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     printf( "\n" );
100 }
101 
102 /* Run an Mbed TLS function and bail out if it fails.
103  * A string description of the error code can be recovered with:
104  * programs/util/strerror <value> */
105 #define CHK( expr )                                             \
106     do                                                          \
107     {                                                           \
108         ret = ( expr );                                         \
109         if( ret != 0 )                                          \
110         {                                                       \
111             printf( "Error %d at line %d: %s\n",                \
112                     ret,                                        \
113                     __LINE__,                                   \
114                     #expr );                                    \
115             goto exit;                                          \
116         }                                                       \
117     } while( 0 )
118 
119 /*
120  * Prepare encryption material:
121  * - interpret command-line argument
122  * - set up key
123  * - outputs: context and tag length, which together hold all the information
124  */
aead_prepare(const char * info,mbedtls_cipher_context_t * ctx,size_t * tag_len)125 static int aead_prepare( const char *info,
126                            mbedtls_cipher_context_t *ctx,
127                            size_t *tag_len )
128 {
129     int ret;
130 
131     /* Convert arg to type + tag_len */
132     mbedtls_cipher_type_t type;
133     if( strcmp( info, "aes128-gcm" ) == 0 ) {
134         type = MBEDTLS_CIPHER_AES_128_GCM;
135         *tag_len = 16;
136     } else if( strcmp( info, "aes256-gcm" ) == 0 ) {
137         type = MBEDTLS_CIPHER_AES_256_GCM;
138         *tag_len = 16;
139     } else if( strcmp( info, "aes128-gcm_8" ) == 0 ) {
140         type = MBEDTLS_CIPHER_AES_128_GCM;
141         *tag_len = 8;
142     } else if( strcmp( info, "chachapoly" ) == 0 ) {
143         type = MBEDTLS_CIPHER_CHACHA20_POLY1305;
144         *tag_len = 16;
145     } else {
146         puts( usage );
147         return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
148     }
149 
150     /* Prepare context for the given type */
151     CHK( mbedtls_cipher_setup( ctx,
152                                mbedtls_cipher_info_from_type( type ) ) );
153 
154     /* Import key */
155     int key_len = mbedtls_cipher_get_key_bitlen( ctx );
156     CHK( mbedtls_cipher_setkey( ctx, key_bytes, key_len, MBEDTLS_ENCRYPT ) );
157 
158 exit:
159     return( ret );
160 }
161 
162 /*
163  * Print out some information.
164  *
165  * All of this information was present in the command line argument, but his
166  * function demonstrates how each piece can be recovered from (ctx, tag_len).
167  */
aead_info(const mbedtls_cipher_context_t * ctx,size_t tag_len)168 static void aead_info( const mbedtls_cipher_context_t *ctx, size_t tag_len )
169 {
170     mbedtls_cipher_type_t type = mbedtls_cipher_get_type( ctx );
171     const mbedtls_cipher_info_t *info = mbedtls_cipher_info_from_type( type );
172     const char *ciph = mbedtls_cipher_info_get_name( info );
173     int key_bits = mbedtls_cipher_get_key_bitlen( ctx );
174     mbedtls_cipher_mode_t mode = mbedtls_cipher_get_cipher_mode( ctx );
175 
176     const char *mode_str = mode == MBEDTLS_MODE_GCM ? "GCM"
177                          : mode == MBEDTLS_MODE_CHACHAPOLY ? "ChachaPoly"
178                          : "???";
179 
180     printf( "%s, %d, %s, %u\n",
181             ciph, key_bits, mode_str, (unsigned) tag_len );
182 }
183 
184 /*
185  * Encrypt a 2-part message.
186  */
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)187 static int aead_encrypt( mbedtls_cipher_context_t *ctx, size_t tag_len,
188         const unsigned char *iv, size_t iv_len,
189         const unsigned char *ad, size_t ad_len,
190         const unsigned char *part1, size_t part1_len,
191         const unsigned char *part2, size_t part2_len )
192 {
193     int ret;
194     size_t olen;
195 #define MAX_TAG_LENGTH 16
196     unsigned char out[MSG_MAX_SIZE + MAX_TAG_LENGTH];
197     unsigned char *p = out;
198 
199     CHK( mbedtls_cipher_set_iv( ctx, iv, iv_len ) );
200     CHK( mbedtls_cipher_reset( ctx ) );
201     CHK( mbedtls_cipher_update_ad( ctx, ad, ad_len ) );
202     CHK( mbedtls_cipher_update( ctx, part1, part1_len, p, &olen ) );
203     p += olen;
204     CHK( mbedtls_cipher_update( ctx, part2, part2_len, p, &olen ) );
205     p += olen;
206     CHK( mbedtls_cipher_finish( ctx, p, &olen ) );
207     p += olen;
208     CHK( mbedtls_cipher_write_tag( ctx, p, tag_len ) );
209     p += tag_len;
210 
211     olen = p - out;
212     print_buf( "out", out, olen );
213 
214 exit:
215     return( ret );
216 }
217 
218 /*
219  * AEAD demo: set up key/alg, print out info, encrypt messages.
220  */
aead_demo(const char * info)221 static int aead_demo( const char *info )
222 {
223     int ret = 0;
224 
225     mbedtls_cipher_context_t ctx;
226     size_t tag_len;
227 
228     mbedtls_cipher_init( &ctx );
229 
230     CHK( aead_prepare( info, &ctx, &tag_len ) );
231 
232     aead_info( &ctx, tag_len );
233 
234     CHK( aead_encrypt( &ctx, tag_len,
235                          iv1, sizeof( iv1 ), add_data1, sizeof( add_data1 ),
236                          msg1_part1, sizeof( msg1_part1 ),
237                          msg1_part2, sizeof( msg1_part2 ) ) );
238     CHK( aead_encrypt( &ctx, tag_len,
239                          iv2, sizeof( iv2 ), add_data2, sizeof( add_data2 ),
240                          msg2_part1, sizeof( msg2_part1 ),
241                          msg2_part2, sizeof( msg2_part2 ) ) );
242 
243 exit:
244     mbedtls_cipher_free( &ctx );
245 
246     return( ret );
247 }
248 
249 
250 /*
251  * Main function
252  */
main(int argc,char ** argv)253 int main( int argc, char **argv )
254 {
255     /* Check usage */
256     if( argc != 2 )
257     {
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