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 */
26int 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