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 ssl3.netscape.com:443, first a connection is established with RC4-MD5.
82 If it is then resumed, we end up using DES-CBC3-SHA. It should be
83 RC4-MD5 according to 7.6.1.3, 'cipher_suite'.
85 Netscape-Enterprise/2.01 (https://merchant.netscape.com) has this bug.
86 It only really shows up when connecting via SSLv2/v3 then reconnecting
87 via SSLv3. The cipher list changes....
89 NEW INFORMATION. Try connecting with a cipher list of just
90 DES-CBC-SHA:RC4-MD5. For some weird reason, each new connection uses
91 RC4-MD5, but a re-connect tries to use DES-CBC-SHA. So netscape, when
92 doing a re-connect, always takes the first cipher in the cipher list.
94 =item SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
98 =item SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
102 =item SSL_OP_MSIE_SSLV2_RSA_PADDING
104 As of OpenSSL 0.9.7h and 0.9.8a, this option has no effect.
106 =item SSL_OP_SSLEAY_080_CLIENT_DH_BUG
110 =item SSL_OP_TLS_D5_BUG
114 =item SSL_OP_TLS_BLOCK_PADDING_BUG
118 =item SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
120 Disables a countermeasure against a SSL 3.0/TLS 1.0 protocol
121 vulnerability affecting CBC ciphers, which cannot be handled by some
122 broken SSL implementations. This option has no effect for connections
127 All of the above bug workarounds.
131 It is usually safe to use B<SSL_OP_ALL> to enable the bug workaround
132 options if compatibility with somewhat broken implementations is
135 The following B<modifying> options are available:
139 =item SSL_OP_TLS_ROLLBACK_BUG
141 Disable version rollback attack detection.
143 During the client key exchange, the client must send the same information
144 about acceptable SSL/TLS protocol levels as during the first hello. Some
145 clients violate this rule by adapting to the server's answer. (Example:
146 the client sends a SSLv2 hello and accepts up to SSLv3.1=TLSv1, the server
147 only understands up to SSLv3. In this case the client must still use the
148 same SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with respect
149 to the server's answer and violate the version rollback protection.)
151 =item SSL_OP_SINGLE_DH_USE
153 Always create a new key when using temporary/ephemeral DH parameters
154 (see L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>).
155 This option must be used to prevent small subgroup attacks, when
156 the DH parameters were not generated using "strong" primes
157 (e.g. when using DSA-parameters, see L<dhparam(1)|dhparam(1)>).
158 If "strong" primes were used, it is not strictly necessary to generate
159 a new DH key during each handshake but it is also recommended.
160 B<SSL_OP_SINGLE_DH_USE> should therefore be enabled whenever
161 temporary/ephemeral DH parameters are used.
163 =item SSL_OP_EPHEMERAL_RSA
165 Always use ephemeral (temporary) RSA key when doing RSA operations
166 (see L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>).
167 According to the specifications this is only done, when a RSA key
168 can only be used for signature operations (namely under export ciphers
169 with restricted RSA keylength). By setting this option, ephemeral
170 RSA keys are always used. This option breaks compatibility with the
171 SSL/TLS specifications and may lead to interoperability problems with
172 clients and should therefore never be used. Ciphers with EDH (ephemeral
173 Diffie-Hellman) key exchange should be used instead.
175 =item SSL_OP_CIPHER_SERVER_PREFERENCE
177 When choosing a cipher, use the server's preferences instead of the client
178 preferences. When not set, the SSL server will always follow the clients
179 preferences. When set, the SSLv3/TLSv1 server will choose following its
180 own preferences. Because of the different protocol, for SSLv2 the server
181 will send its list of preferences to the client and the client chooses.
183 =item SSL_OP_PKCS1_CHECK_1
187 =item SSL_OP_PKCS1_CHECK_2
191 =item SSL_OP_NETSCAPE_CA_DN_BUG
193 If we accept a netscape connection, demand a client cert, have a
194 non-self-signed CA which does not have its CA in netscape, and the
195 browser has a cert, it will crash/hang. Works for 3.x and 4.xbeta
197 =item SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
201 =item SSL_OP_NO_SSLv2
203 Do not use the SSLv2 protocol.
205 =item SSL_OP_NO_SSLv3
207 Do not use the SSLv3 protocol.
209 =item SSL_OP_NO_TLSv1
211 Do not use the TLSv1 protocol.
213 =item SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
215 When performing renegotiation as a server, always start a new session
216 (i.e., session resumption requests are only accepted in the initial
217 handshake). This option is not needed for clients.
219 =item SSL_OP_NO_TICKET
221 Normally clients and servers will, where possible, transparently make use
222 of RFC4507bis tickets for stateless session resumption.
224 If this option is set this functionality is disabled and tickets will
225 not be used by clients or servers.
227 =item SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
229 Allow legacy insecure renegotiation between OpenSSL and unpatched clients or
230 servers. See the B<SECURE RENEGOTIATION> section for more details.
