ssl_ticket.c

00001 /*
00002  *  TLS server tickets callbacks implementation
00003  *
00004  *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
00005  *  SPDX-License-Identifier: Apache-2.0
00006  *
00007  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
00008  *  not use this file except in compliance with the License.
00009  *  You may obtain a copy of the License at
00010  *
00011  *  http://www.apache.org/licenses/LICENSE-2.0
00012  *
00013  *  Unless required by applicable law or agreed to in writing, software
00014  *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
00015  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00016  *  See the License for the specific language governing permissions and
00017  *  limitations under the License.
00018  *
00019  *  This file is part of mbed TLS (https://tls.mbed.org)
00020  */
00021 
00022 #if !defined(MBEDTLS_CONFIG_FILE)
00023 #include "mbedtls/config.h"
00024 #else
00025 #include MBEDTLS_CONFIG_FILE
00026 #endif
00027 
00028 #if defined(MBEDTLS_SSL_TICKET_C)
00029 
00030 #include "mbedtls/ssl_ticket.h"
00031 
00032 #if defined(MBEDTLS_PLATFORM_C)
00033 #include "mbedtls/platform.h"
00034 #else
00035 #include <stdlib.h>
00036 #define mbedtls_calloc    calloc
00037 #define mbedtls_free       free
00038 #endif
00039 
00040 #include <string.h>
00041 
00042 /* Implementation that should never be optimized out by the compiler */
00043 static void mbedtls_zeroize( void *v, size_t n ) {
00044     volatile unsigned char *p = v; while( n-- ) *p++ = 0;
00045 }
00046 
00047 /*
00048  * Initialze context
00049  */
00050 void mbedtls_ssl_ticket_init( mbedtls_ssl_ticket_context *ctx )
00051 {
00052     memset( ctx, 0, sizeof( mbedtls_ssl_ticket_context ) );
00053 
00054 #if defined(MBEDTLS_THREADING_C)
00055     mbedtls_mutex_init( &ctx->mutex );
00056 #endif
00057 }
00058 
00059 #define MAX_KEY_BYTES 32    /* 256 bits */
00060 
00061 /*
00062  * Generate/update a key
00063  */
00064 static int ssl_ticket_gen_key( mbedtls_ssl_ticket_context *ctx,
00065                                unsigned char index )
00066 {
00067     int ret;
00068     unsigned char buf[MAX_KEY_BYTES];
00069     mbedtls_ssl_ticket_key *key = ctx->keys  + index;
00070 
00071 #if defined(MBEDTLS_HAVE_TIME)
00072     key->generation_time  = (uint32_t) time( NULL );
00073 #endif
00074 
00075     if( ( ret = ctx->f_rng( ctx->p_rng , key->name , sizeof( key->name  ) ) ) != 0 )
00076         return( ret );
00077 
00078     if( ( ret = ctx->f_rng( ctx->p_rng , buf, sizeof( buf ) ) ) != 0 )
00079         return( ret );
00080 
00081     /* With GCM and CCM, same context can encrypt & decrypt */
00082     ret = mbedtls_cipher_setkey( &key->ctx , buf,
00083                                  mbedtls_cipher_get_key_bitlen( &key->ctx  ),
00084                                  MBEDTLS_ENCRYPT );
00085 
00086     mbedtls_zeroize( buf, sizeof( buf ) );
00087 
00088     return( ret );
00089 }
00090 
00091 /*
00092  * Rotate/generate keys if necessary
00093  */
00094 static int ssl_ticket_update_keys( mbedtls_ssl_ticket_context *ctx )
00095 {
00096 #if !defined(MBEDTLS_HAVE_TIME)
00097     ((void) ctx);
00098 #else
00099     if( ctx->ticket_lifetime  != 0 )
00100     {
00101         uint32_t current_time = (uint32_t) time( NULL );
00102         uint32_t key_time = ctx->keys [ctx->active ].generation_time ;
00103 
00104         if( current_time > key_time &&
00105             current_time - key_time < ctx->ticket_lifetime )
00106         {
00107             return( 0 );
00108         }
00109 
00110         ctx->active  = 1 - ctx->active ;
00111 
00112         return( ssl_ticket_gen_key( ctx, ctx->active  ) );
00113     }
00114     else
00115 #endif /* MBEDTLS_HAVE_TIME */
00116         return( 0 );
00117 }
00118 
00119 /*
00120  * Setup context for actual use
00121  */
00122 int mbedtls_ssl_ticket_setup( mbedtls_ssl_ticket_context *ctx,
00123     int (*f_rng)(void *, unsigned char *, size_t), void *p_rng,
00124     mbedtls_cipher_type_t cipher,
00125     uint32_t lifetime )
00126 {
00127     int ret;
00128     const mbedtls_cipher_info_t *cipher_info;
00129 
