ssl_internal.h

00001 /**
00002  * \file ssl_ticket.h
00003  *
00004  * \brief Internal functions shared by the SSL modules
00005  *
00006  *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
00007  *  SPDX-License-Identifier: Apache-2.0
00008  *
00009  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
00010  *  not use this file except in compliance with the License.
00011  *  You may obtain a copy of the License at
00012  *
00013  *  http://www.apache.org/licenses/LICENSE-2.0
00014  *
00015  *  Unless required by applicable law or agreed to in writing, software
00016  *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
00017  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00018  *  See the License for the specific language governing permissions and
00019  *  limitations under the License.
00020  *
00021  *  This file is part of mbed TLS (https://tls.mbed.org)
00022  */
00023 #ifndef MBEDTLS_SSL_INTERNAL_H
00024 #define MBEDTLS_SSL_INTERNAL_H
00025 
00026 #include "ssl.h"
00027 
00028 #if defined(MBEDTLS_MD5_C)
00029 #include "md5.h"
00030 #endif
00031 
00032 #if defined(MBEDTLS_SHA1_C)
00033 #include "sha1.h"
00034 #endif
00035 
00036 #if defined(MBEDTLS_SHA256_C)
00037 #include "sha256.h"
00038 #endif
00039 
00040 #if defined(MBEDTLS_SHA512_C)
00041 #include "sha512.h"
00042 #endif
00043 
00044 #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
00045 #include "ecjpake.h"
00046 #endif
00047 
00048 #if ( defined(__ARMCC_VERSION) || defined(_MSC_VER) ) && \
00049     !defined(inline) && !defined(__cplusplus)
00050 #define inline __inline
00051 #endif
00052 
00053 /* Determine minimum supported version */
00054 #define MBEDTLS_SSL_MIN_MAJOR_VERSION           MBEDTLS_SSL_MAJOR_VERSION_3
00055 
00056 #if defined(MBEDTLS_SSL_PROTO_SSL3)
00057 #define MBEDTLS_SSL_MIN_MINOR_VERSION           MBEDTLS_SSL_MINOR_VERSION_0
00058 #else
00059 #if defined(MBEDTLS_SSL_PROTO_TLS1)
00060 #define MBEDTLS_SSL_MIN_MINOR_VERSION           MBEDTLS_SSL_MINOR_VERSION_1
00061 #else
00062 #if defined(MBEDTLS_SSL_PROTO_TLS1_1)
00063 #define MBEDTLS_SSL_MIN_MINOR_VERSION           MBEDTLS_SSL_MINOR_VERSION_2
00064 #else
00065 #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
00066 #define MBEDTLS_SSL_MIN_MINOR_VERSION           MBEDTLS_SSL_MINOR_VERSION_3
00067 #endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
00068 #endif /* MBEDTLS_SSL_PROTO_TLS1_1 */
00069 #endif /* MBEDTLS_SSL_PROTO_TLS1   */
00070 #endif /* MBEDTLS_SSL_PROTO_SSL3   */
00071 
00072 /* Determine maximum supported version */
00073 #define MBEDTLS_SSL_MAX_MAJOR_VERSION           MBEDTLS_SSL_MAJOR_VERSION_3
00074 
00075 #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
00076 #define MBEDTLS_SSL_MAX_MINOR_VERSION           MBEDTLS_SSL_MINOR_VERSION_3
00077 #else
00078 #if defined(MBEDTLS_SSL_PROTO_TLS1_1)
00079 #define MBEDTLS_SSL_MAX_MINOR_VERSION           MBEDTLS_SSL_MINOR_VERSION_2
00080 #else
00081 #if defined(MBEDTLS_SSL_PROTO_TLS1)
00082 #define MBEDTLS_SSL_MAX_MINOR_VERSION           MBEDTLS_SSL_MINOR_VERSION_1
00083 #else
00084 #if defined(MBEDTLS_SSL_PROTO_SSL3)
00085 #define MBEDTLS_SSL_MAX_MINOR_VERSION           MBEDTLS_SSL_MINOR_VERSION_0
00086 #endif /* MBEDTLS_SSL_PROTO_SSL3   */
00087 #endif /* MBEDTLS_SSL_PROTO_TLS1   */
00088 #endif /* MBEDTLS_SSL_PROTO_TLS1_1 */
00089 #endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
00090 
00091 #define MBEDTLS_SSL_INITIAL_HANDSHAKE           0
00092 #define MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS   1   /* In progress */
00093 #define MBEDTLS_SSL_RENEGOTIATION_DONE          2   /* Done or aborted */
00094 #define MBEDTLS_SSL_RENEGOTIATION_PENDING       3   /* Requested (server only) */
00095 
00096 /*
00097  * DTLS retransmission states, see RFC 6347 4.2.4
00098  *
00099  * The SENDING state is merged in PREPARING for initial sends,
00100  * but is distinct for resends.
