1SSL_CTX_set_options(3) OpenSSL SSL_CTX_set_options(3)
2
6 SSL_CTX_set_options, SSL_set_options, SSL_CTX_clear_options,
7 SSL_clear_options, SSL_CTX_get_options, SSL_get_options,
8 SSL_get_secure_renegotiation_support - manipulate SSL options
9
11 #include <openssl/ssl.h>
12 long SSL_CTX_set_options(SSL_CTX *ctx, long options);
14 long SSL_set_options(SSL *ssl, long options);
15 long SSL_CTX_clear_options(SSL_CTX *ctx, long options);
17 long SSL_clear_options(SSL *ssl, long options);
18 long SSL_CTX_get_options(SSL_CTX *ctx);
20 long SSL_get_options(SSL *ssl);
21 long SSL_get_secure_renegotiation_support(SSL *ssl);
23
25 Note: all these functions are implemented using macros.
26 SSL_CTX_set_options() adds the options set via bitmask in options to
28 ctx. Options already set before are not cleared!
29 SSL_set_options() adds the options set via bitmask in options to ssl.
31 Options already set before are not cleared!
32 SSL_CTX_clear_options() clears the options set via bitmask in options
34 to ctx.
35 SSL_clear_options() clears the options set via bitmask in options to
37 ssl.
38 SSL_CTX_get_options() returns the options set for ctx.
40 SSL_get_options() returns the options set for ssl.
42 SSL_get_secure_renegotiation_support() indicates whether the peer
44 supports secure renegotiation.
45
47 The behaviour of the SSL library can be changed by setting several
48 options. The options are coded as bitmasks and can be combined by a
49 logical or operation (|).
50 SSL_CTX_set_options() and SSL_set_options() affect the (external)
52 protocol behaviour of the SSL library. The (internal) behaviour of the
53 API can be changed by using the similar SSL_CTX_set_mode(3) and
54 SSL_set_mode() functions.
55 During a handshake, the option settings of the SSL object are used.
57 When a new SSL object is created from a context using SSL_new(), the
58 current option setting is copied. Changes to ctx do not affect already
59 created SSL objects. SSL_clear() does not affect the settings.
60 The following bug workaround options are available:
62 SSL_OP_MICROSOFT_SESS_ID_BUG
64 www.microsoft.com - when talking SSLv2, if session-id reuse is
65 performed, the session-id passed back in the server-finished
66 message is different from the one decided upon.
67 SSL_OP_NETSCAPE_CHALLENGE_BUG
69 Netscape-Commerce/1.12, when talking SSLv2, accepts a 32 byte
70 challenge but then appears to only use 16 bytes when generating the
71 encryption keys. Using 16 bytes is ok but it should be ok to use
72 32. According to the SSLv3 spec, one should use 32 bytes for the
73 challenge when operating in SSLv2/v3 compatibility mode, but as
74 mentioned above, this breaks this server so 16 bytes is the way to
75 go.
76 SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
78 As of OpenSSL 0.9.8q and 1.0.0c, this option has no effect.
79 SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
81 ...
82 SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
84 ...
85 SSL_OP_SAFARI_ECDHE_ECDSA_BUG
87 Don't prefer ECDHE-ECDSA ciphers when the client appears to be
88 Safari on OS X. OS X 10.8..10.8.3 has broken support for ECDHE-
89 ECDSA ciphers.
90 SSL_OP_SSLEAY_080_CLIENT_DH_BUG
92 ...
93 SSL_OP_TLS_D5_BUG
95 ...
96 SSL_OP_TLS_BLOCK_PADDING_BUG
98 ...
99 SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
101 Disables a countermeasure against a SSL 3.0/TLS 1.0 protocol
102 vulnerability affecting CBC ciphers, which cannot be handled by
103 some broken SSL implementations. This option has no effect for
104 connections using other ciphers.
105 SSL_OP_TLSEXT_PADDING
107 Adds a padding extension to ensure the ClientHello size is never
108 between 256 and 511 bytes in length. This is needed as a workaround
109 for some implementations.
110 SSL_OP_ALL
112 All of the above bug workarounds.
113 It is usually safe to use SSL_OP_ALL to enable the bug workaround
115 options if compatibility with somewhat broken implementations is
116 desired.