00130     ctx->f_rng = f_rng;
00131     ctx->p_rng  = p_rng;
00132 
00133     ctx->ticket_lifetime  = lifetime;
00134 
00135     cipher_info = mbedtls_cipher_info_from_type( cipher);
00136     if( cipher_info == NULL )
00137         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
00138 
00139     if( cipher_info->mode != MBEDTLS_MODE_GCM &&
00140         cipher_info->mode != MBEDTLS_MODE_CCM )
00141     {
00142         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
00143     }
00144 
00145     if( cipher_info->key_bitlen > 8 * MAX_KEY_BYTES )
00146         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
00147 
00148     if( ( ret = mbedtls_cipher_setup( &ctx->keys [0].ctx , cipher_info ) ) != 0 ||
00149         ( ret = mbedtls_cipher_setup( &ctx->keys [1].ctx , cipher_info ) ) != 0 )
00150     {
00151         return( ret );
00152     }
00153 
00154     if( ( ret = ssl_ticket_gen_key( ctx, 0 ) ) != 0 ||
00155         ( ret = ssl_ticket_gen_key( ctx, 1 ) ) != 0 )
00156     {
00157         return( ret );
00158     }
00159 
00160     return( 0 );
00161 }
00162 
00163 /*
00164  * Serialize a session in the following format:
00165  *  0   .   n-1     session structure, n = sizeof(mbedtls_ssl_session)
00166  *  n   .   n+2     peer_cert length = m (0 if no certificate)
00167  *  n+3 .   n+2+m   peer cert ASN.1
00168  */
00169 static int ssl_save_session( const mbedtls_ssl_session *session,
00170                              unsigned char *buf, size_t buf_len,
00171                              size_t *olen )
00172 {
00173     unsigned char *p = buf;
00174     size_t left = buf_len;
00175 #if defined(MBEDTLS_X509_CRT_PARSE_C)
00176     size_t cert_len;
00177 #endif /* MBEDTLS_X509_CRT_PARSE_C */
00178 
00179     if( left < sizeof( mbedtls_ssl_session ) )
00180         return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
00181 
00182     memcpy( p, session, sizeof( mbedtls_ssl_session ) );
00183     p += sizeof( mbedtls_ssl_session );
00184     left -= sizeof( mbedtls_ssl_session );
00185 
00186 #if defined(MBEDTLS_X509_CRT_PARSE_C)
00187     if( session->peer_cert == NULL )
00188         cert_len = 0;
00189     else
00190         cert_len = session->peer_cert->raw.len;
00191 
00192     if( left < 3 + cert_len )
00193         return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
00194 
00195     *p++ = (unsigned char)( cert_len >> 16 & 0xFF );
00196     *p++ = (unsigned char)( cert_len >>  8 & 0xFF );
00197     *p++ = (unsigned char)( cert_len       & 0xFF );
00198 
00199     if( session->peer_cert != NULL )
00200         memcpy( p, session->peer_cert->raw.p, cert_len );
00201 
00202     p += cert_len;
00203 #endif /* MBEDTLS_X509_CRT_PARSE_C */
00204 
00205     *olen = p - buf;
00206 
00207     return( 0 );
00208 }
00209 
00210 /*
00211  * Unserialise session, see ssl_save_session()
00212  */
00213 static int ssl_load_session( mbedtls_ssl_session *session,
00214                              const unsigned char *buf, size_t len )
00215 {
00216     const unsigned char *p = buf;
00217     const unsigned char * const end = buf + len;
00218 #if defined(MBEDTLS_X509_CRT_PARSE_C)
00219     size_t cert_len;
00220 #endif /* MBEDTLS_X509_CRT_PARSE_C */
00221 
00222     if( p + sizeof( mbedtls_ssl_session ) > end )
00223         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
00224 
00225     memcpy( session, p, sizeof( mbedtls_ssl_session ) );
00226     p += sizeof( mbedtls_ssl_session );
00227 
00228 #if defined(MBEDTLS_X509_CRT_PARSE_C)
00229     if( p + 3 > end )
00230         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
00231 
00232     cert_len = ( p[0] << 16 ) | ( p[1] << 8 ) | p[2];
00233     p += 3;
00234 
00235     if( cert_len == 0 )
00236     {
00237         session->peer_cert = NULL;
00238     }
00239     else
00240     {
00241         int ret;
00242 
00243         if( p + cert_len > end )
00244             return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
00245 
00246         session->peer_cert = mbedtls_calloc( 1, sizeof( mbedtls_x509_crt ) );
00247 
00248         if( session->peer_cert == NULL )
