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 bitwise 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 As of OpenSSL 1.0.0 this option has no effect.
68 =item SSL_OP_NETSCAPE_CHALLENGE_BUG
70 As of OpenSSL 1.0.0 this option has no effect.
72 =item SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
74 As of OpenSSL 0.9.8q and 1.0.0c, this option has no effect.
76 =item SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
80 =item SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
84 =item SSL_OP_SAFARI_ECDHE_ECDSA_BUG
86 Don't prefer ECDHE-ECDSA ciphers when the client appears to be Safari on OS X.
87 OS X 10.8..10.8.3 has broken support for ECDHE-ECDSA ciphers.
89 =item SSL_OP_SSLEAY_080_CLIENT_DH_BUG
93 =item SSL_OP_TLS_D5_BUG
97 =item SSL_OP_TLS_BLOCK_PADDING_BUG
101 =item SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
103 Disables a countermeasure against a SSL 3.0/TLS 1.0 protocol
104 vulnerability affecting CBC ciphers, which cannot be handled by some
105 broken SSL implementations. This option has no effect for connections
108 =item SSL_OP_TLSEXT_PADDING
110 Adds a padding extension to ensure the ClientHello size is never between
111 256 and 511 bytes in length. This is needed as a workaround for some
116 All of the above bug workarounds.
120 It is usually safe to use B<SSL_OP_ALL> to enable the bug workaround
121 options if compatibility with somewhat broken implementations is
124 The following B<modifying> options are available:
128 =item SSL_OP_TLS_ROLLBACK_BUG
130 Disable version rollback attack detection.
132 During the client key exchange, the client must send the same information
133 about acceptable SSL/TLS protocol levels as during the first hello. Some
134 clients violate this rule by adapting to the server's answer. (Example:
135 the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server
136 only understands up to SSLv3. In this case the client must still use the
137 same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect
138 to the server's answer and violate the version rollback protection.)
140 =item SSL_OP_SINGLE_DH_USE
142 Always create a new key when using temporary/ephemeral DH parameters
143 (see L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>).
144 This option must be used to prevent small subgroup attacks, when
145 the DH parameters were not generated using "strong" primes
146 (e.g. when using DSA-parameters, see L<dhparam(1)|dhparam(1)>).
147 If "strong" primes were used, it is not strictly necessary to generate
148 a new DH key during each handshake but it is also recommended.
149 B<SSL_OP_SINGLE_DH_USE> should therefore be enabled whenever
150 temporary/ephemeral DH parameters are used.
152 =item SSL_OP_EPHEMERAL_RSA
154 This option is no longer implemented and is treated as no op.
156 =item SSL_OP_CIPHER_SERVER_PREFERENCE
158 When choosing a cipher, use the server's preferences instead of the client
159 preferences. When not set, the SSL server will always follow the clients
160 preferences. When set, the SSLv3/TLSv1 server will choose following its
161 own preferences. Because of the different protocol, for SSLv2 the server
162 will send its list of preferences to the client and the client chooses.
164 =item SSL_OP_PKCS1_CHECK_1
168 =item SSL_OP_PKCS1_CHECK_2
173 =item SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
177 =item SSL_OP_NO_SSLv2
179 Do not use the SSLv2 protocol.
181 =item SSL_OP_NO_SSLv3
183 Do not use the SSLv3 protocol.
185 =item SSL_OP_NO_TLSv1
187 Do not use the TLSv1 protocol.
189 =item SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
191 When performing renegotiation as a server, always start a new session
192 (i.e., session resumption requests are only accepted in the initial
193 handshake). This option is not needed for clients.
195 =item SSL_OP_NO_TICKET
197 Normally clients and servers will, where possible, transparently make use
198 of RFC4507bis tickets for stateless session resumption.
200 If this option is set this functionality is disabled and tickets will
201 not be used by clients or servers.
203 =item SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
205 Allow legacy insecure renegotiation between OpenSSL and unpatched clients or
206 servers. See the B<SECURE RENEGOTIATION> section for more details.
208 =item SSL_OP_LEGACY_SERVER_CONNECT
210 Allow legacy insecure renegotiation between OpenSSL and unpatched servers
211 B<only>: this option is currently set by default. See the
212 B<SECURE RENEGOTIATION> section for more details.
216 =head1 SECURE RENEGOTIATION
218 OpenSSL 0.9.8m and later always attempts to use secure renegotiation as
219 described in RFC5746. This counters the prefix attack described in
220 CVE-2009-3555 and elsewhere.
222 The deprecated and highly broken SSLv2 protocol does not support
223 renegotiation at all: its use is B<strongly> discouraged.