00101  *
00102  * Note: initial state is wrong for server, but is not used anyway.
00103  */
00104 #define MBEDTLS_SSL_RETRANS_PREPARING       0
00105 #define MBEDTLS_SSL_RETRANS_SENDING         1
00106 #define MBEDTLS_SSL_RETRANS_WAITING         2
00107 #define MBEDTLS_SSL_RETRANS_FINISHED        3
00108 
00109 /*
00110  * Allow extra bytes for record, authentication and encryption overhead:
00111  * counter (8) + header (5) + IV(16) + MAC (16-48) + padding (0-256)
00112  * and allow for a maximum of 1024 of compression expansion if
00113  * enabled.
00114  */
00115 #if defined(MBEDTLS_ZLIB_SUPPORT)
00116 #define MBEDTLS_SSL_COMPRESSION_ADD          1024
00117 #else
00118 #define MBEDTLS_SSL_COMPRESSION_ADD             0
00119 #endif
00120 
00121 #if defined(MBEDTLS_ARC4_C) || defined(MBEDTLS_CIPHER_MODE_CBC)
00122 /* Ciphersuites using HMAC */
00123 #if defined(MBEDTLS_SHA512_C)
00124 #define MBEDTLS_SSL_MAC_ADD                 48  /* SHA-384 used for HMAC */
00125 #elif defined(MBEDTLS_SHA256_C)
00126 #define MBEDTLS_SSL_MAC_ADD                 32  /* SHA-256 used for HMAC */
00127 #else
00128 #define MBEDTLS_SSL_MAC_ADD                 20  /* SHA-1   used for HMAC */
00129 #endif
00130 #else
00131 /* AEAD ciphersuites: GCM and CCM use a 128 bits tag */
00132 #define MBEDTLS_SSL_MAC_ADD                 16
00133 #endif
00134 
00135 #if defined(MBEDTLS_CIPHER_MODE_CBC)
00136 #define MBEDTLS_SSL_PADDING_ADD            256
00137 #else
00138 #define MBEDTLS_SSL_PADDING_ADD              0
00139 #endif
00140 
00141 #define MBEDTLS_SSL_BUFFER_LEN  ( MBEDTLS_SSL_MAX_CONTENT_LEN               \
00142                         + MBEDTLS_SSL_COMPRESSION_ADD               \
00143                         + 29 /* counter + header + IV */    \
00144                         + MBEDTLS_SSL_MAC_ADD                       \
00145                         + MBEDTLS_SSL_PADDING_ADD                   \
00146                         )
00147 
00148 /*
00149  * TLS extension flags (for extensions with outgoing ServerHello content
00150  * that need it (e.g. for RENEGOTIATION_INFO the server already knows because
00151  * of state of the renegotiation flag, so no indicator is required)
00152  */
00153 #define MBEDTLS_TLS_EXT_SUPPORTED_POINT_FORMATS_PRESENT (1 << 0)
00154 #define MBEDTLS_TLS_EXT_ECJPAKE_KKPP_OK                 (1 << 1)
00155 
00156 #ifdef __cplusplus
00157 extern "C" {
00158 #endif
00159 
00160 /*
00161  * This structure contains the parameters only needed during handshake.
