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)> 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_SSLREF2_REUSE_CERT_TYPE_BUG
68 =item SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
72 =item SSL_OP_SAFARI_ECDHE_ECDSA_BUG
74 Don't prefer ECDHE-ECDSA ciphers when the client appears to be Safari on OS X.
75 OS X 10.8..10.8.3 has broken support for ECDHE-ECDSA ciphers.
77 =item SSL_OP_SSLEAY_080_CLIENT_DH_BUG
81 =item SSL_OP_TLS_D5_BUG
85 =item SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
87 Disables a countermeasure against a SSL 3.0/TLS 1.0 protocol
88 vulnerability affecting CBC ciphers, which cannot be handled by some
89 broken SSL implementations. This option has no effect for connections
92 =item SSL_OP_TLSEXT_PADDING
94 Adds a padding extension to ensure the ClientHello size is never between
95 256 and 511 bytes in length. This is needed as a workaround for some
100 All of the above bug workarounds.
104 It is usually safe to use B<SSL_OP_ALL> to enable the bug workaround
105 options if compatibility with somewhat broken implementations is
108 The following B<modifying> options are available:
112 =item SSL_OP_TLS_ROLLBACK_BUG
114 Disable version rollback attack detection.
116 During the client key exchange, the client must send the same information
117 about acceptable SSL/TLS protocol levels as during the first hello. Some
118 clients violate this rule by adapting to the server's answer. (Example:
119 the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server
120 only understands up to SSLv3. In this case the client must still use the
121 same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect
122 to the server's answer and violate the version rollback protection.)
124 =item SSL_OP_SINGLE_DH_USE
126 Always create a new key when using temporary/ephemeral DH parameters
127 (see L<SSL_CTX_set_tmp_dh_callback(3)>).
128 This option must be used to prevent small subgroup attacks, when
129 the DH parameters were not generated using "strong" primes
130 (e.g. when using DSA-parameters, see L<dhparam(1)>).
131 If "strong" primes were used, it is not strictly necessary to generate
132 a new DH key during each handshake but it is also recommended.
133 B<SSL_OP_SINGLE_DH_USE> should therefore be enabled whenever
134 temporary/ephemeral DH parameters are used.
136 =item SSL_OP_EPHEMERAL_RSA
138 This option is no longer implemented and is treated as no op.
140 =item SSL_OP_CIPHER_SERVER_PREFERENCE
142 When choosing a cipher, use the server's preferences instead of the client
143 preferences. When not set, the SSL server will always follow the clients
144 preferences. When set, the SSL/TLS server will choose following its
147 =item SSL_OP_PKCS1_CHECK_1
151 =item SSL_OP_PKCS1_CHECK_2
156 =item SSL_OP_NO_SSLv3
158 Do not use the SSLv3 protocol.
160 =item SSL_OP_NO_TLSv1
162 Do not use the TLSv1 protocol.
164 =item SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
166 When performing renegotiation as a server, always start a new session
167 (i.e., session resumption requests are only accepted in the initial
168 handshake). This option is not needed for clients.
170 =item SSL_OP_NO_TICKET
172 Normally clients and servers will, where possible, transparently make use
173 of RFC4507bis tickets for stateless session resumption.
175 If this option is set this functionality is disabled and tickets will
176 not be used by clients or servers.
178 =item SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
180 Allow legacy insecure renegotiation between OpenSSL and unpatched clients or
181 servers. See the B<SECURE RENEGOTIATION> section for more details.
183 =item SSL_OP_LEGACY_SERVER_CONNECT
185 Allow legacy insecure renegotiation between OpenSSL and unpatched servers
186 B<only>: this option is currently set by default. See the
187 B<SECURE RENEGOTIATION> section for more details.
191 =head1 SECURE RENEGOTIATION
193 OpenSSL always attempts to use secure renegotiation as
194 described in RFC5746. This counters the prefix attack described in
195 CVE-2009-3555 and elsewhere.
197 This attack has far reaching consequences which application writers should be
198 aware of. In the description below an implementation supporting secure
199 renegotiation is referred to as I<patched>. A server not supporting secure
200 renegotiation is referred to as I<unpatched>.
202 The following sections describe the operations permitted by OpenSSL's secure
203 renegotiation implementation.
205 =head2 Patched client and server
207 Connections and renegotiation are always permitted by OpenSSL implementations.
209 =head2 Unpatched client and patched OpenSSL server
211 The initial connection succeeds but client renegotiation is denied by the
212 server with a B<no_renegotiation> warning alert if TLS v1.0 is used or a fatal
213 B<handshake_failure> alert in SSL v3.0.
215 If the patched OpenSSL server attempts to renegotiate a fatal
216 B<handshake_failure> alert is sent. This is because the server code may be
217 unaware of the unpatched nature of the client.
219 If the option B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then
220 renegotiation B<always> succeeds.
222 =head2 Patched OpenSSL client and unpatched server.
224 If the option B<SSL_OP_LEGACY_SERVER_CONNECT> or
225 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then initial connections
226 and renegotiation between patched OpenSSL clients and unpatched servers
227 succeeds. If neither option is set then initial connections to unpatched
230 The option B<SSL_OP_LEGACY_SERVER_CONNECT> is currently set by default even
231 though it has security implications: otherwise it would be impossible to
232 connect to unpatched servers (i.e. all of them initially) and this is clearly
233 not acceptable. Renegotiation is permitted because this does not add any
234 additional security issues: during an attack clients do not see any
235 renegotiations anyway.
237 As more servers become patched the option B<SSL_OP_LEGACY_SERVER_CONNECT> will
238 B<not> be set by default in a future version of OpenSSL.
240 OpenSSL client applications wishing to ensure they can connect to unpatched
241 servers should always B<set> B<SSL_OP_LEGACY_SERVER_CONNECT>
243 OpenSSL client applications that want to ensure they can B<not> connect to
244 unpatched servers (and thus avoid any security issues) should always B<clear>
245 B<SSL_OP_LEGACY_SERVER_CONNECT> using SSL_CTX_clear_options() or
248 The difference between the B<SSL_OP_LEGACY_SERVER_CONNECT> and
249 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> options is that
250 B<SSL_OP_LEGACY_SERVER_CONNECT> enables initial connections and secure
251 renegotiation between OpenSSL clients and unpatched servers B<only>, while
252 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> allows initial connections
253 and renegotiation between OpenSSL and unpatched clients or servers.
257 SSL_CTX_set_options() and SSL_set_options() return the new options bitmask
258 after adding B<options>.
260 SSL_CTX_clear_options() and SSL_clear_options() return the new options bitmask
261 after clearing B<options>.
263 SSL_CTX_get_options() and SSL_get_options() return the current bitmask.
265 SSL_get_secure_renegotiation_support() returns 1 is the peer supports
266 secure renegotiation and 0 if it does not.
270 L<ssl(3)>, L<SSL_new(3)>, L<SSL_clear(3)>,
271 L<SSL_CTX_set_tmp_dh_callback(3)>,
272 L<SSL_CTX_set_tmp_rsa_callback(3)>,
277 The attempt to always try to use secure renegotiation was added in