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| 123 | .rm #[ #] #H #V #F C |
| 124 | .\" ======================================================================== |
| 125 | .\" |
| 126 | .IX Title "SSL_CTX_set_options 3" |
| 127 | .TH SSL_CTX_set_options 3 "2011-02-08" "1.0.0d" "OpenSSL" |
| 128 | .\" For nroff, turn off justification. Always turn off hyphenation; it makes |
| 129 | .\" way too many mistakes in technical documents. |
| 130 | .if n .ad l |
| 131 | .nh |
| 132 | .SH "NAME" |
| 133 | SSL_CTX_set_options, SSL_set_options, SSL_CTX_clear_options, SSL_clear_options, SSL_CTX_get_options, SSL_get_options, SSL_get_secure_renegotiation_support \- manipulate SSL options |
| 134 | .SH "SYNOPSIS" |
| 135 | .IX Header "SYNOPSIS" |
| 136 | .Vb 1 |
| 137 | \& #include <openssl/ssl.h> |
| 138 | \& |
| 139 | \& long SSL_CTX_set_options(SSL_CTX *ctx, long options); |
| 140 | \& long SSL_set_options(SSL *ssl, long options); |
| 141 | \& |
| 142 | \& long SSL_CTX_clear_options(SSL_CTX *ctx, long options); |
| 143 | \& long SSL_clear_options(SSL *ssl, long options); |
| 144 | \& |
| 145 | \& long SSL_CTX_get_options(SSL_CTX *ctx); |
| 146 | \& long SSL_get_options(SSL *ssl); |
| 147 | \& |
| 148 | \& long SSL_get_secure_renegotiation_support(SSL *ssl); |
| 149 | .Ve |
| 150 | .SH "DESCRIPTION" |
| 151 | .IX Header "DESCRIPTION" |
| 152 | Note: all these functions are implemented using macros. |
| 153 | .PP |
| 154 | \&\fISSL_CTX_set_options()\fR adds the options set via bitmask in \fBoptions\fR to \fBctx\fR. |
| 155 | Options already set before are not cleared! |
| 156 | .PP |
| 157 | \&\fISSL_set_options()\fR adds the options set via bitmask in \fBoptions\fR to \fBssl\fR. |
| 158 | Options already set before are not cleared! |
| 159 | .PP |
| 160 | \&\fISSL_CTX_clear_options()\fR clears the options set via bitmask in \fBoptions\fR |
| 161 | to \fBctx\fR. |
| 162 | .PP |
| 163 | \&\fISSL_clear_options()\fR clears the options set via bitmask in \fBoptions\fR to \fBssl\fR. |
| 164 | .PP |
| 165 | \&\fISSL_CTX_get_options()\fR returns the options set for \fBctx\fR. |
| 166 | .PP |
| 167 | \&\fISSL_get_options()\fR returns the options set for \fBssl\fR. |
| 168 | .PP |
| 169 | \&\fISSL_get_secure_renegotiation_support()\fR indicates whether the peer supports |
| 170 | secure renegotiation. |
| 171 | .SH "NOTES" |
| 172 | .IX Header "NOTES" |
| 173 | The behaviour of the \s-1SSL\s0 library can be changed by setting several options. |
| 174 | The options are coded as bitmasks and can be combined by a logical \fBor\fR |
| 175 | operation (|). |
| 176 | .PP |
| 177 | \&\fISSL_CTX_set_options()\fR and \fISSL_set_options()\fR affect the (external) |
| 178 | protocol behaviour of the \s-1SSL\s0 library. The (internal) behaviour of |
| 179 | the \s-1API\s0 can be changed by using the similar |
| 180 | \&\fISSL_CTX_set_mode\fR\|(3) and \fISSL_set_mode()\fR functions. |
| 181 | .PP |
| 182 | During a handshake, the option settings of the \s-1SSL\s0 object are used. When |
| 183 | a new \s-1SSL\s0 object is created from a context using \fISSL_new()\fR, the current |
| 184 | option setting is copied. Changes to \fBctx\fR do not affect already created |
| 185 | \&\s-1SSL\s0 objects. \fISSL_clear()\fR does not affect the settings. |
| 186 | .PP |
| 187 | The following \fBbug workaround\fR options are available: |
| 188 | .IP "\s-1SSL_OP_MICROSOFT_SESS_ID_BUG\s0" 4 |
| 189 | .IX Item "SSL_OP_MICROSOFT_SESS_ID_BUG" |
| 190 | www.microsoft.com \- when talking SSLv2, if session-id reuse is |
| 191 | performed, the session-id passed back in the server-finished message |
| 192 | is different from the one decided upon. |
