cbc.cpp

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/*
* CBC 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/cbc.h>
#include <botan/mode_pad.h>
#include <botan/internal/rounding.h>

namespace Botan {

CBC_Mode::CBC_Mode(BlockCipher* cipher, BlockCipherModePaddingMethod* padding) :
   m_cipher(cipher),
   m_padding(padding),
   m_state(m_cipher->block_size())
   {
   if(m_padding && !m_padding->valid_blocksize(cipher->block_size()))
      throw Invalid_Argument("Padding " + m_padding->name() +
                             " cannot be used with " +
                             cipher->name() + "/CBC");
   }

void CBC_Mode::clear()
   {
   m_cipher->clear();
   reset();
   }

void CBC_Mode::reset()
   {
   zeroise(m_state);
   }

std::string CBC_Mode::name() const
   {
   if(m_padding)
      return cipher().name() + "/CBC/" + padding().name();
   else
      return cipher().name() + "/CBC/CTS";
   }

size_t CBC_Mode::update_granularity() const
   {
   return cipher().parallel_bytes();
   }

Key_Length_Specification CBC_Mode::key_spec() const
   {
   return cipher().key_spec();
   }

size_t CBC_Mode::default_nonce_length() const
   {
   return block_size();
   }

bool CBC_Mode::valid_nonce_length(size_t n) const
   {
   return (n == 0 || n == block_size());
   }

void CBC_Mode::key_schedule(const uint8_t key[], size_t length)
   {
   m_cipher->set_key(key, length);
   }

void CBC_Mode::start_msg(const uint8_t nonce[], size_t nonce_len)
   {
   if(!valid_nonce_length(nonce_len))
      throw Invalid_IV_Length(name(), nonce_len);

   /*
   * A nonce of zero length means carry the last ciphertext value over
   * as the new IV, as unfortunately some protocols require this. If
   * this is the first message then we use an IV of all zeros.
   */
   if(nonce_len)
      m_state.assign(nonce, nonce + nonce_len);
   }

size_t CBC_Encryption::minimum_final_size() const
   {
   return 0;
   }

size_t CBC_Encryption::output_length(size_t input_length) const
   {
   if(input_length == 0)
      return block_size();
   else
      return round_up(input_length, block_size());
   }

size_t CBC_Encryption::process(uint8_t buf[], size_t sz)
   {
   const size_t BS = block_size();

   BOTAN_ASSERT(sz % BS == 0, "CBC input is full blocks");
   const size_t blocks = sz / BS;

   if(blocks > 0)
      {
      xor_buf(&buf[0], state_ptr(), BS);
      cipher().encrypt(&buf[0]);

      for(size_t i = 1; i != blocks; ++i)
         {
         xor_buf(&buf[BS*i], &buf[BS*(i-1)], BS);
         cipher().encrypt(&buf[BS*i]);
         }

      state().assign(&buf[BS*(blocks-1)], &buf[BS*blocks]);
      }

   return sz;
   }

void CBC_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
   {
   BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");

   const size_t BS = block_size();

   const size_t bytes_in_final_block = (buffer.size()-offset) % BS;

   padding().add_padding(buffer, bytes_in_final_block, BS);

   if((buffer.size()-offset) % BS)
      throw Exception("Did not pad to full block size in " + name());

   update(buffer, offset);
   }

bool CTS_Encryption::valid_nonce_length(size_t n) const
   {
   return (n == block_size());
   }

size_t CTS_Encryption::minimum_final_size() const
   {
   return block_size() + 1;
   }

size_t CTS_Encryption::output_length(size_t input_length) const
   {
   return input_length; // no ciphertext expansion in CTS
   }

void CTS_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
   {
   BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
   uint8_t* buf = buffer.data() + offset;
   const size_t sz = buffer.size() - offset;

   const size_t BS = block_size();

   if(sz < BS + 1)
      throw Encoding_Error(name() + ": insufficient data to encrypt");

   if(sz % BS == 0)
      {
      update(buffer, offset);

