/*

* GCM GHASH

* (C) 2013,2015,2017 Jack Lloyd

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

*

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

*/

#include <botan/ghash.h>

#include <botan/internal/ct_utils.h>

#include <botan/loadstor.h>

#include <botan/cpuid.h>

#include <botan/exceptn.h>

#if defined(BOTAN_HAS_GCM_CLMUL_CPU)

  #include <botan/internal/clmul_cpu.h>

#endif

#if defined(BOTAN_HAS_GCM_CLMUL_SSSE3)

  #include <botan/internal/clmul_ssse3.h>

#endif

namespace Botan {

std::string GHASH::provider() const

   {

#if defined(BOTAN_HAS_GCM_CLMUL_CPU)

   if(CPUID::has_carryless_multiply())

      return "clmul";

#endif

#if defined(BOTAN_HAS_GCM_CLMUL_SSSE3)

   if(CPUID::has_ssse3())

      return "ssse3";

#endif

   return "base";

   }

void GHASH::gcm_multiply(secure_vector<uint8_t>& x,

                         const uint8_t input[],

                         size_t blocks)

   {

#if defined(BOTAN_HAS_GCM_CLMUL_CPU)

   if(CPUID::has_carryless_multiply())

      {

      return gcm_multiply_clmul(x.data(), m_H_pow.data(), input, blocks);

      }

#endif

#if defined(BOTAN_HAS_GCM_CLMUL_SSSE3)

   if(CPUID::has_ssse3())

      {

      return gcm_multiply_ssse3(x.data(), m_HM.data(), input, blocks);

      }

#endif

   CT::poison(x.data(), x.size());

   const uint64_t ALL_BITS = 0xFFFFFFFFFFFFFFFF;

   uint64_t X[2] = {

      load_be<uint64_t>(x.data(), 0),

      load_be<uint64_t>(x.data(), 1)

   };

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

      {

      X[0] ^= load_be<uint64_t>(input, 2*b);

      X[1] ^= load_be<uint64_t>(input, 2*b+1);

      uint64_t Z[2] = { 0, 0 };

      for(size_t i = 0; i != 64; ++i)

         {

         const uint64_t X0MASK = (ALL_BITS + (X[0] >> 63)) ^ ALL_BITS;

         const uint64_t X1MASK = (ALL_BITS + (X[1] >> 63)) ^ ALL_BITS;

         X[0] <<= 1;

         X[1] <<= 1;

         Z[0] ^= m_HM[4*i  ] & X0MASK;

         Z[1] ^= m_HM[4*i+1] & X0MASK;

         Z[0] ^= m_HM[4*i+2] & X1MASK;

         Z[1] ^= m_HM[4*i+3] & X1MASK;

         }

      X[0] = Z[0];

      X[1] = Z[1];

      }

   store_be<uint64_t>(x.data(), X[0], X[1]);

   CT::unpoison(x.data(), x.size());

   }

void GHASH::ghash_update(secure_vector<uint8_t>& ghash,

                         const uint8_t input[], size_t length)

   {

   verify_key_set(!m_HM.empty());

   /*

   This assumes if less than block size input then we're just on the

   final block and should pad with zeros

   */

   const size_t full_blocks = length / GCM_BS;

   const size_t final_bytes = length - (full_blocks * GCM_BS);

   if(full_blocks > 0)

      {

      gcm_multiply(ghash, input, full_blocks);

      }

   if(final_bytes)

      {

      uint8_t last_block[GCM_BS] = { 0 };

      copy_mem(last_block, input + full_blocks * GCM_BS, final_bytes);

      gcm_multiply(ghash, last_block, 1);

      secure_scrub_memory(last_block, final_bytes);

      }

   }

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

   {

   m_H.assign(key, key+length);

   m_H_ad.resize(GCM_BS);

   m_ad_len = 0;

   m_text_len = 0;

   uint64_t H0 = load_be<uint64_t>(m_H.data(), 0);

   uint64_t H1 = load_be<uint64_t>(m_H.data(), 1);

   const uint64_t R = 0xE100000000000000;

   m_HM.resize(256);

   // precompute the multiples of H

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

      {

      for(size_t j = 0; j != 64; ++j)

         {

         /*

         we interleave H^1, H^65, H^2, H^66, H3, H67, H4, H68

         to make indexing nicer in the multiplication code

         */

         m_HM[4*j+2*i] = H0;

         m_HM[4*j+2*i+1] = H1;

         // GCM's bit ops are reversed so we carry out of the bottom

         const uint64_t carry = R * (H1 & 1);

         H1 = (H1 >> 1) | (H0 << 63);

         H0 = (H0 >> 1) ^ carry;

         }

      }

#if defined(BOTAN_HAS_GCM_CLMUL_CPU)

   if(CPUID::has_carryless_multiply())

      {

      m_H_pow.resize(8);

      gcm_clmul_precompute(m_H.data(), m_H_pow.data());

      }

#endif

   }

void GHASH::start(const uint8_t nonce[], size_t len)

   {

   BOTAN_ARG_CHECK(len == 16, "GHASH requires a 128-bit nonce");

   m_nonce.assign(nonce, nonce + len);

   m_ghash = m_H_ad;

   }

void GHASH::set_associated_data(const uint8_t input[], size_t length)

   {

   if(m_ghash.empty() == false)

      throw Invalid_State("Too late to set AD in GHASH");

   zeroise(m_H_ad);

   ghash_update(m_H_ad, input, length);

   m_ad_len = length;

   }

void GHASH::update_associated_data(const uint8_t ad[], size_t length)

   {

   verify_key_set(m_ghash.size() == GCM_BS);

   m_ad_len += length;

   ghash_update(m_ghash, ad, length);

   }

void GHASH::update(const uint8_t input[], size_t length)

   {

   verify_key_set(m_ghash.size() == GCM_BS);

   m_text_len += length;

   ghash_update(m_ghash, input, length);

   }

void GHASH::add_final_block(secure_vector<uint8_t>& hash,

                            size_t ad_len, size_t text_len)

   {

   /*

   * stack buffer is fine here since the text len is public

   * and the length of the AD is probably not sensitive either.

   */

   uint8_t final_block[GCM_BS];

   store_be<uint64_t>(final_block, 8*ad_len, 8*text_len);

   ghash_update(hash, final_block, GCM_BS);

   }

void GHASH::final(uint8_t mac[], size_t mac_len)

   {

   BOTAN_ARG_CHECK(mac_len > 0 && mac_len <= 16, "GHASH output length");

   add_final_block(m_ghash, m_ad_len, m_text_len);

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

      mac[i] = m_ghash[i] ^ m_nonce[i];

   m_ghash.clear();

   m_text_len = 0;

   }

void GHASH::nonce_hash(secure_vector<uint8_t>& y0, const uint8_t nonce[], size_t nonce_len)

   {

   BOTAN_ASSERT(m_ghash.size() == 0, "nonce_hash called during wrong time");

   ghash_update(y0, nonce, nonce_len);

   add_final_block(y0, 0, nonce_len);

   }

void GHASH::clear()

   {

   zap(m_H);

   zap(m_HM);

   reset();

   }

void GHASH::reset()

   {

   zeroise(m_H_ad);

   m_ghash.clear();

   m_nonce.clear();

   m_text_len = m_ad_len = 0;

   }

}