xref: /freebsd/crypto/openssl/doc/man3/SSL_CONF_cmd.pod (revision a90b9d0159070121c221b966469c3e36d912bf82)
1=pod
2
3=head1 NAME
4
5SSL_CONF_cmd_value_type,
6SSL_CONF_cmd - send configuration command
7
8=head1 SYNOPSIS
9
10 #include <openssl/ssl.h>
11
12 int SSL_CONF_cmd(SSL_CONF_CTX *ctx, const char *option, const char *value);
13 int SSL_CONF_cmd_value_type(SSL_CONF_CTX *ctx, const char *option);
14
15=head1 DESCRIPTION
16
17The function SSL_CONF_cmd() performs configuration operation B<option> with
18optional parameter B<value> on B<ctx>. Its purpose is to simplify application
19configuration of B<SSL_CTX> or B<SSL> structures by providing a common
20framework for command line options or configuration files.
21
22SSL_CONF_cmd_value_type() returns the type of value that B<option> refers to.
23
24=head1 SUPPORTED COMMAND LINE COMMANDS
25
26Currently supported B<option> names for command lines (i.e. when the
27flag B<SSL_CONF_FLAG_CMDLINE> is set) are listed below. Note: all B<option>
28names are case sensitive. Unless otherwise stated commands can be used by
29both clients and servers and the B<value> parameter is not used. The default
30prefix for command line commands is B<-> and that is reflected below.
31
32=over 4
33
34=item B<-bugs>
35
36Various bug workarounds are set, same as setting B<SSL_OP_ALL>.
37
38=item B<-no_comp>
39
40Disables support for SSL/TLS compression, same as setting
41B<SSL_OP_NO_COMPRESSION>.
42As of OpenSSL 1.1.0, compression is off by default.
43
44=item B<-comp>
45
46Enables support for SSL/TLS compression, same as clearing
47B<SSL_OP_NO_COMPRESSION>.
48This command was introduced in OpenSSL 1.1.0.
49As of OpenSSL 1.1.0, compression is off by default.
50
51=item B<-no_ticket>
52
53Disables support for session tickets, same as setting B<SSL_OP_NO_TICKET>.
54
55=item B<-serverpref>
56
57Use server and not client preference order when determining which cipher suite,
58signature algorithm or elliptic curve to use for an incoming connection.
59Equivalent to B<SSL_OP_CIPHER_SERVER_PREFERENCE>. Only used by servers.
60
61=item B<-client_renegotiation>
62
63Allows servers to accept client-initiated renegotiation. Equivalent to
64setting B<SSL_OP_ALLOW_CLIENT_RENEGOTIATION>.
65Only used by servers.
66
67=item B<-legacy_renegotiation>
68
69Permits the use of unsafe legacy renegotiation. Equivalent to setting
70B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION>.
71
72=item B<-no_renegotiation>
73
74Disables all attempts at renegotiation in TLSv1.2 and earlier, same as setting
75B<SSL_OP_NO_RENEGOTIATION>.
76
77=item B<-no_resumption_on_reneg>
78
79Sets B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION>. Only used by servers.
80
81=item B<-legacy_server_connect>, B<-no_legacy_server_connect>
82
83Permits or prohibits the use of unsafe legacy renegotiation for OpenSSL
84clients only. Equivalent to setting or clearing B<SSL_OP_LEGACY_SERVER_CONNECT>.
85
86=item B<-prioritize_chacha>
87
88Prioritize ChaCha ciphers when the client has a ChaCha20 cipher at the top of
89its preference list. This usually indicates a client without AES hardware
90acceleration (e.g. mobile) is in use. Equivalent to B<SSL_OP_PRIORITIZE_CHACHA>.
91Only used by servers. Requires B<-serverpref>.
92
93=item B<-allow_no_dhe_kex>
94
95In TLSv1.3 allow a non-(ec)dhe based key exchange mode on resumption. This means
96that there will be no forward secrecy for the resumed session.
97
98=item B<-strict>
99
100Enables strict mode protocol handling. Equivalent to setting
101B<SSL_CERT_FLAG_TLS_STRICT>.
