/*
* 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());
   }

}