doc/man3/SSL_CONF_cmd.pod

   1 =pod
   2
   3 =head1 NAME
   4
   5 SSL_CONF_cmd_value_type,
   6 SSL_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
  17 The function SSL_CONF_cmd() performs configuration operation B<option> with
  18 optional parameter B<value> on B<ctx>. Its purpose is to simplify application
  19 configuration of B<SSL_CTX> or B<SSL> structures by providing a common
  20 framework for command line options or configuration files.
  21
  22 SSL_CONF_cmd_value_type() returns the type of value that B<option> refers to.
  23
  24 =head1 SUPPORTED COMMAND LINE COMMANDS
  25
  26 Currently supported B<option> names for command lines (i.e. when the
  27 flag B<SSL_CONF_FLAG_CMDLINE> is set) are listed below. Note: all B<option>
  28 names are case sensitive. Unless otherwise stated commands can be used by
  29 both clients and servers and the B<value> parameter is not used. The default
  30 prefix for command line commands is B<-> and that is reflected below.
  31
  32 =over 4
  33
  34 =item B<-bugs>
  35
  36 Various bug workarounds are set, same as setting B<SSL_OP_ALL>.
  37
  38 =item B<-no_comp>
  39
  40 Disables support for SSL/TLS compression, same as setting
  41 B<SSL_OP_NO_COMPRESSION>.
  42 As of OpenSSL 1.1.0, compression is off by default.
  43
  44 =item B<-comp>
  45
  46 Enables support for SSL/TLS compression, same as clearing
  47 B<SSL_OP_NO_COMPRESSION>.
  48 This command was introduced in OpenSSL 1.1.0.
  49 As of OpenSSL 1.1.0, compression is off by default.
  50
  51 =item B<-no_ticket>
  52
  53 Disables support for session tickets, same as setting B<SSL_OP_NO_TICKET>.
  54
  55 =item B<-serverpref>
  56
  57 Use server and not client preference order when determining which cipher suite,
  58 signature algorithm or elliptic curve to use for an incoming connection.
  59 Equivalent to B<SSL_OP_CIPHER_SERVER_PREFERENCE>. Only used by servers.
  60
  61 =item B<-client_renegotiation>
  62
  63 Allows servers to accept client-initiated renegotiation. Equivalent to
  64 setting B<SSL_OP_ALLOW_CLIENT_RENEGOTIATION>.
  65 Only used by servers.
  66
  67 =item B<-legacyrenegotiation>
  68
  69 Permits the use of unsafe legacy renegotiation. Equivalent to setting
  70 B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION>.
  71
  72 =item B<-no_renegotiation>
  73
  74 Disables all attempts at renegotiation in TLSv1.2 and earlier, same as setting
  75 B<SSL_OP_NO_RENEGOTIATION>.
  76
  77 =item B<-no_resumption_on_reneg>
  78
  79 Sets 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
  83 Permits or prohibits the use of unsafe legacy renegotiation for OpenSSL
  84 clients only. Equivalent to setting or clearing B<SSL_OP_LEGACY_SERVER_CONNECT>.
  85
  86 =item B<-prioritize_chacha>
  87
  88 Prioritize ChaCha ciphers when the client has a ChaCha20 cipher at the top of
  89 its preference list. This usually indicates a client without AES hardware
  90 acceleration (e.g. mobile) is in use. Equivalent to B<SSL_OP_PRIORITIZE_CHACHA>.
  91 Only used by servers. Requires B<-serverpref>.
  92
  93 =item B<-allow_no_dhe_kex>
  94
  95 In TLSv1.3 allow a non-(ec)dhe based key exchange mode on resumption. This means
  96 that there will be no forward secrecy for the resumed session.
  97
  98 =item B<-strict>
  99
 100 Enables strict mode protocol handling. Equivalent to setting
 101 B<SSL_CERT_FLAG_TLS_STRICT>.
 102
 103 =item B<-sigalgs> I<algs>
 104
 105 This sets the supported signature algorithms for TLSv1.2 and TLSv1.3.
 106 For clients this value is used directly for the supported signature
 107 algorithms extension. For servers it is used to determine which signature
 108 algorithms to support.