102
103=item B<-sigalgs> I<algs>
104
105This sets the supported signature algorithms for TLSv1.2 and TLSv1.3.
106For clients this value is used directly for the supported signature
107algorithms extension. For servers it is used to determine which signature
108algorithms to support.
109
110The B<algs> argument should be a colon separated list of signature
111algorithms in order of decreasing preference of the form B<algorithm+hash>
112or B<signature_scheme>. B<algorithm> is one of B<RSA>, B<DSA> or B<ECDSA> and
113B<hash> is a supported algorithm OID short name such as B<SHA1>, B<SHA224>,
114B<SHA256>, B<SHA384> of B<SHA512>.  Note: algorithm and hash names are case
115sensitive.  B<signature_scheme> is one of the signature schemes defined in
116TLSv1.3, specified using the IETF name, e.g., B<ecdsa_secp256r1_sha256>,
117B<ed25519>, or B<rsa_pss_pss_sha256>.
118
119If this option is not set then all signature algorithms supported by the
120OpenSSL library are permissible.
121
122Note: algorithms which specify a PKCS#1 v1.5 signature scheme (either by
123using B<RSA> as the B<algorithm> or by using one of the B<rsa_pkcs1_*>
124identifiers) are ignored in TLSv1.3 and will not be negotiated.
125
126=item B<-client_sigalgs> I<algs>
127
128This sets the supported signature algorithms associated with client
129authentication for TLSv1.2 and TLSv1.3.  For servers the B<algs> is used
130in the B<signature_algorithms> field of a B<CertificateRequest> message.
131For clients it is used to determine which signature algorithm to use with
132the client certificate.  If a server does not request a certificate this
133option has no effect.
134
135The syntax of B<algs> is identical to B<-sigalgs>. If not set, then the
136value set for B<-sigalgs> will be used instead.
137
138=item B<-groups> I<groups>
139
140This sets the supported groups. For clients, the groups are sent using
141the supported groups extension. For servers, it is used to determine which
142group to use. This setting affects groups used for signatures (in TLSv1.2
143and earlier) and key exchange. The first group listed will also be used
144for the B<key_share> sent by a client in a TLSv1.3 B<ClientHello>.
145
146The B<groups> argument is a colon separated list of groups. The group can
147be either the B<NIST> name (e.g. B<P-256>), some other commonly used name
148where applicable (e.g. B<X25519>, B<ffdhe2048>) or an OpenSSL OID name
149(e.g. B<prime256v1>). Group names are case sensitive. The list should be
150in order of preference with the most preferred group first.
151
152Currently supported groups for B<TLSv1.3> are B<P-256>, B<P-384>, B<P-521>,
153B<X25519>, B<X448>, B<ffdhe2048>, B<ffdhe3072>, B<ffdhe4096>, B<ffdhe6144>,
154B<ffdhe8192>.
155
156=item B<-curves> I<groups>
157
158This is a synonym for the B<-groups> command.
159
160=item B<-named_curve> I<curve>
161
162This sets the temporary curve used for ephemeral ECDH modes. Only used
163by servers.
164
165The B<groups> argument is a curve name or the special value B<auto> which
166picks an appropriate curve based on client and server preferences. The
167curve can be either the B<NIST> name (e.g. B<P-256>) or an OpenSSL OID name
168(e.g. B<prime256v1>). Curve names are case sensitive.
169
170=item B<-cipher> I<ciphers>
171
172Sets the TLSv1.2 and below ciphersuite list to B<ciphers>. This list will be
173combined with any configured TLSv1.3 ciphersuites. Note: syntax checking
174of B<ciphers> is currently not performed unless a B<SSL> or B<SSL_CTX>
175structure is associated with B<ctx>.
176
177=item B<-ciphersuites> I<1.3ciphers>
178
179Sets the available ciphersuites for TLSv1.3 to value. This is a
180colon-separated list of TLSv1.3 ciphersuite names in order of preference. This
181list will be combined any configured TLSv1.2 and below ciphersuites.
182See L<openssl-ciphers(1)> for more information.