      // swap last two blocks
      for(size_t i = 0; i != BS; ++i)
         std::swap(buffer[buffer.size()-BS+i], buffer[buffer.size()-2*BS+i]);
      }
   else
      {
      const size_t full_blocks = ((sz / BS) - 1) * BS;
      const size_t final_bytes = sz - full_blocks;
      BOTAN_ASSERT(final_bytes > BS && final_bytes < 2*BS, "Left over size in expected range");

      secure_vector<uint8_t> last(buf + full_blocks, buf + full_blocks + final_bytes);
      buffer.resize(full_blocks + offset);
      update(buffer, offset);

      xor_buf(last.data(), state_ptr(), BS);
      cipher().encrypt(last.data());

      for(size_t i = 0; i != final_bytes - BS; ++i)
         {
         last[i] ^= last[i + BS];
         last[i + BS] ^= last[i];
         }

      cipher().encrypt(last.data());

      buffer += last;
      }
   }

size_t CBC_Decryption::output_length(size_t input_length) const
   {
   return input_length; // precise for CTS, worst case otherwise
   }

size_t CBC_Decryption::minimum_final_size() const
   {
   return block_size();
   }

size_t CBC_Decryption::process(uint8_t buf[], size_t sz)
   {
   const size_t BS = block_size();

   BOTAN_ASSERT(sz % BS == 0, "Input is full blocks");
   size_t blocks = sz / BS;

   while(blocks)
      {
      const size_t to_proc = std::min(BS * blocks, m_tempbuf.size());

      cipher().decrypt_n(buf, m_tempbuf.data(), to_proc / BS);

      xor_buf(m_tempbuf.data(), state_ptr(), BS);
      xor_buf(&m_tempbuf[BS], buf, to_proc - BS);
      copy_mem(state_ptr(), buf + (to_proc - BS), BS);

      copy_mem(buf, m_tempbuf.data(), to_proc);

      buf += to_proc;
      blocks -= to_proc / BS;
      }

   return sz;
   }

void CBC_Decryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
   {
   BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
   const size_t sz = buffer.size() - offset;

   const size_t BS = block_size();

   if(sz == 0 || sz % BS)
      throw Decoding_Error(name() + ": Ciphertext not a multiple of block size");

   update(buffer, offset);

   const size_t pad_bytes = BS - padding().unpad(&buffer[buffer.size()-BS], BS);
   buffer.resize(buffer.size() - pad_bytes); // remove padding
   if(pad_bytes == 0 && padding().name() != "NoPadding")
      {
      throw Decoding_Error(name());
      }
   }

void CBC_Decryption::reset()
   {
   zeroise(state());
   zeroise(m_tempbuf);
   }

bool CTS_Decryption::valid_nonce_length(size_t n) const
   {
   return (n == block_size());
   }

size_t CTS_Decryption::minimum_final_size() const
   {
   return block_size() + 1;
   }

void CTS_Decryption::finish(secure_vector<uint8_t>& buffer, size_t offset)
   {
   BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
   const size_t sz = buffer.size() - offset;
   uint8_t* buf = buffer.data() + offset;

   const size_t BS = block_size();

   if(sz < BS + 1)
      throw Encoding_Error(name() + ": insufficient data to decrypt");

   if(sz % BS == 0)
      {
      // swap last two blocks

      for(size_t i = 0; i != BS; ++i)
         std::swap(buffer[buffer.size()-BS+i], buffer[buffer.size()-2*BS+i]);

      update(buffer, offset);
      }
   else
      {
      const size_t full_blocks = ((sz / BS) - 1) * BS;
      const size_t final_bytes = sz - full_blocks;
      BOTAN_ASSERT(final_bytes > BS && final_bytes < 2*BS, "Left over size in expected range");

      secure_vector<uint8_t> last(buf + full_blocks, buf + full_blocks + final_bytes);
      buffer.resize(full_blocks + offset);
      update(buffer, offset);

      cipher().decrypt(last.data());

      xor_buf(last.data(), &last[BS], final_bytes - BS);

      for(size_t i = 0; i != final_bytes - BS; ++i)
         std::swap(last[i], last[i + BS]);

      cipher().decrypt(last.data());
      xor_buf(last.data(), state_ptr(), BS);

      buffer += last;
      }
   }

}