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