| 193 | .IP "\s-1SSL_OP_NETSCAPE_CHALLENGE_BUG\s0" 4 |
| 194 | .IX Item "SSL_OP_NETSCAPE_CHALLENGE_BUG" |
| 195 | Netscape\-Commerce/1.12, when talking SSLv2, accepts a 32 byte |
| 196 | challenge but then appears to only use 16 bytes when generating the |
| 197 | encryption keys. Using 16 bytes is ok but it should be ok to use 32. |
| 198 | According to the SSLv3 spec, one should use 32 bytes for the challenge |
| 199 | when operating in SSLv2/v3 compatibility mode, but as mentioned above, |
| 200 | this breaks this server so 16 bytes is the way to go. |
| 201 | .IP "\s-1SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG\s0" 4 |
| 202 | .IX Item "SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG" |
| 203 | As of OpenSSL 0.9.8q and 1.0.0c, this option has no effect. |
| 204 | .IP "\s-1SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG\s0" 4 |
| 205 | .IX Item "SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG" |
| 206 | \&... |
| 207 | .IP "\s-1SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER\s0" 4 |
| 208 | .IX Item "SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER" |
| 209 | \&... |
| 210 | .IP "\s-1SSL_OP_MSIE_SSLV2_RSA_PADDING\s0" 4 |
| 211 | .IX Item "SSL_OP_MSIE_SSLV2_RSA_PADDING" |
| 212 | As of OpenSSL 0.9.7h and 0.9.8a, this option has no effect. |
| 213 | .IP "\s-1SSL_OP_SSLEAY_080_CLIENT_DH_BUG\s0" 4 |
| 214 | .IX Item "SSL_OP_SSLEAY_080_CLIENT_DH_BUG" |
| 215 | \&... |
| 216 | .IP "\s-1SSL_OP_TLS_D5_BUG\s0" 4 |
| 217 | .IX Item "SSL_OP_TLS_D5_BUG" |
| 218 | \&... |
| 219 | .IP "\s-1SSL_OP_TLS_BLOCK_PADDING_BUG\s0" 4 |
| 220 | .IX Item "SSL_OP_TLS_BLOCK_PADDING_BUG" |
| 221 | \&... |
| 222 | .IP "\s-1SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS\s0" 4 |
| 223 | .IX Item "SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS" |
| 224 | Disables a countermeasure against a \s-1SSL\s0 3.0/TLS 1.0 protocol |
| 225 | vulnerability affecting \s-1CBC\s0 ciphers, which cannot be handled by some |
| 226 | broken \s-1SSL\s0 implementations. This option has no effect for connections |
| 227 | using other ciphers. |
| 228 | .IP "\s-1SSL_OP_ALL\s0" 4 |
| 229 | .IX Item "SSL_OP_ALL" |
| 230 | All of the above bug workarounds. |
| 231 | .PP |
| 232 | It is usually safe to use \fB\s-1SSL_OP_ALL\s0\fR to enable the bug workaround |
| 233 | options if compatibility with somewhat broken implementations is |
| 234 | desired. |
| 235 | .PP |
| 236 | The following \fBmodifying\fR options are available: |
| 237 | .IP "\s-1SSL_OP_TLS_ROLLBACK_BUG\s0" 4 |
| 238 | .IX Item "SSL_OP_TLS_ROLLBACK_BUG" |
| 239 | Disable version rollback attack detection. |
| 240 | .Sp |
| 241 | During the client key exchange, the client must send the same information |
| 242 | about acceptable \s-1SSL/TLS\s0 protocol levels as during the first hello. Some |
| 243 | clients violate this rule by adapting to the server's answer. (Example: |
| 244 | the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server |
| 245 | only understands up to SSLv3. In this case the client must still use the |
| 246 | same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect |
| 247 | to the server's answer and violate the version rollback protection.) |
| 248 | .IP "\s-1SSL_OP_SINGLE_DH_USE\s0" 4 |
| 249 | .IX Item "SSL_OP_SINGLE_DH_USE" |
| 250 | Always create a new key when using temporary/ephemeral \s-1DH\s0 parameters |
| 251 | (see \fISSL_CTX_set_tmp_dh_callback\fR\|(3)). |
| 252 | This option must be used to prevent small subgroup attacks, when |
| 253 | the \s-1DH\s0 parameters were not generated using \*(L"strong\*(R" primes |
| 254 | (e.g. when using DSA-parameters, see \fIdhparam\fR\|(1)). |
