crypto/aes.c

/****************************************************************************
 * crypto/aes.c
 * $OpenBSD: aes.c,v 1.2 2020/07/22 13:54:30 tobhe Exp $
 *
 * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
 *
 * Modified for OpenBSD by Thomas Pornin and Mike Belopuhov.
 *
 * 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.
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <string.h>
#include <sys/types.h>
#include <crypto/aes.h>

/****************************************************************************
 * Public Functions
 ****************************************************************************/

static inline void enc32le(FAR void *dst, uint32_t x)
{
  FAR unsigned char *buf = dst;

  buf[0] = (unsigned char)x;
  buf[1] = (unsigned char)(x >> 8);
  buf[2] = (unsigned char)(x >> 16);
  buf[3] = (unsigned char)(x >> 24);
}

static inline uint32_t dec32le(FAR const void *src)
{
  FAR const unsigned char *buf = src;

  return (uint32_t)buf[0]
    | ((uint32_t)buf[1] << 8)
    | ((uint32_t)buf[2] << 16)
    | ((uint32_t)buf[3] << 24);
}

/* This constant-time implementation is "bitsliced": the 128-bit state is
 * split over eight 32-bit words q* in the following way:
 *
 * -- Input block consists in 16 bytes:
 *    a00 a10 a20 a30 a01 a11 a21 a31 a02 a12 a22 a32 a03 a13 a23 a33
 * In the terminology of FIPS 197, this is a 4x4 matrix which is read
 * column by column.
 *
 * -- Each byte is split into eight bits which are distributed over the
 * eight words, at the same rank. Thus, for a byte x at rank k, bit 0
 * (least significant) of x will be at rank k in q0 (if that bit is b,
 * then it contributes "b << k" to the value of q0), bit 1 of x will be
 * at rank k in q1, and so on.
 *
 * -- Ranks given to bits are in "row order" and are either all even, or
 * all odd. Two independent AES states are thus interleaved, one using
 * the even ranks, the other the odd ranks. Row order means:
 *    a00 a01 a02 a03 a10 a11 a12 a13 a20 a21 a22 a23 a30 a31 a32 a33
 *
 * Converting input bytes from two AES blocks to bitslice representation
 * is done in the following way:
 * -- Decode first block into the four words q0 q2 q4 q6, in that order,
 * using little-endian convention.
 * -- Decode second block into the four words q1 q3 q5 q7, in that order,
 * using little-endian convention.
 * -- Call aes_ct_ortho().
 *
 * Converting back to bytes is done by using the reverse operations. Note
 * that aes_ct_ortho() is its own inverse.
 */

/* The AES S-box, as a bitsliced constant-time version. The input array
 * consists in eight 32-bit words; 32 S-box instances are computed in
 * parallel. Bits 0 to 7 of each S-box input (bit 0 is least significant)
 * are spread over the words 0 to 7, at the same rank.
 */

static void aes_ct_bitslice_sbox(FAR uint32_t *q)
{
  /* This S-box implementation is a straightforward translation of
   * the circuit described by Boyar and Peralta in "A new
   * combinational logic minimization technique with applications
   * to cryptology" (https://eprint.iacr.org/2009/191.pdf).
   *
   * Note that variables x* (input) and s* (output) are numbered
   * in "reverse" order (x0 is the high bit, x7 is the low bit).
   */

