aes-ccm.c revision 9bce59c7fef20e34a05f04d1e33a4076083dca0c 
1/*
2 * Counter with CBC-MAC (CCM) with AES
3 *
4 * Copyright (c) 2010-2012, 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
17static void xor_aes_block(u8 *dst, const u8 *src)
18{
19	u32 *d = (u32 *) dst;
20	u32 *s = (u32 *) src;
21	*d++ ^= *s++;
22	*d++ ^= *s++;
23	*d++ ^= *s++;
24	*d++ ^= *s++;
25}
26
27
28static void aes_ccm_auth_start(void *aes, size_t M, size_t L, const u8 *nonce,
29			       const u8 *aad, size_t aad_len, size_t plain_len,
30			       u8 *x)
31{
32	u8 aad_buf[2 * AES_BLOCK_SIZE];
33	u8 b[AES_BLOCK_SIZE];
34
35	/* Authentication */
36	/* B_0: Flags | Nonce N | l(m) */
37	b[0] = aad_len ? 0x40 : 0 /* Adata */;
38	b[0] |= (((M - 2) / 2) /* M' */ << 3);
39	b[0] |= (L - 1) /* L' */;
40	os_memcpy(&b[1], nonce, 15 - L);
41	WPA_PUT_BE16(&b[AES_BLOCK_SIZE - L], plain_len);
42
43	wpa_hexdump_key(MSG_EXCESSIVE, "CCM B_0", b, AES_BLOCK_SIZE);
44	aes_encrypt(aes, b, x); /* X_1 = E(K, B_0) */
45
46	if (!aad_len)
47		return;
48
49	WPA_PUT_BE16(aad_buf, aad_len);
50	os_memcpy(aad_buf + 2, aad, aad_len);
51	os_memset(aad_buf + 2 + aad_len, 0, sizeof(aad_buf) - 2 - aad_len);
52
53	xor_aes_block(aad_buf, x);
54	aes_encrypt(aes, aad_buf, x); /* X_2 = E(K, X_1 XOR B_1) */
55
56	if (aad_len > AES_BLOCK_SIZE - 2) {
57		xor_aes_block(&aad_buf[AES_BLOCK_SIZE], x);
58		/* X_3 = E(K, X_2 XOR B_2) */
59		aes_encrypt(aes, &aad_buf[AES_BLOCK_SIZE], x);
60	}
61}
62
63
64static void aes_ccm_auth(void *aes, const u8 *data, size_t len, u8 *x)
65{
66	size_t last = len % AES_BLOCK_SIZE;
67	size_t i;
68
69	for (i = 0; i < len / AES_BLOCK_SIZE; i++) {
70		/* X_i+1 = E(K, X_i XOR B_i) */
71		xor_aes_block(x, data);
72		data += AES_BLOCK_SIZE;
73		aes_encrypt(aes, x, x);
74	}
75	if (last) {
76		/* XOR zero-padded last block */
77		for (i = 0; i < last; i++)
78			x[i] ^= *data++;
79		aes_encrypt(aes, x, x);
80	}
81}
82
83
84static void aes_ccm_encr_start(size_t L, const u8 *nonce, u8 *a)
85{
86	/* A_i = Flags | Nonce N | Counter i */
87	a[0] = L - 1; /* Flags = L' */
88	os_memcpy(&a[1], nonce, 15 - L);
89}
90
91
92static void aes_ccm_encr(void *aes, size_t L, const u8 *in, size_t len, u8 *out,
93			 u8 *a)
94{
95	size_t last = len % AES_BLOCK_SIZE;
96	size_t i;
97
98	/* crypt = msg XOR (S_1 | S_2 | ... | S_n) */
99	for (i = 1; i <= len / AES_BLOCK_SIZE; i++) {
100		WPA_PUT_BE16(&a[AES_BLOCK_SIZE - 2], i);
101		/* S_i = E(K, A_i) */
102		aes_encrypt(aes, a, out);
103		xor_aes_block(out, in);
104		out += AES_BLOCK_SIZE;
105		in += AES_BLOCK_SIZE;
106	}
107	if (last) {
108		WPA_PUT_BE16(&a[AES_BLOCK_SIZE - 2], i);
109		aes_encrypt(aes, a, out);
110		/* XOR zero-padded last block */
111		for (i = 0; i < last; i++)
112			*out++ ^= *in++;