| 255 | If \*(L"strong\*(R" primes were used, it is not strictly necessary to generate |
| 256 | a new \s-1DH\s0 key during each handshake but it is also recommended. |
| 257 | \&\fB\s-1SSL_OP_SINGLE_DH_USE\s0\fR should therefore be enabled whenever |
| 258 | temporary/ephemeral \s-1DH\s0 parameters are used. |
| 259 | .IP "\s-1SSL_OP_EPHEMERAL_RSA\s0" 4 |
| 260 | .IX Item "SSL_OP_EPHEMERAL_RSA" |
| 261 | Always use ephemeral (temporary) \s-1RSA\s0 key when doing \s-1RSA\s0 operations |
| 262 | (see \fISSL_CTX_set_tmp_rsa_callback\fR\|(3)). |
| 263 | According to the specifications this is only done, when a \s-1RSA\s0 key |
| 264 | can only be used for signature operations (namely under export ciphers |
| 265 | with restricted \s-1RSA\s0 keylength). By setting this option, ephemeral |
| 266 | \&\s-1RSA\s0 keys are always used. This option breaks compatibility with the |
| 267 | \&\s-1SSL/TLS\s0 specifications and may lead to interoperability problems with |
| 268 | clients and should therefore never be used. Ciphers with \s-1EDH\s0 (ephemeral |
| 269 | Diffie-Hellman) key exchange should be used instead. |
| 270 | .IP "\s-1SSL_OP_CIPHER_SERVER_PREFERENCE\s0" 4 |
| 271 | .IX Item "SSL_OP_CIPHER_SERVER_PREFERENCE" |
| 272 | When choosing a cipher, use the server's preferences instead of the client |
| 273 | preferences. When not set, the \s-1SSL\s0 server will always follow the clients |
| 274 | preferences. When set, the SSLv3/TLSv1 server will choose following its |
| 275 | own preferences. Because of the different protocol, for SSLv2 the server |
| 276 | will send its list of preferences to the client and the client chooses. |
| 277 | .IP "\s-1SSL_OP_PKCS1_CHECK_1\s0" 4 |
| 278 | .IX Item "SSL_OP_PKCS1_CHECK_1" |
| 279 | \&... |
| 280 | .IP "\s-1SSL_OP_PKCS1_CHECK_2\s0" 4 |
| 281 | .IX Item "SSL_OP_PKCS1_CHECK_2" |
| 282 | \&... |
| 283 | .IP "\s-1SSL_OP_NETSCAPE_CA_DN_BUG\s0" 4 |
| 284 | .IX Item "SSL_OP_NETSCAPE_CA_DN_BUG" |
| 285 | If we accept a netscape connection, demand a client cert, have a |
| 286 | non-self-signed \s-1CA\s0 which does not have its \s-1CA\s0 in netscape, and the |
| 287 | browser has a cert, it will crash/hang. Works for 3.x and 4.xbeta |
| 288 | .IP "\s-1SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG\s0" 4 |
| 289 | .IX Item "SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG" |
| 290 | \&... |
| 291 | .IP "SSL_OP_NO_SSLv2" 4 |
| 292 | .IX Item "SSL_OP_NO_SSLv2" |
| 293 | Do not use the SSLv2 protocol. |
| 294 | .IP "SSL_OP_NO_SSLv3" 4 |
| 295 | .IX Item "SSL_OP_NO_SSLv3" |
| 296 | Do not use the SSLv3 protocol. |
| 297 | .IP "SSL_OP_NO_TLSv1" 4 |
| 298 | .IX Item "SSL_OP_NO_TLSv1" |
| 299 | Do not use the TLSv1 protocol. |
| 300 | .IP "\s-1SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION\s0" 4 |
| 301 | .IX Item "SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION" |
| 302 | When performing renegotiation as a server, always start a new session |
| 303 | (i.e., session resumption requests are only accepted in the initial |
| 304 | handshake). This option is not needed for clients. |
| 305 | .IP "\s-1SSL_OP_NO_TICKET\s0" 4 |
| 306 | .IX Item "SSL_OP_NO_TICKET" |
| 307 | Normally clients and servers will, where possible, transparently make use |
| 308 | of RFC4507bis tickets for stateless session resumption. |
| 309 | .Sp |
| 310 | If this option is set this functionality is disabled and tickets will |
| 311 | not be used by clients or servers. |
| 312 | .IP "\s-1SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION\s0" 4 |
| 313 | .IX Item "SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION" |
| 314 | Allow legacy insecure renegotiation between OpenSSL and unpatched clients or |
