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
117 All of the above bug workarounds.
121 It is usually safe to use B<SSL_OP_ALL> to enable the bug workaround
122 options if compatibility with somewhat broken implementations is
125 The following B<modifying> options are available:
129 =item SSL_OP_TLS_ROLLBACK_BUG
131 Disable version rollback attack detection.
133 During the client key exchange, the client must send the same information
134 about acceptable SSL/TLS protocol levels as during the first hello. Some
135 clients violate this rule by adapting to the server's answer. (Example:
136 the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server
137 only understands up to SSLv3. In this case the client must still use the
138 same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect
139 to the server's answer and violate the version rollback protection.)
141 =item SSL_OP_SINGLE_DH_USE
143 Always create a new key when using temporary/ephemeral DH parameters
144 (see L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>).
145 This option must be used to prevent small subgroup attacks, when
146 the DH parameters were not generated using "strong" primes
147 (e.g. when using DSA-parameters, see L<dhparam(1)|dhparam(1)>).
148 If "strong" primes were used, it is not strictly necessary to generate
149 a new DH key during each handshake but it is also recommended.
150 B<SSL_OP_SINGLE_DH_USE> should therefore be enabled whenever
151 temporary/ephemeral DH parameters are used.
153 =item SSL_OP_EPHEMERAL_RSA
155 This option is no longer implemented and is treated as no op.
157 =item SSL_OP_CIPHER_SERVER_PREFERENCE
159 When choosing a cipher, use the server's preferences instead of the client
160 preferences. When not set, the SSL server will always follow the clients
161 preferences. When set, the SSLv3/TLSv1 server will choose following its
162 own preferences. Because of the different protocol, for SSLv2 the server
163 will send its list of preferences to the client and the client chooses.
165 =item SSL_OP_PKCS1_CHECK_1
169 =item SSL_OP_PKCS1_CHECK_2
173 =item SSL_OP_NETSCAPE_CA_DN_BUG
175 If we accept a netscape connection, demand a client cert, have a
176 non-self-signed CA which does not have its CA in netscape, and the
177 browser has a cert, it will crash/hang. Works for 3.x and 4.xbeta
179 =item SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
183 =item SSL_OP_NO_SSLv2
185 Do not use the SSLv2 protocol.
187 =item SSL_OP_NO_SSLv3
189 Do not use the SSLv3 protocol.
191 =item SSL_OP_NO_TLSv1
193 Do not use the TLSv1 protocol.
195 =item SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
197 When performing renegotiation as a server, always start a new session
198 (i.e., session resumption requests are only accepted in the initial
199 handshake). This option is not needed for clients.
201 =item SSL_OP_NO_TICKET
203 Normally clients and servers will, where possible, transparently make use
204 of RFC4507bis tickets for stateless session resumption if extension support
205 is explicitly set when OpenSSL is compiled.
207 If this option is set this functionality is disabled and tickets will
208 not be used by clients or servers.
210 =item SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
212 Allow legacy insecure renegotiation between OpenSSL and unpatched clients or
213 servers. See the B<SECURE RENEGOTIATION> section for more details.
215 =item SSL_OP_LEGACY_SERVER_CONNECT
217 Allow legacy insecure renegotiation between OpenSSL and unpatched servers
218 B<only>: this option is currently set by default. See the
219 B<SECURE RENEGOTIATION> section for more details.
223 =head1 SECURE RENEGOTIATION
225 OpenSSL 0.9.8m and later always attempts to use secure renegotiation as
226 described in RFC5746. This counters the prefix attack described in
227 CVE-2009-3555 and elsewhere.
229 The deprecated and highly broken SSLv2 protocol does not support
230 renegotiation at all: its use is B<strongly> discouraged.
232 This attack has far reaching consequences which application writers should be
233 aware of. In the description below an implementation supporting secure
234 renegotiation is referred to as I<patched>. A server not supporting secure
235 renegotiation is referred to as I<unpatched>.
237 The following sections describe the operations permitted by OpenSSL's secure
238 renegotiation implementation.
