text: //
  // SHA256.cpp
  //
  // Taken from http://www.zedwood.com/article/cpp-sha256-function
  //
  
  #include <cstring>
  #include <fstream>
  #include "SHA256.h"
  
  const unsigned int SHA256::sha256_k[64] = //UL = uint32
              {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 SHA256::transform(const unsigned char *message, unsigned int block_nb)
  {
      uint32 w[64];
      uint32 wv[8];
      uint32 t1, t2;
      const unsigned char *sub_block;
      int i;
      int j;
      for (i = 0; i < (int) block_nb; i++) {
          sub_block = message + (i << 6);
          for (j = 0; j < 16; j++) {
              SHA2_PACK32(&sub_block[j << 2], &w[j]);
          }
          for (j = 16; j < 64; j++) {
              w[j] =  SHA256_F4(w[j -  2]) + w[j -  7] + SHA256_F3(w[j - 15]) + w[j - 16];
          }
          for (j = 0; j < 8; j++) {
              wv[j] = m_h[j];
          }
          for (j = 0; j < 64; j++) {
              t1 = wv[7] + SHA256_F2(wv[4]) + SHA2_CH(wv[4], wv[5], wv[6])
                  + sha256_k[j] + w[j];
              t2 = SHA256_F1(wv[0]) + SHA2_MAJ(wv[0], wv[1], wv[2]);
              wv[7] = wv[6];
              wv[6] = wv[5];
              wv[5] = wv[4];
              wv[4] = wv[3] + t1;
              wv[3] = wv[2];
              wv[2] = wv[1];
              wv[1] = wv[0];
              wv[0] = t1 + t2;
          }
          for (j = 0; j < 8; j++) {
              m_h[j] += wv[j];
          }
      }
  }
  
  void SHA256::init()
  {
      m_h[0] = 0x6a09e667;
      m_h[1] = 0xbb67ae85;
      m_h[2] = 0x3c6ef372;
      m_h[3] = 0xa54ff53a;
      m_h[4] = 0x510e527f;
      m_h[5] = 0x9b05688c;
      m_h[6] = 0x1f83d9ab;
      m_h[7] = 0x5be0cd19;
      m_len = 0;
      m_tot_len = 0;
  }
  
  void SHA256::update(const unsigned char *message, unsigned int len)
  {
      unsigned int block_nb;
      unsigned int new_len, rem_len, tmp_len;
      const unsigned char *shifted_message;
      tmp_len = SHA224_256_BLOCK_SIZE - m_len;
      rem_len = len < tmp_len ? len : tmp_len;
      memcpy(&m_block[m_len], message, rem_len);
      if (m_len + len < SHA224_256_BLOCK_SIZE) {
          m_len += len;
          return;
      }
      new_len = len - rem_len;
      block_nb = new_len / SHA224_256_BLOCK_SIZE;
      shifted_message = message + rem_len;
      transform(m_block, 1);
      transform(shifted_message, block_nb);
      rem_len = new_len % SHA224_256_BLOCK_SIZE;
      memcpy(m_block, &shifted_message[block_nb << 6], rem_len);
      m_len = rem_len;
      m_tot_len += (block_nb + 1) << 6;
  }
  
  void SHA256::final(unsigned char *digest)
  {
      unsigned int block_nb;
      unsigned int pm_len;
      unsigned int len_b;
      int i;
      block_nb = (1 + ((SHA224_256_BLOCK_SIZE - 9)
                       < (m_len % SHA224_256_BLOCK_SIZE)));
      len_b = (m_tot_len + m_len) << 3;
      pm_len = block_nb << 6;
      memset(m_block + m_len, 0, pm_len - m_len);
      m_block[m_len] = 0x80;
      SHA2_UNPACK32(len_b, m_block + pm_len - 4);
      transform(m_block, block_nb);
      for (i = 0 ; i < 8; i++) {
          SHA2_UNPACK32(m_h[i], &digest[i << 2]);
      }
  }
  
  std::string sha256(std::string input)
  {
      unsigned char digest[SHA256::DIGEST_SIZE];
      memset(digest,0,SHA256::DIGEST_SIZE);
  
      SHA256 ctx = SHA256();
      ctx.init();
      ctx.update( (unsigned char*)input.c_str(), input.length());
      ctx.final(digest);
  
      char buf[2*SHA256::DIGEST_SIZE+1];
      buf[2*SHA256::DIGEST_SIZE] = 0;
      for (int i = 0; i < SHA256::DIGEST_SIZE; i++)
          sprintf(buf+i*2, "%02x", digest[i]);
      return std::string(buf);
  }
  