  uint32_t x0;
  uint32_t x1;
  uint32_t x2;
  uint32_t x3;
  uint32_t x4;
  uint32_t x5;
  uint32_t x6;
  uint32_t x7;
  uint32_t y1;
  uint32_t y2;
  uint32_t y3;
  uint32_t y4;
  uint32_t y5;
  uint32_t y6;
  uint32_t y7;
  uint32_t y8;
  uint32_t y9;
  uint32_t y10;
  uint32_t y11;
  uint32_t y12;
  uint32_t y13;
  uint32_t y14;
  uint32_t y15;
  uint32_t y16;
  uint32_t y17;
  uint32_t y18;
  uint32_t y19;
  uint32_t y20;
  uint32_t y21;
  uint32_t z0;
  uint32_t z1;
  uint32_t z2;
  uint32_t z3;
  uint32_t z4;
  uint32_t z5;
  uint32_t z6;
  uint32_t z7;
  uint32_t z8;
  uint32_t z9;
  uint32_t z10;
  uint32_t z11;
  uint32_t z12;
  uint32_t z13;
  uint32_t z14;
  uint32_t z15;
  uint32_t z16;
  uint32_t z17;
  uint32_t t0;
  uint32_t t1;
  uint32_t t2;
  uint32_t t3;
  uint32_t t4;
  uint32_t t5;
  uint32_t t6;
  uint32_t t7;
  uint32_t t8;
  uint32_t t9;
  uint32_t t10;
  uint32_t t11;
  uint32_t t12;
  uint32_t t13;
  uint32_t t14;
  uint32_t t15;
  uint32_t t16;
  uint32_t t17;
  uint32_t t18;
  uint32_t t19;
  uint32_t t20;
  uint32_t t21;
  uint32_t t22;
  uint32_t t23;
  uint32_t t24;
  uint32_t t25;
  uint32_t t26;
  uint32_t t27;
  uint32_t t28;
  uint32_t t29;
  uint32_t t30;
  uint32_t t31;
  uint32_t t32;
  uint32_t t33;
  uint32_t t34;
  uint32_t t35;
  uint32_t t36;
  uint32_t t37;
  uint32_t t38;
  uint32_t t39;
  uint32_t t40;
  uint32_t t41;
  uint32_t t42;
  uint32_t t43;
  uint32_t t44;
  uint32_t t45;
  uint32_t t46;
  uint32_t t47;
  uint32_t t48;
  uint32_t t49;
  uint32_t t50;
  uint32_t t51;
  uint32_t t52;
  uint32_t t53;
  uint32_t t54;
  uint32_t t55;
  uint32_t t56;
  uint32_t t57;
  uint32_t t58;
  uint32_t t59;
  uint32_t t60;
  uint32_t t61;
  uint32_t t62;
  uint32_t t63;
  uint32_t t64;
  uint32_t t65;
  uint32_t t66;
  uint32_t t67;
  uint32_t s0;
  uint32_t s1;
  uint32_t s2;
  uint32_t s3;
  uint32_t s4;
  uint32_t s5;
  uint32_t s6;
  uint32_t s7;

  x0 = q[7];
  x1 = q[6];
  x2 = q[5];
  x3 = q[4];
  x4 = q[3];
  x5 = q[2];
  x6 = q[1];
  x7 = q[0];

  /* Top linear transformation. */

  y14 = x3 ^ x5;
  y13 = x0 ^ x6;
  y9 = x0 ^ x3;
  y8 = x0 ^ x5;
  t0 = x1 ^ x2;
  y1 = t0 ^ x7;
  y4 = y1 ^ x3;
  y12 = y13 ^ y14;
  y2 = y1 ^ x0;
  y5 = y1 ^ x6;
  y3 = y5 ^ y8;
  t1 = x4 ^ y12;
  y15 = t1 ^ x5;
  y20 = t1 ^ x1;
  y6 = y15 ^ x7;
  y10 = y15 ^ t0;
  y11 = y20 ^ y9;
  y7 = x7 ^ y11;
  y17 = y10 ^ y11;
  y19 = y10 ^ y8;
  y16 = t0 ^ y11;
  y21 = y13 ^ y16;
  y18 = x0 ^ y16;

  /* Non-linear section. */

  t2 = y12 & y15;
  t3 = y3 & y6;
  t4 = t3 ^ t2;
  t5 = y4 & x7;
  t6 = t5 ^ t2;
  t7 = y13 & y16;
  t8 = y5 & y1;
  t9 = t8 ^ t7;
  t10 = y2 & y7;
  t11 = t10 ^ t7;
  t12 = y9 & y11;
  t13 = y14 & y17;
  t14 = t13 ^ t12;
  t15 = y8 & y10;
  t16 = t15 ^ t12;
  t17 = t4 ^ t14;
  t18 = t6 ^ t16;
  t19 = t9 ^ t14;
  t20 = t11 ^ t16;
  t21 = t17 ^ y20;
  t22 = t18 ^ y19;
  t23 = t19 ^ y21;
  t24 = t20 ^ y18;

  t25 = t21 ^ t22;
  t26 = t21 & t23;
  t27 = t24 ^ t26;
  t28 = t25 & t27;
  t29 = t28 ^ t22;
  t30 = t23 ^ t24;
  t31 = t22 ^ t26;
  t32 = t31 & t30;
  t33 = t32 ^ t24;
  t34 = t23 ^ t33;
  t35 = t27 ^ t33;
  t36 = t24 & t35;
  t37 = t36 ^ t34;
  t38 = t27 ^ t36;
  t39 = t29 & t38;
  t40 = t25 ^ t39;