 109
 110 The B<algs> argument should be a colon separated list of signature
 111 algorithms in order of decreasing preference of the form B<algorithm+hash>
 112 or B<signature_scheme>. B<algorithm> is one of B<RSA>, B<DSA> or B<ECDSA> and
 113 B<hash> is a supported algorithm OID short name such as B<SHA1>, B<SHA224>,
 114 B<SHA256>, B<SHA384> of B<SHA512>.  Note: algorithm and hash names are case
 115 sensitive.  B<signature_scheme> is one of the signature schemes defined in
 116 TLSv1.3, specified using the IETF name, e.g., B<ecdsa_secp256r1_sha256>,
 117 B<ed25519>, or B<rsa_pss_pss_sha256>.
 118
 119 If this option is not set then all signature algorithms supported by the
 120 OpenSSL library are permissible.
 121
 122 Note: algorithms which specify a PKCS#1 v1.5 signature scheme (either by
 123 using B<RSA> as the B<algorithm> or by using one of the B<rsa_pkcs1_*>
 124 identifiers) are ignored in TLSv1.3 and will not be negotiated.
 125
 126 =item B<-client_sigalgs> I<algs>
 127
 128 This sets the supported signature algorithms associated with client
 129 authentication for TLSv1.2 and TLSv1.3.  For servers the B<algs> is used
 130 in the B<signature_algorithms> field of a B<CertificateRequest> message.
 131 For clients it is used to determine which signature algorithm to use with
 132 the client certificate.  If a server does not request a certificate this
 133 option has no effect.
 134
 135 The syntax of B<algs> is identical to B<-sigalgs>. If not set, then the
 136 value set for B<-sigalgs> will be used instead.
 137
 138 =item B<-groups> I<groups>
 139
 140 This sets the supported groups. For clients, the groups are sent using
 141 the supported groups extension. For servers, it is used to determine which
 142 group to use. This setting affects groups used for signatures (in TLSv1.2
 143 and earlier) and key exchange. The first group listed will also be used
 144 for the B<key_share> sent by a client in a TLSv1.3 B<ClientHello>.
 145
 146 The B<groups> argument is a colon separated list of groups. The group can
 147 be either the B<NIST> name (e.g. B<P-256>), some other commonly used name
 148 where 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
 150 in order of preference with the most preferred group first.
 151
 152 Currently supported groups for B<TLSv1.3> are B<P-256>, B<P-384>, B<P-521>,
 153 B<X25519>, B<X448>, B<ffdhe2048>, B<ffdhe3072>, B<ffdhe4096>, B<ffdhe6144>,
 154 B<ffdhe8192>.
 155
 156 =item B<-curves> I<groups>
 157
 158 This is a synonym for the B<-groups> command.
 159
 160 =item B<-named_curve> I<curve>
 161
 162 This sets the temporary curve used for ephemeral ECDH modes. Only used
 163 by servers.
 164
 165 The B<groups> argument is a curve name or the special value B<auto> which
 166 picks an appropriate curve based on client and server preferences. The
 167 curve 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
 172 Sets the TLSv1.2 and below ciphersuite list to B<ciphers>. This list will be
 173 combined with any configured TLSv1.3 ciphersuites. Note: syntax checking
 174 of B<ciphers> is currently not performed unless a B<SSL> or B<SSL_CTX>
 175 structure is associated with B<ctx>.
 176
 177 =item B<-ciphersuites> I<1.3ciphers>
 178
 179 Sets the available ciphersuites for TLSv1.3 to value. This is a
 180 colon-separated list of TLSv1.3 ciphersuite names in order of preference. This
 181 list will be combined any configured TLSv1.2 and below ciphersuites.
 182 See L<openssl-ciphers(1)> for more information.
 183
 184 =item B<-min_protocol> I<minprot>, B<-max_protocol> I<maxprot>
 185
 186 Sets the minimum and maximum supported protocol.
 187 Currently supported protocol values are B<SSLv3>, B<TLSv1>, B<TLSv1.1>,
 188 B<TLSv1.2>, B<TLSv1.3> for TLS; B<DTLSv1>, B<DTLSv1.2> for DTLS, and B<None>
 189 for no limit.
 190 If either the lower or upper bound is not specified then only the other bound
 191 applies, if specified.
 192 If your application supports both TLS and DTLS you can specify any of these
 193 options twice, once with a bound for TLS and again with an appropriate bound
 194 for DTLS.
 195 To restrict the supported protocol versions use these commands rather than the
 196 deprecated alternative commands below.
