/*

* CFB mode

* (C) 1999-2007,2013 Jack Lloyd

* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity

*

* Botan is released under the Simplified BSD License (see license.txt)

*/

#ifndef BOTAN_MODE_CFB_H_

#define BOTAN_MODE_CFB_H_

#include <botan/block_cipher.h>

#include <botan/cipher_mode.h>

namespace Botan {

/**

* CFB Mode

*/

class CFB_Mode : public Cipher_Mode {

   public:

      std::string name() const final;

      size_t update_granularity() const final;

      size_t ideal_granularity() const final;

      size_t minimum_final_size() const final;

      Key_Length_Specification key_spec() const final;

      size_t output_length(size_t input_length) const final;

      size_t default_nonce_length() const final;

      bool valid_nonce_length(size_t n) const final;

      void clear() final;

      void reset() final;

      bool has_keying_material() const final;

   protected:

      CFB_Mode(std::unique_ptr<BlockCipher> cipher, size_t feedback_bits);

      void shift_register();

      size_t feedback() const { return m_feedback_bytes; }

      const BlockCipher& cipher() const { return *m_cipher; }

      size_t block_size() const { return m_block_size; }

      secure_vector<uint8_t> m_state;

      secure_vector<uint8_t> m_keystream;

      size_t m_keystream_pos = 0;

   private:

      void start_msg(const uint8_t nonce[], size_t nonce_len) override;

      void key_schedule(std::span<const uint8_t> key) override;

      std::unique_ptr<BlockCipher> m_cipher;

      const size_t m_block_size;

      const size_t m_feedback_bytes;

};

/**

* CFB Encryption

*/

class CFB_Encryption final : public CFB_Mode {

   public:

      /**

      * If feedback_bits is zero, cipher->block_size() bytes will be used.

      * @param cipher block cipher to use

      * @param feedback_bits number of bits fed back into the shift register,

      * must be a multiple of 8

      */

      CFB_Encryption(std::unique_ptr<BlockCipher> cipher, size_t feedback_bits) :

            CFB_Mode(std::move(cipher), feedback_bits) {}

   private:

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

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

};

/**

* CFB Decryption

*/

class CFB_Decryption final : public CFB_Mode {

   public:

      /**

      * If feedback_bits is zero, cipher->block_size() bytes will be used.

      * @param cipher block cipher to use

      * @param feedback_bits number of bits fed back into the shift register,

      * must be a multiple of 8

      */

      CFB_Decryption(std::unique_ptr<BlockCipher> cipher, size_t feedback_bits) :

            CFB_Mode(std::move(cipher), feedback_bits) {}

   private:

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

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

};

}  // namespace Botan

#endif