  t41 = t40 ^ t37;
  t42 = t29 ^ t33;
  t43 = t29 ^ t40;
  t44 = t33 ^ t37;
  t45 = t42 ^ t41;
  z0 = t44 & y15;
  z1 = t37 & y6;
  z2 = t33 & x7;
  z3 = t43 & y16;
  z4 = t40 & y1;
  z5 = t29 & y7;
  z6 = t42 & y11;
  z7 = t45 & y17;
  z8 = t41 & y10;
  z9 = t44 & y12;
  z10 = t37 & y3;
  z11 = t33 & y4;
  z12 = t43 & y13;
  z13 = t40 & y5;
  z14 = t29 & y2;
  z15 = t42 & y9;
  z16 = t45 & y14;
  z17 = t41 & y8;

  /* Bottom linear transformation. */

  t46 = z15 ^ z16;
  t47 = z10 ^ z11;
  t48 = z5 ^ z13;
  t49 = z9 ^ z10;
  t50 = z2 ^ z12;
  t51 = z2 ^ z5;
  t52 = z7 ^ z8;
  t53 = z0 ^ z3;
  t54 = z6 ^ z7;
  t55 = z16 ^ z17;
  t56 = z12 ^ t48;
  t57 = t50 ^ t53;
  t58 = z4 ^ t46;
  t59 = z3 ^ t54;
  t60 = t46 ^ t57;
  t61 = z14 ^ t57;
  t62 = t52 ^ t58;
  t63 = t49 ^ t58;
  t64 = z4 ^ t59;
  t65 = t61 ^ t62;
  t66 = z1 ^ t63;
  s0 = t59 ^ t63;
  s6 = t56 ^ ~t62;
  s7 = t48 ^ ~t60;
  t67 = t64 ^ t65;
  s3 = t53 ^ t66;
  s4 = t51 ^ t66;
  s5 = t47 ^ t65;
  s1 = t64 ^ ~s3;
  s2 = t55 ^ ~t67;

  q[7] = s0;
  q[6] = s1;
  q[5] = s2;
  q[4] = s3;
  q[3] = s4;
  q[2] = s5;
  q[1] = s6;
  q[0] = s7;
}

/* Perform bytewise orthogonalization of eight 32-bit words. Bytes
 * of q0..q7 are spread over all words: for a byte x that occurs
 * at rank i in q[j] (byte x uses bits 8*i to 8*i+7 in q[j]), the bit
 * of rank k in x (0 <= k <= 7) goes to q[k] at rank 8*i+j.
 *
 * This operation is an involution.
 */

static void aes_ct_ortho(FAR uint32_t *q)
{
#define SWAPN(cl, ch, s, x, y)   do { \
    uint32_t a, b; \
    a = (x); \
    b = (y); \
    (x) = (a & (uint32_t)cl) | ((b & (uint32_t)cl) << (s)); \
    (y) = ((a & (uint32_t)ch) >> (s)) | (b & (uint32_t)ch); \
  } while (0)

#define SWAP2(x, y)   SWAPN(0x55555555, 0xaaaaaaaa, 1, x, y)
#define SWAP4(x, y)   SWAPN(0x33333333, 0xcccccccc, 2, x, y)
#define SWAP8(x, y)   SWAPN(0x0f0f0f0f, 0xf0f0f0f0, 4, x, y)

  SWAP2(q[0], q[1]);
  SWAP2(q[2], q[3]);
  SWAP2(q[4], q[5]);
  SWAP2(q[6], q[7]);

  SWAP4(q[0], q[2]);
  SWAP4(q[1], q[3]);
  SWAP4(q[4], q[6]);
  SWAP4(q[5], q[7]);

  SWAP8(q[0], q[4]);
  SWAP8(q[1], q[5]);
  SWAP8(q[2], q[6]);
  SWAP8(q[3], q[7]);
}

static inline uint32_t sub_word(uint32_t x)
{
  uint32_t q[8];
  int i;

  for (i = 0; i < 8; i++)
    {
      q[i] = x;
    }

  aes_ct_ortho(q);
  aes_ct_bitslice_sbox(q);
  aes_ct_ortho(q);
  return q[0];
}

static const unsigned char rcon[] =
{
  0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36
};

