1 /**
2  * Cipher API multi-part AEAD demonstration.
3  *
4  * This program AEAD-encrypts a message, using the algorithm and key size
5  * specified on the command line, using the multi-part API.
6  *
7  * It comes with a companion program psa/aead_demo.c, which does the same
8  * operations with the PSA Crypto API. The goal is that comparing the two
9  * programs will help people migrating to the PSA Crypto API.
10  *
11  * When used with multi-part AEAD operations, the `mbedtls_cipher_context`
12  * serves a triple purpose (1) hold the key, (2) store the algorithm when no
13  * operation is active, and (3) save progress information for the current
14  * operation. With PSA those roles are held by disinct objects: (1) a
15  * psa_key_id_t to hold the key, a (2) psa_algorithm_t to represent the
16  * algorithm, and (3) a psa_operation_t for multi-part progress.
17  *
18  * On the other hand, with PSA, the algorithms encodes the desired tag length;
19  * with Cipher the desired tag length needs to be tracked separately.
20  *
21  * This program and its companion psa/aead_demo.c illustrate this by doing the
22  * same sequence of multi-part AEAD computation with both APIs; looking at the
23  * two side by side should make the differences and similarities clear.
24  */
25 
26 /*
27  *  Copyright The Mbed TLS Contributors
28  *  SPDX-License-Identifier: Apache-2.0
29  *
30  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
31  *  not use this file except in compliance with the License.
32  *  You may obtain a copy of the License at
33  *
34  *  http://www.apache.org/licenses/LICENSE-2.0
35  *
36  *  Unless required by applicable law or agreed to in writing, software
37  *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
38  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
39  *  See the License for the specific language governing permissions and
40  *  limitations under the License.
41  */
42 
43 /* First include Mbed TLS headers to get the Mbed TLS configuration and
44  * platform definitions that we'll use in this program. Also include
45  * standard C headers for functions we'll use here. */
46 #include "mbedtls/build_info.h"
47 
48 #include "mbedtls/cipher.h"
49 
50 #include <stdlib.h>
51 #include <stdio.h>
52 #include <string.h>
53 
54 /* If the build options we need are not enabled, compile a placeholder. */
55 #if !defined(MBEDTLS_CIPHER_C) || \
56     !defined(MBEDTLS_AES_C) || !defined(MBEDTLS_GCM_C) || \
57     !defined(MBEDTLS_CHACHAPOLY_C)
main(void)58 int main(void)
59 {
60     printf("MBEDTLS_MD_C and/or "
61            "MBEDTLS_AES_C and/or MBEDTLS_GCM_C and/or "
62            "MBEDTLS_CHACHAPOLY_C not defined\r\n");
63     return 0;
64 }
65 #else
66 
67 /* The real program starts here. */
68 
69 const char usage[] =
70     "Usage: cipher_aead_demo [aes128-gcm|aes256-gcm|aes128-gcm_8|chachapoly]";
71 
72 /* Dummy data for encryption: IV/nonce, additional data, 2-part message */
73 const unsigned char iv1[12] = { 0x00 };
74 const unsigned char add_data1[] = { 0x01, 0x02 };
75 const unsigned char msg1_part1[] = { 0x03, 0x04 };
76 const unsigned char msg1_part2[] = { 0x05, 0x06, 0x07 };
77 
78 /* Dummy data (2nd message) */
79 const unsigned char iv2[12] = { 0x10 };
80 const unsigned char add_data2[] = { 0x11, 0x12 };
81 const unsigned char msg2_part1[] = { 0x13, 0x14 };
82 const unsigned char msg2_part2[] = { 0x15, 0x16, 0x17 };
83 
84 /* Maximum total size of the messages */
85 #define MSG1_SIZE (sizeof(msg1_part1) + sizeof(msg1_part2))
86 #define MSG2_SIZE (sizeof(msg2_part1) + sizeof(msg2_part2))
87 #define MSG_MAX_SIZE (MSG1_SIZE > MSG2_SIZE ? MSG1_SIZE : MSG2_SIZE)
88 
89 /* Dummy key material - never do this in production!
90  * 32-byte is enough to all the key size supported by this program. */
91 const unsigned char key_bytes[32] = { 0x2a };
92 
93 /* Print the contents of a buffer in hex */
print_buf(const char * title,unsigned char * buf,size_t len)94 void print_buf(const char *title, unsigned char *buf, size_t len)
95 {
96     printf("%s:", title);
97     for (size_t i = 0; i < len; i++) {
98         printf(" %02x", buf[i]);
99     }
100     printf("\n");
101 }
102 
103 /* Run an Mbed TLS function and bail out if it fails.
