size() const override { return m_tag_size; }

      void clear() override;

      void reset() override;

      std::string provider() const override;
   protected:
      GCM_Mode(BlockCipher* cipher, size_t tag_size);

      ~GCM_Mode();

      static const size_t GCM_BS = 16;

      const size_t m_tag_size;
      const std::string m_cipher_name;

      std::unique_ptr<StreamCipher> m_ctr;
      std::unique_ptr<GHASH> m_ghash;
   private:
      void start_msg(const uint8_t nonce[], size_t nonce_len) override;

      void key_schedule(const uint8_t key[], size_t length) override;
   };

/**
* GCM Encryption
*/
class BOTAN_PUBLIC_API(2,0) GCM_Encryption final : public GCM_Mode
   {
   public:
      /**
      * @param cipher the 128 bit block cipher to use
      * @param tag_size is how big the auth tag will be
      */
      GCM_Encryption(BlockCipher* cipher, size_t tag_size = 16) :
         GCM_Mode(cipher, tag_size) {}

      size_t output_length(size_t input_length) const override
         { return input_length + tag_size(); }

      size_t minimum_final_size() const override { return 0; }

      size_t process(uint8_t buf[], size_t size) override;

      void finish(secure_vector<uint8_t>& final_block, size_t offset = 0) override;
   };

/**
* GCM Decryption
*/
class BOTAN_PUBLIC_API(2,0) GCM_Decryption final : public GCM_Mode
   {
   public:
      /**
      * @param cipher the 128 bit block cipher to use
      * @param tag_size is how big the auth tag will be
      */
      GCM_Decryption(BlockCipher* cipher, size_t tag_size = 16) :
         GCM_Mode(cipher, tag_size) {}

      size_t output_length(size_t input_length) const override
         {
         BOTAN_ASSERT(input_length >= tag_size(), "Sufficient input");
         return input_length - tag_size();
         }

      size_t minimum_final_size() const override { return tag_size(); }

      size_t process(uint8_t buf[], size_t size) override;

      void finish(secure_vector<uint8_t>& final_block, size_t offset = 0) override;
   };

}

#endif