/* Base key schedule code. The function sub_word() must be defined
 * below. Subkeys are produced in little-endian convention (but not
 * bitsliced). Key length is expressed in bytes.
 */

static unsigned aes_keysched_base(FAR uint32_t *skey,
                                  FAR const void *key, size_t key_len)
{
  unsigned num_rounds;
  int i;
  int j;
  int k;
  int nk;
  int nkf;
  uint32_t tmp;

  switch (key_len)
    {
      case 16:
        num_rounds = 10;
        break;
      case 24:
        num_rounds = 12;
        break;
      case 32:
        num_rounds = 14;
        break;
      default:
        return 0;
    }

  nk = (int)(key_len >> 2);
  nkf = (int)((num_rounds + 1) << 2);
  for (i = 0; i < nk; i++)
    {
      tmp = dec32le((FAR const unsigned char *)key + (i << 2));
      skey[i] = tmp;
    }

  tmp = skey[(key_len >> 2) - 1];
  for (i = nk, j = 0, k = 0; i < nkf; i++)
    {
      if (j == 0)
        {
          tmp = (tmp << 24) | (tmp >> 8);
          tmp = sub_word(tmp) ^ rcon[k];
        }
      else if (nk > 6 && j == 4)
        {
          tmp = sub_word(tmp);
        }

      tmp ^= skey[i - nk];
      skey[i] = tmp;
      if (++j == nk)
        {
          j = 0;
          k++;
        }
    }

  return num_rounds;
}

/* AES key schedule, constant-time version. skey[] is filled with n+1
 * 128-bit subkeys, where n is the number of rounds (10 to 14, depending
 * on key size). The number of rounds is returned. If the key size is
 * invalid (not 16, 24 or 32), then 0 is returned.
 */

unsigned aes_ct_keysched(FAR uint32_t *comp_skey,
                         FAR const void *key,
                         size_t key_len)
{
  uint32_t skey[60];
  unsigned u;
  unsigned num_rounds;

  num_rounds = aes_keysched_base(skey, key, key_len);
  for (u = 0; u <= num_rounds; u++)
    {
      uint32_t q[8];

      q[0] = q[1] = skey[(u << 2) + 0];
      q[2] = q[3] = skey[(u << 2) + 1];
      q[4] = q[5] = skey[(u << 2) + 2];
      q[6] = q[7] = skey[(u << 2) + 3];
      aes_ct_ortho(q);
      comp_skey[(u << 2) + 0] =
        (q[0] & 0x55555555) | (q[1] & 0xaaaaaaaa);
      comp_skey[(u << 2) + 1] =
        (q[2] & 0x55555555) | (q[3] & 0xaaaaaaaa);
      comp_skey[(u << 2) + 2] =
        (q[4] & 0x55555555) | (q[5] & 0xaaaaaaaa);
      comp_skey[(u << 2) + 3] =
        (q[6] & 0x55555555) | (q[7] & 0xaaaaaaaa);
    }

  return num_rounds;
}

/* Expand AES subkeys as produced by aes_ct_keysched(), into
 * a larger array suitable for aes_ct_bitslice_encrypt() and
 * aes_ct_bitslice_decrypt().
 */

void aes_ct_skey_expand(FAR uint32_t *skey,
                        unsigned num_rounds,
                        FAR const uint32_t *comp_skey)
{
  unsigned u;
  unsigned v;
  unsigned n;

  n = (num_rounds + 1) << 2;
  for (u = 0, v = 0; u < n; u ++, v += 2)
    {
      uint32_t x;
      uint32_t y;

      x = y = comp_skey[u];
      x &= 0x55555555;
      skey[v + 0] = x | (x << 1);
      y &= 0xaaaaaaaa;
      skey[v + 1] = y | (y >> 1);
    }
}

static inline void add_round_key(FAR uint32_t *q, FAR const uint32_t *sk)
{
  q[0] ^= sk[0];
  q[1] ^= sk[1];
  q[2] ^= sk[2];
  q[3] ^= sk[3];
  q[4] ^= sk[4];
  q[5] ^= sk[5];
  q[6] ^= sk[6];
  q[7] ^= sk[7];
}

static inline void shift_rows(FAR uint32_t *q)
{
  int i;

  for (i = 0; i < 8; i++)
    {
      uint32_t x;

