/*

* 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/internal/ghash.h>

#include <botan/exceptn.h>

#include <botan/internal/cpuid.h>

#include <botan/internal/ct_utils.h>

#include <botan/internal/loadstor.h>

namespace Botan {

std::string GHASH::provider() const {

#if defined(BOTAN_HAS_GHASH_CLMUL_CPU)

   if(CPUID::has_carryless_multiply()) {

      return "clmul";

   }

#endif

#if defined(BOTAN_HAS_GHASH_CLMUL_VPERM)

   if(CPUID::has_vperm()) {

      return "vperm";

   }

#endif

   return "base";

}

void GHASH::ghash_multiply(secure_vector<uint8_t>& x, std::span<const uint8_t> input, size_t blocks) {

#if defined(BOTAN_HAS_GHASH_CLMUL_CPU)

   if(CPUID::has_carryless_multiply()) {

      BOTAN_ASSERT_NOMSG(!m_H_pow.empty());

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

   }

#endif

#if defined(BOTAN_HAS_GHASH_CLMUL_VPERM)

   if(CPUID::has_vperm()) {

      return ghash_multiply_vperm(x.data(), m_HM.data(), input.data(), 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.data(), 2 * b);

      X[1] ^= load_be<uint64_t>(input.data(), 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, std::span<const uint8_t> input) {

   assert_key_material_set(!m_H.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 = input.size() / GCM_BS;

   const size_t final_bytes = input.size() - (full_blocks * GCM_BS);

   if(full_blocks > 0) {

      ghash_multiply(ghash, input.first(full_blocks * GCM_BS), full_blocks);

   }

   if(final_bytes) {

      uint8_t last_block[GCM_BS] = {0};

      copy_mem(last_block, input.subspan(full_blocks * GCM_BS).data(), final_bytes);

      ghash_multiply(ghash, last_block, 1);

      secure_scrub_memory(last_block, final_bytes);

   }

}

bool GHASH::has_keying_material() const {

   return !m_ghash.empty();

}

void GHASH::key_schedule(std::span<const uint8_t> key) {

   m_H.assign(key.begin(), key.end());  // TODO: C++23 - std::vector<>::assign_range()

   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_GHASH_CLMUL_CPU)

   if(CPUID::has_carryless_multiply()) {

      m_H_pow.resize(8);

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

   }

#endif

}

void GHASH::start(std::span<const uint8_t> nonce) {

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

   m_nonce.assign(nonce.begin(), nonce.end());  // TODO: C++23: assign_range

   m_ghash = m_H_ad;

}

void GHASH::set_associated_data(std::span<const uint8_t> input) {

   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);

   m_ad_len = input.size();

}

void GHASH::update_associated_data(std::span<const uint8_t> ad) {

   assert_key_material_set();

   m_ad_len += ad.size();

   ghash_update(m_ghash, ad);

}

void GHASH::update(std::span<const uint8_t> input) {

   assert_key_material_set();

   m_text_len += input.size();

   ghash_update(m_ghash, input);

}

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(std::span<uint8_t> mac) {

   BOTAN_ARG_CHECK(!mac.empty() && mac.size() <= 16, "GHASH output length");

   assert_key_material_set();

   add_final_block(m_ghash, m_ad_len, m_text_len);

   for(size_t i = 0; i != mac.size(); ++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, std::span<const uint8_t> nonce) {

   BOTAN_ASSERT(m_ghash.empty(), "nonce_hash called during wrong time");

   ghash_update(y0, nonce);

   add_final_block(y0, 0, nonce.size());

}

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;

}

}  // namespace Botan