/*

* XTS Mode

* (C) 2009,2013 Jack Lloyd

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

*

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

*/

#include <botan/internal/xts.h>

#include <botan/internal/poly_dbl.h>

namespace Botan {

XTS_Mode::XTS_Mode(std::unique_ptr<BlockCipher> cipher) :

   m_cipher(std::move(cipher)),

   m_cipher_block_size(m_cipher->block_size()),

   m_cipher_parallelism(m_cipher->parallel_bytes()),

   m_tweak_blocks(m_cipher_parallelism / m_cipher_block_size)

   {

   if(poly_double_supported_size(m_cipher_block_size) == false)

      {

      throw Invalid_Argument("Cannot use " + m_cipher->name() + " with XTS");

      }

   m_tweak_cipher = m_cipher->new_object();

   }

void XTS_Mode::clear()

   {

   m_cipher->clear();

   m_tweak_cipher->clear();

   reset();

   }

size_t XTS_Mode::update_granularity() const

   {

   return m_cipher_block_size;

   }

size_t XTS_Mode::ideal_granularity() const

   {

   return m_cipher_parallelism;

   }

void XTS_Mode::reset()

   {

   m_tweak.clear();

   }

std::string XTS_Mode::name() const

   {

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

   }

size_t XTS_Mode::minimum_final_size() const

   {

   return cipher_block_size();

   }

Key_Length_Specification XTS_Mode::key_spec() const

   {

   return cipher().key_spec().multiple(2);

   }

size_t XTS_Mode::default_nonce_length() const

   {

   return cipher_block_size();

   }

bool XTS_Mode::valid_nonce_length(size_t n) const

   {

   return cipher_block_size() == n;

   }

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

   {

   const size_t key_half = length / 2;

   if(length % 2 == 1 || !m_cipher->valid_keylength(key_half))

      throw Invalid_Key_Length(name(), length);

   m_cipher->set_key(key, key_half);

   m_tweak_cipher->set_key(&key[key_half], key_half);

   }

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

   {

   if(!valid_nonce_length(nonce_len))

      throw Invalid_IV_Length(name(), nonce_len);

   m_tweak.resize(m_cipher_parallelism);

   copy_mem(m_tweak.data(), nonce, nonce_len);

   m_tweak_cipher->encrypt(m_tweak.data());

   update_tweak(0);

   }

void XTS_Mode::update_tweak(size_t which)

   {

   const size_t BS = m_tweak_cipher->block_size();

   if(which > 0)

      poly_double_n_le(m_tweak.data(), &m_tweak[(which-1)*BS], BS);

   const size_t blocks_in_tweak = tweak_blocks();

   for(size_t i = 1; i < blocks_in_tweak; ++i)

      poly_double_n_le(&m_tweak[i*BS], &m_tweak[(i-1)*BS], BS);

   }

size_t XTS_Encryption::output_length(size_t input_length) const

   {

   return input_length;

   }

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

   {

   BOTAN_STATE_CHECK(tweak_set());

   const size_t BS = cipher_block_size();

   BOTAN_ARG_CHECK(sz % BS == 0, "Input is not full blocks");

   size_t blocks = sz / BS;

   const size_t blocks_in_tweak = tweak_blocks();

   while(blocks)

      {

      const size_t to_proc = std::min(blocks, blocks_in_tweak);

      cipher().encrypt_n_xex(buf, tweak(), to_proc);

      buf += to_proc * BS;

      blocks -= to_proc;

      update_tweak(to_proc);

      }

   return sz;

   }

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

   {

   BOTAN_ARG_CHECK(buffer.size() >= offset, "Offset is out of range");

   const size_t sz = buffer.size() - offset;

   uint8_t* buf = buffer.data() + offset;

   BOTAN_ARG_CHECK(sz >= minimum_final_size(),

                   "missing sufficient final input in XTS encrypt");

   const size_t BS = cipher_block_size();

   if(sz % BS == 0)

      {

      update(buffer, offset);

      }

   else

      {

      // steal ciphertext

      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, tweak(), BS);

      cipher().encrypt(last);

      xor_buf(last, tweak(), BS);

      for(size_t i = 0; i != final_bytes - BS; ++i)

         {

         last[i] ^= last[i + BS];

         last[i + BS] ^= last[i];

         last[i] ^= last[i + BS];

         }

      xor_buf(last, tweak() + BS, BS);

      cipher().encrypt(last);

      xor_buf(last, tweak() + BS, BS);

      buffer += last;

      }

   }

size_t XTS_Decryption::output_length(size_t input_length) const

   {

   return input_length;

   }

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

   {

   BOTAN_STATE_CHECK(tweak_set());

   const size_t BS = cipher_block_size();

   BOTAN_ARG_CHECK(sz % BS == 0, "Input is not full blocks");

   size_t blocks = sz / BS;

   const size_t blocks_in_tweak = tweak_blocks();

   while(blocks)

      {

      const size_t to_proc = std::min(blocks, blocks_in_tweak);

      cipher().decrypt_n_xex(buf, tweak(), to_proc);

      buf += to_proc * BS;

      blocks -= to_proc;

      update_tweak(to_proc);

      }

   return sz;

   }

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

   {

   BOTAN_ARG_CHECK(buffer.size() >= offset, "Offset is out of range");

   const size_t sz = buffer.size() - offset;

   uint8_t* buf = buffer.data() + offset;

   BOTAN_ARG_CHECK(sz >= minimum_final_size(),

                   "missing sufficient final input in XTS decrypt");

   const size_t BS = cipher_block_size();

   if(sz % BS == 0)

      {

      update(buffer, offset);

      }

   else

      {

      // steal ciphertext

      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, tweak() + BS, BS);

      cipher().decrypt(last);

      xor_buf(last, tweak() + BS, BS);

      for(size_t i = 0; i != final_bytes - BS; ++i)

         {

         last[i] ^= last[i + BS];

         last[i + BS] ^= last[i];

         last[i] ^= last[i + BS];

         }

      xor_buf(last, tweak(), BS);

      cipher().decrypt(last);

      xor_buf(last, tweak(), BS);

      buffer += last;

      }

   }

}