      x = q[i];
      q[i] = (x & 0x000000ff)
        | ((x & 0x0000fc00) >> 2) | ((x & 0x00000300) << 6)
        | ((x & 0x00f00000) >> 4) | ((x & 0x000f0000) << 4)
        | ((x & 0xc0000000) >> 6) | ((x & 0x3f000000) << 2);
    }
}

static inline uint32_t rotr16(uint32_t x)
{
  return (x << 16) | (x >> 16);
}

static inline void mix_columns(FAR uint32_t *q)
{
  uint32_t q0;
  uint32_t q1;
  uint32_t q2;
  uint32_t q3;
  uint32_t q4;
  uint32_t q5;
  uint32_t q6;
  uint32_t q7;
  uint32_t r0;
  uint32_t r1;
  uint32_t r2;
  uint32_t r3;
  uint32_t r4;
  uint32_t r5;
  uint32_t r6;
  uint32_t r7;

  q0 = q[0];
  q1 = q[1];
  q2 = q[2];
  q3 = q[3];
  q4 = q[4];
  q5 = q[5];
  q6 = q[6];
  q7 = q[7];
  r0 = (q0 >> 8) | (q0 << 24);
  r1 = (q1 >> 8) | (q1 << 24);
  r2 = (q2 >> 8) | (q2 << 24);
  r3 = (q3 >> 8) | (q3 << 24);
  r4 = (q4 >> 8) | (q4 << 24);
  r5 = (q5 >> 8) | (q5 << 24);
  r6 = (q6 >> 8) | (q6 << 24);
  r7 = (q7 >> 8) | (q7 << 24);

  q[0] = q7 ^ r7 ^ r0 ^ rotr16(q0 ^ r0);
  q[1] = q0 ^ r0 ^ q7 ^ r7 ^ r1 ^ rotr16(q1 ^ r1);
  q[2] = q1 ^ r1 ^ r2 ^ rotr16(q2 ^ r2);
  q[3] = q2 ^ r2 ^ q7 ^ r7 ^ r3 ^ rotr16(q3 ^ r3);
  q[4] = q3 ^ r3 ^ q7 ^ r7 ^ r4 ^ rotr16(q4 ^ r4);
  q[5] = q4 ^ r4 ^ r5 ^ rotr16(q5 ^ r5);
  q[6] = q5 ^ r5 ^ r6 ^ rotr16(q6 ^ r6);
  q[7] = q6 ^ r6 ^ r7 ^ rotr16(q7 ^ r7);
}

/* Compute AES encryption on bitsliced data. Since input is stored on
 * eight 32-bit words, two block encryptions are actually performed
 * in parallel.
 */

void aes_ct_bitslice_encrypt(unsigned num_rounds,
                             FAR const uint32_t *skey,
                             FAR uint32_t *q)
{
  unsigned u;

  add_round_key(q, skey);
  for (u = 1; u < num_rounds; u++)
    {
      aes_ct_bitslice_sbox(q);
      shift_rows(q);
      mix_columns(q);
      add_round_key(q, skey + (u << 3));
    }

  aes_ct_bitslice_sbox(q);
  shift_rows(q);
  add_round_key(q, skey + (num_rounds << 3));
}

/* Like aes_ct_bitslice_sbox(), but for the inverse S-box. */

void aes_ct_bitslice_invsbox(FAR uint32_t *q)
{
  /* AES S-box is:
   *   S(x) = A(I(x)) ^ 0x63
   * where I() is inversion in GF(256), and A() is a linear
   * transform (0 is formally defined to be its own inverse).
   * Since inversion is an involution, the inverse S-box can be
   * computed from the S-box as:
   *   iS(x) = B(S(B(x ^ 0x63)) ^ 0x63)
   * where B() is the inverse of A(). Indeed, for any y in GF(256):
   *   iS(S(y)) = B(A(I(B(A(I(y)) ^ 0x63 ^ 0x63))) ^ 0x63 ^ 0x63) = y
   *
   * Note: we reuse the implementation of the forward S-box,
   * instead of duplicating it here, so that total code size is
   * lower. By merging the B() transforms into the S-box circuit
   * we could make faster CBC decryption, but CBC decryption is
   * already quite faster than CBC encryption because we can
   * process two blocks in parallel.
   */

