/*

* OCB Mode

* (C) 2013,2017 Jack Lloyd

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

*

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

*/

#include <botan/ocb.h>

#include <botan/block_cipher.h>

#include <botan/internal/poly_dbl.h>

#include <botan/internal/bit_ops.h>

namespace Botan {

// Has to be in Botan namespace so unique_ptr can reference it

class L_computer final

   {

   public:

      explicit L_computer(const BlockCipher& cipher) :

         m_BS(cipher.block_size()),

         m_max_blocks(cipher.parallel_bytes() / m_BS)

         {

         m_L_star.resize(m_BS);

         cipher.encrypt(m_L_star);

         m_L_dollar = poly_double(star());

         m_L.push_back(poly_double(dollar()));

         while(m_L.size() < 8)

            m_L.push_back(poly_double(m_L.back()));

         m_offset_buf.resize(m_BS * m_max_blocks);

         }

      void init(const secure_vector<uint8_t>& offset)

         {

         m_offset = offset;

         }

      bool initialized() const { return m_offset.empty() == false; }

      const secure_vector<uint8_t>& star() const { return m_L_star; }

      const secure_vector<uint8_t>& dollar() const { return m_L_dollar; }

      const secure_vector<uint8_t>& offset() const { return m_offset; }

      const secure_vector<uint8_t>& get(size_t i) const

         {

         while(m_L.size() <= i)

            m_L.push_back(poly_double(m_L.back()));

         return m_L[i];

         }

      const uint8_t*

      compute_offsets(size_t block_index, size_t blocks)

         {

         BOTAN_ASSERT(blocks <= m_max_blocks, "OCB offsets");

         uint8_t* offsets = m_offset_buf.data();

         if(block_index % 4 == 0)

            {

            const secure_vector<uint8_t>& L0 = get(0);

            const secure_vector<uint8_t>& L1 = get(1);

            while(blocks >= 4)

               {

               // ntz(4*i+1) == 0

               // ntz(4*i+2) == 1

               // ntz(4*i+3) == 0

               block_index += 4;

               const size_t ntz4 = var_ctz32(static_cast<uint32_t>(block_index));

               xor_buf(offsets, m_offset.data(), L0.data(), m_BS);

               offsets += m_BS;

               xor_buf(offsets, offsets - m_BS, L1.data(), m_BS);

               offsets += m_BS;

               xor_buf(m_offset.data(), L1.data(), m_BS);

               copy_mem(offsets, m_offset.data(), m_BS);

               offsets += m_BS;

               xor_buf(m_offset.data(), get(ntz4).data(), m_BS);

               copy_mem(offsets, m_offset.data(), m_BS);

               offsets += m_BS;

               blocks -= 4;

               }

            }

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

            { // could be done in parallel

            const size_t ntz = var_ctz32(static_cast<uint32_t>(block_index + i + 1));

            xor_buf(m_offset.data(), get(ntz).data(), m_BS);

            copy_mem(offsets, m_offset.data(), m_BS);

            offsets += m_BS;

            }

         return m_offset_buf.data();

         }

   private:

      secure_vector<uint8_t> poly_double(const secure_vector<uint8_t>& in) const

         {

         secure_vector<uint8_t> out(in.size());

         poly_double_n(out.data(), in.data(), out.size());

         return out;

         }

      const size_t m_BS, m_max_blocks;

      secure_vector<uint8_t> m_L_dollar, m_L_star;

      secure_vector<uint8_t> m_offset;

      mutable std::vector<secure_vector<uint8_t>> m_L;

      secure_vector<uint8_t> m_offset_buf;

   };

namespace {

/*

* OCB's HASH

*/

secure_vector<uint8_t> ocb_hash(const L_computer& L,

                                const BlockCipher& cipher,

                                const uint8_t ad[], size_t ad_len)

   {

   const size_t BS = cipher.block_size();

   secure_vector<uint8_t> sum(BS);

   secure_vector<uint8_t> offset(BS);

   secure_vector<uint8_t> buf(BS);

   const size_t ad_blocks = (ad_len / BS);

   const size_t ad_remainder = (ad_len % BS);