183
184=item B<-min_protocol> I<minprot>, B<-max_protocol> I<maxprot>
185
186Sets the minimum and maximum supported protocol.
187Currently supported protocol values are B<SSLv3>, B<TLSv1>, B<TLSv1.1>,
188B<TLSv1.2>, B<TLSv1.3> for TLS; B<DTLSv1>, B<DTLSv1.2> for DTLS, and B<None>
189for no limit.
190If either the lower or upper bound is not specified then only the other bound
191applies, if specified.
192If your application supports both TLS and DTLS you can specify any of these
193options twice, once with a bound for TLS and again with an appropriate bound
194for DTLS.
195To restrict the supported protocol versions use these commands rather than the
196deprecated alternative commands below.
197
198=item B<-record_padding> I<padding>
199
200Attempts to pad TLSv1.3 records so that they are a multiple of B<padding>
201in length on send. A B<padding> of 0 or 1 turns off padding. Otherwise,
202the B<padding> must be >1 or <=16384.
203
204=item B<-debug_broken_protocol>
205
206Ignored.
207
208=item B<-no_middlebox>
209
210Turn off "middlebox compatibility", as described below.
211
212=back
213
214=head2 Additional Options
215
216The following options are accepted by SSL_CONF_cmd(), but are not
217processed by the OpenSSL commands.
218
219=over 4
220
221=item B<-cert> I<file>
222
223Attempts to use B<file> as the certificate for the appropriate context. It
224currently uses SSL_CTX_use_certificate_chain_file() if an B<SSL_CTX>
225structure is set or SSL_use_certificate_file() with filetype PEM if an
226B<SSL> structure is set. This option is only supported if certificate
227operations are permitted.
228
229=item B<-key> I<file>
230
231Attempts to use B<file> as the private key for the appropriate context. This
232option is only supported if certificate operations are permitted. Note:
233if no B<-key> option is set then a private key is not loaded unless the
234flag B<SSL_CONF_FLAG_REQUIRE_PRIVATE> is set.
235
236=item B<-dhparam> I<file>
237
238Attempts to use B<file> as the set of temporary DH parameters for
239the appropriate context. This option is only supported if certificate
240operations are permitted.
241
242=item B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>, B<-no_tls1_3>
243
244Disables protocol support for SSLv3, TLSv1.0, TLSv1.1, TLSv1.2 or TLSv1.3 by
245setting the corresponding options B<SSL_OP_NO_SSLv3>, B<SSL_OP_NO_TLSv1>,
246B<SSL_OP_NO_TLSv1_1>, B<SSL_OP_NO_TLSv1_2> and B<SSL_OP_NO_TLSv1_3>
247respectively. These options are deprecated, use B<-min_protocol> and
248B<-max_protocol> instead.
249
250=item B<-anti_replay>, B<-no_anti_replay>
251
252Switches replay protection, on or off respectively. With replay protection on,
253OpenSSL will automatically detect if a session ticket has been used more than
254once, TLSv1.3 has been negotiated, and early data is enabled on the server. A
255full handshake is forced if a session ticket is used a second or subsequent
256time. Anti-Replay is on by default unless overridden by a configuration file and
257is only used by servers. Anti-replay measures are required for compliance with
258the TLSv1.3 specification. Some applications may be able to mitigate the replay
259risks in other ways and in such cases the built-in OpenSSL functionality is not
260required. Switching off anti-replay is equivalent to B<SSL_OP_NO_ANTI_REPLAY>.
261
262=back
263
264=head1 SUPPORTED CONFIGURATION FILE COMMANDS
265
266Currently supported B<option> names for configuration files (i.e., when the
267flag B<SSL_CONF_FLAG_FILE> is set) are listed below. All configuration file
268B<option> names are case insensitive so B<signaturealgorithms> is recognised
269as well as B<SignatureAlgorithms>. Unless otherwise stated the B<value> names
270are also case insensitive.
271
272Note: the command prefix (if set) alters the recognised B<option> values.