  uint32_t q0;
  uint32_t q1;
  uint32_t q2;
  uint32_t q3;
  uint32_t q4;
  uint32_t q5;
  uint32_t q6;
  uint32_t q7;

  q0 = ~q[0];
  q1 = ~q[1];
  q2 = q[2];
  q3 = q[3];
  q4 = q[4];
  q5 = ~q[5];
  q6 = ~q[6];
  q7 = q[7];
  q[7] = q1 ^ q4 ^ q6;
  q[6] = q0 ^ q3 ^ q5;
  q[5] = q7 ^ q2 ^ q4;
  q[4] = q6 ^ q1 ^ q3;
  q[3] = q5 ^ q0 ^ q2;
  q[2] = q4 ^ q7 ^ q1;
  q[1] = q3 ^ q6 ^ q0;
  q[0] = q2 ^ q5 ^ q7;

  aes_ct_bitslice_sbox(q);

  q0 = ~q[0];
  q1 = ~q[1];
  q2 = q[2];
  q3 = q[3];
  q4 = q[4];
  q5 = ~q[5];
  q6 = ~q[6];
  q7 = q[7];
  q[7] = q1 ^ q4 ^ q6;
  q[6] = q0 ^ q3 ^ q5;
  q[5] = q7 ^ q2 ^ q4;
  q[4] = q6 ^ q1 ^ q3;
  q[3] = q5 ^ q0 ^ q2;
  q[2] = q4 ^ q7 ^ q1;
  q[1] = q3 ^ q6 ^ q0;
  q[0] = q2 ^ q5 ^ q7;
}

static inline void inv_shift_rows(FAR uint32_t *q)
{
  int i;

  for (i = 0; i < 8; i++)
    {
      uint32_t x;

      x = q[i];
      q[i] = (x & 0x000000ff)
        | ((x & 0x00003f00) << 2) | ((x & 0x0000c000) >> 6)
        | ((x & 0x000f0000) << 4) | ((x & 0x00f00000) >> 4)
        | ((x & 0x03000000) << 6) | ((x & 0xfc000000) >> 2);
    }
}

static void inv_mix_columns(FAR uint32_t *q)
{
  uint32_t q0;
  uint32_t q1;
  uint32_t q2;
  uint32_t q3;
  uint32_t q4;
  uint32_t q5;
  uint32_t q6;
  uint32_t q7;
  uint32_t r0;
  uint32_t r1;
  uint32_t r2;
  uint32_t r3;
  uint32_t r4;
  uint32_t r5;
  uint32_t r6;
  uint32_t r7;

  q0 = q[0];
  q1 = q[1];
  q2 = q[2];
  q3 = q[3];
  q4 = q[4];
  q5 = q[5];
  q6 = q[6];
  q7 = q[7];
  r0 = (q0 >> 8) | (q0 << 24);
  r1 = (q1 >> 8) | (q1 << 24);
  r2 = (q2 >> 8) | (q2 << 24);
  r3 = (q3 >> 8) | (q3 << 24);
  r4 = (q4 >> 8) | (q4 << 24);
  r5 = (q5 >> 8) | (q5 << 24);
  r6 = (q6 >> 8) | (q6 << 24);
  r7 = (q7 >> 8) | (q7 << 24);

  q[0] = q5 ^ q6 ^ q7 ^ r0 ^ r5 ^
         r7 ^ rotr16(q0 ^ q5 ^ q6 ^ r0 ^ r5);

  q[1] = q0 ^ q5 ^ r0 ^ r1 ^ r5 ^
         r6 ^ r7 ^ rotr16(q1 ^ q5 ^ q7 ^ r1 ^ r5 ^ r6);

  q[2] = q0 ^ q1 ^ q6 ^ r1 ^ r2 ^
         r6 ^ r7 ^ rotr16(q0 ^ q2 ^ q6 ^ r2 ^ r6 ^ r7);

  q[3] = q0 ^ q1 ^ q2 ^ q5 ^ q6 ^
         r0 ^ r2 ^ r3 ^ r5 ^
         rotr16(q0 ^ q1 ^ q3 ^ q5 ^ q6 ^ q7 ^ r0 ^ r3 ^ r5 ^ r7);

  q[4] = q1 ^ q2 ^ q3 ^ q5 ^ r1 ^
         r3 ^ r4 ^ r5 ^ r6 ^ r7 ^
         rotr16(q1 ^ q2 ^ q4 ^ q5 ^ q7 ^ r1 ^ r4 ^ r5 ^ r6);

