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_MSIE_SSLV2_RSA_PADDING
87 As of OpenSSL 0.9.7h and 0.9.8a, this option has no effect.
88 SSL_OP_SSLEAY_080_CLIENT_DH_BUG
90 ...
91 SSL_OP_TLS_D5_BUG
93 ...
94 SSL_OP_TLS_BLOCK_PADDING_BUG
96 ...
97 SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
99 Disables a countermeasure against a SSL 3.0/TLS 1.0 protocol
100 vulnerability affecting CBC ciphers, which cannot be handled by
101 some broken SSL implementations. This option has no effect for
102 connections using other ciphers.
103 SSL_OP_ALL
105 All of the above bug workarounds.
106 It is usually safe to use SSL_OP_ALL to enable the bug workaround
108 options if compatibility with somewhat broken implementations is
109 desired.
110 The following modifying options are available:
112 SSL_OP_TLS_ROLLBACK_BUG
114 Disable version rollback attack detection.
115 During the client key exchange, the client must send the same
117 information about acceptable SSL/TLS protocol levels as during the
118 first hello. Some clients violate this rule by adapting to the
119 server's answer. (Example: the client sends a SSLv2 hello and
120 accepts up to SSLv3.1=TLSv1, the server only understands up to
121 SSLv3. In this case the client must still use the same
122 SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with
123 respect to the server's answer and violate the version rollback
124 protection.)
125 SSL_OP_SINGLE_DH_USE
127 Always create a new key when using temporary/ephemeral DH
128 parameters (see SSL_CTX_set_tmp_dh_callback(3)). This option must
129 be used to prevent small subgroup attacks, when the DH parameters
130 were not generated using "strong" primes (e.g. when using DSA-
131 parameters, see dhparam(1)). If "strong" primes were used, it is
132 not strictly necessary to generate a new DH key during each
133 handshake but it is also recommended. SSL_OP_SINGLE_DH_USE should
134 therefore be enabled whenever temporary/ephemeral DH parameters are
135 used.
136 SSL_OP_EPHEMERAL_RSA
138 Always use ephemeral (temporary) RSA key when doing RSA operations
139 (see SSL_CTX_set_tmp_rsa_callback(3)). According to the
140 specifications this is only done, when a RSA key can only be used
141 for signature operations (namely under export ciphers with
142 restricted RSA keylength). By setting this option, ephemeral RSA
143 keys are always used. This option breaks compatibility with the
144 SSL/TLS specifications and may lead to interoperability problems
145 with clients and should therefore never be used. Ciphers with EDH
146 (ephemeral Diffie-Hellman) key exchange should be used instead.
147 SSL_OP_CIPHER_SERVER_PREFERENCE
149 When choosing a cipher, use the server's preferences instead of the
150 client preferences. When not set, the SSL server will always follow
151 the clients preferences. When set, the SSLv3/TLSv1 server will
152 choose following its own preferences. Because of the different
153 protocol, for SSLv2 the server will send its list of preferences to
154 the client and the client chooses.
155 SSL_OP_PKCS1_CHECK_1
157 ...
158 SSL_OP_PKCS1_CHECK_2
160 ...
161 SSL_OP_NETSCAPE_CA_DN_BUG
163 If we accept a netscape connection, demand a client cert, have a
164 non-self-signed CA which does not have its CA in netscape, and the
165 browser has a cert, it will crash/hang. Works for 3.x and 4.xbeta
166 SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG
168 ...
169 SSL_OP_NO_SSLv2
171 Do not use the SSLv2 protocol.
172 SSL_OP_NO_SSLv3
174 Do not use the SSLv3 protocol.
175 SSL_OP_NO_TLSv1
177 Do not use the TLSv1 protocol.
178 SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
180 When performing renegotiation as a server, always start a new
181 session (i.e., session resumption requests are only accepted in the
182 initial handshake). This option is not needed for clients.
183 SSL_OP_NO_TICKET
185 Normally clients and servers will, where possible, transparently
186 make use of RFC4507bis tickets for stateless session resumption.
187 If this option is set this functionality is disabled and tickets
189 will not be used by clients or servers.
190 SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
192 Allow legacy insecure renegotiation between OpenSSL and unpatched
193 clients or servers. See the SECURE RENEGOTIATION section for more
194 details.
195 SSL_OP_LEGACY_SERVER_CONNECT
197 Allow legacy insecure renegotiation between OpenSSL and unpatched
198 servers only: this option is currently set by default. See the
199 SECURE RENEGOTIATION section for more details.
200
202 OpenSSL 0.9.8m and later always attempts to use secure renegotiation as
203 described in RFC5746. This counters the prefix attack described in
204 CVE-2009-3555 and elsewhere.
205 The deprecated and highly broken SSLv2 protocol does not support
207 renegotiation at all: its use is strongly discouraged.