240 =head2 Patched client and server
242 Connections and renegotiation are always permitted by OpenSSL implementations.
244 =head2 Unpatched client and patched OpenSSL server
246 The initial connection succeeds but client renegotiation is denied by the
247 server with a B<no_renegotiation> warning alert if TLS v1.0 is used or a fatal
248 B<handshake_failure> alert in SSL v3.0.
250 If the patched OpenSSL server attempts to renegotiate a fatal
251 B<handshake_failure> alert is sent. This is because the server code may be
252 unaware of the unpatched nature of the client.
254 If the option B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then
255 renegotiation B<always> succeeds.
257 B<NB:> a bug in OpenSSL clients earlier than 0.9.8m (all of which are
258 unpatched) will result in the connection hanging if it receives a
259 B<no_renegotiation> alert. OpenSSL versions 0.9.8m and later will regard
260 a B<no_renegotiation> alert as fatal and respond with a fatal
261 B<handshake_failure> alert. This is because the OpenSSL API currently has
262 no provision to indicate to an application that a renegotiation attempt
265 =head2 Patched OpenSSL client and unpatched server.
267 If the option B<SSL_OP_LEGACY_SERVER_CONNECT> or
268 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then initial connections
269 and renegotiation between patched OpenSSL clients and unpatched servers
270 succeeds. If neither option is set then initial connections to unpatched
273 The option B<SSL_OP_LEGACY_SERVER_CONNECT> is currently set by default even
274 though it has security implications: otherwise it would be impossible to
275 connect to unpatched servers (i.e. all of them initially) and this is clearly
276 not acceptable. Renegotiation is permitted because this does not add any
277 additional security issues: during an attack clients do not see any
278 renegotiations anyway.
280 As more servers become patched the option B<SSL_OP_LEGACY_SERVER_CONNECT> will
281 B<not> be set by default in a future version of OpenSSL.
283 OpenSSL client applications wishing to ensure they can connect to unpatched
284 servers should always B<set> B<SSL_OP_LEGACY_SERVER_CONNECT>
286 OpenSSL client applications that want to ensure they can B<not> connect to
287 unpatched servers (and thus avoid any security issues) should always B<clear>
288 B<SSL_OP_LEGACY_SERVER_CONNECT> using SSL_CTX_clear_options() or
291 The difference between the B<SSL_OP_LEGACY_SERVER_CONNECT> and
292 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> options is that
293 B<SSL_OP_LEGACY_SERVER_CONNECT> enables initial connections and secure
294 renegotiation between OpenSSL clients and unpatched servers B<only>, while
295 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> allows initial connections
296 and renegotiation between OpenSSL and unpatched clients or servers.
300 SSL_CTX_set_options() and SSL_set_options() return the new options bitmask
301 after adding B<options>.
303 SSL_CTX_clear_options() and SSL_clear_options() return the new options bitmask
304 after clearing B<options>.
306 SSL_CTX_get_options() and SSL_get_options() return the current bitmask.
308 SSL_get_secure_renegotiation_support() returns 1 is the peer supports
309 secure renegotiation and 0 if it does not.
313 L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>,
314 L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>,
315 L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>,
316 L<dhparam(1)|dhparam(1)>
320 B<SSL_OP_CIPHER_SERVER_PREFERENCE> and
321 B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> have been added in
324 B<SSL_OP_TLS_ROLLBACK_BUG> has been added in OpenSSL 0.9.6 and was automatically
325 enabled with B<SSL_OP_ALL>. As of 0.9.7, it is no longer included in B<SSL_OP_ALL>
326 and must be explicitly set.
328 B<SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS> has been added in OpenSSL 0.9.6e.
329 Versions up to OpenSSL 0.9.6c do not include the countermeasure that
330 can be disabled with this option (in OpenSSL 0.9.6d, it was always
333 SSL_CTX_clear_options() and SSL_clear_options() were first added in OpenSSL
336 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION>, B<SSL_OP_LEGACY_SERVER_CONNECT>
337 and the function SSL_get_secure_renegotiation_support() were first added in