1SSL_CTX_SET_OPTIONS(3)              OpenSSL             SSL_CTX_SET_OPTIONS(3)
2
3
4

NAME

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

SYNOPSIS

11        #include <openssl/ssl.h>
12
13        long SSL_CTX_set_options(SSL_CTX *ctx, long options);
14        long SSL_set_options(SSL *ssl, long options);
15
16        long SSL_CTX_clear_options(SSL_CTX *ctx, long options);
17        long SSL_clear_options(SSL *ssl, long options);
18
19        long SSL_CTX_get_options(SSL_CTX *ctx);
20        long SSL_get_options(SSL *ssl);
21
22        long SSL_get_secure_renegotiation_support(SSL *ssl);
23

DESCRIPTION

25       SSL_CTX_set_options() adds the options set via bit mask in options to
26       ctx.  Options already set before are not cleared!
27
28       SSL_set_options() adds the options set via bit mask in options to ssl.
29       Options already set before are not cleared!
30
31       SSL_CTX_clear_options() clears the options set via bit mask in options
32       to ctx.
33
34       SSL_clear_options() clears the options set via bit mask in options to
35       ssl.
36
37       SSL_CTX_get_options() returns the options set for ctx.
38
39       SSL_get_options() returns the options set for ssl.
40
41       SSL_get_secure_renegotiation_support() indicates whether the peer
42       supports secure renegotiation.  Note, this is implemented via a macro.
43

