1 /*
2 * DTLS cookie callbacks implementation
3 *
4 * Copyright The Mbed TLS Contributors
5 * SPDX-License-Identifier: Apache-2.0
6 *
7 * Licensed under the Apache License, Version 2.0 (the "License"); you may
8 * not use this file except in compliance with the License.
9 * You may obtain a copy of the License at
10 *
11 * http://www.apache.org/licenses/LICENSE-2.0
12 *
13 * Unless required by applicable law or agreed to in writing, software
14 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
15 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 * See the License for the specific language governing permissions and
17 * limitations under the License.
18 */
19 /*
20 * These session callbacks use a simple chained list
21 * to store and retrieve the session information.
22 */
23
24 #include "common.h"
25
26 #if defined(MBEDTLS_SSL_COOKIE_C)
27
28 #if defined(MBEDTLS_PLATFORM_C)
29 #include "mbedtls/platform.h"
30 #else
31 #define mbedtls_calloc calloc
32 #define mbedtls_free free
33 #endif
34
35 #include "mbedtls/ssl_cookie.h"
36 #include "mbedtls/ssl_internal.h"
37 #include "mbedtls/error.h"
38 #include "mbedtls/platform_util.h"
39 #include "mbedtls/constant_time.h"
40
41 #include <string.h>
42
43 /*
44 * If DTLS is in use, then at least one of SHA-1, SHA-256, SHA-512 is
45 * available. Try SHA-256 first, 512 wastes resources since we need to stay
46 * with max 32 bytes of cookie for DTLS 1.0
47 */
48 #if defined(MBEDTLS_SHA256_C)
49 #define COOKIE_MD MBEDTLS_MD_SHA224
50 #define COOKIE_MD_OUTLEN 32
51 #define COOKIE_HMAC_LEN 28
52 #elif defined(MBEDTLS_SHA512_C)
53 #define COOKIE_MD MBEDTLS_MD_SHA384
54 #define COOKIE_MD_OUTLEN 48
55 #define COOKIE_HMAC_LEN 28
56 #elif defined(MBEDTLS_SHA1_C)
57 #define COOKIE_MD MBEDTLS_MD_SHA1
58 #define COOKIE_MD_OUTLEN 20
59 #define COOKIE_HMAC_LEN 20
60 #else
61 #error "DTLS hello verify needs SHA-1 or SHA-2"
62 #endif
63
64 /*
65 * Cookies are formed of a 4-bytes timestamp (or serial number) and
66 * an HMAC of timestemp and client ID.
67 */
68 #define COOKIE_LEN ( 4 + COOKIE_HMAC_LEN )
69
mbedtls_ssl_cookie_init(mbedtls_ssl_cookie_ctx * ctx)70 void mbedtls_ssl_cookie_init( mbedtls_ssl_cookie_ctx *ctx )
71 {
72 mbedtls_md_init( &ctx->hmac_ctx );
73 #if !defined(MBEDTLS_HAVE_TIME)
74 ctx->serial = 0;
75 #endif
76 ctx->timeout = MBEDTLS_SSL_COOKIE_TIMEOUT;
77
78 #if defined(MBEDTLS_THREADING_C)
79 mbedtls_mutex_init( &ctx->mutex );
80 #endif
81 }
82
mbedtls_ssl_cookie_set_timeout(mbedtls_ssl_cookie_ctx * ctx,unsigned long delay)83 void mbedtls_ssl_cookie_set_timeout( mbedtls_ssl_cookie_ctx *ctx, unsigned long delay )
84 {
85 ctx->timeout = delay;
86 }
87
mbedtls_ssl_cookie_free(mbedtls_ssl_cookie_ctx * ctx)88 void mbedtls_ssl_cookie_free( mbedtls_ssl_cookie_ctx *ctx )
89 {
90 mbedtls_md_free( &ctx->hmac_ctx );
91
92 #if defined(MBEDTLS_THREADING_C)
93 mbedtls_mutex_free( &ctx->mutex );
94 #endif
95
96 mbedtls_platform_zeroize( ctx, sizeof( mbedtls_ssl_cookie_ctx ) );
97 }
98
mbedtls_ssl_cookie_setup(mbedtls_ssl_cookie_ctx * ctx,int (* f_rng)(void *,unsigned char *,size_t),void * p_rng)99 int mbedtls_ssl_cookie_setup( mbedtls_ssl_cookie_ctx *ctx,
100 int (*f_rng)(void *, unsigned char *, size_t),
101 void *p_rng )
102 {
103 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
104 unsigned char key[COOKIE_MD_OUTLEN];
105
106 if( ( ret = f_rng( p_rng, key, sizeof( key ) ) ) != 0 )
107 return( ret );
108
109 ret = mbedtls_md_setup( &ctx->hmac_ctx, mbedtls_md_info_from_type( COOKIE_MD ), 1 );
110 if( ret != 0 )
111 return( ret );
112
113 ret = mbedtls_md_hmac_starts( &ctx->hmac_ctx, key, sizeof( key ) );
114 if( ret != 0 )
115 return( ret );
116
117 mbedtls_platform_zeroize( key, sizeof( key ) );
118
119 return( 0 );
120 }
121
122 /*
123 * Generate the HMAC part of a cookie
124 */
ssl_cookie_hmac(mbedtls_md_context_t * hmac_ctx,const unsigned char time[4],unsigned char ** p,unsigned char * end,const unsigned char * cli_id,size_t cli_id_len)125 static int ssl_cookie_hmac( mbedtls_md_context_t *hmac_ctx,