273
274=over 4
275
276=item B<CipherString>
277
278Sets the ciphersuite list for TLSv1.2 and below to B<value>. This list will be
279combined with any configured TLSv1.3 ciphersuites. Note: syntax
280checking of B<value> is currently not performed unless an B<SSL> or B<SSL_CTX>
281structure is associated with B<ctx>.
282
283=item B<Ciphersuites>
284
285Sets the available ciphersuites for TLSv1.3 to B<value>. This is a
286colon-separated list of TLSv1.3 ciphersuite names in order of preference. This
287list will be combined any configured TLSv1.2 and below ciphersuites.
288See L<openssl-ciphers(1)> for more information.
289
290=item B<Certificate>
291
292Attempts to use the file B<value> as the certificate for the appropriate
293context. It currently uses SSL_CTX_use_certificate_chain_file() if an B<SSL_CTX>
294structure is set or SSL_use_certificate_file() with filetype PEM if an B<SSL>
295structure is set. This option is only supported if certificate operations
296are permitted.
297
298=item B<PrivateKey>
299
300Attempts to use the file B<value> as the private key for the appropriate
301context. This option is only supported if certificate operations
302are permitted. Note: if no B<PrivateKey> option is set then a private key is
303not loaded unless the B<SSL_CONF_FLAG_REQUIRE_PRIVATE> is set.
304
305=item B<ChainCAFile>, B<ChainCAPath>, B<VerifyCAFile>, B<VerifyCAPath>
306
307These options indicate a file or directory used for building certificate
308chains or verifying certificate chains. These options are only supported
309if certificate operations are permitted.
310
311=item B<RequestCAFile>
312
313This option indicates a file containing a set of certificates in PEM form.
314The subject names of the certificates are sent to the peer in the
315B<certificate_authorities> extension for TLS 1.3 (in ClientHello or
316CertificateRequest) or in a certificate request for previous versions or
317TLS.
318
319=item B<ServerInfoFile>
320
321Attempts to use the file B<value> in the "serverinfo" extension using the
322function SSL_CTX_use_serverinfo_file.
323
324=item B<DHParameters>
325
326Attempts to use the file B<value> as the set of temporary DH parameters for
327the appropriate context. This option is only supported if certificate
328operations are permitted.
329
330=item B<RecordPadding>
331
332Attempts to pad TLSv1.3 records so that they are a multiple of B<value> in
333length on send. A B<value> of 0 or 1 turns off padding. Otherwise, the
334B<value> must be >1 or <=16384.
335
336=item B<SignatureAlgorithms>
337
338This sets the supported signature algorithms for TLSv1.2 and TLSv1.3.
339For clients this
340value is used directly for the supported signature algorithms extension. For
341servers it is used to determine which signature algorithms to support.
342
343The B<value> argument should be a colon separated list of signature algorithms
344in order of decreasing preference of the form B<algorithm+hash> or
345B<signature_scheme>. B<algorithm>
346is one of B<RSA>, B<DSA> or B<ECDSA> and B<hash> is a supported algorithm
347OID short name such as B<SHA1>, B<SHA224>, B<SHA256>, B<SHA384> of B<SHA512>.
348Note: algorithm and hash names are case sensitive.
349B<signature_scheme> is one of the signature schemes defined in TLSv1.3,
350specified using the IETF name, e.g., B<ecdsa_secp256r1_sha256>, B<ed25519>,
351or B<rsa_pss_pss_sha256>.
352
353If this option is not set then all signature algorithms supported by the
354OpenSSL library are permissible.
355
356Note: algorithms which specify a PKCS#1 v1.5 signature scheme (either by
357using B<RSA> as the B<algorithm> or by using one of the B<rsa_pkcs1_*>
358identifiers) are ignored in TLSv1.3 and will not be negotiated.
359
360=item B<ClientSignatureAlgorithms>
361
362This sets the supported signature algorithms associated with client
363authentication for TLSv1.2 and TLSv1.3.
364For servers the value is used in the
365B<signature_algorithms> field of a B<CertificateRequest> message.
366For clients it is
367used to determine which signature algorithm to use with the client certificate.
368If a server does not request a certificate this option has no effect.
369
370The syntax of B<value> is identical to B<SignatureAlgorithms>. If not set then
371the value set for B<SignatureAlgorithms> will be used instead.