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

      {

      // this loop could run in parallel

      offset ^= L.get(var_ctz32(static_cast<uint32_t>(i+1)));

      buf = offset;

      xor_buf(buf.data(), &ad[BS*i], BS);

      cipher.encrypt(buf);

      sum ^= buf;

      }

   if(ad_remainder)

      {

      offset ^= L.star();

      buf = offset;

      xor_buf(buf.data(), &ad[BS*ad_blocks], ad_remainder);

      buf[ad_remainder] ^= 0x80;

      cipher.encrypt(buf);

      sum ^= buf;

      }

   return sum;

   }

}

OCB_Mode::OCB_Mode(BlockCipher* cipher, size_t tag_size) :

   m_cipher(cipher),

   m_checksum(m_cipher->parallel_bytes()),

   m_ad_hash(m_cipher->block_size()),

   m_tag_size(tag_size),

   m_block_size(m_cipher->block_size()),

   m_par_blocks(m_cipher->parallel_bytes() / m_block_size)

   {

   const size_t BS = block_size();

   /*

   * draft-krovetz-ocb-wide-d1 specifies OCB for several other block

   * sizes but only 128, 192, 256 and 512 bit are currently supported

   * by this implementation.

   */

   BOTAN_ARG_CHECK(BS == 16 || BS == 24 || BS == 32 || BS == 64,

                   "Invalid block size for OCB");

   BOTAN_ARG_CHECK(m_tag_size % 4 == 0 &&

                   m_tag_size >= 8 && m_tag_size <= BS &&

                   m_tag_size <= 32,

                   "Invalid OCB tag length");

   }

OCB_Mode::~OCB_Mode() { /* for unique_ptr destructor */ }

void OCB_Mode::clear()

   {

   m_cipher->clear();

   m_L.reset(); // add clear here?

   reset();

   }

void OCB_Mode::reset()

   {

   m_block_index = 0;

   zeroise(m_ad_hash);

   zeroise(m_checksum);

   m_last_nonce.clear();

   m_stretch.clear();

   }

bool OCB_Mode::valid_nonce_length(size_t length) const

   {

   if(length == 0)

      return false;

   if(block_size() == 16)

      return length < 16;

   else

      return length < (block_size() - 1);

   }

std::string OCB_Mode::name() const

   {

   return m_cipher->name() + "/OCB"; // include tag size?

   }

size_t OCB_Mode::update_granularity() const

   {

   return (m_par_blocks * block_size());

   }

Key_Length_Specification OCB_Mode::key_spec() const

   {

   return m_cipher->key_spec();

   }

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

   {

   m_cipher->set_key(key, length);

   m_L.reset(new L_computer(*m_cipher));

   }

void OCB_Mode::set_associated_data(const uint8_t ad[], size_t ad_len)

   {

   verify_key_set(m_L != nullptr);

   m_ad_hash = ocb_hash(*m_L, *m_cipher, ad, ad_len);

   }

secure_vector<uint8_t>

OCB_Mode::update_nonce(const uint8_t nonce[], size_t nonce_len)

   {

   const size_t BS = block_size();

   BOTAN_ASSERT(BS == 16 || BS == 24 || BS == 32 || BS == 64,

                "OCB block size is supported");

   const size_t MASKLEN = (BS == 16 ? 6 : ((BS == 24) ? 7 : 8));

   const uint8_t BOTTOM_MASK =

      static_cast<uint8_t>((static_cast<uint16_t>(1) << MASKLEN) - 1);

   secure_vector<uint8_t> nonce_buf(BS);

   copy_mem(&nonce_buf[BS - nonce_len], nonce, nonce_len);

   nonce_buf[0] = static_cast<uint8_t>(((tag_size()*8) % (BS*8)) << (BS <= 16 ? 1 : 0));

   nonce_buf[BS - nonce_len - 1] ^= 1;

   const uint8_t bottom = nonce_buf[BS-1] & BOTTOM_MASK;

   nonce_buf[BS-1] &= ~BOTTOM_MASK;

   const bool need_new_stretch = (m_last_nonce != nonce_buf);

   if(need_new_stretch)

