Line data    Source code

       1             : /*
       2             :  * AES key unwrap (128-bit KEK, 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 (128-bit KEK) (RFC3394)
      18             :  * @kek: Key encryption key (KEK)
      19             :  * @n: Length of the plaintext key in 64-bit units; e.g., 2 = 128-bit = 16
      20             :  * bytes
      21             :  * @cipher: Wrapped key to be unwrapped, (n + 1) * 64 bits
      22             :  * @plain: Plaintext key, n * 64 bits
      23             :  * Returns: 0 on success, -1 on failure (e.g., integrity verification failed)
      24             :  */
      25         663 : int aes_unwrap(const u8 *kek, int n, const u8 *cipher, u8 *plain)
      26             : {
      27             :         u8 a[8], *r, b[16];
      28             :         int i, j;
      29             :         void *ctx;
      30             : 
      31             :         /* 1) Initialize variables. */
      32         663 :         os_memcpy(a, cipher, 8);
      33         663 :         r = plain;
      34         663 :         os_memcpy(r, cipher + 8, 8 * n);
      35             : 
      36         663 :         ctx = aes_decrypt_init(kek, 16);
      37         663 :         if (ctx == NULL)
      38           0 :                 return -1;
      39             : 
      40             :         /* 2) Compute intermediate values.
      41             :          * For j = 5 to 0
      42             :          *     For i = n to 1
      43             :          *         B = AES-1(K, (A ^ t) | R[i]) where t = n*j+i
      44             :          *         A = MSB(64, B)
      45             :          *         R[i] = LSB(64, B)
      46             :          */
      47        4641 :         for (j = 5; j >= 0; j--) {
      48        3978 :                 r = plain + (n - 1) * 8;
      49       32322 :                 for (i = n; i >= 1; i--) {
      50       28344 :                         os_memcpy(b, a, 8);
      51       28344 :                         b[7] ^= n * j + i;
      52             : 
      53       28344 :                         os_memcpy(b + 8, r, 8);
      54       28344 :                         aes_decrypt(ctx, b, b);
      55       28344 :                         os_memcpy(a, b, 8);
      56       28344 :                         os_memcpy(r, b + 8, 8);
      57       28344 :                         r -= 8;
      58             :                 }
      59             :         }
      60         663 :         aes_decrypt_deinit(ctx);
      61             : 
      62             :         /* 3) Output results.
      63             :          *
      64             :          * These are already in @plain due to the location of temporary
      65             :          * variables. Just verify that the IV matches with the expected value.
      66             :          */
      67        5943 :         for (i = 0; i < 8; i++) {
      68        5283 :                 if (a[i] != 0xa6)
      69           3 :                         return -1;
      70             :         }
      71             : 
      72         660 :         return 0;
      73             : }