1 /*
2  * AES key unwrap (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 (RFC3394)
18  * @kek: Key encryption key (KEK)
19  * @kek_len: Length of KEK in octets
20  * @n: Length of the plaintext key in 64-bit units; e.g., 2 = 128-bit = 16
21  * bytes
22  * @cipher: Wrapped key to be unwrapped, (n + 1) * 64 bits
23  * @plain: Plaintext key, n * 64 bits
24  * Returns: 0 on success, -1 on failure (e.g., integrity verification failed)
25  */
aes_unwrap(const u8 * kek,size_t kek_len,int n,const u8 * cipher,u8 * plain)26 int aes_unwrap(const u8 *kek, size_t kek_len, int n, const u8 *cipher,
27 	       u8 *plain)
28 {
29 	u8 a[8], *r, b[AES_BLOCK_SIZE];
30 	int i, j;
31 	void *ctx;
32 	unsigned int t;
33 
34 	/* 1) Initialize variables. */
35 	os_memcpy(a, cipher, 8);
36 	r = plain;
37 	os_memcpy(r, cipher + 8, 8 * n);
38 
39 	ctx = aes_decrypt_init(kek, kek_len);
40 	if (ctx == NULL)
41 		return -1;
42 
43 	/* 2) Compute intermediate values.
44 	 * For j = 5 to 0
45 	 *     For i = n to 1
46 	 *         B = AES-1(K, (A ^ t) | R[i]) where t = n*j+i
47 	 *         A = MSB(64, B)
48 	 *         R[i] = LSB(64, B)
49 	 */
50 	for (j = 5; j >= 0; j--) {
51 		r = plain + (n - 1) * 8;
52 		for (i = n; i >= 1; i--) {
53 			os_memcpy(b, a, 8);
54 			t = n * j + i;
55 			b[7] ^= t;
56 			b[6] ^= t >> 8;
57 			b[5] ^= t >> 16;
58 			b[4] ^= t >> 24;
59 
60 			os_memcpy(b + 8, r, 8);
61 			aes_decrypt(ctx, b, b);
62 			os_memcpy(a, b, 8);
63 			os_memcpy(r, b + 8, 8);
64 			r -= 8;
65 		}
66 	}
67 	aes_decrypt_deinit(ctx);
68 
69 	/* 3) Output results.
70 	 *
71 	 * These are already in @plain due to the location of temporary
72 	 * variables. Just verify that the IV matches with the expected value.
73 	 */
74 	for (i = 0; i < 8; i++) {
75 		if (a[i] != 0xa6)
76 			return -1;
77 	}
78 
79 	return 0;
80 }
81