232 =item SSL_OP_LEGACY_SERVER_CONNECT
234 Allow legacy insecure renegotiation between OpenSSL and unpatched servers
235 B<only>: this option is currently set by default. See the
236 B<SECURE RENEGOTIATION> section for more details.
240 =head1 SECURE RENEGOTIATION
242 OpenSSL 0.9.8m and later always attempts to use secure renegotiation as
243 described in RFC5746. This counters the prefix attack described in
244 CVE-2009-3555 and elsewhere.
246 The deprecated and highly broken SSLv2 protocol does not support
247 renegotiation at all: its use is B<strongly> discouraged.
249 This attack has far reaching consequences which application writers should be
250 aware of. In the description below an implementation supporting secure
251 renegotiation is referred to as I<patched>. A server not supporting secure
252 renegotiation is referred to as I<unpatched>.
254 The following sections describe the operations permitted by OpenSSL's secure
255 renegotiation implementation.
257 =head2 Patched client and server
259 Connections and renegotiation are always permitted by OpenSSL implementations.
261 =head2 Unpatched client and patched OpenSSL server
263 The initial connection suceeds but client renegotiation is denied by the
264 server with a B<no_renegotiation> warning alert if TLS v1.0 is used or a fatal
265 B<handshake_failure> alert in SSL v3.0.
267 If the patched OpenSSL server attempts to renegotiate a fatal
268 B<handshake_failure> alert is sent. This is because the server code may be
269 unaware of the unpatched nature of the client.
271 If the option B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then
272 renegotiation B<always> succeeds.
274 B<NB:> a bug in OpenSSL clients earlier than 0.9.8m (all of which are
275 unpatched) will result in the connection hanging if it receives a
276 B<no_renegotiation> alert. OpenSSL versions 0.9.8m and later will regard
277 a B<no_renegotiation> alert as fatal and respond with a fatal
278 B<handshake_failure> alert. This is because the OpenSSL API currently has
279 no provision to indicate to an application that a renegotiation attempt
282 =head2 Patched OpenSSL client and unpatched server.
284 If the option B<SSL_OP_LEGACY_SERVER_CONNECT> or
285 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then initial connections
286 and renegotiation between patched OpenSSL clients and unpatched servers
287 succeeds. If neither option is set then initial connections to unpatched
290 The option B<SSL_OP_LEGACY_SERVER_CONNECT> is currently set by default even
291 though it has security implications: otherwise it would be impossible to
292 connect to unpatched servers (i.e. all of them initially) and this is clearly
293 not acceptable. Renegotiation is permitted because this does not add any
294 additional security issues: during an attack clients do not see any
295 renegotiations anyway.
297 As more servers become patched the option B<SSL_OP_LEGACY_SERVER_CONNECT> will
298 B<not> be set by default in a future version of OpenSSL.
300 OpenSSL client applications wishing to ensure they can connect to unpatched
301 servers should always B<set> B<SSL_OP_LEGACY_SERVER_CONNECT>
303 OpenSSL client applications that want to ensure they can B<not> connect to
304 unpatched servers (and thus avoid any security issues) should always B<clear>
305 B<SSL_OP_LEGACY_SERVER_CONNECT> using SSL_CTX_clear_options() or
308 The difference between the B<SSL_OP_LEGACY_SERVER_CONNECT> and
309 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> options is that
310 B<SSL_OP_LEGACY_SERVER_CONNECT> enables initial connections and secure
311 renegotiation between OpenSSL clients and unpatched servers B<only>, while
312 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> allows initial connections
313 and renegotiation between OpenSSL and unpatched clients or servers.
317 SSL_CTX_set_options() and SSL_set_options() return the new options bitmask
318 after adding B<options>.
320 SSL_CTX_clear_options() and SSL_clear_options() return the new options bitmask
321 after clearing B<options>.
323 SSL_CTX_get_options() and SSL_get_options() return the current bitmask.
325 SSL_get_secure_renegotiation_support() returns 1 is the peer supports
326 secure renegotiation and 0 if it does not.
330 L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>,
331 L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>,
332 L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>,
333 L<dhparam(1)|dhparam(1)>
337 B<SSL_OP_CIPHER_SERVER_PREFERENCE> and
338 B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> have been added in
341 B<SSL_OP_TLS_ROLLBACK_BUG> has been added in OpenSSL 0.9.6 and was automatically
342 enabled with B<SSL_OP_ALL>. As of 0.9.7, it is no longer included in B<SSL_OP_ALL>
343 and must be explicitly set.
345 B<SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS> has been added in OpenSSL 0.9.6e.
346 Versions up to OpenSSL 0.9.6c do not include the countermeasure that
347 can be disabled with this option (in OpenSSL 0.9.6d, it was always
350 SSL_CTX_clear_options() and SSL_clear_options() were first added in OpenSSL
353 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION>, B<SSL_OP_LEGACY_SERVER_CONNECT>
354 and the function SSL_get_secure_renegotiation_support() were first added in