104  * A string description of the error code can be recovered with:
105  * programs/util/strerror <value> */
106 #define CHK(expr)                                             \
107     do                                                          \
108     {                                                           \
109         ret = (expr);                                         \
110         if (ret != 0)                                          \
111         {                                                       \
112             printf("Error %d at line %d: %s\n",                \
113                    ret,                                        \
114                    __LINE__,                                   \
115                    #expr);                                    \
116             goto exit;                                          \
117         }                                                       \
118     } while (0)
119 
120 /*
121  * Prepare encryption material:
122  * - interpret command-line argument
123  * - set up key
124  * - outputs: context and tag length, which together hold all the information
125  */
aead_prepare(const char * info,mbedtls_cipher_context_t * ctx,size_t * tag_len)126 static int aead_prepare(const char *info,
127                         mbedtls_cipher_context_t *ctx,
128                         size_t *tag_len)
129 {
130     int ret;
131 
132     /* Convert arg to type + tag_len */
133     mbedtls_cipher_type_t type;
134     if (strcmp(info, "aes128-gcm") == 0) {
135         type = MBEDTLS_CIPHER_AES_128_GCM;
136         *tag_len = 16;
137     } else if (strcmp(info, "aes256-gcm") == 0) {
138         type = MBEDTLS_CIPHER_AES_256_GCM;
139         *tag_len = 16;
140     } else if (strcmp(info, "aes128-gcm_8") == 0) {
141         type = MBEDTLS_CIPHER_AES_128_GCM;
142         *tag_len = 8;
143     } else if (strcmp(info, "chachapoly") == 0) {
144         type = MBEDTLS_CIPHER_CHACHA20_POLY1305;
145         *tag_len = 16;
146     } else {
147         puts(usage);
148         return MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA;
149     }
150 
151     /* Prepare context for the given type */
152     CHK(mbedtls_cipher_setup(ctx,
153                              mbedtls_cipher_info_from_type(type)));
154 
155     /* Import key */
156     int key_len = mbedtls_cipher_get_key_bitlen(ctx);
157     CHK(mbedtls_cipher_setkey(ctx, key_bytes, key_len, MBEDTLS_ENCRYPT));
158 
159 exit:
160     return ret;
161 }
162 
163 /*
164  * Print out some information.
165  *
166  * All of this information was present in the command line argument, but his
167  * function demonstrates how each piece can be recovered from (ctx, tag_len).
168  */
aead_info(const mbedtls_cipher_context_t * ctx,size_t tag_len)169 static void aead_info(const mbedtls_cipher_context_t *ctx, size_t tag_len)
170 {
171     mbedtls_cipher_type_t type = mbedtls_cipher_get_type(ctx);
172     const mbedtls_cipher_info_t *info = mbedtls_cipher_info_from_type(type);
173     const char *ciph = mbedtls_cipher_info_get_name(info);
174     int key_bits = mbedtls_cipher_get_key_bitlen(ctx);
175     mbedtls_cipher_mode_t mode = mbedtls_cipher_get_cipher_mode(ctx);
176 
177     const char *mode_str = mode == MBEDTLS_MODE_GCM ? "GCM"
178                          : mode == MBEDTLS_MODE_CHACHAPOLY ? "ChachaPoly"
179                          : "???";
180 
181     printf("%s, %d, %s, %u\n",
182            ciph, key_bits, mode_str, (unsigned) tag_len);
183 }
184 
185 /*
186  * Encrypt a 2-part message.
187  */
aead_encrypt(mbedtls_cipher_context_t * ctx,size_t tag_len,const unsigned char * iv,size_t iv_len,const unsigned char * ad,size_t ad_len,const unsigned char * part1,size_t part1_len,const unsigned char * part2,size_t part2_len)188 static int aead_encrypt(mbedtls_cipher_context_t *ctx, size_t tag_len,
189                         const unsigned char *iv, size_t iv_len,
190                         const unsigned char *ad, size_t ad_len,
191                         const unsigned char *part1, size_t part1_len,
192                         const unsigned char *part2, size_t part2_len)
193 {
194     int ret;
195     size_t olen;
196 #define MAX_TAG_LENGTH 16
197     unsigned char out[MSG_MAX_SIZE + MAX_TAG_LENGTH];
198     unsigned char *p = out;
199 
200     CHK(mbedtls_cipher_set_iv(ctx, iv, iv_len));
201     CHK(mbedtls_cipher_reset(ctx));
202     CHK(mbedtls_cipher_update_ad(ctx, ad, ad_len));
203     CHK(mbedtls_cipher_update(ctx, part1, part1_len, p, &olen));
204     p += olen;
205     CHK(mbedtls_cipher_update(ctx, part2, part2_len, p, &olen));
206     p += olen;
207     CHK(mbedtls_cipher_finish(ctx, p, &olen));
208     p += olen;
209     CHK(mbedtls_cipher_write_tag(ctx, p, tag_len));
210     p += tag_len;
211 
212     olen = p - out;
213     print_buf("out", out, olen);
214 
215 exit:
216     return ret;
217 }
218 
219 /*
220  * AEAD demo: set up key/alg, print out info, encrypt messages.
221  */
aead_demo(const char * info)222 static int aead_demo(const char *info)
223 {
224     int ret = 0;
225 
226     mbedtls_cipher_context_t ctx;
227     size_t tag_len;
228 
229     mbedtls_cipher_init(&ctx);
230 
231     CHK(aead_prepare(info, &ctx, &tag_len));
232 
233     aead_info(&ctx, tag_len);
234 
235     CHK(aead_encrypt(&ctx, tag_len,
236                      iv1, sizeof(iv1), add_data1, sizeof(add_data1),
237                      msg1_part1, sizeof(msg1_part1),
238                      msg1_part2, sizeof(msg1_part2)));
239     CHK(aead_encrypt(&ctx, tag_len,
240                      iv2, sizeof(iv2), add_data2, sizeof(add_data2),
241                      msg2_part1, sizeof(msg2_part1),
242                      msg2_part2, sizeof(msg2_part2)));
243 
244 exit:
245     mbedtls_cipher_free(&ctx);
246 
247     return ret;
248 }
249 
250 
251 /*
252  * Main function
253  */
main(int argc,char ** argv)254 int main(int argc, char **argv)
255 {
256     /* Check usage */
257     if (argc != 2) {
258         puts(usage);
259         return 1;
260     }
261 
262     int ret;
263 
264     /* Run the demo */
265     CHK(aead_demo(argv[1]));
266 
267 exit:
268     return ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
269 }
270 
271 #endif
272