126 const unsigned char time[4],
127 unsigned char **p, unsigned char *end,
128 const unsigned char *cli_id, size_t cli_id_len )
129 {
130 unsigned char hmac_out[COOKIE_MD_OUTLEN];
131
132 MBEDTLS_SSL_CHK_BUF_PTR( *p, end, COOKIE_HMAC_LEN );
133
134 if( mbedtls_md_hmac_reset( hmac_ctx ) != 0 ||
135 mbedtls_md_hmac_update( hmac_ctx, time, 4 ) != 0 ||
136 mbedtls_md_hmac_update( hmac_ctx, cli_id, cli_id_len ) != 0 ||
137 mbedtls_md_hmac_finish( hmac_ctx, hmac_out ) != 0 )
138 {
139 return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
140 }
141
142 memcpy( *p, hmac_out, COOKIE_HMAC_LEN );
143 *p += COOKIE_HMAC_LEN;
144
145 return( 0 );
146 }
147
148 /*
149 * Generate cookie for DTLS ClientHello verification
150 */
mbedtls_ssl_cookie_write(void * p_ctx,unsigned char ** p,unsigned char * end,const unsigned char * cli_id,size_t cli_id_len)151 int mbedtls_ssl_cookie_write( void *p_ctx,
152 unsigned char **p, unsigned char *end,
153 const unsigned char *cli_id, size_t cli_id_len )
154 {
155 int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
156 mbedtls_ssl_cookie_ctx *ctx = (mbedtls_ssl_cookie_ctx *) p_ctx;
157 unsigned long t;
158
159 if( ctx == NULL || cli_id == NULL )
160 return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
161
162 MBEDTLS_SSL_CHK_BUF_PTR( *p, end, COOKIE_LEN );
163
164 #if defined(MBEDTLS_HAVE_TIME)
165 t = (unsigned long) mbedtls_time( NULL );
166 #else
167 t = ctx->serial++;
168 #endif
169
170 MBEDTLS_PUT_UINT32_BE(t, *p, 0);
171 *p += 4;
172
173 #if defined(MBEDTLS_THREADING_C)
174 if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
175 return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_SSL_INTERNAL_ERROR, ret ) );
176 #endif
177
178 ret = ssl_cookie_hmac( &ctx->hmac_ctx, *p - 4,
179 p, end, cli_id, cli_id_len );
180
181 #if defined(MBEDTLS_THREADING_C)
182 if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
183 return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_SSL_INTERNAL_ERROR,
184 MBEDTLS_ERR_THREADING_MUTEX_ERROR ) );
185 #endif
186
187 return( ret );
188 }
189
190 /*
191 * Check a cookie
192 */
mbedtls_ssl_cookie_check(void * p_ctx,const unsigned char * cookie,size_t cookie_len,const unsigned char * cli_id,size_t cli_id_len)193 int mbedtls_ssl_cookie_check( void *p_ctx,
194 const unsigned char *cookie, size_t cookie_len,
195 const unsigned char *cli_id, size_t cli_id_len )
196 {
197 unsigned char ref_hmac[COOKIE_HMAC_LEN];
198 int ret = 0;
199 unsigned char *p = ref_hmac;
200 mbedtls_ssl_cookie_ctx *ctx = (mbedtls_ssl_cookie_ctx *) p_ctx;
201 unsigned long cur_time, cookie_time;
202
203 if( ctx == NULL || cli_id == NULL )
204 return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
205
206 if( cookie_len != COOKIE_LEN )
207 return( -1 );
208
209 #if defined(MBEDTLS_THREADING_C)
210 if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
211 return( MBEDTLS_ERROR_ADD( MBEDTLS_ERR_SSL_INTERNAL_ERROR, ret ) );
212 #endif
213
214 if( ssl_cookie_hmac( &ctx->hmac_ctx, cookie,
215 &p, p + sizeof( ref_hmac ),
216 cli_id, cli_id_len ) != 0 )
217 ret = -1;
218
219 #if defined(MBEDTLS_THREADING_C)
220 if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
221 {
222 ret = MBEDTLS_ERROR_ADD( MBEDTLS_ERR_SSL_INTERNAL_ERROR,
223 MBEDTLS_ERR_THREADING_MUTEX_ERROR );
224 }
225 #endif
226
227 if( ret != 0 )
228 goto exit;
229
230 if( mbedtls_ct_memcmp( cookie + 4, ref_hmac, sizeof( ref_hmac ) ) != 0 )
231 {
232 ret = -1;
233 goto exit;
234 }
235
236 #if defined(MBEDTLS_HAVE_TIME)
237 cur_time = (unsigned long) mbedtls_time( NULL );
238 #else
239 cur_time = ctx->serial;
240 #endif
241
242 cookie_time = ( (unsigned long) cookie[0] << 24 ) |
243 ( (unsigned long) cookie[1] << 16 ) |
244 ( (unsigned long) cookie[2] << 8 ) |
245 ( (unsigned long) cookie[3] );
246
247 if( ctx->timeout != 0 && cur_time - cookie_time > ctx->timeout )
248 {
249 ret = -1;
250 goto exit;
251 }
252
253 exit:
254 mbedtls_platform_zeroize( ref_hmac, sizeof( ref_hmac ) );
255 return( ret );
256 }
257 #endif /* MBEDTLS_SSL_COOKIE_C */
258
