ret_t aes256_key_expansion()

in src/random/aes.c [57:94]

• 28 lines of code
• 2 McCabe index (conditional complexity)

ret_t aes256_key_expansion(OUT aes256_ks_t *ks, IN const aes256_key_t *key)
{
  // Rotation: [b0, b1, b2, b3] --> [b1, b2, b3, b0]
  const __m128i rotation_mask = SETONE128_I32(0x0c0f0e0d);

  __m128i con = SETONE128_I32(1);
  __m128i t1;
  __m128i t2;

  ks->keys[0] = LOAD128(&key->raw[0]);
  ks->keys[1] = LOAD128(&key->raw[BYTES_IN_XMM]);

  __m128i in0 = ks->keys[0];
  __m128i in1 = ks->keys[1];

  for(size_t i = 0; i < 6; i++) {
    // Odd rounds
    t1  = AESENCLAST(SHUF128_I8(in1, rotation_mask), con);
    con = SLL128_I32(con, 1);
    ROUND(in0, t2);
    in0 ^= t2 ^ t1;
    ks->keys[2 * (i + 1) + 0] = in0;

    // Even rounds
    t1 = AESENCLAST(SHUF128_I32(in0, 0xff), _mm_setzero_si128());
    ROUND(in1, t2);
    in1 ^= t2 ^ t1;
    ks->keys[2 * (i + 1) + 1] = in1;
  }

  t1 = SHUF128_I8(in1, rotation_mask);
  t1 = AESENCLAST(t1, con);
  ROUND(in0, t2);
  in0 ^= t2 ^ t1;
  ks->keys[AES256_ROUNDS] = in0;

  return SUCCESS;
}