      {

      m_last_nonce = nonce_buf;

      m_cipher->encrypt(nonce_buf);

      /*

      The loop bounds (BS vs BS/2) are derived from the relation

      between the block size and the MASKLEN. Using the terminology

      of draft-krovetz-ocb-wide, we have to derive enough bits in

      ShiftedKtop to read up to BLOCKLEN+bottom bits from Stretch.

                 +----------+---------+-------+---------+

                 | BLOCKLEN | RESIDUE | SHIFT | MASKLEN |

                 +----------+---------+-------+---------+

                 |       32 |     141 |    17 |    4    |

                 |       64 |      27 |    25 |    5    |

                 |       96 |    1601 |    33 |    6    |

                 |      128 |     135 |     8 |    6    |

                 |      192 |     135 |    40 |    7    |

                 |      256 |    1061 |     1 |    8    |

                 |      384 |    4109 |    80 |    8    |

                 |      512 |     293 |   176 |    8    |

                 |     1024 |  524355 |   352 |    9    |

                 +----------+---------+-------+---------+

      */

      if(BS == 16)

         {

         for(size_t i = 0; i != BS / 2; ++i)

            nonce_buf.push_back(nonce_buf[i] ^ nonce_buf[i+1]);

         }

      else if(BS == 24)

         {

         for(size_t i = 0; i != 16; ++i)

            nonce_buf.push_back(nonce_buf[i] ^ nonce_buf[i+5]);

         }

      else if(BS == 32)

         {

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

            nonce_buf.push_back(nonce_buf[i] ^ (nonce_buf[i] << 1) ^ (nonce_buf[i+1] >> 7));

         }

      else if(BS == 64)

         {

         for(size_t i = 0; i != BS / 2; ++i)

            nonce_buf.push_back(nonce_buf[i] ^ nonce_buf[i+22]);

         }

      m_stretch = nonce_buf;

      }

   // now set the offset from stretch and bottom

   const size_t shift_bytes = bottom / 8;

   const size_t shift_bits  = bottom % 8;

   BOTAN_ASSERT(m_stretch.size() >= BS + shift_bytes + 1, "Size ok");

   secure_vector<uint8_t> offset(BS);

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

      {

      offset[i]  = (m_stretch[i+shift_bytes] << shift_bits);

      offset[i] |= (m_stretch[i+shift_bytes+1] >> (8-shift_bits));

      }

   return offset;

   }

void OCB_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_L != nullptr);

   m_L->init(update_nonce(nonce, nonce_len));

   zeroise(m_checksum);

   m_block_index = 0;

   }

void OCB_Encryption::encrypt(uint8_t buffer[], size_t blocks)

   {

   verify_key_set(m_L != nullptr);

   BOTAN_STATE_CHECK(m_L->initialized());

   const size_t BS = block_size();

   while(blocks)

      {

      const size_t proc_blocks = std::min(blocks, par_blocks());

      const size_t proc_bytes = proc_blocks * BS;

      const uint8_t* offsets = m_L->compute_offsets(m_block_index, proc_blocks);

      xor_buf(m_checksum.data(), buffer, proc_bytes);

      m_cipher->encrypt_n_xex(buffer, offsets, proc_blocks);

      buffer += proc_bytes;

      blocks -= proc_blocks;

      m_block_index += proc_blocks;

      }

   }

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

   {

   BOTAN_ASSERT(sz % update_granularity() == 0, "Invalid OCB input size");

   encrypt(buf, sz / block_size());

   return sz;

   }

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

   {

   verify_key_set(m_L != nullptr);

   const size_t BS = block_size();

   BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");

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

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

   secure_vector<uint8_t> mac(BS);

   if(sz)