117 The following modifying options are available:
119 SSL_OP_TLS_ROLLBACK_BUG
121 Disable version rollback attack detection.
122 During the client key exchange, the client must send the same
124 information about acceptable SSL/TLS protocol levels as during the
125 first hello. Some clients violate this rule by adapting to the
126 server's answer. (Example: the client sends a SSLv2 hello and
127 accepts up to SSLv3.1=TLSv1, the server only understands up to
128 SSLv3. In this case the client must still use the same
129 SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with
130 respect to the server's answer and violate the version rollback
131 protection.)
132 SSL_OP_SINGLE_DH_USE
134 Always create a new key when using temporary/ephemeral DH
135 parameters (see SSL_CTX_set_tmp_dh_callback(3)). This option must
136 be used to prevent small subgroup attacks, when the DH parameters
137 were not generated using "strong" primes (e.g. when using DSA-
138 parameters, see dhparam(1)). If "strong" primes were used, it is
139 not strictly necessary to generate a new DH key during each
140 handshake but it is also recommended. SSL_OP_SINGLE_DH_USE should
141 therefore be enabled whenever temporary/ephemeral DH parameters are
142 used.
143 SSL_OP_EPHEMERAL_RSA
145 This option is no longer implemented and is treated as no op.
146 SSL_OP_CIPHER_SERVER_PREFERENCE
148 When choosing a cipher, use the server's preferences instead of the
149 client preferences. When not set, the SSL server will always follow
150 the clients preferences. When set, the SSLv3/TLSv1 server will
151 choose following its own preferences. Because of the different
152 protocol, for SSLv2 the server will send its list of preferences to
153 the client and the client chooses.
154 SSL_OP_PKCS1_CHECK_1
156 ...
157 SSL_OP_PKCS1_CHECK_2
159 ...
160 SSL_OP_NETSCAPE_CA_DN_BUG
162 If we accept a netscape connection, demand a client cert, have a
163 non-self-signed CA which does not have its CA in netscape, and the
164 browser has a cert, it will crash/hang. Works for 3.x and 4.xbeta
165 SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
167 ...
168 SSL_OP_NO_SSLv2
170 Do not use the SSLv2 protocol. As of OpenSSL 1.0.2g the
171 SSL_OP_NO_SSLv2 option is set by default.
172 SSL_OP_NO_SSLv3
174 Do not use the SSLv3 protocol. It is recommended that applications
175 should set this option.
176 SSL_OP_NO_TLSv1
178 Do not use the TLSv1 protocol.
179 SSL_OP_NO_TLSv1_1
181 Do not use the TLSv1.1 protocol.
182 SSL_OP_NO_TLSv1_2
184 Do not use the TLSv1.2 protocol.
185 SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
187 When performing renegotiation as a server, always start a new
188 session (i.e., session resumption requests are only accepted in the
189 initial handshake). This option is not needed for clients.
190 SSL_OP_NO_TICKET
192 Normally clients and servers will, where possible, transparently
193 make use of RFC4507bis tickets for stateless session resumption.
194 If this option is set this functionality is disabled and tickets
196 will not be used by clients or servers.
197 SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
199 Allow legacy insecure renegotiation between OpenSSL and unpatched
200 clients or servers. See the SECURE RENEGOTIATION section for more
201 details.
202 SSL_OP_LEGACY_SERVER_CONNECT
204 Allow legacy insecure renegotiation between OpenSSL and unpatched
205 servers only: this option is currently set by default. See the
206 SECURE RENEGOTIATION section for more details.
207
209 OpenSSL 0.9.8m and later always attempts to use secure renegotiation as
210 described in RFC5746. This counters the prefix attack described in
211 CVE-2009-3555 and elsewhere.
212 The deprecated and highly broken SSLv2 protocol does not support
214 renegotiation at all: its use is strongly discouraged.
215 This attack has far reaching consequences which application writers
217 should be aware of. In the description below an implementation
218 supporting secure renegotiation is referred to as patched. A server not
219 supporting secure renegotiation is referred to as unpatched.
220 The following sections describe the operations permitted by OpenSSL's
222 secure renegotiation implementation.
