text: /**
   * @file   libcrypt/include/sha256.hpp
   * @author Brad Conte (brad AT bradconte.com)
   * @author Peter Züger
   * @date   27.02.2019
   * @brief  sha256 hash implementation
   *
   * The MIT License (MIT)
   *
   * Copyright (c) 2019 Peter Züger
   *
   * Permission is hereby granted, free of charge, to any person
   * obtaining a copy of this software and associated documentation
   * files (the "Software"), to deal in the Software without
   * restriction, including without limitation the rights to use, copy,
   * modify, merge, publish, distribute, sublicense, and/or sell copies
   * of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be
   * included in all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
   * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
   * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
   * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
   * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
   * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
   * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
   * SOFTWARE.
   */
  #ifndef LIBCRYPT_SHA256_HPP
  #define LIBCRYPT_SHA256_HPP
  
  #include <array>
  #include <cstdint>
  #include <iterator>
  
  #include "impl.hpp"
  
  namespace crypt{
      class sha256{
          std::array<std::uint8_t, 64> data;
          std::uint32_t datalen;
          std::uint64_t bitlen;
          std::array<std::uint32_t, 8> state;
          inline constexpr static std::array<std::uint32_t, 64> k{
              0x428a2f98,0x71374491,0xb5c0fbcf,0xe9b5dba5,0x3956c25b,0x59f111f1,0x923f82a4,0xab1c5ed5,
              0xd807aa98,0x12835b01,0x243185be,0x550c7dc3,0x72be5d74,0x80deb1fe,0x9bdc06a7,0xc19bf174,
              0xe49b69c1,0xefbe4786,0x0fc19dc6,0x240ca1cc,0x2de92c6f,0x4a7484aa,0x5cb0a9dc,0x76f988da,
              0x983e5152,0xa831c66d,0xb00327c8,0xbf597fc7,0xc6e00bf3,0xd5a79147,0x06ca6351,0x14292967,
              0x27b70a85,0x2e1b2138,0x4d2c6dfc,0x53380d13,0x650a7354,0x766a0abb,0x81c2c92e,0x92722c85,
              0xa2bfe8a1,0xa81a664b,0xc24b8b70,0xc76c51a3,0xd192e819,0xd6990624,0xf40e3585,0x106aa070,
              0x19a4c116,0x1e376c08,0x2748774c,0x34b0bcb5,0x391c0cb3,0x4ed8aa4a,0x5b9cca4f,0x682e6ff3,
              0x748f82ee,0x78a5636f,0x84c87814,0x8cc70208,0x90befffa,0xa4506ceb,0xbef9a3f7,0xc67178f2
          };
  
          void transform(){
              using namespace impl;
              std::array<std::uint32_t, 64> m;
              std::uint32_t a, b, c, d, e, f, g, h, i, j, t1, t2;
  
              for(i = 0, j = 0; i < 16; ++i, j += 4)
                  m[i] = static_cast<std::uint32_t>((data[j]     << 24) |
                                                    (data[j + 1] << 16) |
                                                    (data[j + 2] <<  8) |
                                                    (data[j + 3]      )   );
              for(; i < 64; ++i)
                  m[i] = SIG1(m[i - 2]) + m[i - 7] + SIG0(m[i - 15]) + m[i - 16];
  
              a = state[0];
              b = state[1];
              c = state[2];
              d = state[3];
              e = state[4];
              f = state[5];
              g = state[6];
              h = state[7];
  
              for(i = 0; i < 64; ++i){
                  t1 = h + EP1(e) + CH(e,f,g) + k[i] + m[i];
                  t2 = EP0(a) + MAJ(a,b,c);
                  h = g;
                  g = f;
                  f = e;
                  e = d + t1;
                  d = c;
                  c = b;
                  b = a;
                  a = t1 + t2;
              }
  
              state[0] += a;
              state[1] += b;
              state[2] += c;
              state[3] += d;
              state[4] += e;
              state[5] += f;
              state[6] += g;
              state[7] += h;
          }
  
      public:
          sha256(){
              reset();
          }
  
          void reset(){
              datalen = 0;
              bitlen = 0;
              state[0] = 0x6a09e667;
              state[1] = 0xbb67ae85;
              state[2] = 0x3c6ef372;
              state[3] = 0xa54ff53a;
              state[4] = 0x510e527f;
              state[5] = 0x9b05688c;
              state[6] = 0x1f83d9ab;
              state[7] = 0x5be0cd19;
          }
  
          template<typename T>
          void update(const T& byte){
              static_assert((sizeof(T) == 1),
                            "crypt::sha256::update: T must be byte");
              data[datalen] = static_cast<std::uint8_t>(byte);
              datalen++;
              if(datalen == data.size()){
                  transform();
                  bitlen += 512;
                  datalen = 0;
              }
          }
  
          template<typename Iterator>
          void update(Iterator first, Iterator last){
              static_assert((sizeof(typename std::iterator_traits<Iterator>::value_type) == 1),
                            "crypt::sha256::update: T::value_type must be byte");
              for(; first != last; ++first){
                  update(*first);
              }
          }
  
          std::array<std::uint8_t, 32> final(){
              std::array<std::uint8_t, 32> hash;
              std::uint32_t i = datalen;
  
              // Pad whatever data is left in the buffer.
              if(datalen < 56){
                  data[i++] = 0x80;
                  while(i < 56)
                      data[i++] = 0x00;
              }else{
                  data[i++] = 0x80;
                  while(i < 64)
                      data[i++] = 0x00;
                  transform();
                  for(std::size_t j = 0; j < 56; j++)
                      data[j] = 0;
              }
  
              // Append to the padding the total message's length in bits and transform.
              bitlen += datalen * 8;
              data[63] = static_cast<std::uint8_t>(bitlen);
              data[62] = static_cast<std::uint8_t>(bitlen >> 8);
              data[61] = static_cast<std::uint8_t>(bitlen >> 16);
              data[60] = static_cast<std::uint8_t>(bitlen >> 24);
              data[59] = static_cast<std::uint8_t>(bitlen >> 32);
              data[58] = static_cast<std::uint8_t>(bitlen >> 40);
              data[57] = static_cast<std::uint8_t>(bitlen >> 48);
              data[56] = static_cast<std::uint8_t>(bitlen >> 56);
              transform();
  
              // Since this implementation uses little endian byte ordering and SHA uses big endian,
              // reverse all the bytes when copying the final state to the output hash.
              for(i = 0; i < 4; ++i){
                  hash[i]      = (state[0] >> (24 - i * 8)) & 0x000000ff;
                  hash[i + 4]  = (state[1] >> (24 - i * 8)) & 0x000000ff;
                  hash[i + 8]  = (state[2] >> (24 - i * 8)) & 0x000000ff;
                  hash[i + 12] = (state[3] >> (24 - i * 8)) & 0x000000ff;
                  hash[i + 16] = (state[4] >> (24 - i * 8)) & 0x000000ff;
                  hash[i + 20] = (state[5] >> (24 - i * 8)) & 0x000000ff;
                  hash[i + 24] = (state[6] >> (24 - i * 8)) & 0x000000ff;
                  hash[i + 28] = (state[7] >> (24 - i * 8)) & 0x000000ff;
              }
  
              return hash;
          }
      };
  }
  
  #endif /* LIBCRYPT_SHA256_HPP */
  