 197
 198 =item B<-record_padding> I<padding>
 199
 200 Attempts to pad TLSv1.3 records so that they are a multiple of B<padding>
 201 in length on send. A B<padding> of 0 or 1 turns off padding. Otherwise,
 202 the B<padding> must be >1 or <=16384.
 203
 204 =item B<-debug_broken_protocol>
 205
 206 Ignored.
 207
 208 =item B<-no_middlebox>
 209
 210 Turn off "middlebox compatibility", as described below.
 211
 212 =back
 213
 214 =head2 Additional Options
 215
 216 The following options are accepted by SSL_CONF_cmd(), but are not
 217 processed by the OpenSSL commands.
 218
 219 =over 4
 220
 221 =item B<-cert> I<file>
 222
 223 Attempts to use B<file> as the certificate for the appropriate context. It
 224 currently uses SSL_CTX_use_certificate_chain_file() if an B<SSL_CTX>
 225 structure is set or SSL_use_certificate_file() with filetype PEM if an
 226 B<SSL> structure is set. This option is only supported if certificate
 227 operations are permitted.
 228
 229 =item B<-key> I<file>
 230
 231 Attempts to use B<file> as the private key for the appropriate context. This
 232 option is only supported if certificate operations are permitted. Note:
 233 if no B<-key> option is set then a private key is not loaded unless the
 234 flag B<SSL_CONF_FLAG_REQUIRE_PRIVATE> is set.
 235
 236 =item B<-dhparam> I<file>
 237
 238 Attempts to use B<file> as the set of temporary DH parameters for
 239 the appropriate context. This option is only supported if certificate
 240 operations are permitted.
 241
 242 =item B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>, B<-no_tls1_3>
 243
 244 Disables protocol support for SSLv3, TLSv1.0, TLSv1.1, TLSv1.2 or TLSv1.3 by
 245 setting the corresponding options B<SSL_OP_NO_SSLv3>, B<SSL_OP_NO_TLSv1>,
 246 B<SSL_OP_NO_TLSv1_1>, B<SSL_OP_NO_TLSv1_2> and B<SSL_OP_NO_TLSv1_3>
 247 respectively. These options are deprecated, use B<-min_protocol> and
 248 B<-max_protocol> instead.
 249
 250 =item B<-anti_replay>, B<-no_anti_replay>
 251
 252 Switches replay protection, on or off respectively. With replay protection on,
 253 OpenSSL will automatically detect if a session ticket has been used more than
 254 once, TLSv1.3 has been negotiated, and early data is enabled on the server. A
 255 full handshake is forced if a session ticket is used a second or subsequent
 256 time. Anti-Replay is on by default unless overridden by a configuration file and
 257 is only used by servers. Anti-replay measures are required for compliance with
 258 the TLSv1.3 specification. Some applications may be able to mitigate the replay
 259 risks in other ways and in such cases the built-in OpenSSL functionality is not
 260 required. Switching off anti-replay is equivalent to B<SSL_OP_NO_ANTI_REPLAY>.
 261
 262 =back
 263
 264 =head1 SUPPORTED CONFIGURATION FILE COMMANDS
 265
 266 Currently supported B<option> names for configuration files (i.e., when the
 267 flag B<SSL_CONF_FLAG_FILE> is set) are listed below. All configuration file
 268 B<option> names are case insensitive so B<signaturealgorithms> is recognised
 269 as well as B<SignatureAlgorithms>. Unless otherwise stated the B<value> names
 270 are also case insensitive.
 271
 272 Note: the command prefix (if set) alters the recognised B<option> values.
 273
 274 =over 4
 275
 276 =item B<CipherString>
 277
 278 Sets the ciphersuite list for TLSv1.2 and below to B<value>. This list will be
 279 combined with any configured TLSv1.3 ciphersuites. Note: syntax
 280 checking of B<value> is currently not performed unless an B<SSL> or B<SSL_CTX>
 281 structure is associated with B<ctx>.
 282
 283 =item B<Ciphersuites>
 284
 285 Sets the available ciphersuites for TLSv1.3 to B<value>. This is a
 286 colon-separated list of TLSv1.3 ciphersuite names in order of preference. This
 287 list will be combined any configured TLSv1.2 and below ciphersuites.
