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, SSL_OP_LEGACY_SERVER_CONNECT
229 See the B<SECURE RENEGOTIATION> section for a discussion of the purpose of
234 =head1 SECURE RENEGOTIATION
236 OpenSSL 0.9.8m and later always attempts to use secure renegotiation as
237 described in draft-ietf-tls-renegotiation (FIXME: replace by RFC). This
238 counters the prefix attack described in CVE-2009-3555 and elsewhere.
240 The deprecated and highly broken SSLv2 protocol does not support secure
241 renegotiation at all: its use is B<strongly> discouraged.
243 This attack has far reaching consequences which application writers should be
244 aware of. In the description below an implementation supporting secure
245 renegotiation is referred to as I<patched>. A server not supporting secure
246 renegotiation is referred to as I<unpatched>.
248 The following sections describe the operations permitted by OpenSSL's secure
249 renegotiation implementation.
251 =head2 Patched client and server
253 Connections and renegotiation are always permitted by OpenSSL implementations.
255 =head2 Unpatched client and patched OpenSSL server
257 The initial connection suceeds but client renegotiation is denied by the
258 server with a B<no_renegotiation> warning alert if TLS v1.0 is used or a fatal
259 B<handshake_failure> alert in SSL v3.0.
261 If the patched OpenSSL server attempts to renegotiate a fatal
262 B<handshake_failure> alert is sent. This is because the server code may be
263 unaware of the unpatched nature of the client.
265 If the option B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set then
266 renegotiation B<always> succeeds.
268 B<NB:> a bug in OpenSSL clients earlier than 0.9.8m (all of which are
269 unpatched) will result in the connection hanging if it receives a
270 B<no_renegotiation> alert. OpenSSL versions 0.9.8m and later will regard
271 a B<no_renegotiation> alert as fatal and respond with a fatal
272 B<handshake_failure> alert. This is because the OpenSSL API currently has
273 no provision to indicate to an application that a renegotiation attempt
276 =head2 Patched OpenSSL client and unpatched server.
278 If the option B<SSL_OP_LEGACY_SERVER_CONNECT> is set then initial connections
279 between patched OpenSSL clients and unpatched servers succeed. This option
280 is currently set by default even though it has security implications: otherwise
281 it would be impossible to connect to unpatched servers (i.e. all of them
282 initially) and this is clearly not acceptable.
284 As more servers become patched the option B<SSL_OP_LEGACY_SERVER_CONNECT> will
285 B<not> be set by default in a future version of OpenSSL.
287 OpenSSL client applications wishing to ensure they can connect to unpatched
288 servers should always B<set> B<SSL_OP_LEGACY_SERVER_CONNECT>
290 OpenSSL client applications that want to ensure they can B<not> connect to
291 unpatched servers (and thus avoid any security issues) should always B<clear>
292 B<SSL_OP_LEGACY_SERVER_CONNECT> using SSL_CTX_clear_options() or
295 Renegotiation between a patched OpenSSL client and unpatched server follows
296 the same scheme as between an unpatched client and a patched OpenSSL server:
297 i.e. it is not permitted unless the option
298 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION> is set.
302 SSL_CTX_set_options() and SSL_set_options() return the new options bitmask
303 after adding B<options>.
305 SSL_CTX_clear_options() and SSL_clear_options() return the new options bitmask
306 after clearing B<options>.
308 SSL_CTX_get_options() and SSL_get_options() return the current bitmask.
310 SSL_get_secure_renegotiation_support() returns 1 is the peer supports
311 secure renegotiation and 0 if it does not.
315 L<ssl(3)|ssl(3)>, L<SSL_new(3)|SSL_new(3)>, L<SSL_clear(3)|SSL_clear(3)>,
316 L<SSL_CTX_set_tmp_dh_callback(3)|SSL_CTX_set_tmp_dh_callback(3)>,
317 L<SSL_CTX_set_tmp_rsa_callback(3)|SSL_CTX_set_tmp_rsa_callback(3)>,
318 L<dhparam(1)|dhparam(1)>
322 B<SSL_OP_CIPHER_SERVER_PREFERENCE> and
323 B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> have been added in
326 B<SSL_OP_TLS_ROLLBACK_BUG> has been added in OpenSSL 0.9.6 and was automatically
327 enabled with B<SSL_OP_ALL>. As of 0.9.7, it is no longer included in B<SSL_OP_ALL>
328 and must be explicitly set.
330 B<SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS> has been added in OpenSSL 0.9.6e.
331 Versions up to OpenSSL 0.9.6c do not include the countermeasure that
332 can be disabled with this option (in OpenSSL 0.9.6d, it was always
335 SSL_CTX_clear_options() and SSL_clear_options() were first added in OpenSSL
338 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION>, B<SSL_OP_LEGACY_SERVER_CONNECT>
339 and the function SSL_get_secure_renegotiation_support() were first added in