/*

* SIV Mode Encryption

* (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/siv.h>

#include <botan/block_cipher.h>

#include <botan/cmac.h>

#include <botan/internal/poly_dbl.h>

#include <botan/ctr.h>

namespace Botan {

SIV_Mode::SIV_Mode(BlockCipher* cipher) :

   m_name(cipher->name() + "/SIV"),

   m_ctr(new CTR_BE(cipher->clone(), 8)),

   m_mac(new CMAC(cipher)),

   m_bs(cipher->block_size())

   {

   // Not really true but only 128 bit allowed at the moment

   if(m_bs != 16)

      throw Invalid_Argument("SIV requires a 128 bit block cipher");

   }

SIV_Mode::~SIV_Mode()

   {

   // for ~unique_ptr

   }

void SIV_Mode::clear()

   {

   m_ctr->clear();

   m_mac->clear();

   reset();

   }

void SIV_Mode::reset()

   {

   m_nonce.clear();

   m_msg_buf.clear();

   m_ad_macs.clear();

   }

std::string SIV_Mode::name() const

   {

   return m_name;

   }

bool SIV_Mode::valid_nonce_length(size_t) const

   {

   return true;

   }

size_t SIV_Mode::update_granularity() const

   {

   /*

   This value does not particularly matter as regardless SIV_Mode::update

   buffers all input, so in theory this could be 1. However as for instance

   Transform_Filter creates update_granularity() uint8_t buffers, use a

   somewhat large size to avoid bouncing on a tiny buffer.

   */

   return 128;

   }

Key_Length_Specification SIV_Mode::key_spec() const

   {

   return m_mac->key_spec().multiple(2);

   }

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

   {

   const size_t keylen = length / 2;

   m_mac->set_key(key, keylen);

   m_ctr->set_key(key + keylen, keylen);

   m_ad_macs.clear();

   }

void SIV_Mode::set_associated_data_n(size_t n, const uint8_t ad[], size_t length)

   {

   const size_t max_ads = block_size() * 8 - 2;

   if(n > max_ads)

      throw Invalid_Argument(name() + " allows no more than " + std::to_string(max_ads) + " ADs");

   if(n >= m_ad_macs.size())

      m_ad_macs.resize(n+1);

   m_ad_macs[n] = m_mac->process(ad, length);

   }

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

   {

   if(!valid_nonce_length(nonce_len))

      throw Invalid_IV_Length(name(), nonce_len);

   if(nonce_len)

      m_nonce = m_mac->process(nonce, nonce_len);

   else

      m_nonce.clear();

   m_msg_buf.clear();

   }

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

   {

   // all output is saved for processing in finish

   m_msg_buf.insert(m_msg_buf.end(), buf, buf + sz);

   return 0;

   }

secure_vector<uint8_t> SIV_Mode::S2V(const uint8_t* text, size_t text_len)

   {

   const std::vector<uint8_t> zeros(block_size());

   secure_vector<uint8_t> V = m_mac->process(zeros.data(), zeros.size());

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

      {

      poly_double_n(V.data(), V.size());

      V ^= m_ad_macs[i];

      }

   if(m_nonce.size())

      {

      poly_double_n(V.data(), V.size());

      V ^= m_nonce;

      }

   if(text_len < block_size())

      {

      poly_double_n(V.data(), V.size());

      xor_buf(V.data(), text, text_len);

      V[text_len] ^= 0x80;

      return m_mac->process(V);

      }

   m_mac->update(text, text_len - block_size());

   xor_buf(V.data(), &text[text_len - block_size()], block_size());

   m_mac->update(V);

   return m_mac->final();

   }

void SIV_Mode::set_ctr_iv(secure_vector<uint8_t> V)

   {

   V[m_bs-8] &= 0x7F;

   V[m_bs-4] &= 0x7F;

   ctr().set_iv(V.data(), V.size());

   }

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

   {

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

   buffer.insert(buffer.begin() + offset, msg_buf().begin(), msg_buf().end());

   msg_buf().clear();

   const secure_vector<uint8_t> V = S2V(buffer.data() + offset, buffer.size() - offset);

   buffer.insert(buffer.begin() + offset, V.begin(), V.end());

   if(buffer.size() != offset + V.size())

      {

      set_ctr_iv(V);

      ctr().cipher1(&buffer[offset + V.size()], buffer.size() - offset - V.size());

      }

   }

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

   {

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

   if(msg_buf().size() > 0)

      {

      buffer.insert(buffer.begin() + offset, msg_buf().begin(), msg_buf().end());

      msg_buf().clear();

      }

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

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

   secure_vector<uint8_t> V(buffer.data() + offset,

                            buffer.data() + offset + block_size());

   if(buffer.size() != offset + V.size())

      {

      set_ctr_iv(V);

      ctr().cipher(buffer.data() + offset + V.size(),

                   buffer.data() + offset,

                   buffer.size() - offset - V.size());

      }

   const secure_vector<uint8_t> T = S2V(buffer.data() + offset, buffer.size() - offset - V.size());

   if(!constant_time_compare(T.data(), V.data(), T.size()))

      throw Invalid_Authentication_Tag("SIV tag check failed");

   buffer.resize(buffer.size() - tag_size());

   }

}