 288 See L<openssl-ciphers(1)> for more information.
 289
 290 =item B<Certificate>
 291
 292 Attempts to use the file B<value> as the certificate for the appropriate
 293 context. It currently uses SSL_CTX_use_certificate_chain_file() if an B<SSL_CTX>
 294 structure is set or SSL_use_certificate_file() with filetype PEM if an B<SSL>
 295 structure is set. This option is only supported if certificate operations
 296 are permitted.
 297
 298 =item B<PrivateKey>
 299
 300 Attempts to use the file B<value> as the private key for the appropriate
 301 context. This option is only supported if certificate operations
 302 are permitted. Note: if no B<PrivateKey> option is set then a private key is
 303 not loaded unless the B<SSL_CONF_FLAG_REQUIRE_PRIVATE> is set.
 304
 305 =item B<ChainCAFile>, B<ChainCAPath>, B<VerifyCAFile>, B<VerifyCAPath>
 306
 307 These options indicate a file or directory used for building certificate
 308 chains or verifying certificate chains. These options are only supported
 309 if certificate operations are permitted.
 310
 311 =item B<RequestCAFile>
 312
 313 This option indicates a file containing a set of certificates in PEM form.
 314 The subject names of the certificates are sent to the peer in the
 315 B<certificate_authorities> extension for TLS 1.3 (in ClientHello or
 316 CertificateRequest) or in a certificate request for previous versions or
 317 TLS.
 318
 319 =item B<ServerInfoFile>
 320
 321 Attempts to use the file B<value> in the "serverinfo" extension using the
 322 function SSL_CTX_use_serverinfo_file.
 323
 324 =item B<DHParameters>
 325
 326 Attempts to use the file B<value> as the set of temporary DH parameters for
 327 the appropriate context. This option is only supported if certificate
 328 operations are permitted.
 329
 330 =item B<RecordPadding>
 331
 332 Attempts to pad TLSv1.3 records so that they are a multiple of B<value> in
 333 length on send. A B<value> of 0 or 1 turns off padding. Otherwise, the
 334 B<value> must be >1 or <=16384.
 335
 336 =item B<SignatureAlgorithms>
 337
 338 This sets the supported signature algorithms for TLSv1.2 and TLSv1.3.
 339 For clients this
 340 value is used directly for the supported signature algorithms extension. For
 341 servers it is used to determine which signature algorithms to support.
 342
 343 The B<value> argument should be a colon separated list of signature algorithms
 344 in order of decreasing preference of the form B<algorithm+hash> or
 345 B<signature_scheme>. B<algorithm>
 346 is one of B<RSA>, B<DSA> or B<ECDSA> and B<hash> is a supported algorithm
 347 OID short name such as B<SHA1>, B<SHA224>, B<SHA256>, B<SHA384> of B<SHA512>.
 348 Note: algorithm and hash names are case sensitive.
 349 B<signature_scheme> is one of the signature schemes defined in TLSv1.3,
 350 specified using the IETF name, e.g., B<ecdsa_secp256r1_sha256>, B<ed25519>,
 351 or B<rsa_pss_pss_sha256>.
 352
 353 If this option is not set then all signature algorithms supported by the
 354 OpenSSL library are permissible.
 355
 356 Note: algorithms which specify a PKCS#1 v1.5 signature scheme (either by
 357 using B<RSA> as the B<algorithm> or by using one of the B<rsa_pkcs1_*>
 358 identifiers) are ignored in TLSv1.3 and will not be negotiated.
 359
 360 =item B<ClientSignatureAlgorithms>
 361
 362 This sets the supported signature algorithms associated with client
 363 authentication for TLSv1.2 and TLSv1.3.
 364 For servers the value is used in the
 365 B<signature_algorithms> field of a B<CertificateRequest> message.
 366 For clients it is
 367 used to determine which signature algorithm to use with the client certificate.
 368 If a server does not request a certificate this option has no effect.
 369
 370 The syntax of B<value> is identical to B<SignatureAlgorithms>. If not set then
 371 the value set for B<SignatureAlgorithms> will be used instead.
 372
 373 =item B<Groups>
 374
 375 This sets the supported groups. For clients, the groups are
 376 sent using the supported groups extension. For servers, it is used
 377 to determine which group to use. This setting affects groups used for
 378 signatures (in TLSv1.2 and earlier) and key exchange. The first group listed
 379 will also be used for the B<key_share> sent by a client in a TLSv1.3
 380 B<ClientHello>.
 381
 382 The B<value> argument is a colon separated list of groups. The group can be
 383 either the B<NIST> name (e.g. B<P-256>), some other commonly used name where
 384 applicable (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
 386 order of preference with the most preferred group first.
