aes-unwrap.c revision 8d520ff1dc2da35cdca849e982051b86468016d8 
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 */
31int 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}
80