Line data    Source code

       1             : /*
       2             :  * AES key unwrap (RFC3394)
       3             :  *
       4             :  * Copyright (c) 2003-2007, Jouni Malinen <j@w1.fi>
       5             :  *
       6             :  * This software may be distributed under the terms of the BSD license.
       7             :  * See README for more details.
       8             :  */
       9             : 
      10             : #include "includes.h"
      11             : 
      12             : #include "common.h"
      13             : #include "aes.h"
      14             : #include "aes_wrap.h"
      15             : 
      16             : /**
      17             :  * aes_unwrap - Unwrap key with AES Key Wrap Algorithm (RFC3394)
      18             :  * @kek: Key encryption key (KEK)
      19             :  * @kek_len: Length of KEK in octets
      20             :  * @n: Length of the plaintext key in 64-bit units; e.g., 2 = 128-bit = 16
      21             :  * bytes
      22             :  * @cipher: Wrapped key to be unwrapped, (n + 1) * 64 bits
      23             :  * @plain: Plaintext key, n * 64 bits
      24             :  * Returns: 0 on success, -1 on failure (e.g., integrity verification failed)
      25             :  */
      26          19 : int aes_unwrap(const u8 *kek, size_t kek_len, int n, const u8 *cipher,
      27             :                u8 *plain)
      28             : {
      29             :         u8 a[8], *r, b[AES_BLOCK_SIZE];
      30             :         int i, j;
      31             :         void *ctx;
      32             :         unsigned int t;
      33             : 
      34             :         /* 1) Initialize variables. */
      35          19 :         os_memcpy(a, cipher, 8);
      36          19 :         r = plain;
      37          19 :         os_memcpy(r, cipher + 8, 8 * n);
      38             : 
      39          19 :         ctx = aes_decrypt_init(kek, kek_len);
      40          19 :         if (ctx == NULL)
      41           0 :                 return -1;
      42             : 
      43             :         /* 2) Compute intermediate values.
      44             :          * For j = 5 to 0
      45             :          *     For i = n to 1
      46             :          *         B = AES-1(K, (A ^ t) | R[i]) where t = n*j+i
      47             :          *         A = MSB(64, B)
      48             :          *         R[i] = LSB(64, B)
      49             :          */
      50         133 :         for (j = 5; j >= 0; j--) {
      51         114 :                 r = plain + (n - 1) * 8;
      52        1200 :                 for (i = n; i >= 1; i--) {
      53        1086 :                         os_memcpy(b, a, 8);
      54        1086 :                         t = n * j + i;
      55        1086 :                         b[7] ^= t;
      56        1086 :                         b[6] ^= t >> 8;
      57        1086 :                         b[5] ^= t >> 16;
      58        1086 :                         b[4] ^= t >> 24;
      59             : 
      60        1086 :                         os_memcpy(b + 8, r, 8);
      61        1086 :                         aes_decrypt(ctx, b, b);
      62        1086 :                         os_memcpy(a, b, 8);
      63        1086 :                         os_memcpy(r, b + 8, 8);
      64        1086 :                         r -= 8;
      65             :                 }
      66             :         }
      67          19 :         aes_decrypt_deinit(ctx);
      68             : 
      69             :         /* 3) Output results.
      70             :          *
      71             :          * These are already in @plain due to the location of temporary
      72             :          * variables. Just verify that the IV matches with the expected value.
      73             :          */
      74         147 :         for (i = 0; i < 8; i++) {
      75         131 :                 if (a[i] != 0xa6)
      76           3 :                         return -1;
      77             :         }
      78             : 
      79          16 :         return 0;
      80             : }