5 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
9 #include <openssl/ssl.h>
11 long SSL_CTX_set_options(SSL_CTX *ctx, long options);
12 long SSL_set_options(SSL *ssl, long options);
14 long SSL_CTX_clear_options(SSL_CTX *ctx, long options);
15 long SSL_clear_options(SSL *ssl, long options);
17 long SSL_CTX_get_options(SSL_CTX *ctx);
18 long SSL_get_options(SSL *ssl);
20 long SSL_get_secure_renegotiation_support(SSL *ssl);
24 Note: all these functions are implemented using macros.
26 SSL_CTX_set_options() adds the options set via bitmask in B<options> to B<ctx>.
27 Options already set before are not cleared!
29 SSL_set_options() adds the options set via bitmask in B<options> to B<ssl>.
30 Options already set before are not cleared!
32 SSL_CTX_clear_options() clears the options set via bitmask in B<options>
35 SSL_clear_options() clears the options set via bitmask in B<options> to B<ssl>.
37 SSL_CTX_get_options() returns the options set for B<ctx>.
39 SSL_get_options() returns the options set for B<ssl>.
41 SSL_get_secure_renegotiation_support() indicates whether the peer supports
46 The behaviour of the SSL library can be changed by setting several options.
47 The options are coded as bitmasks and can be combined by a logical B<or>
50 SSL_CTX_set_options() and SSL_set_options() affect the (external)
51 protocol behaviour of the SSL library. The (internal) behaviour of
52 the API can be changed by using the similar
53 L<SSL_CTX_set_mode(3)|SSL_CTX_set_mode(3)> and SSL_set_mode() functions.
55 During a handshake, the option settings of the SSL object are used. When
56 a new SSL object is created from a context using SSL_new(), the current
57 option setting is copied. Changes to B<ctx> do not affect already created
58 SSL objects. SSL_clear() does not affect the settings.
60 The following B<bug workaround> options are available:
64 =item SSL_OP_MICROSOFT_SESS_ID_BUG
66 www.microsoft.com - when talking SSLv2, if session-id reuse is
67 performed, the session-id passed back in the server-finished message
68 is different from the one decided upon.
70 =item SSL_OP_NETSCAPE_CHALLENGE_BUG
72 Netscape-Commerce/1.12, when talking SSLv2, accepts a 32 byte
73 challenge but then appears to only use 16 bytes when generating the
74 encryption keys. Using 16 bytes is ok but it should be ok to use 32.
75 According to the SSLv3 spec, one should use 32 bytes for the challenge
76 when operating in SSLv2/v3 compatibility mode, but as mentioned above,
77 this breaks this server so 16 bytes is the way to go.
79 =item SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
81 As of OpenSSL 0.9.8q and 1.0.0c, this option has no effect.
83 =item SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
87 =item SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
91 =item SSL_OP_SAFARI_ECDHE_ECDSA_BUG
93 Don't prefer ECDHE-ECDSA ciphers when the client appears to be Safari on OS X.
94 OS X 10.8..10.8.3 has broken support for ECDHE-ECDSA ciphers.
96 =item SSL_OP_SSLEAY_080_CLIENT_DH_BUG
100 =item SSL_OP_TLS_D5_BUG
104 =item SSL_OP_TLS_BLOCK_PADDING_BUG
108 =item SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
110 Disables a countermeasure against a SSL 3.0/TLS 1.0 protocol
111 vulnerability affecting CBC ciphers, which cannot be handled by some
112 broken SSL implementations. This option has no effect for connections
115 =item SSL_OP_TLSEXT_PADDING
117 Adds a padding extension to ensure the ClientHello size is never between
118 256 and 511 bytes in length. This is needed as a workaround for some
123 All of the above bug workarounds.
127 It is usually safe to use B<SSL_OP_ALL> to enable the bug workaround
128 options if compatibility with somewhat broken implementations is
131 The following B<modifying> options are available:
135 =item SSL_OP_TLS_ROLLBACK_BUG
137 Disable version rollback attack detection.
139 During the client key exchange, the client must send the same information
140 about acceptable SSL/TLS protocol levels as during the first hello. Some
141 clients violate this rule by adapting to the server's answer. (Example:
142 the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server
143 only understands up to SSLv3. In this case the client must still use the
144 same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect
145 to the server's answer and violate the version rollback protection.)
