/*
* Counter mode
* (C) 1999-2011,2014 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/ctr.h>
#include <botan/internal/xor_buf.h>

namespace Botan {

CTR_BE::CTR_BE(BlockCipher* ciph) :
   m_cipher(ciph),
   m_counter(256 * m_cipher->block_size()),
   m_pad(m_counter.size()),
   m_pad_pos(0)
   {
   }

void CTR_BE::clear()
   {
   m_cipher->clear();
   zeroise(m_pad);
   zeroise(m_counter);
   m_pad_pos = 0;
   }

void CTR_BE::key_schedule(const byte key[], size_t key_len)
   {
   m_cipher->set_key(key, key_len);

   // Set a default all-zeros IV
   set_iv(nullptr, 0);
   }

std::string CTR_BE::name() const
   {
   return ("CTR-BE(" + m_cipher->name() + ")");
   }

void CTR_BE::cipher(const byte in[], byte out[], size_t length)
   {
   while(length >= m_pad.size() - m_pad_pos)
      {
      xor_buf(out, in, &m_pad[m_pad_pos], m_pad.size() - m_pad_pos);
      length -= (m_pad.size() - m_pad_pos);
      in += (m_pad.size() - m_pad_pos);
      out += (m_pad.size() - m_pad_pos);
      increment_counter();
      }
   xor_buf(out, in, &m_pad[m_pad_pos], length);
   m_pad_pos += length;
   }

void CTR_BE::set_iv(const byte iv[], size_t iv_len)
   {
   if(!valid_iv_length(iv_len))
      throw Invalid_IV_Length(name(), iv_len);

   const size_t bs = m_cipher->block_size();

   zeroise(m_counter);

   buffer_insert(m_counter, 0, iv, iv_len);

   // Set m_counter blocks to IV, IV + 1, ... IV + 255
   for(size_t i = 1; i != 256; ++i)
      {
      buffer_insert(m_counter, i*bs, &m_counter[(i-1)*bs], bs);

      for(size_t j = 0; j != bs; ++j)
         if(++m_counter[i*bs + (bs - 1 - j)])
            break;
      }

   m_cipher->encrypt_n(&m_counter[0], &m_pad[0], 256);
   m_pad_pos = 0;
   }

/*
* Increment the counter and update the buffer
*/
void CTR_BE::increment_counter()
   {
   const size_t bs = m_cipher->block_size();

   /*
   * Each counter value always needs to be incremented by 256,
   * so we don't touch the lowest byte and instead treat it as
   * an increment of one starting with the next byte.
   */
   for(size_t i = 0; i != 256; ++i)
      {
      for(size_t j = 1; j != bs; ++j)
         if(++m_counter[i*bs + (bs - 1 - j)])
            break;
      }

   m_cipher->encrypt_n(&m_counter[0], &m_pad[0], 256);
   m_pad_pos = 0;
   }

}