| 315 | servers. See the \fB\s-1SECURE\s0 \s-1RENEGOTIATION\s0\fR section for more details. |
| 316 | .IP "\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0" 4 |
| 317 | .IX Item "SSL_OP_LEGACY_SERVER_CONNECT" |
| 318 | Allow legacy insecure renegotiation between OpenSSL and unpatched servers |
| 319 | \&\fBonly\fR: this option is currently set by default. See the |
| 320 | \&\fB\s-1SECURE\s0 \s-1RENEGOTIATION\s0\fR section for more details. |
| 321 | .SH "SECURE RENEGOTIATION" |
| 322 | .IX Header "SECURE RENEGOTIATION" |
| 323 | OpenSSL 0.9.8m and later always attempts to use secure renegotiation as |
| 324 | described in \s-1RFC5746\s0. This counters the prefix attack described in |
| 325 | \&\s-1CVE\-2009\-3555\s0 and elsewhere. |
| 326 | .PP |
| 327 | The deprecated and highly broken SSLv2 protocol does not support |
| 328 | renegotiation at all: its use is \fBstrongly\fR discouraged. |
| 329 | .PP |
| 330 | This attack has far reaching consequences which application writers should be |
| 331 | aware of. In the description below an implementation supporting secure |
| 332 | renegotiation is referred to as \fIpatched\fR. A server not supporting secure |
| 333 | renegotiation is referred to as \fIunpatched\fR. |
| 334 | .PP |
| 335 | The following sections describe the operations permitted by OpenSSL's secure |
| 336 | renegotiation implementation. |
| 337 | .SS "Patched client and server" |
| 338 | .IX Subsection "Patched client and server" |
| 339 | Connections and renegotiation are always permitted by OpenSSL implementations. |
| 340 | .SS "Unpatched client and patched OpenSSL server" |
| 341 | .IX Subsection "Unpatched client and patched OpenSSL server" |
| 342 | The initial connection suceeds but client renegotiation is denied by the |
| 343 | server with a \fBno_renegotiation\fR warning alert if \s-1TLS\s0 v1.0 is used or a fatal |
| 344 | \&\fBhandshake_failure\fR alert in \s-1SSL\s0 v3.0. |
| 345 | .PP |
| 346 | If the patched OpenSSL server attempts to renegotiate a fatal |
| 347 | \&\fBhandshake_failure\fR alert is sent. This is because the server code may be |
| 348 | unaware of the unpatched nature of the client. |
| 349 | .PP |
| 350 | If the option \fB\s-1SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION\s0\fR is set then |
| 351 | renegotiation \fBalways\fR succeeds. |
| 352 | .PP |
| 353 | \&\fB\s-1NB:\s0\fR a bug in OpenSSL clients earlier than 0.9.8m (all of which are |
| 354 | unpatched) will result in the connection hanging if it receives a |
| 355 | \&\fBno_renegotiation\fR alert. OpenSSL versions 0.9.8m and later will regard |
| 356 | a \fBno_renegotiation\fR alert as fatal and respond with a fatal |
| 357 | \&\fBhandshake_failure\fR alert. This is because the OpenSSL \s-1API\s0 currently has |
| 358 | no provision to indicate to an application that a renegotiation attempt |
| 359 | was refused. |
| 360 | .SS "Patched OpenSSL client and unpatched server." |
| 361 | .IX Subsection "Patched OpenSSL client and unpatched server." |
| 362 | If the option \fB\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0\fR or |
| 363 | \&\fB\s-1SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION\s0\fR is set then initial connections |
| 364 | and renegotiation between patched OpenSSL clients and unpatched servers |
| 365 | succeeds. If neither option is set then initial connections to unpatched |
| 366 | servers will fail. |
| 367 | .PP |
| 368 | The option \fB\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0\fR is currently set by default even |
| 369 | though it has security implications: otherwise it would be impossible to |
| 370 | connect to unpatched servers (i.e. all of them initially) and this is clearly |