147 =item SSL_OP_SINGLE_DH_USE
149 Always create a new key when using temporary/ephemeral DH parameters
150 (see L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>).
151 This option must be used to prevent small subgroup attacks, when
152 the DH parameters were not generated using "strong" primes
153 (e.g. when using DSA-parameters, see L<dhparam(1)|dhparam(1)>).
154 If "strong" primes were used, it is not strictly necessary to generate
155 a new DH key during each handshake but it is also recommended.
156 B<SSL_OP_SINGLE_DH_USE> should therefore be enabled whenever
157 temporary/ephemeral DH parameters are used.
159 =item SSL_OP_EPHEMERAL_RSA
161 This option is no longer implemented and is treated as no op.
163 =item SSL_OP_CIPHER_SERVER_PREFERENCE
165 When choosing a cipher, use the server's preferences instead of the client
166 preferences. When not set, the SSL server will always follow the clients
167 preferences. When set, the SSLv3/TLSv1 server will choose following its
168 own preferences. Because of the different protocol, for SSLv2 the server
169 will send its list of preferences to the client and the client chooses.
171 =item SSL_OP_PKCS1_CHECK_1
175 =item SSL_OP_PKCS1_CHECK_2
179 =item SSL_OP_NETSCAPE_CA_DN_BUG
181 If we accept a netscape connection, demand a client cert, have a
182 non-self-signed CA which does not have its CA in netscape, and the
183 browser has a cert, it will crash/hang. Works for 3.x and 4.xbeta
185 =item SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
189 =item SSL_OP_NO_SSLv2
191 Do not use the SSLv2 protocol.
192 As of OpenSSL 1.0.2g the B<SSL_OP_NO_SSLv2> option is set by default.
194 =item SSL_OP_NO_SSLv3
196 Do not use the SSLv3 protocol.
197 It is recommended that applications should set this option.
199 =item SSL_OP_NO_TLSv1
201 Do not use the TLSv1 protocol.
203 =item SSL_OP_NO_TLSv1_1
205 Do not use the TLSv1.1 protocol.
207 =item SSL_OP_NO_TLSv1_2
209 Do not use the TLSv1.2 protocol.
211 =item SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
213 When performing renegotiation as a server, always start a new session
214 (i.e., session resumption requests are only accepted in the initial
215 handshake). This option is not needed for clients.
217 =item SSL_OP_NO_TICKET
219 Normally clients and servers will, where possible, transparently make use
220 of RFC4507bis tickets for stateless session resumption.
222 If this option is set this functionality is disabled and tickets will
223 not be used by clients or servers.
225 =item SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
227 Allow legacy insecure renegotiation between OpenSSL and unpatched clients or
228 servers. See the B<SECURE RENEGOTIATION> section for more details.
230 =item SSL_OP_LEGACY_SERVER_CONNECT
232 Allow legacy insecure renegotiation between OpenSSL and unpatched servers
233 B<only>: this option is currently set by default. See the
234 B<SECURE RENEGOTIATION> section for more details.
238 =head1 SECURE RENEGOTIATION
240 OpenSSL 0.9.8m and later always attempts to use secure renegotiation as
241 described in RFC5746. This counters the prefix attack described in
242 CVE-2009-3555 and elsewhere.
244 The deprecated and highly broken SSLv2 protocol does not support
245 renegotiation at all: its use is B<strongly> discouraged.
247 This attack has far reaching consequences which application writers should be
248 aware of. In the description below an implementation supporting secure
249 renegotiation is referred to as I<patched>. A server not supporting secure
250 renegotiation is referred to as I<unpatched>.
252 The following sections describe the operations permitted by OpenSSL's secure
253 renegotiation implementation.
