static void KeyExpansion()

in reversing/nomoreseacrypts/src/aes.c [88:159]

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

static void KeyExpansion(uint8_t* RoundKey, const uint8_t* Key, uint8_t sbox[256])
{
  unsigned i, j, k;
  uint8_t tempa[4]; // Used for the column/row operations

  // 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.
  for (i = Nk; i < Nb * (Nr + 1); ++i)
  {
    {
      k = (i - 1) * 4;
      tempa[0]=RoundKey[k + 0];
      tempa[1]=RoundKey[k + 1];
      tempa[2]=RoundKey[k + 2];
      tempa[3]=RoundKey[k + 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()
      {
        const uint8_t u8tmp = tempa[0];
        tempa[0] = tempa[1];
        tempa[1] = tempa[2];
        tempa[2] = tempa[3];
        tempa[3] = u8tmp;
      }

      // 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] = sbox[tempa[0]];
        tempa[1] = sbox[tempa[1]];
        tempa[2] = sbox[tempa[2]];
        tempa[3] = sbox[tempa[3]];
      }

      tempa[0] = tempa[0] ^ Rcon[i/Nk];
    }

    if (i % Nk == 4)
    {
      // Function Subword()
      {
        tempa[0] = sbox[tempa[0]];
        tempa[1] = sbox[tempa[1]];
        tempa[2] = sbox[tempa[2]];
        tempa[3] = sbox[tempa[3]];
      }
    }

    j = i * 4; k=(i - Nk) * 4;
    RoundKey[j + 0] = RoundKey[k + 0] ^ tempa[0];
    RoundKey[j + 1] = RoundKey[k + 1] ^ tempa[1];
    RoundKey[j + 2] = RoundKey[k + 2] ^ tempa[2];
    RoundKey[j + 3] = RoundKey[k + 3] ^ tempa[3];
  }
}