1214501Srpaulo/*
2214501Srpaulo * AES key unwrap (128-bit KEK, RFC3394)
3214501Srpaulo *
4214501Srpaulo * Copyright (c) 2003-2007, Jouni Malinen <j@w1.fi>
5214501Srpaulo *
6252726Srpaulo * This software may be distributed under the terms of the BSD license.
7252726Srpaulo * See README for more details.
8214501Srpaulo */
9214501Srpaulo
10214501Srpaulo#include "includes.h"
11214501Srpaulo
12214501Srpaulo#include "common.h"
13214501Srpaulo#include "aes.h"
14214501Srpaulo#include "aes_wrap.h"
15214501Srpaulo
16214501Srpaulo/**
17214501Srpaulo * aes_unwrap - Unwrap key with AES Key Wrap Algorithm (128-bit KEK) (RFC3394)
18214501Srpaulo * @kek: Key encryption key (KEK)
19214501Srpaulo * @n: Length of the plaintext key in 64-bit units; e.g., 2 = 128-bit = 16
20214501Srpaulo * bytes
21214501Srpaulo * @cipher: Wrapped key to be unwrapped, (n + 1) * 64 bits
22214501Srpaulo * @plain: Plaintext key, n * 64 bits
23214501Srpaulo * Returns: 0 on success, -1 on failure (e.g., integrity verification failed)
24214501Srpaulo */
25214501Srpauloint aes_unwrap(const u8 *kek, int n, const u8 *cipher, u8 *plain)
26214501Srpaulo{
27214501Srpaulo	u8 a[8], *r, b[16];
28214501Srpaulo	int i, j;
29214501Srpaulo	void *ctx;
30214501Srpaulo
31214501Srpaulo	/* 1) Initialize variables. */
32214501Srpaulo	os_memcpy(a, cipher, 8);
33214501Srpaulo	r = plain;
34214501Srpaulo	os_memcpy(r, cipher + 8, 8 * n);
35214501Srpaulo
36214501Srpaulo	ctx = aes_decrypt_init(kek, 16);
37214501Srpaulo	if (ctx == NULL)
38214501Srpaulo		return -1;
39214501Srpaulo
40214501Srpaulo	/* 2) Compute intermediate values.
41214501Srpaulo	 * For j = 5 to 0
42214501Srpaulo	 *     For i = n to 1
43214501Srpaulo	 *         B = AES-1(K, (A ^ t) | R[i]) where t = n*j+i
44214501Srpaulo	 *         A = MSB(64, B)
45214501Srpaulo	 *         R[i] = LSB(64, B)
46214501Srpaulo	 */
47214501Srpaulo	for (j = 5; j >= 0; j--) {
48214501Srpaulo		r = plain + (n - 1) * 8;
49214501Srpaulo		for (i = n; i >= 1; i--) {
50214501Srpaulo			os_memcpy(b, a, 8);
51214501Srpaulo			b[7] ^= n * j + i;
52214501Srpaulo
53214501Srpaulo			os_memcpy(b + 8, r, 8);
54214501Srpaulo			aes_decrypt(ctx, b, b);
55214501Srpaulo			os_memcpy(a, b, 8);
56214501Srpaulo			os_memcpy(r, b + 8, 8);
57214501Srpaulo			r -= 8;
58214501Srpaulo		}
59214501Srpaulo	}
60214501Srpaulo	aes_decrypt_deinit(ctx);
61214501Srpaulo
62214501Srpaulo	/* 3) Output results.
63214501Srpaulo	 *
64214501Srpaulo	 * These are already in @plain due to the location of temporary
65214501Srpaulo	 * variables. Just verify that the IV matches with the expected value.
66214501Srpaulo	 */
67214501Srpaulo	for (i = 0; i < 8; i++) {
68214501Srpaulo		if (a[i] != 0xa6)
69214501Srpaulo			return -1;
70214501Srpaulo	}
71214501Srpaulo
72214501Srpaulo	return 0;
73214501Srpaulo}
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