/*

 * AES key unwrap (RFC3394)

 *

 * Copyright (c) 2003-2007, Jouni Malinen <j@w1.fi>

 *

 * This software may be distributed under the terms of the BSD license.

 * See README for more details.

 */

#include "includes.h"

#include "common.h"

#include "aes.h"

#include "aes_wrap.h"

/**

 * aes_unwrap - Unwrap key with AES Key Wrap Algorithm (RFC3394)

 * @kek: Key encryption key (KEK)

 * @kek_len: Length of KEK in octets

 * @n: Length of the plaintext key in 64-bit units; e.g., 2 = 128-bit = 16

 * bytes

 * @cipher: Wrapped key to be unwrapped, (n + 1) * 64 bits

 * @plain: Plaintext key, n * 64 bits

 * Returns: 0 on success, -1 on failure (e.g., integrity verification failed)

 */

int aes_unwrap(const u8 *kek, size_t kek_len, int n, const u8 *cipher,

         u8 *plain)

{

  u8 a[8], *r, b[AES_BLOCK_SIZE];

  int i, j;

  void *ctx;

  unsigned int t;

  /* 1) Initialize variables. */

  os_memcpy(a, cipher, 8);

  r = plain;

  os_memcpy(r, cipher + 8, 8 * n);

  ctx = aes_decrypt_init(kek, kek_len);

  if (ctx == NULL)

    return -1;

  /* 2) Compute intermediate values.

   * For j = 5 to 0

   *     For i = n to 1

   *         B = AES-1(K, (A ^ t) | R[i]) where t = n*j+i

   *         A = MSB(64, B)

   *         R[i] = LSB(64, B)

   */

  for (j = 5; j >= 0; j--) {

    r = plain + (n - 1) * 8;

    for (i = n; i >= 1; i--) {

      os_memcpy(b, a, 8);

      t = n * j + i;

      b[7] ^= t;

      b[6] ^= t >> 8;

      b[5] ^= t >> 16;

      b[4] ^= t >> 24;

      os_memcpy(b + 8, r, 8);

      aes_decrypt(ctx, b, b);

      os_memcpy(a, b, 8);

      os_memcpy(r, b + 8, 8);

      r -= 8;

    }

  }

  aes_decrypt_deinit(ctx);

  /* 3) Output results.

   *

   * These are already in @plain due to the location of temporary

   * variables. Just verify that the IV matches with the expected value.

   */

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

    if (a[i] != 0xa6)

      return -1;

  }

  return 0;

}