/*

* 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/exceptn.h>

#include <botan/loadstor.h>

#include <botan/internal/bit_ops.h>

namespace Botan {

CTR_BE::CTR_BE(BlockCipher* ciph) :

   m_cipher(ciph),

   m_block_size(m_cipher->block_size()),

   m_ctr_size(m_block_size),

   m_ctr_blocks(m_cipher->parallel_bytes() / m_block_size),

   m_counter(m_cipher->parallel_bytes()),

   m_pad(m_counter.size()),

   m_pad_pos(0)

   {

   }

CTR_BE::CTR_BE(BlockCipher* cipher, size_t ctr_size) :

   m_cipher(cipher),

   m_block_size(m_cipher->block_size()),

   m_ctr_size(ctr_size),

   m_ctr_blocks(m_cipher->parallel_bytes() / m_block_size),

   m_counter(m_cipher->parallel_bytes()),

   m_pad(m_counter.size()),

   m_pad_pos(0)

   {

   BOTAN_ARG_CHECK(m_ctr_size >= 4 && m_ctr_size <= m_block_size,

                   "Invalid CTR-BE counter size");

   }

void CTR_BE::clear()

   {

   m_cipher->clear();

   zeroise(m_pad);

   zeroise(m_counter);

   zap(m_iv);

   m_pad_pos = 0;

   }

size_t CTR_BE::default_iv_length() const

   {

   return m_block_size;

   }

bool CTR_BE::valid_iv_length(size_t iv_len) const

   {

   return (iv_len <= m_block_size);

   }

Key_Length_Specification CTR_BE::key_spec() const

   {

   return m_cipher->key_spec();

   }

CTR_BE* CTR_BE::clone() const

   {

   return new CTR_BE(m_cipher->clone(), m_ctr_size);

   }

void CTR_BE::key_schedule(const uint8_t 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

   {

   if(m_ctr_size == m_block_size)

      return ("CTR-BE(" + m_cipher->name() + ")");

   else

      return ("CTR-BE(" + m_cipher->name() + "," + std::to_string(m_ctr_size) + ")");

   }

void CTR_BE::cipher(const uint8_t in[], uint8_t out[], size_t length)

   {

   verify_key_set(m_iv.empty() == false);

   const uint8_t* pad_bits = &m_pad[0];

   const size_t pad_size = m_pad.size();

   if(m_pad_pos > 0)

      {

      const size_t avail = pad_size - m_pad_pos;

      const size_t take = std::min(length, avail);

      xor_buf(out, in, pad_bits + m_pad_pos, take);

      length -= take;

      in += take;

      out += take;

      m_pad_pos += take;

      if(take == avail)

         {

         add_counter(m_ctr_blocks);

         m_cipher->encrypt_n(m_counter.data(), m_pad.data(), m_ctr_blocks);

         m_pad_pos = 0;

         }

      }

   while(length >= pad_size)

      {

      xor_buf(out, in, pad_bits, pad_size);

      length -= pad_size;

      in += pad_size;

      out += pad_size;

      add_counter(m_ctr_blocks);

      m_cipher->encrypt_n(m_counter.data(), m_pad.data(), m_ctr_blocks);

      }

   xor_buf(out, in, pad_bits, length);

   m_pad_pos += length;

   }

void CTR_BE::set_iv(const uint8_t iv[], size_t iv_len)

   {

   if(!valid_iv_length(iv_len))

      throw Invalid_IV_Length(name(), iv_len);

   m_iv.resize(m_block_size);

   zeroise(m_iv);

   buffer_insert(m_iv, 0, iv, iv_len);

   seek(0);

   }

void CTR_BE::add_counter(const uint64_t counter)

   {

   const size_t ctr_size = m_ctr_size;

   const size_t ctr_blocks = m_ctr_blocks;

   const size_t BS = m_block_size;

   if(ctr_size == 4)

      {

      const size_t off = (BS - 4);

      const uint32_t low32 = static_cast<uint32_t>(counter + load_be<uint32_t>(&m_counter[off], 0));

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

         {

         store_be(uint32_t(low32 + i), &m_counter[i*BS+off]);

         }

      }

   else if(ctr_size == 8)

      {

      const size_t off = (BS - 8);

      const uint64_t low64 = counter + load_be<uint64_t>(&m_counter[off], 0);

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

         {

         store_be(uint64_t(low64 + i), &m_counter[i*BS+off]);

         }

      }

   else if(ctr_size == 16)

      {

      const size_t off = (BS - 16);

      uint64_t b0 = load_be<uint64_t>(&m_counter[off], 0);

      uint64_t b1 = load_be<uint64_t>(&m_counter[off], 1);

      b1 += counter;

      b0 += (b1 < counter) ? 1 : 0; // carry

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

         {

         store_be(b0, &m_counter[i*BS+off]);

         store_be(b1, &m_counter[i*BS+off+8]);

         b1 += 1;

         b0 += (b1 == 0); // carry

         }

      }

   else

      {

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

         {

         uint64_t local_counter = counter;

         uint16_t carry = static_cast<uint8_t>(local_counter);

         for(size_t j = 0; (carry || local_counter) && j != ctr_size; ++j)

            {

            const size_t off = i*BS + (BS-1-j);

            const uint16_t cnt = static_cast<uint16_t>(m_counter[off]) + carry;

            m_counter[off] = static_cast<uint8_t>(cnt);

            local_counter = (local_counter >> 8);

            carry = (cnt >> 8) + static_cast<uint8_t>(local_counter);

            }

         }

      }

   }

void CTR_BE::seek(uint64_t offset)

   {

   verify_key_set(m_iv.empty() == false);

   const uint64_t base_counter = m_ctr_blocks * (offset / m_counter.size());

   zeroise(m_counter);

   buffer_insert(m_counter, 0, m_iv);

   const size_t BS = m_block_size;

   // Set m_counter blocks to IV, IV + 1, ... IV + n

   if(m_ctr_size == 4 && BS >= 8)

      {

      const uint32_t low32 = load_be<uint32_t>(&m_counter[BS-4], 0);

      if(m_ctr_blocks >= 4 && is_power_of_2(m_ctr_blocks))

         {

         size_t written = 1;

         while(written < m_ctr_blocks)

            {

            copy_mem(&m_counter[written*BS], &m_counter[0], BS*written);

            written *= 2;

            }

         }

      else

         {

         for(size_t i = 1; i != m_ctr_blocks; ++i)

            {

            copy_mem(&m_counter[i*BS], &m_counter[0], BS - 4);

            }

         }

      for(size_t i = 1; i != m_ctr_blocks; ++i)

         {

         const uint32_t c = static_cast<uint32_t>(low32 + i);

         store_be(c, &m_counter[(BS-4)+i*BS]);

         }

      }

   else

      {

      // do everything sequentially:

      for(size_t i = 1; i != m_ctr_blocks; ++i)

         {

         buffer_insert(m_counter, i*BS, &m_counter[(i-1)*BS], BS);

         for(size_t j = 0; j != m_ctr_size; ++j)

            if(++m_counter[i*BS + (BS - 1 - j)])

               break;

         }

      }

   if(base_counter > 0)

      add_counter(base_counter);

   m_cipher->encrypt_n(m_counter.data(), m_pad.data(), m_ctr_blocks);

   m_pad_pos = offset % m_counter.size();

   }

}