 387
 388 Currently supported groups for B<TLSv1.3> are B<P-256>, B<P-384>, B<P-521>,
 389 B<X25519>, B<X448>, B<ffdhe2048>, B<ffdhe3072>, B<ffdhe4096>, B<ffdhe6144>,
 390 B<ffdhe8192>.
 391
 392 =item B<Curves>
 393
 394 This is a synonym for the "Groups" command.
 395
 396 =item B<MinProtocol>
 397
 398 This sets the minimum supported SSL, TLS or DTLS version.
 399
 400 Currently supported protocol values are B<SSLv3>, B<TLSv1>, B<TLSv1.1>,
 401 B<TLSv1.2>, B<TLSv1.3>, B<DTLSv1> and B<DTLSv1.2>.
 402 The SSL and TLS bounds apply only to TLS-based contexts, while the DTLS bounds
 403 apply only to DTLS-based contexts.
 404 The command can be repeated with one instance setting a TLS bound, and the
 405 other setting a DTLS bound.
 406 The value B<None> applies to both types of contexts and disables the limits.
 407
 408 =item B<MaxProtocol>
 409
 410 This sets the maximum supported SSL, TLS or DTLS version.
 411
 412 Currently supported protocol values are B<SSLv3>, B<TLSv1>, B<TLSv1.1>,
 413 B<TLSv1.2>, B<TLSv1.3>, B<DTLSv1> and B<DTLSv1.2>.
 414 The SSL and TLS bounds apply only to TLS-based contexts, while the DTLS bounds
 415 apply only to DTLS-based contexts.
 416 The command can be repeated with one instance setting a TLS bound, and the
 417 other setting a DTLS bound.
 418 The value B<None> applies to both types of contexts and disables the limits.
 419
 420 =item B<Protocol>
 421
 422 This can be used to enable or disable certain versions of the SSL,
 423 TLS or DTLS protocol.
 424
 425 The B<value> argument is a comma separated list of supported protocols
 426 to enable or disable.
 427 If a protocol is preceded by B<-> that version is disabled.
 428
 429 All protocol versions are enabled by default.
 430 You need to disable at least one protocol version for this setting have any
 431 effect.
 432 Only enabling some protocol versions does not disable the other protocol
 433 versions.
 434
 435 Currently supported protocol values are B<SSLv3>, B<TLSv1>, B<TLSv1.1>,
 436 B<TLSv1.2>, B<TLSv1.3>, B<DTLSv1> and B<DTLSv1.2>.
 437 The special value B<ALL> refers to all supported versions.
 438
 439 This can't enable protocols that are disabled using B<MinProtocol>
 440 or B<MaxProtocol>, but can disable protocols that are still allowed
 441 by them.
 442
 443 The B<Protocol> command is fragile and deprecated; do not use it.
 444 Use B<MinProtocol> and B<MaxProtocol> instead.
 445 If you do use B<Protocol>, make sure that the resulting range of enabled
 446 protocols has no "holes", e.g. if TLS 1.0 and TLS 1.2 are both enabled, make
 447 sure to also leave TLS 1.1 enabled.
 448
 449 =item B<Options>
 450
 451 The B<value> argument is a comma separated list of various flags to set.
 452 If a flag string is preceded B<-> it is disabled.
 453 See the L<SSL_CTX_set_options(3)> function for more details of
 454 individual options.
 455
 456 Each option is listed below. Where an operation is enabled by default
 457 the B<-flag> syntax is needed to disable it.
 458
 459 B<SessionTicket>: session ticket support, enabled by default. Inverse of
 460 B<SSL_OP_NO_TICKET>: that is B<-SessionTicket> is the same as setting
 461 B<SSL_OP_NO_TICKET>.
 462
 463 B<Compression>: SSL/TLS compression support, enabled by default. Inverse
 464 of B<SSL_OP_NO_COMPRESSION>.
 465
 466 B<EmptyFragments>: use empty fragments as a countermeasure against a
 467 SSL 3.0/TLS 1.0 protocol vulnerability affecting CBC ciphers. It
 468 is set by default. Inverse of B<SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS>.