113	}
114}
115
116
117static void aes_ccm_encr_auth(void *aes, size_t M, u8 *x, u8 *a, u8 *auth)
118{
119	size_t i;
120	u8 tmp[AES_BLOCK_SIZE];
121
122	wpa_hexdump_key(MSG_EXCESSIVE, "CCM T", x, M);
123	/* U = T XOR S_0; S_0 = E(K, A_0) */
124	WPA_PUT_BE16(&a[AES_BLOCK_SIZE - 2], 0);
125	aes_encrypt(aes, a, tmp);
126	for (i = 0; i < M; i++)
127		auth[i] = x[i] ^ tmp[i];
128	wpa_hexdump_key(MSG_EXCESSIVE, "CCM U", auth, M);
129}
130
131
132static void aes_ccm_decr_auth(void *aes, size_t M, u8 *a, const u8 *auth, u8 *t)
133{
134	size_t i;
135	u8 tmp[AES_BLOCK_SIZE];
136
137	wpa_hexdump_key(MSG_EXCESSIVE, "CCM U", auth, M);
138	/* U = T XOR S_0; S_0 = E(K, A_0) */
139	WPA_PUT_BE16(&a[AES_BLOCK_SIZE - 2], 0);
140	aes_encrypt(aes, a, tmp);
141	for (i = 0; i < M; i++)
142		t[i] = auth[i] ^ tmp[i];
143	wpa_hexdump_key(MSG_EXCESSIVE, "CCM T", t, M);
144}
145
146
147/* AES-CCM with fixed L=2 and aad_len <= 30 assumption */
148int aes_ccm_ae(const u8 *key, size_t key_len, const u8 *nonce,
149	       size_t M, const u8 *plain, size_t plain_len,
150	       const u8 *aad, size_t aad_len, u8 *crypt, u8 *auth)
151{
152	const size_t L = 2;
153	void *aes;
154	u8 x[AES_BLOCK_SIZE], a[AES_BLOCK_SIZE];
155
156	if (aad_len > 30 || M > AES_BLOCK_SIZE)
157		return -1;
158
159	aes = aes_encrypt_init(key, key_len);
160	if (aes == NULL)
161		return -1;
162
163	aes_ccm_auth_start(aes, M, L, nonce, aad, aad_len, plain_len, x);
164	aes_ccm_auth(aes, plain, plain_len, x);
165
166	/* Encryption */
167	aes_ccm_encr_start(L, nonce, a);
168	aes_ccm_encr(aes, L, plain, plain_len, crypt, a);
169	aes_ccm_encr_auth(aes, M, x, a, auth);
170
171	aes_encrypt_deinit(aes);
172
173	return 0;
174}
175
176
177/* AES-CCM with fixed L=2 and aad_len <= 30 assumption */
178int aes_ccm_ad(const u8 *key, size_t key_len, const u8 *nonce,
179	       size_t M, const u8 *crypt, size_t crypt_len,
180	       const u8 *aad, size_t aad_len, const u8 *auth, u8 *plain)
181{
182	const size_t L = 2;
183	void *aes;
184	u8 x[AES_BLOCK_SIZE], a[AES_BLOCK_SIZE];
185	u8 t[AES_BLOCK_SIZE];
186
187	if (aad_len > 30 || M > AES_BLOCK_SIZE)
188		return -1;
189
190	aes = aes_encrypt_init(key, key_len);
191	if (aes == NULL)
192		return -1;
193
194	/* Decryption */
195	aes_ccm_encr_start(L, nonce, a);
196	aes_ccm_decr_auth(aes, M, a, auth, t);
197
198	/* plaintext = msg XOR (S_1 | S_2 | ... | S_n) */
199	aes_ccm_encr(aes, L, crypt, crypt_len, plain, a);
200
201	aes_ccm_auth_start(aes, M, L, nonce, aad, aad_len, crypt_len, x);
202	aes_ccm_auth(aes, plain, crypt_len, x);
203
204	aes_encrypt_deinit(aes);
205
206	if (os_memcmp(x, t, M) != 0) {
207		wpa_printf(MSG_EXCESSIVE, "CCM: Auth mismatch");
208		return -1;
209	}
210
211	return 0;
212}
213