  q[5] = q2 ^ q3 ^ q4 ^ q6 ^ r2 ^
         r4 ^ r5 ^ r6 ^ r7 ^
         rotr16(q2 ^ q3 ^ q5 ^ q6 ^ r2 ^ r5 ^ r6 ^ r7);

  q[6] = q3 ^ q4 ^ q5 ^ q7 ^ r3 ^
         r5 ^ r6 ^ r7 ^
         rotr16(q3 ^ q4 ^ q6 ^ q7 ^ r3 ^ r6 ^ r7);

  q[7] = q4 ^ q5 ^ q6 ^ r4 ^ r6 ^
         r7 ^ rotr16(q4 ^ q5 ^ q7 ^ r4 ^ r7);
}

/* Compute AES decryption on bitsliced data.
 * Since input is stored on
 * eight 32-bit words, two block decryptions
 * are actually performed in parallel.
 */

void aes_ct_bitslice_decrypt(unsigned num_rounds,
                             FAR const uint32_t *skey,
                             FAR uint32_t *q)
{
  unsigned u;

  add_round_key(q, skey + (num_rounds << 3));
  for (u = num_rounds - 1; u > 0; u--)
    {
      inv_shift_rows(q);
      aes_ct_bitslice_invsbox(q);
      add_round_key(q, skey + (u << 3));
      inv_mix_columns(q);
    }

  inv_shift_rows(q);
  aes_ct_bitslice_invsbox(q);
  add_round_key(q, skey);
}

int aes_setkey(FAR AES_CTX *ctx, FAR const uint8_t *key, int len)
{
  ctx->num_rounds = aes_ct_keysched(ctx->sk, key, len);
  if (ctx->num_rounds == 0)
    {
      return -1;
    }

  aes_ct_skey_expand(ctx->sk_exp, ctx->num_rounds, ctx->sk);
  return 0;
}

void aes_encrypt_ecb(FAR AES_CTX *ctx, FAR const uint8_t *src,
                     FAR uint8_t *dst, size_t num_blocks)
{
  while (num_blocks > 0)
    {
      uint32_t q[8];

      q[0] = dec32le(src);
      q[2] = dec32le(src + 4);
      q[4] = dec32le(src + 8);
      q[6] = dec32le(src + 12);
      if (num_blocks > 1)
        {
          q[1] = dec32le(src + 16);
          q[3] = dec32le(src + 20);
          q[5] = dec32le(src + 24);
          q[7] = dec32le(src + 28);
        }
      else
        {
          q[1] = 0;
          q[3] = 0;
          q[5] = 0;
          q[7] = 0;
        }

      aes_ct_ortho(q);
      aes_ct_bitslice_encrypt(ctx->num_rounds, ctx->sk_exp, q);
      aes_ct_ortho(q);
      enc32le(dst, q[0]);
      enc32le(dst + 4, q[2]);
      enc32le(dst + 8, q[4]);
      enc32le(dst + 12, q[6]);
      if (num_blocks > 1)
        {
          enc32le(dst + 16, q[1]);
          enc32le(dst + 20, q[3]);
          enc32le(dst + 24, q[5]);
          enc32le(dst + 28, q[7]);
          src += 32;
          dst += 32;
          num_blocks -= 2;
        }
      else
        {
          break;
        }
    }
}

void aes_decrypt_ecb(FAR AES_CTX *ctx, FAR const uint8_t *src,
                     FAR uint8_t *dst, size_t num_blocks)
{
  while (num_blocks > 0)
    {
      uint32_t q[8];

      q[0] = dec32le(src);
      q[2] = dec32le(src + 4);
      q[4] = dec32le(src + 8);
      q[6] = dec32le(src + 12);
      if (num_blocks > 1)
        {
          q[1] = dec32le(src + 16);
          q[3] = dec32le(src + 20);
          q[5] = dec32le(src + 24);
          q[7] = dec32le(src + 28);
        }
      else
        {
          q[1] = 0;
          q[3] = 0;
          q[5] = 0;
          q[7] = 0;
        }