 469
 470 B<Bugs>: enable various bug workarounds. Same as B<SSL_OP_ALL>.
 471
 472 B<DHSingle>: enable single use DH keys, set by default. Inverse of
 473 B<SSL_OP_DH_SINGLE>. Only used by servers.
 474
 475 B<ECDHSingle>: enable single use ECDH keys, set by default. Inverse of
 476 B<SSL_OP_ECDH_SINGLE>. Only used by servers.
 477
 478 B<ServerPreference>: use server and not client preference order when
 479 determining which cipher suite, signature algorithm or elliptic curve
 480 to use for an incoming connection.  Equivalent to
 481 B<SSL_OP_CIPHER_SERVER_PREFERENCE>. Only used by servers.
 482
 483 B<PrioritizeChaCha>: prioritizes ChaCha ciphers when the client has a
 484 ChaCha20 cipher at the top of its preference list. This usually indicates
 485 a mobile client is in use. Equivalent to B<SSL_OP_PRIORITIZE_CHACHA>.
 486 Only used by servers.
 487
 488 B<NoResumptionOnRenegotiation>: set
 489 B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> flag. Only used by servers.
 490
 491 B<NoRenegotiation>: disables all attempts at renegotiation in TLSv1.2 and
 492 earlier, same as setting B<SSL_OP_NO_RENEGOTIATION>.
 493
 494 B<UnsafeLegacyRenegotiation>: permits the use of unsafe legacy renegotiation.
 495 Equivalent to B<SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION>.
 496
 497 B<UnsafeLegacyServerConnect>: permits the use of unsafe legacy renegotiation
 498 for OpenSSL clients only. Equivalent to B<SSL_OP_LEGACY_SERVER_CONNECT>.
 499 Set by default.
 500
 501 B<EncryptThenMac>: use encrypt-then-mac extension, enabled by
 502 default. Inverse of B<SSL_OP_NO_ENCRYPT_THEN_MAC>: that is,
 503 B<-EncryptThenMac> is the same as setting B<SSL_OP_NO_ENCRYPT_THEN_MAC>.
 504
 505 B<AllowNoDHEKEX>: In TLSv1.3 allow a non-(ec)dhe based key exchange mode on
 506 resumption. This means that there will be no forward secrecy for the resumed
 507 session. Equivalent to B<SSL_OP_ALLOW_NO_DHE_KEX>.
 508
 509 B<MiddleboxCompat>: If set then dummy Change Cipher Spec (CCS) messages are sent
 510 in TLSv1.3. This has the effect of making TLSv1.3 look more like TLSv1.2 so that
 511 middleboxes that do not understand TLSv1.3 will not drop the connection. This
 512 option is set by default. A future version of OpenSSL may not set this by
 513 default. Equivalent to B<SSL_OP_ENABLE_MIDDLEBOX_COMPAT>.
 514
 515 B<AntiReplay>: If set then OpenSSL will automatically detect if a session ticket
 516 has been used more than once, TLSv1.3 has been negotiated, and early data is
 517 enabled on the server. A full handshake is forced if a session ticket is used a
 518 second or subsequent time. This option is set by default and is only used by
 519 servers. Anti-replay measures are required to comply with the TLSv1.3
 520 specification. Some applications may be able to mitigate the replay risks in
 521 other ways and in such cases the built-in OpenSSL functionality is not required.
 522 Disabling anti-replay is equivalent to setting B<SSL_OP_NO_ANTI_REPLAY>.
 523
 524 B<ExtendedMasterSecret>: use extended master secret extension, enabled by
 525 default. Inverse of B<SSL_OP_NO_EXTENDED_MASTER_SECRET>: that is,
 526 B<-ExtendedMasterSecret> is the same as setting B<SSL_OP_NO_EXTENDED_MASTER_SECRET>.
 527
 528 B<CANames>: use CA names extension, enabled by
 529 default. Inverse of B<SSL_OP_DISABLE_TLSEXT_CA_NAMES>: that is,
 530 B<-CANames> is the same as setting B<SSL_OP_DISABLE_TLSEXT_CA_NAMES>.
 531
 532 B<KTLS>: Enables kernel TLS if support has been compiled in, and it is supported
 533 by the negotiated ciphersuites and extensions. Equivalent to
 534 B<SSL_OP_ENABLE_KTLS>.
 535
 536 =item B<VerifyMode>
 537
 538 The B<value> argument is a comma separated list of flags to set.
 539
 540 B<Peer> enables peer verification: for clients only.
 541
 542 B<Request> requests but does not require a certificate from the client.
 543 Servers only.
 544
 545 B<Require> requests and requires a certificate from the client: an error
 546 occurs if the client does not present a certificate. Servers only.