NOTES

45       The behaviour of the SSL library can be changed by setting several
46       options.  The options are coded as bit masks and can be combined by a
47       bitwise or operation (|).
48
49       SSL_CTX_set_options() and SSL_set_options() affect the (external)
50       protocol behaviour of the SSL library. The (internal) behaviour of the
51       API can be changed by using the similar SSL_CTX_set_mode(3) and
52       SSL_set_mode() functions.
53
54       During a handshake, the option settings of the SSL object are used.
55       When a new SSL object is created from a context using SSL_new(), the
56       current option setting is copied. Changes to ctx do not affect already
57       created SSL objects. SSL_clear() does not affect the settings.
58
59       The following bug workaround options are available:
60
61       SSL_OP_SAFARI_ECDHE_ECDSA_BUG
62           Don't prefer ECDHE-ECDSA ciphers when the client appears to be
63           Safari on OS X.  OS X 10.8..10.8.3 has broken support for ECDHE-
64           ECDSA ciphers.
65
66       SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
67           Disables a countermeasure against a SSL 3.0/TLS 1.0 protocol
68           vulnerability affecting CBC ciphers, which cannot be handled by
69           some broken SSL implementations.  This option has no effect for
70           connections using other ciphers.
71
72       SSL_OP_TLSEXT_PADDING
73           Adds a padding extension to ensure the ClientHello size is never
74           between 256 and 511 bytes in length. This is needed as a workaround
75           for some implementations.
76
77       SSL_OP_ALL
78           All of the above bug workarounds plus SSL_OP_LEGACY_SERVER_CONNECT
79           as mentioned below.
80
81       It is usually safe to use SSL_OP_ALL to enable the bug workaround
82       options if compatibility with somewhat broken implementations is
83       desired.
84
85       The following modifying options are available:
86
87       SSL_OP_TLS_ROLLBACK_BUG
88           Disable version rollback attack detection.
89
90           During the client key exchange, the client must send the same
91           information about acceptable SSL/TLS protocol levels as during the
92           first hello. Some clients violate this rule by adapting to the
93           server's answer. (Example: the client sends a SSLv2 hello and
94           accepts up to SSLv3.1=TLSv1, the server only understands up to
95           SSLv3. In this case the client must still use the same
96           SSLv3.1=TLSv1 announcement. Some clients step down to SSLv3 with
97           respect to the server's answer and violate the version rollback
98           protection.)
99
100       SSL_OP_CIPHER_SERVER_PREFERENCE
101           When choosing a cipher, use the server's preferences instead of the
102           client preferences. When not set, the SSL server will always follow
103           the clients preferences. When set, the SSL/TLS server will choose
104           following its own preferences.
105
106       SSL_OP_NO_SSLv3, SSL_OP_NO_TLSv1, SSL_OP_NO_TLSv1_1, SSL_OP_NO_TLSv1_2,
107       SSL_OP_NO_TLSv1_3, SSL_OP_NO_DTLSv1, SSL_OP_NO_DTLSv1_2
108           These options turn off the SSLv3, TLSv1, TLSv1.1, TLSv1.2 or
109           TLSv1.3 protocol versions with TLS or the DTLSv1, DTLSv1.2 versions
110           with DTLS, respectively.  As of OpenSSL 1.1.0, these options are
111           deprecated, use SSL_CTX_set_min_proto_version(3) and
112           SSL_CTX_set_max_proto_version(3) instead.
113
114       SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
115           When performing renegotiation as a server, always start a new
116           session (i.e., session resumption requests are only accepted in the
117           initial handshake). This option is not needed for clients.
118
119       SSL_OP_NO_COMPRESSION
120           Do not use compression even if it is supported.
121
122       SSL_OP_NO_QUERY_MTU
123           Do not query the MTU. Only affects DTLS connections.
124
125       SSL_OP_COOKIE_EXCHANGE
126           Turn on Cookie Exchange as described in RFC4347 Section 4.2.1. Only
127           affects DTLS connections.
128
129       SSL_OP_NO_TICKET
130           SSL/TLS supports two mechanisms for resuming sessions: session ids
131           and stateless session tickets.
132
133           When using session ids a copy of the session information is cached
134           on the server and a unique id is sent to the client. When the
135           client wishes to resume it provides the unique id so that the
136           server can retrieve the session information from its cache.
137
138           When using stateless session tickets the server uses a session
139           ticket encryption key to encrypt the session information. This
140           encrypted data is sent to the client as a "ticket". When the client
141           wishes to resume it sends the encrypted data back to the server.
142           The server uses its key to decrypt the data and resume the session.
143           In this way the server can operate statelessly - no session
144           information needs to be cached locally.
145
146           The TLSv1.3 protocol only supports tickets and does not directly
147           support session ids. However, OpenSSL allows two modes of ticket
148           operation in TLSv1.3: stateful and stateless. Stateless tickets
149           work the same way as in TLSv1.2 and below.  Stateful tickets mimic
150           the session id behaviour available in TLSv1.2 and below.  The
151           session information is cached on the server and the session id is
152           wrapped up in a ticket and sent back to the client. When the client
153           wishes to resume, it presents a ticket in the same way as for
154           stateless tickets. The server can then extract the session id from
155           the ticket and retrieve the session information from its cache.
156
157           By default OpenSSL will use stateless tickets. The SSL_OP_NO_TICKET
158           option will cause stateless tickets to not be issued. In TLSv1.2
159           and below this means no ticket gets sent to the client at all. In
160           TLSv1.3 a stateful ticket will be sent. This is a server-side
161           option only.
162
163           In TLSv1.3 it is possible to suppress all tickets (stateful and
164           stateless) from being sent by calling SSL_CTX_set_num_tickets(3) or
165           SSL_set_num_tickets(3).
166
167       SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
168           Allow legacy insecure renegotiation between OpenSSL and unpatched
169           clients or servers. See the SECURE RENEGOTIATION section for more
170           details.
171
172       SSL_OP_LEGACY_SERVER_CONNECT
173           Allow legacy insecure renegotiation between OpenSSL and unpatched
174           servers only: this option is currently set by default. See the
175           SECURE RENEGOTIATION section for more details.
176
177       SSL_OP_NO_ENCRYPT_THEN_MAC
178           Normally clients and servers will transparently attempt to
179           negotiate the RFC7366 Encrypt-then-MAC option on TLS and DTLS
180           connection.
181
182           If this option is set, Encrypt-then-MAC is disabled. Clients will
183           not propose, and servers will not accept the extension.
184
185       SSL_OP_NO_RENEGOTIATION
186           Disable all renegotiation in TLSv1.2 and earlier. Do not send
187           HelloRequest messages, and ignore renegotiation requests via
188           ClientHello.
189
190       SSL_OP_ALLOW_NO_DHE_KEX
191           In TLSv1.3 allow a non-(ec)dhe based key exchange mode on
192           resumption. This means that there will be no forward secrecy for
193           the resumed session.
194
195       SSL_OP_PRIORITIZE_CHACHA
196           When SSL_OP_CIPHER_SERVER_PREFERENCE is set, temporarily
197           reprioritize ChaCha20-Poly1305 ciphers to the top of the server
198           cipher list if a ChaCha20-Poly1305 cipher is at the top of the
199           client cipher list. This helps those clients (e.g. mobile) use
200           ChaCha20-Poly1305 if that cipher is anywhere in the server cipher
201           list; but still allows other clients to use AES and other ciphers.
202           Requires SSL_OP_CIPHER_SERVER_PREFERENCE.
203
204       SSL_OP_ENABLE_MIDDLEBOX_COMPAT
205           If set then dummy Change Cipher Spec (CCS) messages are sent in
206           TLSv1.3. This has the effect of making TLSv1.3 look more like
207           TLSv1.2 so that middleboxes that do not understand TLSv1.3 will not
208           drop the connection. Regardless of whether this option is set or
209           not CCS messages received from the peer will always be ignored in
210           TLSv1.3. This option is set by default. To switch it off use
211           SSL_clear_options(). A future version of OpenSSL may not set this
212           by default.
213
214       SSL_OP_NO_ANTI_REPLAY
215           By default, when a server is configured for early data (i.e.,
216           max_early_data > 0), OpenSSL will switch on replay protection. See
217           SSL_read_early_data(3) for a description of the replay protection
218           feature. Anti-replay measures are required to comply with the
219           TLSv1.3 specification. Some applications may be able to mitigate
220           the replay risks in other ways and in such cases the built in
221           OpenSSL functionality is not required. Those applications can turn
222           this feature off by setting this option. This is a server-side
223           opton only. It is ignored by clients.
224
225       The following options no longer have any effect but their identifiers
226       are retained for compatibility purposes:
227
228       SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
229       SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
230       SSL_OP_SSLEAY_080_CLIENT_DH_BUG
231       SSL_OP_TLS_D5_BUG
232       SSL_OP_TLS_BLOCK_PADDING_BUG
233       SSL_OP_MSIE_SSLV2_RSA_PADDING
234       SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
235       SSL_OP_MICROSOFT_SESS_ID_BUG
236       SSL_OP_NETSCAPE_CHALLENGE_BUG
237       SSL_OP_PKCS1_CHECK_1
238       SSL_OP_PKCS1_CHECK_2
239       SSL_OP_SINGLE_DH_USE
240       SSL_OP_SINGLE_ECDH_USE
241       SSL_OP_EPHEMERAL_RSA
242