      {

      const size_t final_full_blocks = sz / BS;

      const size_t remainder_bytes = sz - (final_full_blocks * BS);

      encrypt(buf, final_full_blocks);

      mac = m_L->offset();

      if(remainder_bytes)

         {

         BOTAN_ASSERT(remainder_bytes < BS, "Only a partial block left");

         uint8_t* remainder = &buf[sz - remainder_bytes];

         xor_buf(m_checksum.data(), remainder, remainder_bytes);

         m_checksum[remainder_bytes] ^= 0x80;

         // Offset_*

         mac ^= m_L->star();

         secure_vector<uint8_t> pad(BS);

         m_cipher->encrypt(mac, pad);

         xor_buf(remainder, pad.data(), remainder_bytes);

         }

      }

   else

      {

      mac = m_L->offset();

      }

   // now compute the tag

   // fold checksum

   for(size_t i = 0; i != m_checksum.size(); i += BS)

      {

      xor_buf(mac.data(), m_checksum.data() + i, BS);

      }

   xor_buf(mac.data(), m_L->dollar().data(), BS);

   m_cipher->encrypt(mac);

   xor_buf(mac.data(), m_ad_hash.data(), BS);

   buffer += std::make_pair(mac.data(), tag_size());

   zeroise(m_checksum);

   m_block_index = 0;

   }

void OCB_Decryption::decrypt(uint8_t buffer[], size_t blocks)

   {

   verify_key_set(m_L != nullptr);

   BOTAN_STATE_CHECK(m_L->initialized());

   const size_t BS = block_size();

   while(blocks)

      {

      const size_t proc_blocks = std::min(blocks, par_blocks());

      const size_t proc_bytes = proc_blocks * BS;

      const uint8_t* offsets = m_L->compute_offsets(m_block_index, proc_blocks);

      m_cipher->decrypt_n_xex(buffer, offsets, proc_blocks);

      xor_buf(m_checksum.data(), buffer, proc_bytes);

      buffer += proc_bytes;

      blocks -= proc_blocks;

      m_block_index += proc_blocks;

      }

   }

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

   {

   BOTAN_ASSERT(sz % update_granularity() == 0, "Invalid OCB input size");

   decrypt(buf, sz / block_size());

   return sz;

   }

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

   {

   verify_key_set(m_L != nullptr);

   const size_t BS = block_size();

   BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");

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

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

   BOTAN_ASSERT(sz >= tag_size(), "We have the tag");

   const size_t remaining = sz - tag_size();

   secure_vector<uint8_t> mac(BS);

   if(remaining)

      {

      const size_t final_full_blocks = remaining / BS;

      const size_t final_bytes = remaining - (final_full_blocks * BS);

      decrypt(buf, final_full_blocks);

      mac ^= m_L->offset();

      if(final_bytes)

         {

         BOTAN_ASSERT(final_bytes < BS, "Only a partial block left");

         uint8_t* remainder = &buf[remaining - final_bytes];

         mac ^= m_L->star();

         secure_vector<uint8_t> pad(BS);

         m_cipher->encrypt(mac, pad); // P_*

         xor_buf(remainder, pad.data(), final_bytes);

         xor_buf(m_checksum.data(), remainder, final_bytes);

         m_checksum[final_bytes] ^= 0x80;

         }

      }

   else

      mac = m_L->offset();

   // compute the mac

   // fold checksum

   for(size_t i = 0; i != m_checksum.size(); i += BS)

      {

      xor_buf(mac.data(), m_checksum.data() + i, BS);

      }

   mac ^= m_L->dollar();

   m_cipher->encrypt(mac);

   mac ^= m_ad_hash;

   // reset state

   zeroise(m_checksum);

   m_block_index = 0;

   // compare mac

   const uint8_t* included_tag = &buf[remaining];

   if(!constant_time_compare(mac.data(), included_tag, tag_size()))

      throw Invalid_Authentication_Tag("OCB tag check failed");

   // remove tag from end of message

   buffer.resize(remaining + offset);

   }

}