00249             return( MBEDTLS_ERR_SSL_ALLOC_FAILED );
00250 
00251         mbedtls_x509_crt_init( session->peer_cert );
00252 
00253         if( ( ret = mbedtls_x509_crt_parse_der( session->peer_cert,
00254                                         p, cert_len ) ) != 0 )
00255         {
00256             mbedtls_x509_crt_free( session->peer_cert );
00257             mbedtls_free( session->peer_cert );
00258             session->peer_cert = NULL;
00259             return( ret );
00260         }
00261 
00262         p += cert_len;
00263     }
00264 #endif /* MBEDTLS_X509_CRT_PARSE_C */
00265 
00266     if( p != end )
00267         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
00268 
00269     return( 0 );
00270 }
00271 
00272 /*
00273  * Create session ticket, with the following structure:
00274  *
00275  *    struct {
00276  *        opaque key_name[4];
00277  *        opaque iv[12];
00278  *        opaque encrypted_state<0..2^16-1>;
00279  *        opaque tag[16];
00280  *    } ticket;
00281  *
00282  * The key_name, iv, and length of encrypted_state are the additional
00283  * authenticated data.
00284  */
00285 int mbedtls_ssl_ticket_write( void *p_ticket,
00286                               const mbedtls_ssl_session *session,
00287                               unsigned char *start,
00288                               const unsigned char *end,
00289                               size_t *tlen,
00290                               uint32_t *ticket_lifetime )
00291 {
00292     int ret;
00293     mbedtls_ssl_ticket_context *ctx = p_ticket;
00294     mbedtls_ssl_ticket_key *key;
00295     unsigned char *key_name = start;
00296     unsigned char *iv = start + 4;
00297     unsigned char *state_len_bytes = iv + 12;
00298     unsigned char *state = state_len_bytes + 2;
00299     unsigned char *tag;
00300     size_t clear_len, ciph_len;
00301 
00302     *tlen = 0;
00303 
00304     if( ctx == NULL || ctx->f_rng == NULL )
00305         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
00306 
00307     /* We need at least 4 bytes for key_name, 12 for IV, 2 for len 16 for tag,
00308      * in addition to session itself, that will be checked when writing it. */
00309     if( end - start < 4 + 12 + 2 + 16 )
00310         return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
00311 
00312 #if defined(MBEDTLS_THREADING_C)
00313     if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
00314         return( ret );
00315 #endif
00316 
00317     if( ( ret = ssl_ticket_update_keys( ctx ) ) != 0 )
00318         goto cleanup;
00319 
00320     key = &ctx->keys [ctx->active ];
00321 
00322     *ticket_lifetime = ctx->ticket_lifetime ;
00323 
00324     memcpy( key_name, key->name , 4 );
00325 
00326     if( ( ret = ctx->f_rng( ctx->p_rng , iv, 12 ) ) != 0 )
00327         goto cleanup;
00328 
00329     /* Dump session state */
00330     if( ( ret = ssl_save_session( session,
00331                                   state, end - state, &clear_len ) ) != 0 ||
00332         (unsigned long) clear_len > 65535 )
00333     {
00334          goto cleanup;
00335     }
00336     state_len_bytes[0] = ( clear_len >> 8 ) & 0xff;
00337     state_len_bytes[1] = ( clear_len      ) & 0xff;
00338 
00339     /* Encrypt and authenticate */
00340     tag = state + clear_len;
00341     if( ( ret = mbedtls_cipher_auth_encrypt( &key->ctx ,
00342                     iv, 12, key_name, 4 + 12 + 2,
00343                     state, clear_len, state, &ciph_len, tag, 16 ) ) != 0 )
00344     {
00345         goto cleanup;
00346     }
00347     if( ciph_len != clear_len )
00348     {
00349         ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
00350         goto cleanup;
00351     }
00352 
00353     *tlen = 4 + 12 + 2 + 16 + ciph_len;
00354 
00355 cleanup:
00356 #if defined(MBEDTLS_THREADING_C)
00357     if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
00358         return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
00359 #endif
00360 
00361     return( ret );
00362 }
00363 
00364 /*
00365  * Select key based on name
00366  */
00367 static mbedtls_ssl_ticket_key *ssl_ticket_select_key(
