1 /*
2 * aes_icm_mbedtls.c
3 *
4 * AES Integer Counter Mode
5 *
6 * YongCheng Yang
7 */
8
9 /*
10 *
11 * Copyright (c) 2013-2017, Cisco Systems, Inc.
12 * All rights reserved.
13 *
14 * Redistribution and use in source and binary forms, with or without
15 * modification, are permitted provided that the following conditions
16 * are met:
17 *
18 * Redistributions of source code must retain the above copyright
19 * notice, this list of conditions and the following disclaimer.
20 *
21 * Redistributions in binary form must reproduce the above
22 * copyright notice, this list of conditions and the following
23 * disclaimer in the documentation and/or other materials provided
24 * with the distribution.
25 *
26 * Neither the name of the Cisco Systems, Inc. nor the names of its
27 * contributors may be used to endorse or promote products derived
28 * from this software without specific prior written permission.
29 *
30 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
31 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
32 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
33 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
34 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
35 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
36 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
37 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
38 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
39 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
40 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
41 * OF THE POSSIBILITY OF SUCH DAMAGE.
42 *
43 */
44
45 #ifdef HAVE_CONFIG_H
46 #include <config.h>
47 #endif
48 #include <mbedtls/aes.h>
49 #include "aes_icm_ext.h"
50 #include "crypto_types.h"
51 #include "err.h" /* for srtp_debug */
52 #include "alloc.h"
53 #include "cipher_types.h"
54 #include "cipher_test_cases.h"
55
56 srtp_debug_module_t srtp_mod_aes_icm = {
57 0, /* debugging is off by default */
58 "aes icm mbedtls" /* printable module name */
59 };
60
61 /*
62 * integer counter mode works as follows:
63 *
64 * https://tools.ietf.org/html/rfc3711#section-4.1.1
65 *
66 * E(k, IV) || E(k, IV + 1 mod 2^128) || E(k, IV + 2 mod 2^128) ...
67 * IV = (k_s * 2^16) XOR (SSRC * 2^64) XOR (i * 2^16)
68 *
69 * IV SHALL be defined by the SSRC, the SRTP packet index i,
70 * and the SRTP session salting key k_s.
71 *
72 * SSRC: 32bits.
73 * Sequence number: 16bits.
74 * nonce is 64bits. .
75 * packet index = ROC || SEQ. (ROC: Rollover counter)
76 *
77 * 16 bits
78 * <----->
79 * +------+------+------+------+------+------+------+------+
80 * | nonce | packet index | ctr |---+
81 * +------+------+------+------+------+------+------+------+ |
82 * |
83 * +------+------+------+------+------+------+------+------+ v
84 * | salt |000000|->(+)
85 * +------+------+------+------+------+------+------+------+ |
86 * |
87 * +---------+
88 * | encrypt |
89 * +---------+
90 * |
91 * +------+------+------+------+------+------+------+------+ |
92 * | keystream block |<--+
93 * +------+------+------+------+------+------+------+------+
94 *
95 * All fields are big-endian
96 *
97 * ctr is the block counter, which increments from zero for
98 * each packet (16 bits wide)
99 *
100 * packet index is distinct for each packet (48 bits wide)
101 *
102 * nonce can be distinct across many uses of the same key, or
103 * can be a fixed value per key, or can be per-packet randomness
104 * (64 bits)
105 *
106 */
107
108 /*
109 * This function allocates a new instance of this crypto engine.
110 * The key_len parameter should be one of 30, 38, or 46 for
111 * AES-128, AES-192, and AES-256 respectively. Note, this key_len
112 * value is inflated, as it also accounts for the 112 bit salt
113 * value. The tlen argument is for the AEAD tag length, which
114 * isn't used in counter mode.
