1214501Srpaulo/*
2214501Srpaulo * AES key unwrap (128-bit KEK, RFC3394)
3214501Srpaulo *
4214501Srpaulo * Copyright (c) 2003-2007, Jouni Malinen <j@w1.fi>
5214501Srpaulo *
6214501Srpaulo * This program is free software; you can redistribute it and/or modify
7214501Srpaulo * it under the terms of the GNU General Public License version 2 as
8214501Srpaulo * published by the Free Software Foundation.
9214501Srpaulo *
10214501Srpaulo * Alternatively, this software may be distributed under the terms of BSD
11214501Srpaulo * license.
12214501Srpaulo *
13214501Srpaulo * See README and COPYING for more details.
14214501Srpaulo */
15214501Srpaulo
16214501Srpaulo#include "includes.h"
17214501Srpaulo
18214501Srpaulo#include "common.h"
19214501Srpaulo#include "aes.h"
20214501Srpaulo#include "aes_wrap.h"
21214501Srpaulo
22214501Srpaulo/**
23214501Srpaulo * aes_unwrap - Unwrap key with AES Key Wrap Algorithm (128-bit KEK) (RFC3394)
24214501Srpaulo * @kek: Key encryption key (KEK)
25214501Srpaulo * @n: Length of the plaintext key in 64-bit units; e.g., 2 = 128-bit = 16
26214501Srpaulo * bytes
27214501Srpaulo * @cipher: Wrapped key to be unwrapped, (n + 1) * 64 bits
28214501Srpaulo * @plain: Plaintext key, n * 64 bits
29214501Srpaulo * Returns: 0 on success, -1 on failure (e.g., integrity verification failed)
30214501Srpaulo */
31214501Srpauloint aes_unwrap(const u8 *kek, int n, const u8 *cipher, u8 *plain)
32214501Srpaulo{
33214501Srpaulo	u8 a[8], *r, b[16];
34214501Srpaulo	int i, j;
35214501Srpaulo	void *ctx;
36214501Srpaulo
37214501Srpaulo	/* 1) Initialize variables. */
38214501Srpaulo	os_memcpy(a, cipher, 8);
39214501Srpaulo	r = plain;
40214501Srpaulo	os_memcpy(r, cipher + 8, 8 * n);
41214501Srpaulo
42214501Srpaulo	ctx = aes_decrypt_init(kek, 16);
43214501Srpaulo	if (ctx == NULL)
44214501Srpaulo		return -1;
45214501Srpaulo
46214501Srpaulo	/* 2) Compute intermediate values.
47214501Srpaulo	 * For j = 5 to 0
48214501Srpaulo	 *     For i = n to 1
49214501Srpaulo	 *         B = AES-1(K, (A ^ t) | R[i]) where t = n*j+i
50214501Srpaulo	 *         A = MSB(64, B)
51214501Srpaulo	 *         R[i] = LSB(64, B)
52214501Srpaulo	 */
53214501Srpaulo	for (j = 5; j >= 0; j--) {
54214501Srpaulo		r = plain + (n - 1) * 8;
55214501Srpaulo		for (i = n; i >= 1; i--) {
56214501Srpaulo			os_memcpy(b, a, 8);
57214501Srpaulo			b[7] ^= n * j + i;
58214501Srpaulo
59214501Srpaulo			os_memcpy(b + 8, r, 8);
60214501Srpaulo			aes_decrypt(ctx, b, b);
61214501Srpaulo			os_memcpy(a, b, 8);
62214501Srpaulo			os_memcpy(r, b + 8, 8);
63214501Srpaulo			r -= 8;
64214501Srpaulo		}
65214501Srpaulo	}
66214501Srpaulo	aes_decrypt_deinit(ctx);
67214501Srpaulo
68214501Srpaulo	/* 3) Output results.
69214501Srpaulo	 *
70214501Srpaulo	 * These are already in @plain due to the location of temporary
71214501Srpaulo	 * variables. Just verify that the IV matches with the expected value.
72214501Srpaulo	 */
73214501Srpaulo	for (i = 0; i < 8; i++) {
74214501Srpaulo		if (a[i] != 0xa6)
75214501Srpaulo			return -1;
76214501Srpaulo	}
77214501Srpaulo
78214501Srpaulo	return 0;
79214501Srpaulo}
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