372
373=item B<Groups>
374
375This sets the supported groups. For clients, the groups are
376sent using the supported groups extension. For servers, it is used
377to determine which group to use. This setting affects groups used for
378signatures (in TLSv1.2 and earlier) and key exchange. The first group listed
379will also be used for the B<key_share> sent by a client in a TLSv1.3
380B<ClientHello>.
381
382The B<value> argument is a colon separated list of groups. The group can be
383either the B<NIST> name (e.g. B<P-256>), some other commonly used name where
384applicable (e.g. B<X25519>, B<ffdhe2048>) or an OpenSSL OID name
385(e.g. B<prime256v1>). Group names are case sensitive. The list should be in
386order of preference with the most preferred group first.
387
388Currently supported groups for B<TLSv1.3> are B<P-256>, B<P-384>, B<P-521>,
389B<X25519>, B<X448>, B<ffdhe2048>, B<ffdhe3072>, B<ffdhe4096>, B<ffdhe6144>,
390B<ffdhe8192>.
391
392=item B<Curves>
393
394This is a synonym for the "Groups" command.
395
396=item B<MinProtocol>
397
398This sets the minimum supported SSL, TLS or DTLS version.
399
400Currently supported protocol values are B<SSLv3>, B<TLSv1>, B<TLSv1.1>,
401B<TLSv1.2>, B<TLSv1.3>, B<DTLSv1> and B<DTLSv1.2>.
402The SSL and TLS bounds apply only to TLS-based contexts, while the DTLS bounds
403apply only to DTLS-based contexts.
404The command can be repeated with one instance setting a TLS bound, and the
405other setting a DTLS bound.
406The value B<None> applies to both types of contexts and disables the limits.
407
408=item B<MaxProtocol>
409
410This sets the maximum supported SSL, TLS or DTLS version.
411
412Currently supported protocol values are B<SSLv3>, B<TLSv1>, B<TLSv1.1>,
413B<TLSv1.2>, B<TLSv1.3>, B<DTLSv1> and B<DTLSv1.2>.
414The SSL and TLS bounds apply only to TLS-based contexts, while the DTLS bounds
415apply only to DTLS-based contexts.
416The command can be repeated with one instance setting a TLS bound, and the
417other setting a DTLS bound.
418The value B<None> applies to both types of contexts and disables the limits.
419
420=item B<Protocol>
421
422This can be used to enable or disable certain versions of the SSL,
423TLS or DTLS protocol.
424
425The B<value> argument is a comma separated list of supported protocols
426to enable or disable.
427If a protocol is preceded by B<-> that version is disabled.
428
429All protocol versions are enabled by default.
430You need to disable at least one protocol version for this setting have any
431effect.
432Only enabling some protocol versions does not disable the other protocol
433versions.
434
435Currently supported protocol values are B<SSLv3>, B<TLSv1>, B<TLSv1.1>,
436B<TLSv1.2>, B<TLSv1.3>, B<DTLSv1> and B<DTLSv1.2>.
437The special value B<ALL> refers to all supported versions.
438
439This can't enable protocols that are disabled using B<MinProtocol>
440or B<MaxProtocol>, but can disable protocols that are still allowed
441by them.
442
443The B<Protocol> command is fragile and deprecated; do not use it.
444Use B<MinProtocol> and B<MaxProtocol> instead.
445If you do use B<Protocol>, make sure that the resulting range of enabled
446protocols has no "holes", e.g. if TLS 1.0 and TLS 1.2 are both enabled, make
447sure to also leave TLS 1.1 enabled.
448
449=item B<Options>
450
451The B<value> argument is a comma separated list of various flags to set.
452If a flag string is preceded B<-> it is disabled.
453See the L<SSL_CTX_set_options(3)> function for more details of
454individual options.
455
456Each option is listed below. Where an operation is enabled by default
457the B<-flag> syntax is needed to disable it.
458
459B<SessionTicket>: session ticket support, enabled by default. Inverse of
460B<SSL_OP_NO_TICKET>: that is B<-SessionTicket> is the same as setting
461B<SSL_OP_NO_TICKET>.
