void aes256_load_schedule_c()

in src/aes/aes_c.c [131:200]

• 53 lines of code
• 5 McCabe index (conditional complexity)

void aes256_load_schedule_c(const uint8_t* Key, uint8_t* RoundKey) 
{
  uint32_t i, k;
  uint8_t tempa[4]; // Used for the column/row operations
  uint32_t Nk = 8;
  uint32_t Nr = 14;

  // The first round key is the key itself.
  for (i = 0; i < Nk; ++i)
  {
    RoundKey[(i * 4) + 0] = Key[(i * 4) + 0];
    RoundKey[(i * 4) + 1] = Key[(i * 4) + 1];
    RoundKey[(i * 4) + 2] = Key[(i * 4) + 2];
    RoundKey[(i * 4) + 3] = Key[(i * 4) + 3];
  }

  // All other round keys are found from the previous round keys.
  //i == Nk
  for (; i < Nb * (Nr + 1); ++i)
  {
    {
      tempa[0]=RoundKey[(i-1) * 4 + 0];
      tempa[1]=RoundKey[(i-1) * 4 + 1];
      tempa[2]=RoundKey[(i-1) * 4 + 2];
      tempa[3]=RoundKey[(i-1) * 4 + 3];
    }

    if (i % Nk == 0)
    {
      // This function shifts the 4 bytes in a word to the left once.
      // [a0,a1,a2,a3] becomes [a1,a2,a3,a0]

      // Function RotWord()
      {
        k = tempa[0];
        tempa[0] = tempa[1];
        tempa[1] = tempa[2];
        tempa[2] = tempa[3];
        tempa[3] = k;
      }

      // SubWord() is a function that takes a four-byte input word and
      // applies the S-box to each of the four bytes to produce an output word.

      // Function Subword()
      {
        tempa[0] = getSBoxValue(tempa[0]);
        tempa[1] = getSBoxValue(tempa[1]);
        tempa[2] = getSBoxValue(tempa[2]);
        tempa[3] = getSBoxValue(tempa[3]);
      }

      tempa[0] =  tempa[0] ^ Rcon[i/Nk];
    }
    if (i % Nk == 4)
    {
      // Function Subword()
      {
        tempa[0] = getSBoxValue(tempa[0]);
        tempa[1] = getSBoxValue(tempa[1]);
        tempa[2] = getSBoxValue(tempa[2]);
        tempa[3] = getSBoxValue(tempa[3]);
      }
    }
    RoundKey[i * 4 + 0] = RoundKey[(i - Nk) * 4 + 0] ^ tempa[0];
    RoundKey[i * 4 + 1] = RoundKey[(i - Nk) * 4 + 1] ^ tempa[1];
    RoundKey[i * 4 + 2] = RoundKey[(i - Nk) * 4 + 2] ^ tempa[2];
    RoundKey[i * 4 + 3] = RoundKey[(i - Nk) * 4 + 3] ^ tempa[3];
  }
}