00368         mbedtls_ssl_ticket_context *ctx,
00369         const unsigned char name[4] )
00370 {
00371     unsigned char i;
00372 
00373     for( i = 0; i < sizeof( ctx->keys  ) / sizeof( *ctx->keys  ); i++ )
00374         if( memcmp( name, ctx->keys [i].name , 4 ) == 0 )
00375             return( &ctx->keys [i] );
00376 
00377     return( NULL );
00378 }
00379 
00380 /*
00381  * Load session ticket (see mbedtls_ssl_ticket_write for structure)
00382  */
00383 int mbedtls_ssl_ticket_parse( void *p_ticket,
00384                               mbedtls_ssl_session *session,
00385                               unsigned char *buf,
00386                               size_t len )
00387 {
00388     int ret;
00389     mbedtls_ssl_ticket_context *ctx = p_ticket;
00390     mbedtls_ssl_ticket_key *key;
00391     unsigned char *key_name = buf;
00392     unsigned char *iv = buf + 4;
00393     unsigned char *enc_len_p = iv + 12;
00394     unsigned char *ticket = enc_len_p + 2;
00395     unsigned char *tag;
00396     size_t enc_len, clear_len;
00397 
00398     if( ctx == NULL || ctx->f_rng == NULL )
00399         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
00400 
00401     /* See mbedtls_ssl_ticket_write() */
00402     if( len < 4 + 12 + 2 + 16 )
00403         return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
00404 
00405 #if defined(MBEDTLS_THREADING_C)
00406     if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
00407         return( ret );
00408 #endif
00409 
00410     if( ( ret = ssl_ticket_update_keys( ctx ) ) != 0 )
00411         goto cleanup;
00412 
00413     enc_len = ( enc_len_p[0] << 8 ) | enc_len_p[1];
00414     tag = ticket + enc_len;
00415 
00416     if( len != 4 + 12 + 2 + enc_len + 16 )
00417     {
00418         ret = MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
00419         goto cleanup;
00420     }
00421 
00422     /* Select key */
00423     if( ( key = ssl_ticket_select_key( ctx, key_name ) ) == NULL )
00424     {
00425         /* We can't know for sure but this is a likely option unless we're
00426          * under attack - this is only informative anyway */
00427         ret = MBEDTLS_ERR_SSL_SESSION_TICKET_EXPIRED;
00428         goto cleanup;
00429     }
00430 
00431     /* Decrypt and authenticate */
00432     if( ( ret = mbedtls_cipher_auth_decrypt( &key->ctx , iv, 12,
00433                     key_name, 4 + 12 + 2, ticket, enc_len,
00434                     ticket, &clear_len, tag, 16 ) ) != 0 )
00435     {
00436         if( ret == MBEDTLS_ERR_CIPHER_AUTH_FAILED )
00437             ret = MBEDTLS_ERR_SSL_INVALID_MAC;
00438 
00439         goto cleanup;
00440     }
00441     if( clear_len != enc_len )
00442     {
00443         ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
00444         goto cleanup;
00445     }
00446 
00447     /* Actually load session */
00448     if( ( ret = ssl_load_session( session, ticket, clear_len ) ) != 0 )
00449         goto cleanup;
00450 
00451 #if defined(MBEDTLS_HAVE_TIME)
00452     {
00453         /* Check for expiration */
00454         time_t current_time = time( NULL );
00455 
00456         if( current_time < session->start ||
00457             (uint32_t)( current_time - session->start ) > ctx->ticket_lifetime  )
00458         {
00459             ret = MBEDTLS_ERR_SSL_SESSION_TICKET_EXPIRED;
00460             goto cleanup;
00461         }
00462     }
00463 #endif
00464 
00465 cleanup:
00466 #if defined(MBEDTLS_THREADING_C)
00467     if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
00468         return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
00469 #endif
00470 
00471     return( ret );
00472 }
00473 
00474 /*
00475  * Free context
00476  */
00477 void mbedtls_ssl_ticket_free( mbedtls_ssl_ticket_context *ctx )
00478 {
00479     mbedtls_cipher_free( &ctx->keys [0].ctx  );
00480     mbedtls_cipher_free( &ctx->keys [1].ctx  );
00481 
00482 #if defined(MBEDTLS_THREADING_C)
00483     mbedtls_mutex_free( &ctx->mutex );
00484 #endif
00485 
00486     mbedtls_zeroize( ctx, sizeof( mbedtls_ssl_ticket_context ) );
00487 }
00488 
00489 #endif /* MBEDTLS_SSL_TICKET_C */