225 This attack has far reaching consequences which application writers should be
226 aware of. In the description below an implementation supporting secure
227 renegotiation is referred to as I<patched>. A server not supporting secure
228 renegotiation is referred to as I<unpatched>.
230 The following sections describe the operations permitted by OpenSSL's secure
231 renegotiation implementation.
233 =head2 Patched client and server
235 Connections and renegotiation are always permitted by OpenSSL implementations.
237 =head2 Unpatched client and patched OpenSSL server
239 The initial connection succeeds but client renegotiation is denied by the
240 server with a B<no_renegotiation> warning alert if TLS v1.0 is used or a fatal
241 B<handshake_failure> alert in SSL v3.0.
243 If the patched OpenSSL server attempts to renegotiate a fatal
244 B<handshake_failure> alert is sent. This is because the server code may be
245 unaware of the unpatched nature of the client.
247 If the option B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then
248 renegotiation B<always> succeeds.
250 B<NB:> a bug in OpenSSL clients earlier than 0.9.8m (all of which are
251 unpatched) will result in the connection hanging if it receives a
252 B<no_renegotiation> alert. OpenSSL versions 0.9.8m and later will regard
253 a B<no_renegotiation> alert as fatal and respond with a fatal
254 B<handshake_failure> alert. This is because the OpenSSL API currently has
255 no provision to indicate to an application that a renegotiation attempt
258 =head2 Patched OpenSSL client and unpatched server.
260 If the option B<SSL_OP_LEGACY_SERVER_CONNECT> or
261 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then initial connections
262 and renegotiation between patched OpenSSL clients and unpatched servers
263 succeeds. If neither option is set then initial connections to unpatched
266 The option B<SSL_OP_LEGACY_SERVER_CONNECT> is currently set by default even
267 though it has security implications: otherwise it would be impossible to
268 connect to unpatched servers (i.e. all of them initially) and this is clearly
269 not acceptable. Renegotiation is permitted because this does not add any
270 additional security issues: during an attack clients do not see any
271 renegotiations anyway.
273 As more servers become patched the option B<SSL_OP_LEGACY_SERVER_CONNECT> will
274 B<not> be set by default in a future version of OpenSSL.
276 OpenSSL client applications wishing to ensure they can connect to unpatched
277 servers should always B<set> B<SSL_OP_LEGACY_SERVER_CONNECT>
279 OpenSSL client applications that want to ensure they can B<not> connect to
280 unpatched servers (and thus avoid any security issues) should always B<clear>
281 B<SSL_OP_LEGACY_SERVER_CONNECT> using SSL_CTX_clear_options() or
284 The difference between the B<SSL_OP_LEGACY_SERVER_CONNECT> and
285 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> options is that
286 B<SSL_OP_LEGACY_SERVER_CONNECT> enables initial connections and secure
287 renegotiation between OpenSSL clients and unpatched servers B<only>, while
288 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> allows initial connections
289 and renegotiation between OpenSSL and unpatched clients or servers.
293 SSL_CTX_set_options() and SSL_set_options() return the new options bitmask
294 after adding B<options>.
296 SSL_CTX_clear_options() and SSL_clear_options() return the new options bitmask
297 after clearing B<options>.
299 SSL_CTX_get_options() and SSL_get_options() return the current bitmask.
301 SSL_get_secure_renegotiation_support() returns 1 is the peer supports
302 secure renegotiation and 0 if it does not.
306 L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>,
307 L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>,
308 L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>,
309 L<dhparam(1)|dhparam(1)>
313 B<SSL_OP_CIPHER_SERVER_PREFERENCE> and
314 B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> have been added in
317 B<SSL_OP_TLS_ROLLBACK_BUG> has been added in OpenSSL 0.9.6 and was automatically
318 enabled with B<SSL_OP_ALL>. As of 0.9.7, it is no longer included in B<SSL_OP_ALL>
319 and must be explicitly set.
321 B<SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS> has been added in OpenSSL 0.9.6e.
322 Versions up to OpenSSL 0.9.6c do not include the countermeasure that
323 can be disabled with this option (in OpenSSL 0.9.6d, it was always
326 SSL_CTX_clear_options() and SSL_clear_options() were first added in OpenSSL
329 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION>, B<SSL_OP_LEGACY_SERVER_CONNECT>
330 and the function SSL_get_secure_renegotiation_support() were first added in