      aes_ct_ortho(q);
      aes_ct_bitslice_decrypt(ctx->num_rounds, ctx->sk_exp, q);
      aes_ct_ortho(q);
      enc32le(dst, q[0]);
      enc32le(dst + 4, q[2]);
      enc32le(dst + 8, q[4]);
      enc32le(dst + 12, q[6]);
      if (num_blocks > 1)
        {
          enc32le(dst + 16, q[1]);
          enc32le(dst + 20, q[3]);
          enc32le(dst + 24, q[5]);
          enc32le(dst + 28, q[7]);
          src += 32;
          dst += 32;
          num_blocks -= 2;
        }
        else
        {
          break;
        }
    }
}

void aes_encrypt(FAR AES_CTX *ctx, FAR const uint8_t *src, FAR uint8_t *dst)
{
  aes_encrypt_ecb(ctx, src, dst, 1);
}

void aes_decrypt(FAR AES_CTX *ctx, FAR const uint8_t *src, FAR uint8_t *dst)
{
  aes_decrypt_ecb(ctx, src, dst, 1);
}

int aes_keysetup_encrypt(FAR uint32_t *skey, FAR const uint8_t *key, int len)
{
  unsigned r;
  unsigned u;
  uint32_t tkey[60];

  r = aes_keysched_base(tkey, key, len);
  if (r == 0)
    {
      return 0;
    }

  for (u = 0; u < ((r + 1) << 2); u++)
    {
      uint32_t w;

      w = tkey[u];
      skey[u] = (w << 24)
        | ((w & 0x0000ff00) << 8)
        | ((w & 0x00ff0000) >> 8)
        | (w >> 24);
    }

  return r;
}

/* Reduce value x modulo polynomial x^8+x^4+x^3+x+1. This works as
 * long as x fits on 12 bits at most.
 */

static inline uint32_t redgf256(uint32_t x)
{
  uint32_t h;

  h = x >> 8;
  return (x ^ h ^ (h << 1) ^ (h << 3) ^ (h << 4)) & 0xff;
}

/* Multiplication by 0x09 in GF(256). */

static inline uint32_t mul9(uint32_t x)
{
  return redgf256(x ^ (x << 3));
}

/* Multiplication by 0x0B in GF(256). */

static inline uint32_t mulb(uint32_t x)
{
  return redgf256(x ^ (x << 1) ^ (x << 3));
}

/* Multiplication by 0x0D in GF(256). */

static inline uint32_t muld(uint32_t x)
{
  return redgf256(x ^ (x << 2) ^ (x << 3));
}

/* Multiplication by 0x0E in GF(256). */

static inline uint32_t mule(uint32_t x)
{
  return redgf256((x << 1) ^ (x << 2) ^ (x << 3));
}

int aes_keysetup_decrypt(FAR uint32_t *skey,
                         FAR const uint8_t *key,
                         int len)
{
  unsigned r;
  unsigned u;
  uint32_t tkey[60];

  /* Compute encryption subkeys. We get them in big-endian
   * notation.
   */

  r = aes_keysetup_encrypt(tkey, key, len);
  if (r == 0)
    {
      return 0;
    }

  /* Copy the subkeys in reverse order. Also, apply InvMixColumns()
   * on the subkeys (except first and last).
   */

  memcpy(skey + (r << 2), tkey, 4 * sizeof(uint32_t));
  memcpy(skey, tkey + (r << 2), 4 * sizeof(uint32_t));
  for (u = 4; u < (r << 2); u++)
    {
      uint32_t sk;
      uint32_t sk0;
      uint32_t sk1;
      uint32_t sk2;
      uint32_t sk3;
      uint32_t tk;
      uint32_t tk0;
      uint32_t tk1;
      uint32_t tk2;
      uint32_t tk3;

      sk = tkey[u];
      sk0 = sk >> 24;
      sk1 = (sk >> 16) & 0xff;
      sk2 = (sk >> 8) & 0xff;
      sk3 = sk & 0xff;
      tk0 = mule(sk0) ^ mulb(sk1) ^ muld(sk2) ^ mul9(sk3);
      tk1 = mul9(sk0) ^ mule(sk1) ^ mulb(sk2) ^ muld(sk3);
      tk2 = muld(sk0) ^ mul9(sk1) ^ mule(sk2) ^ mulb(sk3);
      tk3 = mulb(sk0) ^ muld(sk1) ^ mul9(sk2) ^ mule(sk3);
      tk = (tk0 << 24) ^ (tk1 << 16) ^ (tk2 << 8) ^ tk3;
      skey[((r - (u >> 2)) << 2) + (u & 3)] = tk;
    }

  return r;
}