462
463B<Compression>: SSL/TLS compression support, disabled by default. Inverse
464of B<SSL_OP_NO_COMPRESSION>.
465
466B<EmptyFragments>: use empty fragments as a countermeasure against a
467SSL 3.0/TLS 1.0 protocol vulnerability affecting CBC ciphers. It
468is set by default. Inverse of B<SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS>.
469
470B<Bugs>: enable various bug workarounds. Same as B<SSL_OP_ALL>.
471
472B<DHSingle>: enable single use DH keys, set by default. Inverse of
473B<SSL_OP_DH_SINGLE>. Only used by servers.
474
475B<ECDHSingle>: enable single use ECDH keys, set by default. Inverse of
476B<SSL_OP_ECDH_SINGLE>. Only used by servers.
477
478B<ServerPreference>: use server and not client preference order when
479determining which cipher suite, signature algorithm or elliptic curve
480to use for an incoming connection.  Equivalent to
481B<SSL_OP_CIPHER_SERVER_PREFERENCE>. Only used by servers.
482
483B<PrioritizeChaCha>: prioritizes ChaCha ciphers when the client has a
484ChaCha20 cipher at the top of its preference list. This usually indicates
485a mobile client is in use. Equivalent to B<SSL_OP_PRIORITIZE_CHACHA>.
486Only used by servers.
487
488B<NoResumptionOnRenegotiation>: set
489B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> flag. Only used by servers.
490
491B<NoRenegotiation>: disables all attempts at renegotiation in TLSv1.2 and
492earlier, same as setting B<SSL_OP_NO_RENEGOTIATION>.
493
494B<UnsafeLegacyRenegotiation>: permits the use of unsafe legacy renegotiation.
495Equivalent to B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION>.
496
497B<UnsafeLegacyServerConnect>: permits the use of unsafe legacy renegotiation
498for OpenSSL clients only. Equivalent to B<SSL_OP_LEGACY_SERVER_CONNECT>.
499
500B<EncryptThenMac>: use encrypt-then-mac extension, enabled by
501default. Inverse of B<SSL_OP_NO_ENCRYPT_THEN_MAC>: that is,
502B<-EncryptThenMac> is the same as setting B<SSL_OP_NO_ENCRYPT_THEN_MAC>.
503
504B<AllowNoDHEKEX>: In TLSv1.3 allow a non-(ec)dhe based key exchange mode on
505resumption. This means that there will be no forward secrecy for the resumed
506session. Equivalent to B<SSL_OP_ALLOW_NO_DHE_KEX>.
507
508B<MiddleboxCompat>: If set then dummy Change Cipher Spec (CCS) messages are sent
509in TLSv1.3. This has the effect of making TLSv1.3 look more like TLSv1.2 so that
510middleboxes that do not understand TLSv1.3 will not drop the connection. This
511option is set by default. A future version of OpenSSL may not set this by
512default. Equivalent to B<SSL_OP_ENABLE_MIDDLEBOX_COMPAT>.
513
514B<AntiReplay>: If set then OpenSSL will automatically detect if a session ticket
515has been used more than once, TLSv1.3 has been negotiated, and early data is
516enabled on the server. A full handshake is forced if a session ticket is used a
517second or subsequent time. This option is set by default and is only used by
518servers. Anti-replay measures are required to comply with the TLSv1.3
519specification. Some applications may be able to mitigate the replay risks in
520other ways and in such cases the built-in OpenSSL functionality is not required.
521Disabling anti-replay is equivalent to setting B<SSL_OP_NO_ANTI_REPLAY>.
522
523B<ExtendedMasterSecret>: use extended master secret extension, enabled by
524default. Inverse of B<SSL_OP_NO_EXTENDED_MASTER_SECRET>: that is,
525B<-ExtendedMasterSecret> is the same as setting B<SSL_OP_NO_EXTENDED_MASTER_SECRET>.
526
527B<CANames>: use CA names extension, enabled by
528default. Inverse of B<SSL_OP_DISABLE_TLSEXT_CA_NAMES>: that is,
529B<-CANames> is the same as setting B<SSL_OP_DISABLE_TLSEXT_CA_NAMES>.
