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 Always use ephemeral (temporary) RSA key when doing RSA operations
156 (see L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>).
157 According to the specifications this is only done, when a RSA key
158 can only be used for signature operations (namely under export ciphers
159 with restricted RSA keylength). By setting this option, ephemeral
160 RSA keys are always used. This option breaks compatibility with the
161 SSL/TLS specifications and may lead to interoperability problems with
162 clients and should therefore never be used. Ciphers with EDH (ephemeral
163 Diffie-Hellman) key exchange should be used instead.
165 =item SSL_OP_CIPHER_SERVER_PREFERENCE
167 When choosing a cipher, use the server's preferences instead of the client
168 preferences. When not set, the SSL server will always follow the clients
169 preferences. When set, the SSLv3/TLSv1 server will choose following its
170 own preferences. Because of the different protocol, for SSLv2 the server
171 will send its list of preferences to the client and the client chooses.
173 =item SSL_OP_PKCS1_CHECK_1
177 =item SSL_OP_PKCS1_CHECK_2
181 =item SSL_OP_NETSCAPE_CA_DN_BUG
183 If we accept a netscape connection, demand a client cert, have a
184 non-self-signed CA which does not have its CA in netscape, and the
185 browser has a cert, it will crash/hang. Works for 3.x and 4.xbeta
187 =item SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
191 =item SSL_OP_NO_SSLv2
193 Do not use the SSLv2 protocol.
195 =item SSL_OP_NO_SSLv3
197 Do not use the SSLv3 protocol.
199 =item SSL_OP_NO_TLSv1
201 Do not use the TLSv1 protocol.
203 =item SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
205 When performing renegotiation as a server, always start a new session
206 (i.e., session resumption requests are only accepted in the initial
207 handshake). This option is not needed for clients.
209 =item SSL_OP_NO_TICKET
211 Normally clients and servers will, where possible, transparently make use
212 of RFC4507bis tickets for stateless session resumption.
214 If this option is set this functionality is disabled and tickets will
215 not be used by clients or servers.
217 =item SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
219 Allow legacy insecure renegotiation between OpenSSL and unpatched clients or
220 servers. See the B<SECURE RENEGOTIATION> section for more details.
222 =item SSL_OP_LEGACY_SERVER_CONNECT
224 Allow legacy insecure renegotiation between OpenSSL and unpatched servers
225 B<only>: this option is currently set by default. See the
226 B<SECURE RENEGOTIATION> section for more details.
230 =head1 SECURE RENEGOTIATION
232 OpenSSL 0.9.8m and later always attempts to use secure renegotiation as
233 described in RFC5746. This counters the prefix attack described in
234 CVE-2009-3555 and elsewhere.
236 The deprecated and highly broken SSLv2 protocol does not support
237 renegotiation at all: its use is B<strongly> discouraged.
239 This attack has far reaching consequences which application writers should be
240 aware of. In the description below an implementation supporting secure
241 renegotiation is referred to as I<patched>. A server not supporting secure
242 renegotiation is referred to as I<unpatched>.
244 The following sections describe the operations permitted by OpenSSL's secure
245 renegotiation implementation.
247 =head2 Patched client and server
249 Connections and renegotiation are always permitted by OpenSSL implementations.
251 =head2 Unpatched client and patched OpenSSL server
253 The initial connection suceeds but client renegotiation is denied by the
254 server with a B<no_renegotiation> warning alert if TLS v1.0 is used or a fatal
255 B<handshake_failure> alert in SSL v3.0.
257 If the patched OpenSSL server attempts to renegotiate a fatal
258 B<handshake_failure> alert is sent. This is because the server code may be
259 unaware of the unpatched nature of the client.
261 If the option B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then
262 renegotiation B<always> succeeds.
264 B<NB:> a bug in OpenSSL clients earlier than 0.9.8m (all of which are
265 unpatched) will result in the connection hanging if it receives a
266 B<no_renegotiation> alert. OpenSSL versions 0.9.8m and later will regard
267 a B<no_renegotiation> alert as fatal and respond with a fatal
268 B<handshake_failure> alert. This is because the OpenSSL API currently has
269 no provision to indicate to an application that a renegotiation attempt
272 =head2 Patched OpenSSL client and unpatched server.
274 If the option B<SSL_OP_LEGACY_SERVER_CONNECT> or
275 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then initial connections
276 and renegotiation between patched OpenSSL clients and unpatched servers
277 succeeds. If neither option is set then initial connections to unpatched
280 The option B<SSL_OP_LEGACY_SERVER_CONNECT> is currently set by default even
281 though it has security implications: otherwise it would be impossible to
282 connect to unpatched servers (i.e. all of them initially) and this is clearly
283 not acceptable. Renegotiation is permitted because this does not add any
284 additional security issues: during an attack clients do not see any
285 renegotiations anyway.
287 As more servers become patched the option B<SSL_OP_LEGACY_SERVER_CONNECT> will
288 B<not> be set by default in a future version of OpenSSL.
290 OpenSSL client applications wishing to ensure they can connect to unpatched
291 servers should always B<set> B<SSL_OP_LEGACY_SERVER_CONNECT>
293 OpenSSL client applications that want to ensure they can B<not> connect to
294 unpatched servers (and thus avoid any security issues) should always B<clear>
295 B<SSL_OP_LEGACY_SERVER_CONNECT> using SSL_CTX_clear_options() or
298 The difference between the B<SSL_OP_LEGACY_SERVER_CONNECT> and
299 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> options is that
300 B<SSL_OP_LEGACY_SERVER_CONNECT> enables initial connections and secure
301 renegotiation between OpenSSL clients and unpatched servers B<only>, while
302 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> allows initial connections
303 and renegotiation between OpenSSL and unpatched clients or servers.
307 SSL_CTX_set_options() and SSL_set_options() return the new options bitmask
308 after adding B<options>.
310 SSL_CTX_clear_options() and SSL_clear_options() return the new options bitmask
311 after clearing B<options>.
313 SSL_CTX_get_options() and SSL_get_options() return the current bitmask.
315 SSL_get_secure_renegotiation_support() returns 1 is the peer supports
316 secure renegotiation and 0 if it does not.
320 L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>,
321 L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>,
322 L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>,
323 L<dhparam(1)|dhparam(1)>
327 B<SSL_OP_CIPHER_SERVER_PREFERENCE> and
328 B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> have been added in
331 B<SSL_OP_TLS_ROLLBACK_BUG> has been added in OpenSSL 0.9.6 and was automatically
332 enabled with B<SSL_OP_ALL>. As of 0.9.7, it is no longer included in B<SSL_OP_ALL>
333 and must be explicitly set.
335 B<SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS> has been added in OpenSSL 0.9.6e.
336 Versions up to OpenSSL 0.9.6c do not include the countermeasure that
337 can be disabled with this option (in OpenSSL 0.9.6d, it was always
340 SSL_CTX_clear_options() and SSL_clear_options() were first added in OpenSSL
343 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION>, B<SSL_OP_LEGACY_SERVER_CONNECT>
344 and the function SSL_get_secure_renegotiation_support() were first added in