| Dmitry Shmidt | 8d520ff | 2011-05-09 14:06:53 -0700 | [diff] [blame] | 1 | /* |
| 2 | * AES key unwrap (128-bit KEK, RFC3394) |
| 3 | * |
| 4 | * Copyright (c) 2003-2007, Jouni Malinen <j@w1.fi> |
| 5 | * |
| 6 | * This program is free software; you can redistribute it and/or modify |
| 7 | * it under the terms of the GNU General Public License version 2 as |
| 8 | * published by the Free Software Foundation. |
| 9 | * |
| 10 | * Alternatively, this software may be distributed under the terms of BSD |
| 11 | * license. |
| 12 | * |
| 13 | * See README and COPYING for more details. |
| 14 | */ |
| 15 | |
| 16 | #include "includes.h" |
| 17 | |
| 18 | #include "common.h" |
| 19 | #include "aes.h" |
| 20 | #include "aes_wrap.h" |
| 21 | |
| 22 | /** |
| 23 | * aes_unwrap - Unwrap key with AES Key Wrap Algorithm (128-bit KEK) (RFC3394) |
| 24 | * @kek: Key encryption key (KEK) |
| 25 | * @n: Length of the plaintext key in 64-bit units; e.g., 2 = 128-bit = 16 |
| 26 | * bytes |
| 27 | * @cipher: Wrapped key to be unwrapped, (n + 1) * 64 bits |
| 28 | * @plain: Plaintext key, n * 64 bits |
| 29 | * Returns: 0 on success, -1 on failure (e.g., integrity verification failed) |
| 30 | */ |
| 31 | int aes_unwrap(const u8 *kek, int n, const u8 *cipher, u8 *plain) |
| 32 | { |
| 33 | u8 a[8], *r, b[16]; |
| 34 | int i, j; |
| 35 | void *ctx; |
| 36 | |
| 37 | /* 1) Initialize variables. */ |
| 38 | os_memcpy(a, cipher, 8); |
| 39 | r = plain; |
| 40 | os_memcpy(r, cipher + 8, 8 * n); |
| 41 | |
| 42 | ctx = aes_decrypt_init(kek, 16); |
| 43 | if (ctx == NULL) |
| 44 | return -1; |
| 45 | |
| 46 | /* 2) Compute intermediate values. |
| 47 | * For j = 5 to 0 |
| 48 | * For i = n to 1 |
| 49 | * B = AES-1(K, (A ^ t) | R[i]) where t = n*j+i |
| 50 | * A = MSB(64, B) |
| 51 | * R[i] = LSB(64, B) |
| 52 | */ |
| 53 | for (j = 5; j >= 0; j--) { |
| 54 | r = plain + (n - 1) * 8; |
| 55 | for (i = n; i >= 1; i--) { |
| 56 | os_memcpy(b, a, 8); |
| 57 | b[7] ^= n * j + i; |
| 58 | |
| 59 | os_memcpy(b + 8, r, 8); |
| 60 | aes_decrypt(ctx, b, b); |
| 61 | os_memcpy(a, b, 8); |
| 62 | os_memcpy(r, b + 8, 8); |
| 63 | r -= 8; |
| 64 | } |
| 65 | } |
| 66 | aes_decrypt_deinit(ctx); |
| 67 | |
| 68 | /* 3) Output results. |
| 69 | * |
| 70 | * These are already in @plain due to the location of temporary |
| 71 | * variables. Just verify that the IV matches with the expected value. |
| 72 | */ |
| 73 | for (i = 0; i < 8; i++) { |
| 74 | if (a[i] != 0xa6) |
| 75 | return -1; |
| 76 | } |
| 77 | |
| 78 | return 0; |
| 79 | } |