115 */
srtp_aes_icm_mbedtls_alloc(srtp_cipher_t ** c,int key_len,int tlen)116 static srtp_err_status_t srtp_aes_icm_mbedtls_alloc(srtp_cipher_t **c,
117 int key_len,
118 int tlen)
119 {
120 srtp_aes_icm_ctx_t *icm;
121
122 debug_print(srtp_mod_aes_icm, "allocating cipher with key length %d",
123 key_len);
124
125 /*
126 * Verify the key_len is valid for one of: AES-128/192/256
127 */
128 if (key_len != SRTP_AES_ICM_128_KEY_LEN_WSALT &&
129 key_len != SRTP_AES_ICM_192_KEY_LEN_WSALT &&
130 key_len != SRTP_AES_ICM_256_KEY_LEN_WSALT) {
131 return srtp_err_status_bad_param;
132 }
133
134 /* allocate memory a cipher of type aes_icm */
135 *c = (srtp_cipher_t *)srtp_crypto_alloc(sizeof(srtp_cipher_t));
136 if (*c == NULL) {
137 return srtp_err_status_alloc_fail;
138 }
139
140 icm = (srtp_aes_icm_ctx_t *)srtp_crypto_alloc(sizeof(srtp_aes_icm_ctx_t));
141 if (icm == NULL) {
142 srtp_crypto_free(*c);
143 *c = NULL;
144 return srtp_err_status_alloc_fail;
145 }
146
147 icm->ctx =
148 (mbedtls_aes_context *)srtp_crypto_alloc(sizeof(mbedtls_aes_context));
149 if (icm->ctx == NULL) {
150 srtp_crypto_free(icm);
151 srtp_crypto_free(*c);
152 *c = NULL;
153 return srtp_err_status_alloc_fail;
154 }
155
156 mbedtls_aes_init(icm->ctx);
157
158 /* set pointers */
159 (*c)->state = icm;
160
161 /* setup cipher parameters */
162 switch (key_len) {
163 case SRTP_AES_ICM_128_KEY_LEN_WSALT:
164 (*c)->algorithm = SRTP_AES_ICM_128;
165 (*c)->type = &srtp_aes_icm_128;
166 icm->key_size = SRTP_AES_128_KEY_LEN;
167 break;
168 case SRTP_AES_ICM_192_KEY_LEN_WSALT:
169 (*c)->algorithm = SRTP_AES_ICM_192;
170 (*c)->type = &srtp_aes_icm_192;
171 icm->key_size = SRTP_AES_192_KEY_LEN;
172 break;
173 case SRTP_AES_ICM_256_KEY_LEN_WSALT:
174 (*c)->algorithm = SRTP_AES_ICM_256;
175 (*c)->type = &srtp_aes_icm_256;
176 icm->key_size = SRTP_AES_256_KEY_LEN;
177 break;
178 }
179
180 /* set key size */
181 (*c)->key_len = key_len;
182
183 return srtp_err_status_ok;
184 }
185
186 /*
187 * This function deallocates an instance of this engine
188 */
srtp_aes_icm_mbedtls_dealloc(srtp_cipher_t * c)189 static srtp_err_status_t srtp_aes_icm_mbedtls_dealloc(srtp_cipher_t *c)
190 {
191 srtp_aes_icm_ctx_t *ctx;
192
193 if (c == NULL) {
194 return srtp_err_status_bad_param;
195 }
196
197 /*
198 * Free the aes context
199 */
200 ctx = (srtp_aes_icm_ctx_t *)c->state;
201 if (ctx != NULL) {
202 mbedtls_aes_free(ctx->ctx);
203 srtp_crypto_free(ctx->ctx);
204 /* zeroize the key material */
205 octet_string_set_to_zero(ctx, sizeof(srtp_aes_icm_ctx_t));
206 srtp_crypto_free(ctx);
207 }
208
209 /* free memory */
210 srtp_crypto_free(c);
211
212 return srtp_err_status_ok;
213 }
214
srtp_aes_icm_mbedtls_context_init(void * cv,const uint8_t * key)215 static srtp_err_status_t srtp_aes_icm_mbedtls_context_init(void *cv,
216 const uint8_t *key)
217 {
218 srtp_aes_icm_ctx_t *c = (srtp_aes_icm_ctx_t *)cv;
219 uint32_t key_size_in_bits = (c->key_size << 3);
220 int errcode = 0;
221
222 /*
223 * set counter and initial values to 'offset' value, being careful not to
224 * go past the end of the key buffer
225 */
226 v128_set_to_zero(&c->counter);
227 v128_set_to_zero(&c->offset);
228 memcpy(&c->counter, key + c->key_size, SRTP_SALT_LEN);
229 memcpy(&c->offset, key + c->key_size, SRTP_SALT_LEN);
230
231 /* force last two octets of the offset to zero (for srtp compatibility) */
232 c->offset.v8[SRTP_SALT_LEN] = c->offset.v8[SRTP_SALT_LEN + 1] = 0;
233 c->counter.v8[SRTP_SALT_LEN] = c->counter.v8[SRTP_SALT_LEN + 1] = 0;
234 debug_print(srtp_mod_aes_icm, "key: %s",
235 srtp_octet_string_hex_string(key, c->key_size));
236 debug_print(srtp_mod_aes_icm, "offset: %s", v128_hex_string(&c->offset));
237
238 switch (c->key_size) {
239 case SRTP_AES_256_KEY_LEN:
240 case SRTP_AES_192_KEY_LEN:
241 case SRTP_AES_128_KEY_LEN:
242 break;
243 default:
244 return srtp_err_status_bad_param;
245 break;
246 }
247
248 errcode = mbedtls_aes_setkey_enc(c->ctx, key, key_size_in_bits);