SECURE RENEGOTIATION

244       OpenSSL always attempts to use secure renegotiation as described in
245       RFC5746. This counters the prefix attack described in CVE-2009-3555 and
246       elsewhere.
247
248       This attack has far reaching consequences which application writers
249       should be aware of. In the description below an implementation
250       supporting secure renegotiation is referred to as patched. A server not
251       supporting secure renegotiation is referred to as unpatched.
252
253       The following sections describe the operations permitted by OpenSSL's
254       secure renegotiation implementation.
255
256   Patched client and server
257       Connections and renegotiation are always permitted by OpenSSL
258       implementations.
259
260   Unpatched client and patched OpenSSL server
261       The initial connection succeeds but client renegotiation is denied by
262       the server with a no_renegotiation warning alert if TLS v1.0 is used or
263       a fatal handshake_failure alert in SSL v3.0.
264
265       If the patched OpenSSL server attempts to renegotiate a fatal
266       handshake_failure alert is sent. This is because the server code may be
267       unaware of the unpatched nature of the client.
268
269       If the option SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION is set then
270       renegotiation always succeeds.
271
272   Patched OpenSSL client and unpatched server.
273       If the option SSL_OP_LEGACY_SERVER_CONNECT or
274       SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION is set then initial
275       connections and renegotiation between patched OpenSSL clients and
276       unpatched servers succeeds. If neither option is set then initial
277       connections to unpatched servers will fail.
278
279       The option SSL_OP_LEGACY_SERVER_CONNECT is currently set by default
280       even though it has security implications: otherwise it would be
281       impossible to connect to unpatched servers (i.e. all of them initially)
282       and this is clearly not acceptable. Renegotiation is permitted because
283       this does not add any additional security issues: during an attack
284       clients do not see any renegotiations anyway.
285
286       As more servers become patched the option SSL_OP_LEGACY_SERVER_CONNECT
287       will not be set by default in a future version of OpenSSL.
288
289       OpenSSL client applications wishing to ensure they can connect to
290       unpatched servers should always set SSL_OP_LEGACY_SERVER_CONNECT
291
292       OpenSSL client applications that want to ensure they can not connect to
293       unpatched servers (and thus avoid any security issues) should always
294       clear SSL_OP_LEGACY_SERVER_CONNECT using SSL_CTX_clear_options() or
295       SSL_clear_options().
296
297       The difference between the SSL_OP_LEGACY_SERVER_CONNECT and
298       SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION options is that
299       SSL_OP_LEGACY_SERVER_CONNECT enables initial connections and secure
300       renegotiation between OpenSSL clients and unpatched servers only, while
301       SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION allows initial connections and
302       renegotiation between OpenSSL and unpatched clients or servers.
303

RETURN VALUES

305       SSL_CTX_set_options() and SSL_set_options() return the new options bit
306       mask after adding options.
307
308       SSL_CTX_clear_options() and SSL_clear_options() return the new options
309       bit mask after clearing options.
310
311       SSL_CTX_get_options() and SSL_get_options() return the current bit
312       mask.
313
314       SSL_get_secure_renegotiation_support() returns 1 is the peer supports
315       secure renegotiation and 0 if it does not.
316

SEE ALSO

318       ssl(7), SSL_new(3), SSL_clear(3), SSL_CTX_set_tmp_dh_callback(3),
319       SSL_CTX_set_min_proto_version(3), dhparam(1)
320

HISTORY

322       The attempt to always try to use secure renegotiation was added in
323       OpenSSL 0.9.8m.
324
325       The SSL_OP_PRIORITIZE_CHACHA and SSL_OP_NO_RENEGOTIATION options were
326       added in OpenSSL 1.1.1.
327
329       Copyright 2001-2020 The OpenSSL Project Authors. All Rights Reserved.
330
331       Licensed under the OpenSSL license (the "License").  You may not use
332       this file except in compliance with the License.  You can obtain a copy
333       in the file LICENSE in the source distribution or at
334       <https://www.openssl.org/source/license.html>.
335
336
337
3381.1.1l                            2021-09-15            SSL_CTX_SET_OPTIONS(3)
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