00162  */
00163 struct mbedtls_ssl_handshake_params
00164 {
00165     /*
00166      * Handshake specific crypto variables
00167      */
00168     int sig_alg;                        /*!<  Hash algorithm for signature   */
00169     int verify_sig_alg;                 /*!<  Signature algorithm for verify */
00170 #if defined(MBEDTLS_DHM_C)
00171     mbedtls_dhm_context dhm_ctx;                /*!<  DHM key exchange        */
00172 #endif
00173 #if defined(MBEDTLS_ECDH_C)
00174     mbedtls_ecdh_context ecdh_ctx;              /*!<  ECDH key exchange       */
00175 #endif
00176 #if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
00177     mbedtls_ecjpake_context ecjpake_ctx;        /*!< EC J-PAKE key exchange */
00178 #if defined(MBEDTLS_SSL_CLI_C)
00179     unsigned char *ecjpake_cache;               /*!< Cache for ClientHello ext */
00180     size_t ecjpake_cache_len;                   /*!< Length of cached data */
00181 #endif
00182 #endif
00183 #if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
00184     defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
00185     const mbedtls_ecp_curve_info **curves;      /*!<  Supported elliptic curves */
00186 #endif
00187 #if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
00188     unsigned char *psk;                 /*!<  PSK from the callback         */
00189     size_t psk_len;                     /*!<  Length of PSK from callback   */
00190 #endif
00191 #if defined(MBEDTLS_X509_CRT_PARSE_C)
00192     mbedtls_ssl_key_cert *key_cert;     /*!< chosen key/cert pair (server)  */
00193 #if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
00194     int sni_authmode;                   /*!< authmode from SNI callback     */
00195     mbedtls_ssl_key_cert *sni_key_cert; /*!< key/cert list from SNI         */
00196     mbedtls_x509_crt *sni_ca_chain;     /*!< trusted CAs from SNI callback  */
00197     mbedtls_x509_crl *sni_ca_crl;       /*!< trusted CAs CRLs from SNI      */
00198 #endif
00199 #endif /* MBEDTLS_X509_CRT_PARSE_C */
00200 #if defined(MBEDTLS_SSL_PROTO_DTLS)
00201     unsigned int out_msg_seq;           /*!<  Outgoing handshake sequence number */
00202     unsigned int in_msg_seq;            /*!<  Incoming handshake sequence number */
00203 
00204     unsigned char *verify_cookie;       /*!<  Cli: HelloVerifyRequest cookie
00205                                               Srv: unused                    */
00206     unsigned char verify_cookie_len;    /*!<  Cli: cookie length
00207                                               Srv: flag for sending a cookie */
00208 
00209     unsigned char *hs_msg;              /*!<  Reassembled handshake message  */
00210 
00211     uint32_t retransmit_timeout;        /*!<  Current value of timeout       */
00212     unsigned char retransmit_state;     /*!<  Retransmission state           */
00213     mbedtls_ssl_flight_item *flight;            /*!<  Current outgoing flight        */
00214     mbedtls_ssl_flight_item *cur_msg;           /*!<  Current message in flight      */
00215     unsigned int in_flight_start_seq;   /*!<  Minimum message sequence in the
00216                                               flight being received          */
00217     mbedtls_ssl_transform *alt_transform_out;   /*!<  Alternative transform for
00218                                               resending messages             */
00219     unsigned char alt_out_ctr[8];       /*!<  Alternative record epoch/counter
00220                                               for resending messages         */
00221 #endif
00222 
00223     /*
00224      * Checksum contexts
00225      */
00226 #if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1) || \