| 371 | not acceptable. Renegotiation is permitted because this does not add any |
| 372 | additional security issues: during an attack clients do not see any |
| 373 | renegotiations anyway. |
| 374 | .PP |
| 375 | As more servers become patched the option \fB\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0\fR will |
| 376 | \&\fBnot\fR be set by default in a future version of OpenSSL. |
| 377 | .PP |
| 378 | OpenSSL client applications wishing to ensure they can connect to unpatched |
| 379 | servers should always \fBset\fR \fB\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0\fR |
| 380 | .PP |
| 381 | OpenSSL client applications that want to ensure they can \fBnot\fR connect to |
| 382 | unpatched servers (and thus avoid any security issues) should always \fBclear\fR |
| 383 | \&\fB\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0\fR using \fISSL_CTX_clear_options()\fR or |
| 384 | \&\fISSL_clear_options()\fR. |
| 385 | .PP |
| 386 | The difference between the \fB\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0\fR and |
| 387 | \&\fB\s-1SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION\s0\fR options is that |
| 388 | \&\fB\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0\fR enables initial connections and secure |
| 389 | renegotiation between OpenSSL clients and unpatched servers \fBonly\fR, while |
| 390 | \&\fB\s-1SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION\s0\fR allows initial connections |
| 391 | and renegotiation between OpenSSL and unpatched clients or servers. |
| 392 | .SH "RETURN VALUES" |
| 393 | .IX Header "RETURN VALUES" |
| 394 | \&\fISSL_CTX_set_options()\fR and \fISSL_set_options()\fR return the new options bitmask |
| 395 | after adding \fBoptions\fR. |
| 396 | .PP |
| 397 | \&\fISSL_CTX_clear_options()\fR and \fISSL_clear_options()\fR return the new options bitmask |
| 398 | after clearing \fBoptions\fR. |
| 399 | .PP |
| 400 | \&\fISSL_CTX_get_options()\fR and \fISSL_get_options()\fR return the current bitmask. |
| 401 | .PP |
| 402 | \&\fISSL_get_secure_renegotiation_support()\fR returns 1 is the peer supports |
| 403 | secure renegotiation and 0 if it does not. |
| 404 | .SH "SEE ALSO" |
| 405 | .IX Header "SEE ALSO" |
| 406 | \&\fIssl\fR\|(3), \fISSL_new\fR\|(3), \fISSL_clear\fR\|(3), |
| 407 | \&\fISSL_CTX_set_tmp_dh_callback\fR\|(3), |
| 408 | \&\fISSL_CTX_set_tmp_rsa_callback\fR\|(3), |
| 409 | \&\fIdhparam\fR\|(1) |
| 410 | .SH "HISTORY" |
| 411 | .IX Header "HISTORY" |
| 412 | \&\fB\s-1SSL_OP_CIPHER_SERVER_PREFERENCE\s0\fR and |
| 413 | \&\fB\s-1SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION\s0\fR have been added in |
| 414 | OpenSSL 0.9.7. |
| 415 | .PP |
| 416 | \&\fB\s-1SSL_OP_TLS_ROLLBACK_BUG\s0\fR has been added in OpenSSL 0.9.6 and was automatically |
| 417 | enabled with \fB\s-1SSL_OP_ALL\s0\fR. As of 0.9.7, it is no longer included in \fB\s-1SSL_OP_ALL\s0\fR |
| 418 | and must be explicitly set. |
| 419 | .PP |
| 420 | \&\fB\s-1SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS\s0\fR has been added in OpenSSL 0.9.6e. |
| 421 | Versions up to OpenSSL 0.9.6c do not include the countermeasure that |
| 422 | can be disabled with this option (in OpenSSL 0.9.6d, it was always |
| 423 | enabled). |
| 424 | .PP |
| 425 | \&\fISSL_CTX_clear_options()\fR and \fISSL_clear_options()\fR were first added in OpenSSL |
| 426 | 0.9.8m. |
| 427 | .PP |
| 428 | \&\fB\s-1SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION\s0\fR, \fB\s-1SSL_OP_LEGACY_SERVER_CONNECT\s0\fR |
| 429 | and the function \fISSL_get_secure_renegotiation_support()\fR were first added in |
| 430 | OpenSSL 0.9.8m. |