530
531B<KTLS>: Enables kernel TLS if support has been compiled in, and it is supported
532by the negotiated ciphersuites and extensions. Equivalent to
533B<SSL_OP_ENABLE_KTLS>.
534
535=item B<VerifyMode>
536
537The B<value> argument is a comma separated list of flags to set.
538
539B<Peer> enables peer verification: for clients only.
540
541B<Request> requests but does not require a certificate from the client.
542Servers only.
543
544B<Require> requests and requires a certificate from the client: an error
545occurs if the client does not present a certificate. Servers only.
546
547B<Once> requests a certificate from a client only on the initial connection:
548not when renegotiating. Servers only.
549
550B<RequestPostHandshake> configures the connection to support requests but does
551not require a certificate from the client post-handshake. A certificate will
552not be requested during the initial handshake. The server application must
553provide a mechanism to request a certificate post-handshake. Servers only.
554TLSv1.3 only.
555
556B<RequiresPostHandshake> configures the connection to support requests and
557requires a certificate from the client post-handshake: an error occurs if the
558client does not present a certificate. A certificate will not be requested
559during the initial handshake. The server application must provide a mechanism
560to request a certificate post-handshake. Servers only. TLSv1.3 only.
561
562=item B<ClientCAFile>, B<ClientCAPath>
563
564A file or directory of certificates in PEM format whose names are used as the
565set of acceptable names for client CAs. Servers only. This option is only
566supported if certificate operations are permitted.
567
568=back
569
570=head1 SUPPORTED COMMAND TYPES
571
572The function SSL_CONF_cmd_value_type() currently returns one of the following
573types:
574
575=over 4
576
577=item B<SSL_CONF_TYPE_UNKNOWN>
578
579The B<option> string is unrecognised, this return value can be use to flag
580syntax errors.
581
582=item B<SSL_CONF_TYPE_STRING>
583
584The value is a string without any specific structure.
585
586=item B<SSL_CONF_TYPE_FILE>
587
588The value is a filename.
589
590=item B<SSL_CONF_TYPE_DIR>
591
592The value is a directory name.
593
594=item B<SSL_CONF_TYPE_NONE>
595
596The value string is not used e.g. a command line option which doesn't take an
597argument.
598
599=back
600
601=head1 NOTES
602
603The order of operations is significant. This can be used to set either defaults
604or values which cannot be overridden. For example if an application calls:
605
606 SSL_CONF_cmd(ctx, "Protocol", "-SSLv3");
607 SSL_CONF_cmd(ctx, userparam, uservalue);
608
609it will disable SSLv3 support by default but the user can override it. If
610however the call sequence is:
611
612 SSL_CONF_cmd(ctx, userparam, uservalue);
613 SSL_CONF_cmd(ctx, "Protocol", "-SSLv3");
614
615SSLv3 is B<always> disabled and attempt to override this by the user are
616ignored.
617
618By checking the return code of SSL_CONF_cmd() it is possible to query if a
619given B<option> is recognised, this is useful if SSL_CONF_cmd() values are
620mixed with additional application specific operations.
621
622For example an application might call SSL_CONF_cmd() and if it returns
623-2 (unrecognised command) continue with processing of application specific
624commands.
625
626Applications can also use SSL_CONF_cmd() to process command lines though the
627utility function SSL_CONF_cmd_argv() is normally used instead. One way
628to do this is to set the prefix to an appropriate value using
629SSL_CONF_CTX_set1_prefix(), pass the current argument to B<option> and the
630following argument to B<value> (which may be NULL).
631
632In this case if the return value is positive then it is used to skip that
633number of arguments as they have been processed by SSL_CONF_cmd(). If -2 is
634returned then B<option> is not recognised and application specific arguments
635can be checked instead. If -3 is returned a required argument is missing
636and an error is indicated. If 0 is returned some other error occurred and
637this can be reported back to the user.