00227     defined(MBEDTLS_SSL_PROTO_TLS1_1)
00228        mbedtls_md5_context fin_md5;
00229       mbedtls_sha1_context fin_sha1;
00230 #endif
00231 #if defined(MBEDTLS_SSL_PROTO_TLS1_2)
00232 #if defined(MBEDTLS_SHA256_C)
00233     mbedtls_sha256_context fin_sha256;
00234 #endif
00235 #if defined(MBEDTLS_SHA512_C)
00236     mbedtls_sha512_context fin_sha512;
00237 #endif
00238 #endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
00239 
00240     void (*update_checksum)(mbedtls_ssl_context *, const unsigned char *, size_t);
00241     void (*calc_verify)(mbedtls_ssl_context *, unsigned char *);
00242     void (*calc_finished)(mbedtls_ssl_context *, unsigned char *, int);
00243     int  (*tls_prf)(const unsigned char *, size_t, const char *,
00244                     const unsigned char *, size_t,
00245                     unsigned char *, size_t);
00246 
00247     size_t pmslen;                      /*!<  premaster length        */
00248 
00249     unsigned char randbytes[64];        /*!<  random bytes            */
00250     unsigned char premaster[MBEDTLS_PREMASTER_SIZE];
00251                                         /*!<  premaster secret        */
00252 
00253     int resume;                         /*!<  session resume indicator*/
00254     int max_major_ver;                  /*!< max. major version client*/
00255     int max_minor_ver;                  /*!< max. minor version client*/
00256     int cli_exts;                       /*!< client extension presence*/
00257 
00258 #if defined(MBEDTLS_SSL_SESSION_TICKETS)
00259     int new_session_ticket;             /*!< use NewSessionTicket?    */
00260 #endif /* MBEDTLS_SSL_SESSION_TICKETS */
00261 #if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
00262     int extended_ms;                    /*!< use Extended Master Secret? */
00263 #endif
00264 };
00265 
00266 /*
00267  * This structure contains a full set of runtime transform parameters
00268  * either in negotiation or active.
00269  */
00270 struct mbedtls_ssl_transform
00271 {
00272     /*
00273      * Session specific crypto layer
00274      */
00275     const mbedtls_ssl_ciphersuite_t *ciphersuite_info;
00276                                         /*!<  Chosen cipersuite_info  */
00277     unsigned int keylen;                /*!<  symmetric key length (bytes)  */
00278     size_t minlen;                      /*!<  min. ciphertext length  */
00279     size_t ivlen;                       /*!<  IV length               */
00280     size_t fixed_ivlen;                 /*!<  Fixed part of IV (AEAD) */
00281     size_t maclen;                      /*!<  MAC length              */
00282 
00283     unsigned char iv_enc[16];           /*!<  IV (encryption)         */
00284     unsigned char iv_dec[16];           /*!<  IV (decryption)         */
00285 
00286 #if defined(MBEDTLS_SSL_PROTO_SSL3)
00287     /* Needed only for SSL v3.0 secret */
00288     unsigned char mac_enc[20];          /*!<  SSL v3.0 secret (enc)   */
00289     unsigned char mac_dec[20];          /*!<  SSL v3.0 secret (dec)   */
00290 #endif /* MBEDTLS_SSL_PROTO_SSL3 */
00291 
00292     mbedtls_md_context_t md_ctx_enc;            /*!<  MAC (encryption)        */
00293     mbedtls_md_context_t md_ctx_dec;            /*!<  MAC (decryption)        */
00294 
00295     mbedtls_cipher_context_t cipher_ctx_enc;    /*!<  encryption context      */
00296     mbedtls_cipher_context_t cipher_ctx_dec;    /*!<  decryption context      */
00297 
00298     /*
00299      * Session specific compression layer
00300      */
00301 #if defined(MBEDTLS_ZLIB_SUPPORT)
00302     z_stream ctx_deflate;               /*!<  compression context     */