 547
 548 B<Once> requests a certificate from a client only on the initial connection:
 549 not when renegotiating. Servers only.
 550
 551 B<RequestPostHandshake> configures the connection to support requests but does
 552 not require a certificate from the client post-handshake. A certificate will
 553 not be requested during the initial handshake. The server application must
 554 provide a mechanism to request a certificate post-handshake. Servers only.
 555 TLSv1.3 only.
 556
 557 B<RequiresPostHandshake> configures the connection to support requests and
 558 requires a certificate from the client post-handshake: an error occurs if the
 559 client does not present a certificate. A certificate will not be requested
 560 during the initial handshake. The server application must provide a mechanism
 561 to request a certificate post-handshake. Servers only. TLSv1.3 only.
 562
 563 =item B<ClientCAFile>, B<ClientCAPath>
 564
 565 A file or directory of certificates in PEM format whose names are used as the
 566 set of acceptable names for client CAs. Servers only. This option is only
 567 supported if certificate operations are permitted.
 568
 569 =back
 570
 571 =head1 SUPPORTED COMMAND TYPES
 572
 573 The function SSL_CONF_cmd_value_type() currently returns one of the following
 574 types:
 575
 576 =over 4
 577
 578 =item B<SSL_CONF_TYPE_UNKNOWN>
 579
 580 The B<option> string is unrecognised, this return value can be use to flag
 581 syntax errors.
 582
 583 =item B<SSL_CONF_TYPE_STRING>
 584
 585 The value is a string without any specific structure.
 586
 587 =item B<SSL_CONF_TYPE_FILE>
 588
 589 The value is a filename.
 590
 591 =item B<SSL_CONF_TYPE_DIR>
 592
 593 The value is a directory name.
 594
 595 =item B<SSL_CONF_TYPE_NONE>
 596
 597 The value string is not used e.g. a command line option which doesn't take an
 598 argument.
 599
 600 =back
 601
 602 =head1 NOTES
 603
 604 The order of operations is significant. This can be used to set either defaults
 605 or values which cannot be overridden. For example if an application calls:
 606
 607  SSL_CONF_cmd(ctx, "Protocol", "-SSLv3");
 608  SSL_CONF_cmd(ctx, userparam, uservalue);
 609
 610 it will disable SSLv3 support by default but the user can override it. If
 611 however the call sequence is:
 612
 613  SSL_CONF_cmd(ctx, userparam, uservalue);
 614  SSL_CONF_cmd(ctx, "Protocol", "-SSLv3");
 615
 616 SSLv3 is B<always> disabled and attempt to override this by the user are
 617 ignored.
 618
 619 By checking the return code of SSL_CONF_cmd() it is possible to query if a
 620 given B<option> is recognised, this is useful if SSL_CONF_cmd() values are
 621 mixed with additional application specific operations.
 622
 623 For example an application might call SSL_CONF_cmd() and if it returns
 624 -2 (unrecognised command) continue with processing of application specific
 625 commands.
 626
 627 Applications can also use SSL_CONF_cmd() to process command lines though the
 628 utility function SSL_CONF_cmd_argv() is normally used instead. One way
 629 to do this is to set the prefix to an appropriate value using
 630 SSL_CONF_CTX_set1_prefix(), pass the current argument to B<option> and the
 631 following argument to B<value> (which may be NULL).
 632
 633 In this case if the return value is positive then it is used to skip that
 634 number of arguments as they have been processed by SSL_CONF_cmd(). If -2 is
 635 returned then B<option> is not recognised and application specific arguments
 636 can be checked instead. If -3 is returned a required argument is missing
 637 and an error is indicated. If 0 is returned some other error occurred and
 638 this can be reported back to the user.
 639
 640 The function SSL_CONF_cmd_value_type() can be used by applications to
 641 check for the existence of a command or to perform additional syntax
 642 checking or translation of the command value. For example if the return
 643 value is B<SSL_CONF_TYPE_FILE> an application could translate a relative
 644 pathname to an absolute pathname.