249 if (errcode != 0) {
250 debug_print(srtp_mod_aes_icm, "errCode: %d", errcode);
251 }
252
253 return srtp_err_status_ok;
254 }
255
256 /*
257 * aes_icm_set_iv(c, iv) sets the counter value to the exor of iv with
258 * the offset
259 */
srtp_aes_icm_mbedtls_set_iv(void * cv,uint8_t * iv,srtp_cipher_direction_t dir)260 static srtp_err_status_t srtp_aes_icm_mbedtls_set_iv(
261 void *cv,
262 uint8_t *iv,
263 srtp_cipher_direction_t dir)
264 {
265 srtp_aes_icm_ctx_t *c = (srtp_aes_icm_ctx_t *)cv;
266 v128_t nonce;
267 c->nc_off = 0;
268 /* set nonce (for alignment) */
269 v128_copy_octet_string(&nonce, iv);
270
271 debug_print(srtp_mod_aes_icm, "setting iv: %s", v128_hex_string(&nonce));
272
273 v128_xor(&c->counter, &c->offset, &nonce);
274
275 debug_print(srtp_mod_aes_icm, "set_counter: %s",
276 v128_hex_string(&c->counter));
277
278 return srtp_err_status_ok;
279 }
280
281 /*
282 * This function encrypts a buffer using AES CTR mode
283 *
284 * Parameters:
285 * c Crypto context
286 * buf data to encrypt
287 * enc_len length of encrypt buffer
288 */
srtp_aes_icm_mbedtls_encrypt(void * cv,unsigned char * buf,unsigned int * enc_len)289 static srtp_err_status_t srtp_aes_icm_mbedtls_encrypt(void *cv,
290 unsigned char *buf,
291 unsigned int *enc_len)
292 {
293 srtp_aes_icm_ctx_t *c = (srtp_aes_icm_ctx_t *)cv;
294
295 int errCode = 0;
296 debug_print(srtp_mod_aes_icm, "rs0: %s", v128_hex_string(&c->counter));
297
298 errCode =
299 mbedtls_aes_crypt_ctr(c->ctx, *enc_len, &(c->nc_off), c->counter.v8,
300 c->stream_block.v8, buf, buf);
301 if (errCode != 0) {
302 debug_print(srtp_mod_aes_icm, "encrypt error: %d", errCode);
303 return srtp_err_status_cipher_fail;
304 }
305
306 return srtp_err_status_ok;
307 }
308
309 /*
310 * Name of this crypto engine
311 */
312 static const char srtp_aes_icm_128_mbedtls_description[] =
313 "AES-128 counter mode using mbedtls";
314 static const char srtp_aes_icm_192_mbedtls_description[] =
315 "AES-192 counter mode using mbedtls";
316 static const char srtp_aes_icm_256_mbedtls_description[] =
317 "AES-256 counter mode using mbedtls";
318
319 /*
320 * This is the function table for this crypto engine.
321 * note: the encrypt function is identical to the decrypt function
322 */
323 const srtp_cipher_type_t srtp_aes_icm_128 = {
324 srtp_aes_icm_mbedtls_alloc, /* */
325 srtp_aes_icm_mbedtls_dealloc, /* */
326 srtp_aes_icm_mbedtls_context_init, /* */
327 0, /* set_aad */
328 srtp_aes_icm_mbedtls_encrypt, /* */
329 srtp_aes_icm_mbedtls_encrypt, /* */
330 srtp_aes_icm_mbedtls_set_iv, /* */
331 0, /* get_tag */
332 srtp_aes_icm_128_mbedtls_description, /* */
333 &srtp_aes_icm_128_test_case_0, /* */
334 SRTP_AES_ICM_128 /* */
335 };
336
337 /*
338 * This is the function table for this crypto engine.
339 * note: the encrypt function is identical to the decrypt function
340 */
341 const srtp_cipher_type_t srtp_aes_icm_192 = {
342 srtp_aes_icm_mbedtls_alloc, /* */
343 srtp_aes_icm_mbedtls_dealloc, /* */
344 srtp_aes_icm_mbedtls_context_init, /* */
345 0, /* set_aad */
346 srtp_aes_icm_mbedtls_encrypt, /* */
347 srtp_aes_icm_mbedtls_encrypt, /* */
348 srtp_aes_icm_mbedtls_set_iv, /* */
349 0, /* get_tag */
350 srtp_aes_icm_192_mbedtls_description, /* */
351 &srtp_aes_icm_192_test_case_0, /* */
352 SRTP_AES_ICM_192 /* */
353 };
354
355 /*
356 * This is the function table for this crypto engine.
357 * note: the encrypt function is identical to the decrypt function
358 */
359 const srtp_cipher_type_t srtp_aes_icm_256 = {
360 srtp_aes_icm_mbedtls_alloc, /* */
361 srtp_aes_icm_mbedtls_dealloc, /* */
362 srtp_aes_icm_mbedtls_context_init, /* */
363 0, /* set_aad */
364 srtp_aes_icm_mbedtls_encrypt, /* */
365 srtp_aes_icm_mbedtls_encrypt, /* */
366 srtp_aes_icm_mbedtls_set_iv, /* */
367 0, /* get_tag */
368 srtp_aes_icm_256_mbedtls_description, /* */
369 &srtp_aes_icm_256_test_case_0, /* */
370 SRTP_AES_ICM_256 /* */
371 };
372