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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  */
aes_unwrap(const u8 * kek,int n,const u8 * cipher,u8 * plain)25 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 	os_memcpy(a, cipher, 8);
33 	r = plain;
34 	os_memcpy(r, cipher + 8, 8 * n);
35 
36 	ctx = aes_decrypt_init(kek, 16);
37 	if (ctx == NULL)
38 		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 	for (j = 5; j >= 0; j--) {
48 		r = plain + (n - 1) * 8;
49 		for (i = n; i >= 1; i--) {
50 			os_memcpy(b, a, 8);
51 			b[7] ^= n * j + i;
52 
53 			os_memcpy(b + 8, r, 8);
54 			aes_decrypt(ctx, b, b);
55 			os_memcpy(a, b, 8);
56 			os_memcpy(r, b + 8, 8);
57 			r -= 8;
58 		}
59 	}
60 	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 	for (i = 0; i < 8; i++) {
68 		if (a[i] != 0xa6)
69 			return -1;
70 	}
71 
72 	return 0;
73 }
74