00303     z_stream ctx_inflate;               /*!<  decompression context   */
00304 #endif
00305 };
00306 
00307 #if defined(MBEDTLS_X509_CRT_PARSE_C)
00308 /*
00309  * List of certificate + private key pairs
00310  */
00311 struct mbedtls_ssl_key_cert
00312 {
00313     mbedtls_x509_crt *cert;                 /*!< cert                       */
00314     mbedtls_pk_context *key;                /*!< private key                */
00315     mbedtls_ssl_key_cert *next;             /*!< next key/cert pair         */
00316 };
00317 #endif /* MBEDTLS_X509_CRT_PARSE_C */
00318 
00319 #if defined(MBEDTLS_SSL_PROTO_DTLS)
00320 /*
00321  * List of handshake messages kept around for resending
00322  */
00323 struct mbedtls_ssl_flight_item
00324 {
00325     unsigned char *p;       /*!< message, including handshake headers   */
00326     size_t len;             /*!< length of p                            */
00327     unsigned char type;     /*!< type of the message: handshake or CCS  */
00328     mbedtls_ssl_flight_item *next;  /*!< next handshake message(s)              */
00329 };
00330 #endif /* MBEDTLS_SSL_PROTO_DTLS */
00331 
00332 
00333 /**
00334  * \brief           Free referenced items in an SSL transform context and clear
00335  *                  memory
00336  *
00337  * \param transform SSL transform context
00338  */
00339 void mbedtls_ssl_transform_free( mbedtls_ssl_transform *transform );
00340 
00341 /**
00342  * \brief           Free referenced items in an SSL handshake context and clear
00343  *                  memory
00344  *
00345  * \param handshake SSL handshake context
00346  */
00347 void mbedtls_ssl_handshake_free( mbedtls_ssl_handshake_params *handshake );
00348 
00349 int mbedtls_ssl_handshake_client_step( mbedtls_ssl_context *ssl );
00350 int mbedtls_ssl_handshake_server_step( mbedtls_ssl_context *ssl );
00351 void mbedtls_ssl_handshake_wrapup( mbedtls_ssl_context *ssl );
00352 
00353 int mbedtls_ssl_send_fatal_handshake_failure( mbedtls_ssl_context *ssl );
00354 
00355 void mbedtls_ssl_reset_checksum( mbedtls_ssl_context *ssl );
00356 int mbedtls_ssl_derive_keys( mbedtls_ssl_context *ssl );
00357 
00358 int mbedtls_ssl_read_record( mbedtls_ssl_context *ssl );
00359 int mbedtls_ssl_fetch_input( mbedtls_ssl_context *ssl, size_t nb_want );
00360 
00361 int mbedtls_ssl_write_record( mbedtls_ssl_context *ssl );
00362 int mbedtls_ssl_flush_output( mbedtls_ssl_context *ssl );
00363 
00364 int mbedtls_ssl_parse_certificate( mbedtls_ssl_context *ssl );
00365 int mbedtls_ssl_write_certificate( mbedtls_ssl_context *ssl );
00366 
00367 int mbedtls_ssl_parse_change_cipher_spec( mbedtls_ssl_context *ssl );
00368 int mbedtls_ssl_write_change_cipher_spec( mbedtls_ssl_context *ssl );
00369 
00370 int mbedtls_ssl_parse_finished( mbedtls_ssl_context *ssl );
00371 int mbedtls_ssl_write_finished( mbedtls_ssl_context *ssl );
00372 
00373 void mbedtls_ssl_optimize_checksum( mbedtls_ssl_context *ssl,
00374                             const mbedtls_ssl_ciphersuite_t *ciphersuite_info );
00375 
00376 #if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
00377 int mbedtls_ssl_psk_derive_premaster( mbedtls_ssl_context *ssl, mbedtls_key_exchange_type_t key_ex );
00378 #endif
00379 
00380 #if defined(MBEDTLS_PK_C)
00381 unsigned char mbedtls_ssl_sig_from_pk( mbedtls_pk_context *pk );
00382 mbedtls_pk_type_t mbedtls_ssl_pk_alg_from_sig( unsigned char sig );
00383 #endif
00384 
00385 mbedtls_md_type_t mbedtls_ssl_md_alg_from_hash( unsigned char hash );
00386 unsigned char mbedtls_ssl_hash_from_md_alg( int md );
00387 
00388 #if defined(MBEDTLS_ECP_C)
00389 int mbedtls_ssl_check_curve( const mbedtls_ssl_context *ssl, mbedtls_ecp_group_id grp_id );
00390 #endif
00391 