255 =head2 Patched client and server
257 Connections and renegotiation are always permitted by OpenSSL implementations.
259 =head2 Unpatched client and patched OpenSSL server
261 The initial connection succeeds but client renegotiation is denied by the
262 server with a B<no_renegotiation> warning alert if TLS v1.0 is used or a fatal
263 B<handshake_failure> alert in SSL v3.0.
265 If the patched OpenSSL server attempts to renegotiate a fatal
266 B<handshake_failure> alert is sent. This is because the server code may be
267 unaware of the unpatched nature of the client.
269 If the option B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then
270 renegotiation B<always> succeeds.
272 B<NB:> a bug in OpenSSL clients earlier than 0.9.8m (all of which are
273 unpatched) will result in the connection hanging if it receives a
274 B<no_renegotiation> alert. OpenSSL versions 0.9.8m and later will regard
275 a B<no_renegotiation> alert as fatal and respond with a fatal
276 B<handshake_failure> alert. This is because the OpenSSL API currently has
277 no provision to indicate to an application that a renegotiation attempt
280 =head2 Patched OpenSSL client and unpatched server.
282 If the option B<SSL_OP_LEGACY_SERVER_CONNECT> or
283 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then initial connections
284 and renegotiation between patched OpenSSL clients and unpatched servers
285 succeeds. If neither option is set then initial connections to unpatched
288 The option B<SSL_OP_LEGACY_SERVER_CONNECT> is currently set by default even
289 though it has security implications: otherwise it would be impossible to
290 connect to unpatched servers (i.e. all of them initially) and this is clearly
291 not acceptable. Renegotiation is permitted because this does not add any
292 additional security issues: during an attack clients do not see any
293 renegotiations anyway.
295 As more servers become patched the option B<SSL_OP_LEGACY_SERVER_CONNECT> will
296 B<not> be set by default in a future version of OpenSSL.
298 OpenSSL client applications wishing to ensure they can connect to unpatched
299 servers should always B<set> B<SSL_OP_LEGACY_SERVER_CONNECT>
301 OpenSSL client applications that want to ensure they can B<not> connect to
302 unpatched servers (and thus avoid any security issues) should always B<clear>
303 B<SSL_OP_LEGACY_SERVER_CONNECT> using SSL_CTX_clear_options() or
306 The difference between the B<SSL_OP_LEGACY_SERVER_CONNECT> and
307 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> options is that
308 B<SSL_OP_LEGACY_SERVER_CONNECT> enables initial connections and secure
309 renegotiation between OpenSSL clients and unpatched servers B<only>, while
310 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> allows initial connections
311 and renegotiation between OpenSSL and unpatched clients or servers.
315 SSL_CTX_set_options() and SSL_set_options() return the new options bitmask
316 after adding B<options>.
318 SSL_CTX_clear_options() and SSL_clear_options() return the new options bitmask
319 after clearing B<options>.
321 SSL_CTX_get_options() and SSL_get_options() return the current bitmask.
323 SSL_get_secure_renegotiation_support() returns 1 is the peer supports
324 secure renegotiation and 0 if it does not.
328 L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>,
329 L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>,
330 L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>,
331 L<dhparam(1)|dhparam(1)>
335 B<SSL_OP_CIPHER_SERVER_PREFERENCE> and
336 B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> have been added in
339 B<SSL_OP_TLS_ROLLBACK_BUG> has been added in OpenSSL 0.9.6 and was automatically
340 enabled with B<SSL_OP_ALL>. As of 0.9.7, it is no longer included in B<SSL_OP_ALL>
341 and must be explicitly set.
343 B<SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS> has been added in OpenSSL 0.9.6e.
344 Versions up to OpenSSL 0.9.6c do not include the countermeasure that
345 can be disabled with this option (in OpenSSL 0.9.6d, it was always
348 SSL_CTX_clear_options() and SSL_clear_options() were first added in OpenSSL
351 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION>, B<SSL_OP_LEGACY_SERVER_CONNECT>
352 and the function SSL_get_secure_renegotiation_support() were first added in