638
639The function SSL_CONF_cmd_value_type() can be used by applications to
640check for the existence of a command or to perform additional syntax
641checking or translation of the command value. For example if the return
642value is B<SSL_CONF_TYPE_FILE> an application could translate a relative
643pathname to an absolute pathname.
644
645=head1 RETURN VALUES
646
647SSL_CONF_cmd() returns 1 if the value of B<option> is recognised and B<value> is
648B<NOT> used and 2 if both B<option> and B<value> are used. In other words it
649returns the number of arguments processed. This is useful when processing
650command lines.
651
652A return value of -2 means B<option> is not recognised.
653
654A return value of -3 means B<option> is recognised and the command requires a
655value but B<value> is NULL.
656
657A return code of 0 indicates that both B<option> and B<value> are valid but an
658error occurred attempting to perform the operation: for example due to an
659error in the syntax of B<value> in this case the error queue may provide
660additional information.
661
662=head1 EXAMPLES
663
664Set supported signature algorithms:
665
666 SSL_CONF_cmd(ctx, "SignatureAlgorithms", "ECDSA+SHA256:RSA+SHA256:DSA+SHA256");
667
668There are various ways to select the supported protocols.
669
670This set the minimum protocol version to TLSv1, and so disables SSLv3.
671This is the recommended way to disable protocols.
672
673 SSL_CONF_cmd(ctx, "MinProtocol", "TLSv1");
674
675The following also disables SSLv3:
676
677 SSL_CONF_cmd(ctx, "Protocol", "-SSLv3");
678
679The following will first enable all protocols, and then disable
680SSLv3.
681If no protocol versions were disabled before this has the same effect as
682"-SSLv3", but if some versions were disables this will re-enable them before
683disabling SSLv3.
684
685 SSL_CONF_cmd(ctx, "Protocol", "ALL,-SSLv3");
686
687Only enable TLSv1.2:
688
689 SSL_CONF_cmd(ctx, "MinProtocol", "TLSv1.2");
690 SSL_CONF_cmd(ctx, "MaxProtocol", "TLSv1.2");
691
692This also only enables TLSv1.2:
693
694 SSL_CONF_cmd(ctx, "Protocol", "-ALL,TLSv1.2");
695
696Disable TLS session tickets:
697
698 SSL_CONF_cmd(ctx, "Options", "-SessionTicket");
699
700Enable compression:
701
702 SSL_CONF_cmd(ctx, "Options", "Compression");
703
704Set supported curves to P-256, P-384:
705
706 SSL_CONF_cmd(ctx, "Curves", "P-256:P-384");
707
708=head1 SEE ALSO
709
710L<ssl(7)>,
711L<SSL_CONF_CTX_new(3)>,
712L<SSL_CONF_CTX_set_flags(3)>,
713L<SSL_CONF_CTX_set1_prefix(3)>,
714L<SSL_CONF_CTX_set_ssl_ctx(3)>,
715L<SSL_CONF_cmd_argv(3)>,
716L<SSL_CTX_set_options(3)>
717
718=head1 HISTORY
719
720The SSL_CONF_cmd() function was added in OpenSSL 1.0.2.
721
722The B<SSL_OP_NO_SSL2> option doesn't have effect since 1.1.0, but the macro
723is retained for backwards compatibility.
724
725The B<SSL_CONF_TYPE_NONE> was added in OpenSSL 1.1.0. In earlier versions of
726OpenSSL passing a command which didn't take an argument would return
727B<SSL_CONF_TYPE_UNKNOWN>.
728
729B<MinProtocol> and B<MaxProtocol> where added in OpenSSL 1.1.0.
730
731B<AllowNoDHEKEX> and B<PrioritizeChaCha> were added in OpenSSL 1.1.1.
732
733The B<UnsafeLegacyServerConnect> option is no longer set by default from
734OpenSSL 3.0.
735
736=head1 COPYRIGHT
737
738Copyright 2012-2022 The OpenSSL Project Authors. All Rights Reserved.
739
740Licensed under the Apache License 2.0 (the "License").  You may not use
741this file except in compliance with the License.  You can obtain a copy
742in the file LICENSE in the source distribution or at
743L<https://www.openssl.org/source/license.html>.
744
745=cut
746