208 This attack has far reaching consequences which application writers
210 should be aware of. In the description below an implementation
211 supporting secure renegotiation is referred to as patched. A server not
212 supporting secure renegotiation is referred to as unpatched.
213 The following sections describe the operations permitted by OpenSSL's
215 secure renegotiation implementation.
216 Patched client and server
218 Connections and renegotiation are always permitted by OpenSSL
219 implementations.
220 Unpatched client and patched OpenSSL server
222 The initial connection suceeds but client renegotiation is denied by
223 the server with a no_renegotiation warning alert if TLS v1.0 is used or
224 a fatal handshake_failure alert in SSL v3.0.
225 If the patched OpenSSL server attempts to renegotiate a fatal
227 handshake_failure alert is sent. This is because the server code may be
228 unaware of the unpatched nature of the client.
229 If the option SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION is set then
231 renegotiation always succeeds.
232 NB: a bug in OpenSSL clients earlier than 0.9.8m (all of which are
234 unpatched) will result in the connection hanging if it receives a
235 no_renegotiation alert. OpenSSL versions 0.9.8m and later will regard a
236 no_renegotiation alert as fatal and respond with a fatal
237 handshake_failure alert. This is because the OpenSSL API currently has
238 no provision to indicate to an application that a renegotiation attempt
239 was refused.
240 Patched OpenSSL client and unpatched server.
242 If the option SSL_OP_LEGACY_SERVER_CONNECT or
243 SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION is set then initial
244 connections and renegotiation between patched OpenSSL clients and
245 unpatched servers succeeds. If neither option is set then initial
246 connections to unpatched servers will fail.
247 The option SSL_OP_LEGACY_SERVER_CONNECT is currently set by default
249 even though it has security implications: otherwise it would be
250 impossible to connect to unpatched servers (i.e. all of them initially)
251 and this is clearly not acceptable. Renegotiation is permitted because
252 this does not add any additional security issues: during an attack
253 clients do not see any renegotiations anyway.
254 As more servers become patched the option SSL_OP_LEGACY_SERVER_CONNECT
256 will not be set by default in a future version of OpenSSL.
257 OpenSSL client applications wishing to ensure they can connect to
259 unpatched servers should always set SSL_OP_LEGACY_SERVER_CONNECT
260 OpenSSL client applications that want to ensure they can not connect to
262 unpatched servers (and thus avoid any security issues) should always
263 clear SSL_OP_LEGACY_SERVER_CONNECT using SSL_CTX_clear_options() or
264 SSL_clear_options().
265 The difference between the SSL_OP_LEGACY_SERVER_CONNECT and
267 SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION options is that
268 SSL_OP_LEGACY_SERVER_CONNECT enables initial connections and secure
269 renegotiation between OpenSSL clients and unpatched servers only, while
270 SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION allows initial connections and
271 renegotiation between OpenSSL and unpatched clients or servers.
272
274 SSL_CTX_set_options() and SSL_set_options() return the new options
275 bitmask after adding options.
276 SSL_CTX_clear_options() and SSL_clear_options() return the new options
278 bitmask after clearing options.
279 SSL_CTX_get_options() and SSL_get_options() return the current bitmask.
281 SSL_get_secure_renegotiation_support() returns 1 is the peer supports
283 secure renegotiation and 0 if it does not.
284
286 ssl(3), SSL_new(3), SSL_clear(3), SSL_CTX_set_tmp_dh_callback(3),
287 SSL_CTX_set_tmp_rsa_callback(3), dhparam(1)
288
290 SSL_OP_CIPHER_SERVER_PREFERENCE and
291 SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION have been added in
292 OpenSSL 0.9.7.
293 SSL_OP_TLS_ROLLBACK_BUG has been added in OpenSSL 0.9.6 and was
295 automatically enabled with SSL_OP_ALL. As of 0.9.7, it is no longer
296 included in SSL_OP_ALL and must be explicitly set.
297 SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS has been added in OpenSSL 0.9.6e.
299 Versions up to OpenSSL 0.9.6c do not include the countermeasure that
300 can be disabled with this option (in OpenSSL 0.9.6d, it was always
301 enabled).
302 SSL_CTX_clear_options() and SSL_clear_options() were first added in
304 OpenSSL 0.9.8m.
305 SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION, SSL_OP_LEGACY_SERVER_CONNECT
307 and the function SSL_get_secure_renegotiation_support() were first
308 added in OpenSSL 0.9.8m.
3091.0.0e 2010-12-02 SSL_CTX_set_options(3)