 645
 646 =head1 RETURN VALUES
 647
 648 SSL_CONF_cmd() returns 1 if the value of B<option> is recognised and B<value> is
 649 B<NOT> used and 2 if both B<option> and B<value> are used. In other words it
 650 returns the number of arguments processed. This is useful when processing
 651 command lines.
 652
 653 A return value of -2 means B<option> is not recognised.
 654
 655 A return value of -3 means B<option> is recognised and the command requires a
 656 value but B<value> is NULL.
 657
 658 A return code of 0 indicates that both B<option> and B<value> are valid but an
 659 error occurred attempting to perform the operation: for example due to an
 660 error in the syntax of B<value> in this case the error queue may provide
 661 additional information.
 662
 663 =head1 EXAMPLES
 664
 665 Set supported signature algorithms:
 666
 667  SSL_CONF_cmd(ctx, "SignatureAlgorithms", "ECDSA+SHA256:RSA+SHA256:DSA+SHA256");
 668
 669 There are various ways to select the supported protocols.
 670
 671 This set the minimum protocol version to TLSv1, and so disables SSLv3.
 672 This is the recommended way to disable protocols.
 673
 674  SSL_CONF_cmd(ctx, "MinProtocol", "TLSv1");
 675
 676 The following also disables SSLv3:
 677
 678  SSL_CONF_cmd(ctx, "Protocol", "-SSLv3");
 679
 680 The following will first enable all protocols, and then disable
 681 SSLv3.
 682 If no protocol versions were disabled before this has the same effect as
 683 "-SSLv3", but if some versions were disables this will re-enable them before
 684 disabling SSLv3.
 685
 686  SSL_CONF_cmd(ctx, "Protocol", "ALL,-SSLv3");
 687
 688 Only enable TLSv1.2:
 689
 690  SSL_CONF_cmd(ctx, "MinProtocol", "TLSv1.2");
 691  SSL_CONF_cmd(ctx, "MaxProtocol", "TLSv1.2");
 692
 693 This also only enables TLSv1.2:
 694
 695  SSL_CONF_cmd(ctx, "Protocol", "-ALL,TLSv1.2");
 696
 697 Disable TLS session tickets:
 698
 699  SSL_CONF_cmd(ctx, "Options", "-SessionTicket");
 700
 701 Enable compression:
 702
 703  SSL_CONF_cmd(ctx, "Options", "Compression");
 704
 705 Set supported curves to P-256, P-384:
 706
 707  SSL_CONF_cmd(ctx, "Curves", "P-256:P-384");
 708
 709 =head1 SEE ALSO
 710
 711 L<ssl(7)>,
 712 L<SSL_CONF_CTX_new(3)>,
 713 L<SSL_CONF_CTX_set_flags(3)>,
 714 L<SSL_CONF_CTX_set1_prefix(3)>,
 715 L<SSL_CONF_CTX_set_ssl_ctx(3)>,
 716 L<SSL_CONF_cmd_argv(3)>,
 717 L<SSL_CTX_set_options(3)>
 718
 719 =head1 HISTORY
 720
 721 The SSL_CONF_cmd() function was added in OpenSSL 1.0.2.
 722
 723 The B<SSL_OP_NO_SSL2> option doesn't have effect since 1.1.0, but the macro
 724 is retained for backwards compatibility.
 725
 726 The B<SSL_CONF_TYPE_NONE> was added in OpenSSL 1.1.0. In earlier versions of
 727 OpenSSL passing a command which didn't take an argument would return
 728 B<SSL_CONF_TYPE_UNKNOWN>.
 729
 730 B<MinProtocol> and B<MaxProtocol> where added in OpenSSL 1.1.0.
 731
 732 B<AllowNoDHEKEX> and B<PrioritizeChaCha> were added in OpenSSL 1.1.1.
 733
 734 =head1 COPYRIGHT
 735
 736 Copyright 2012-2021 The OpenSSL Project Authors. All Rights Reserved.
 737
 738 Licensed under the Apache License 2.0 (the "License").  You may not use
 739 this file except in compliance with the License.  You can obtain a copy
 740 in the file LICENSE in the source distribution or at
 741 L<https://www.openssl.org/source/license.html>.
 742
 743 =cut