223 Patched client and server
225 Connections and renegotiation are always permitted by OpenSSL
226 implementations.
227 Unpatched client and patched OpenSSL server
229 The initial connection succeeds but client renegotiation is denied by
230 the server with a no_renegotiation warning alert if TLS v1.0 is used or
231 a fatal handshake_failure alert in SSL v3.0.
232 If the patched OpenSSL server attempts to renegotiate a fatal
234 handshake_failure alert is sent. This is because the server code may be
235 unaware of the unpatched nature of the client.
236 If the option SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION is set then
238 renegotiation always succeeds.
239 NB: a bug in OpenSSL clients earlier than 0.9.8m (all of which are
241 unpatched) will result in the connection hanging if it receives a
242 no_renegotiation alert. OpenSSL versions 0.9.8m and later will regard a
243 no_renegotiation alert as fatal and respond with a fatal
244 handshake_failure alert. This is because the OpenSSL API currently has
245 no provision to indicate to an application that a renegotiation attempt
246 was refused.
247 Patched OpenSSL client and unpatched server.
249 If the option SSL_OP_LEGACY_SERVER_CONNECT or
250 SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION is set then initial
251 connections and renegotiation between patched OpenSSL clients and
252 unpatched servers succeeds. If neither option is set then initial
253 connections to unpatched servers will fail.
254 The option SSL_OP_LEGACY_SERVER_CONNECT is currently set by default
256 even though it has security implications: otherwise it would be
257 impossible to connect to unpatched servers (i.e. all of them initially)
258 and this is clearly not acceptable. Renegotiation is permitted because
259 this does not add any additional security issues: during an attack
260 clients do not see any renegotiations anyway.
261 As more servers become patched the option SSL_OP_LEGACY_SERVER_CONNECT
263 will not be set by default in a future version of OpenSSL.
264 OpenSSL client applications wishing to ensure they can connect to
266 unpatched servers should always set SSL_OP_LEGACY_SERVER_CONNECT
267 OpenSSL client applications that want to ensure they can not connect to
269 unpatched servers (and thus avoid any security issues) should always
270 clear SSL_OP_LEGACY_SERVER_CONNECT using SSL_CTX_clear_options() or
271 SSL_clear_options().
272 The difference between the SSL_OP_LEGACY_SERVER_CONNECT and
274 SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION options is that
275 SSL_OP_LEGACY_SERVER_CONNECT enables initial connections and secure
276 renegotiation between OpenSSL clients and unpatched servers only, while
277 SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION allows initial connections and
278 renegotiation between OpenSSL and unpatched clients or servers.
279
281 SSL_CTX_set_options() and SSL_set_options() return the new options
282 bitmask after adding options.
283 SSL_CTX_clear_options() and SSL_clear_options() return the new options
285 bitmask after clearing options.
286 SSL_CTX_get_options() and SSL_get_options() return the current bitmask.
288 SSL_get_secure_renegotiation_support() returns 1 is the peer supports
290 secure renegotiation and 0 if it does not.
291
293 ssl(3), SSL_new(3), SSL_clear(3), SSL_CTX_set_tmp_dh_callback(3),
294 SSL_CTX_set_tmp_rsa_callback(3), dhparam(1)
295
297 SSL_OP_CIPHER_SERVER_PREFERENCE and
298 SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION have been added in
299 OpenSSL 0.9.7.
300 SSL_OP_TLS_ROLLBACK_BUG has been added in OpenSSL 0.9.6 and was
302 automatically enabled with SSL_OP_ALL. As of 0.9.7, it is no longer
303 included in SSL_OP_ALL and must be explicitly set.
304 SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS has been added in OpenSSL 0.9.6e.
306 Versions up to OpenSSL 0.9.6c do not include the countermeasure that
307 can be disabled with this option (in OpenSSL 0.9.6d, it was always
308 enabled).
309 SSL_CTX_clear_options() and SSL_clear_options() were first added in
311 OpenSSL 0.9.8m.
312 SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION, SSL_OP_LEGACY_SERVER_CONNECT
314 and the function SSL_get_secure_renegotiation_support() were first
315 added in OpenSSL 0.9.8m.
3161.0.2o 2020-08-01 SSL_CTX_set_options(3)