/*

* CFB Mode

* (C) 1999-2007,2013,2017 Jack Lloyd

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

*

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

*/

#include <botan/internal/cfb.h>

namespace Botan {

CFB_Mode::CFB_Mode(BlockCipher* cipher, size_t feedback_bits) :

   m_cipher(cipher),

   m_block_size(m_cipher->block_size()),

   m_feedback_bytes(feedback_bits ? feedback_bits / 8 : m_block_size)

   {

   if(feedback_bits % 8 || feedback() > cipher->block_size())

      throw Invalid_Argument(name() + ": feedback bits " +

                                  std::to_string(feedback_bits) + " not supported");

   }

void CFB_Mode::clear()

   {

   m_cipher->clear();

   m_keystream.clear();

   reset();

   }

void CFB_Mode::reset()

   {

   m_state.clear();

   zeroise(m_keystream);

   }

std::string CFB_Mode::name() const

   {

   if(feedback() == cipher().block_size())

      return cipher().name() + "/CFB";

   else

      return cipher().name() + "/CFB(" + std::to_string(feedback()*8) + ")";

   }

size_t CFB_Mode::output_length(size_t input_length) const

   {

   return input_length;

   }

size_t CFB_Mode::update_granularity() const

   {

   return feedback();

   }

size_t CFB_Mode::minimum_final_size() const

   {

   return 0;

   }

Key_Length_Specification CFB_Mode::key_spec() const

   {

   return cipher().key_spec();

   }

size_t CFB_Mode::default_nonce_length() const

   {

   return block_size();

   }

bool CFB_Mode::valid_nonce_length(size_t n) const

   {

   return (n == 0 || n == block_size());

   }

void CFB_Mode::key_schedule(const uint8_t key[], size_t length)

   {

   m_cipher->set_key(key, length);

   m_keystream.resize(m_cipher->block_size());

   }

void CFB_Mode::start_msg(const uint8_t nonce[], size_t nonce_len)

   {

   if(!valid_nonce_length(nonce_len))

      throw Invalid_IV_Length(name(), nonce_len);

   verify_key_set(!m_keystream.empty());

   if(nonce_len == 0)

      {

      if(m_state.empty())

         {

         throw Invalid_State("CFB requires a non-empty initial nonce");

         }

      // No reason to encrypt state->keystream_buf, because no change

      }

   else

      {

      m_state.assign(nonce, nonce + nonce_len);

      cipher().encrypt(m_state, m_keystream);

      m_keystream_pos = 0;

      }

   }

void CFB_Mode::shift_register()

   {

   const size_t shift = feedback();

   const size_t carryover = block_size() - shift;

   if(carryover > 0)

      {

      copy_mem(m_state.data(), &m_state[shift], carryover);

      }

   copy_mem(&m_state[carryover], m_keystream.data(), shift);

   cipher().encrypt(m_state, m_keystream);

   m_keystream_pos = 0;

   }

size_t CFB_Encryption::process(uint8_t buf[], size_t sz)

   {

   verify_key_set(!m_keystream.empty());

   BOTAN_STATE_CHECK(m_state.empty() == false);

   const size_t shift = feedback();

   size_t left = sz;

   if(m_keystream_pos != 0)

      {

      const size_t take = std::min<size_t>(left, shift - m_keystream_pos);

      xor_buf(m_keystream.data() + m_keystream_pos, buf, take);

      copy_mem(buf, m_keystream.data() + m_keystream_pos, take);

      m_keystream_pos += take;

      left -= take;

      buf += take;

      if(m_keystream_pos == shift)

         {

         shift_register();

         }

      }

   while(left >= shift)

      {

      xor_buf(m_keystream.data(), buf, shift);

      copy_mem(buf, m_keystream.data(), shift);

      left -= shift;

      buf += shift;

      shift_register();

      }

   if(left > 0)

      {

      xor_buf(m_keystream.data(), buf, left);

      copy_mem(buf, m_keystream.data(), left);

      m_keystream_pos += left;

      }

   return sz;

   }

void CFB_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)

   {

   update(buffer, offset);

   }

namespace {

inline void xor_copy(uint8_t buf[], uint8_t key_buf[], size_t len)

   {

   for(size_t i = 0; i != len; ++i)

      {

      uint8_t k = key_buf[i];

      key_buf[i] = buf[i];

      buf[i] ^= k;

      }

   }

}

size_t CFB_Decryption::process(uint8_t buf[], size_t sz)

   {

   verify_key_set(!m_keystream.empty());

   BOTAN_STATE_CHECK(m_state.empty() == false);

   const size_t shift = feedback();

   size_t left = sz;

   if(m_keystream_pos != 0)

      {

      const size_t take = std::min<size_t>(left, shift - m_keystream_pos);

      xor_copy(buf, m_keystream.data() + m_keystream_pos, take);

      m_keystream_pos += take;

      left -= take;

      buf += take;

      if(m_keystream_pos == shift)

         {

         shift_register();

         }

      }

   while(left >= shift)

      {

      xor_copy(buf, m_keystream.data(), shift);

      left -= shift;

      buf += shift;

      shift_register();

      }

   if(left > 0)

      {

      xor_copy(buf, m_keystream.data(), left);

      m_keystream_pos += left;

      }

   return sz;

   }

void CFB_Decryption::finish(secure_vector<uint8_t>& buffer, size_t offset)

   {

   update(buffer, offset);

   }

}