00392 #if defined(MBEDTLS_KEY_EXCHANGE__WITH_CERT__ENABLED)
00393 int mbedtls_ssl_check_sig_hash( const mbedtls_ssl_context *ssl,
00394                                 mbedtls_md_type_t md );
00395 #endif
00396 
00397 #if defined(MBEDTLS_X509_CRT_PARSE_C)
00398 static inline mbedtls_pk_context *mbedtls_ssl_own_key( mbedtls_ssl_context *ssl )
00399 {
00400     mbedtls_ssl_key_cert *key_cert;
00401 
00402     if( ssl->handshake != NULL && ssl->handshake->key_cert != NULL )
00403         key_cert = ssl->handshake->key_cert;
00404     else
00405         key_cert = ssl->conf->key_cert;
00406 
00407     return( key_cert == NULL ? NULL : key_cert->key );
00408 }
00409 
00410 static inline mbedtls_x509_crt *mbedtls_ssl_own_cert( mbedtls_ssl_context *ssl )
00411 {
00412     mbedtls_ssl_key_cert *key_cert;
00413 
00414     if( ssl->handshake != NULL && ssl->handshake->key_cert != NULL )
00415         key_cert = ssl->handshake->key_cert;
00416     else
00417         key_cert = ssl->conf->key_cert;
00418 
00419     return( key_cert == NULL ? NULL : key_cert->cert );
00420 }
00421 
00422 /*
00423  * Check usage of a certificate wrt extensions:
00424  * keyUsage, extendedKeyUsage (later), and nSCertType (later).
00425  *
00426  * Warning: cert_endpoint is the endpoint of the cert (ie, of our peer when we
00427  * check a cert we received from them)!
00428  *
00429  * Return 0 if everything is OK, -1 if not.
00430  */
00431 int mbedtls_ssl_check_cert_usage( const mbedtls_x509_crt *cert,
00432                           const mbedtls_ssl_ciphersuite_t *ciphersuite,
00433                           int cert_endpoint,
00434                           uint32_t *flags );
00435 #endif /* MBEDTLS_X509_CRT_PARSE_C */
00436 
00437 void mbedtls_ssl_write_version( int major, int minor, int transport,
00438                         unsigned char ver[2] );
00439 void mbedtls_ssl_read_version( int *major, int *minor, int transport,
00440                        const unsigned char ver[2] );
00441 
00442 static inline size_t mbedtls_ssl_hdr_len( const mbedtls_ssl_context *ssl )
00443 {
00444 #if defined(MBEDTLS_SSL_PROTO_DTLS)
00445     if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
00446         return( 13 );
00447 #else
00448     ((void) ssl);
00449 #endif
00450     return( 5 );
00451 }
00452 
00453 static inline size_t mbedtls_ssl_hs_hdr_len( const mbedtls_ssl_context *ssl )
00454 {
00455 #if defined(MBEDTLS_SSL_PROTO_DTLS)
00456     if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
00457         return( 12 );
00458 #else
00459     ((void) ssl);
00460 #endif
00461     return( 4 );
00462 }
00463 
00464 #if defined(MBEDTLS_SSL_PROTO_DTLS)
00465 void mbedtls_ssl_send_flight_completed( mbedtls_ssl_context *ssl );
00466 void mbedtls_ssl_recv_flight_completed( mbedtls_ssl_context *ssl );
00467 int mbedtls_ssl_resend( mbedtls_ssl_context *ssl );
00468 #endif
00469 
00470 /* Visible for testing purposes only */
00471 #if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
00472 int mbedtls_ssl_dtls_replay_check( mbedtls_ssl_context *ssl );
00473 void mbedtls_ssl_dtls_replay_update( mbedtls_ssl_context *ssl );
00474 #endif
00475 
00476 /* constant-time buffer comparison */
00477 static inline int mbedtls_ssl_safer_memcmp( const void *a, const void *b, size_t n )
00478 {
00479     size_t i;
00480     const unsigned char *A = (const unsigned char *) a;
00481     const unsigned char *B = (const unsigned char *) b;
00482     unsigned char diff = 0;
00483 
00484     for( i = 0; i < n; i++ )
00485         diff |= A[i] ^ B[i];
00486 
00487     return( diff );
00488 }
00489 
00490 #ifdef __cplusplus
00491 }
00492 #endif
00493 
00494 #endif /* ssl_internal.h */