doc/man1/openssl-s_server.pod.in

   1 =pod
   2 {- OpenSSL::safe::output_do_not_edit_headers(); -}
   3
   4 =head1 NAME
   5
   6 openssl-s_server - SSL/TLS server program
   7
   8 =head1 SYNOPSIS
   9
  10 B<openssl> B<s_server>
  11 [B<-help>]
  12 [B<-port> I<+int>]
  13 [B<-accept> I<val>]
  14 [B<-unix> I<val>]
  15 [B<-4>]
  16 [B<-6>]
  17 [B<-unlink>]
  18 [B<-context> I<val>]
  19 [B<-verify> I<int>]
  20 [B<-Verify> I<int>]
  21 [B<-cert> I<infile>]
  22 [B<-naccept> I<+int>]
  23 [B<-serverinfo> I<val>]
  24 [B<-certform> B<DER>|B<PEM>]
  25 [B<-key> I<infile>]
  26 [B<-keyform> B<DER>|B<PEM>]
  27 [B<-pass> I<val>]
  28 [B<-dcert> I<infile>]
  29 [B<-dcertform> B<DER>|B<PEM>]
  30 [B<-dkey> I<infile>]
  31 [B<-dkeyform> B<DER>|B<PEM>]
  32 [B<-dpass> I<val>]
  33 [B<-nbio_test>]
  34 [B<-crlf>]
  35 [B<-debug>]
  36 [B<-msg>]
  37 [B<-msgfile> I<outfile>]
  38 [B<-state>]
  39 [B<-nocert>]
  40 [B<-quiet>]
  41 [B<-no_resume_ephemeral>]
  42 [B<-www>]
  43 [B<-WWW>]
  44 [B<-servername>]
  45 [B<-servername_fatal>]
  46 [B<-cert2> I<infile>]
  47 [B<-key2> I<infile>]
  48 [B<-tlsextdebug>]
  49 [B<-HTTP>]
  50 [B<-id_prefix> I<val>]
  51 [B<-keymatexport> I<val>]
  52 [B<-keymatexportlen> I<+int>]
  53 [B<-CRL> I<infile>]
  54 [B<-crl_download>]
  55 [B<-cert_chain> I<infile>]
  56 [B<-dcert_chain> I<infile>]
  57 [B<-chainCApath> I<dir>]
  58 [B<-verifyCApath> I<dir>]
  59 [B<-chainCAstore> I<uri>]
  60 [B<-verifyCAstore> I<uri>]
  61 [B<-no_cache>]
  62 [B<-ext_cache>]
  63 [B<-verify_return_error>]
  64 [B<-verify_quiet>]
  65 [B<-build_chain>]
  66 [B<-chainCAfile> I<infile>]
  67 [B<-verifyCAfile> I<infile>]
  68 [B<-ign_eof>]
  69 [B<-no_ign_eof>]
  70 [B<-status>]
  71 [B<-status_verbose>]
  72 [B<-status_timeout> I<int>]
  73 [B<-status_url> I<val>]
  74 [B<-status_file> I<infile>]
  75 [B<-trace>]
  76 [B<-security_debug>]
  77 [B<-security_debug_verbose>]
  78 [B<-brief>]
  79 [B<-rev>]
  80 [B<-async>]
  81 [B<-ssl_config> I<val>]
  82 [B<-max_send_frag> I<+int>]
  83 [B<-split_send_frag> I<+int>]
  84 [B<-max_pipelines> I<+int>]
  85 [B<-read_buf> I<+int>]
  86 [B<-bugs>]
  87 [B<-no_comp>]
  88 [B<-comp>]
  89 [B<-no_ticket>]
  90 [B<-num_tickets>]
  91 [B<-serverpref>]
  92 [B<-legacy_renegotiation>]
  93 [B<-no_renegotiation>]
  94 [B<-legacy_server_connect>]
  95 [B<-no_resumption_on_reneg>]
  96 [B<-no_legacy_server_connect>]
  97 [B<-allow_no_dhe_kex>]
  98 [B<-prioritize_chacha>]
  99 [B<-strict>]
 100 [B<-sigalgs> I<val>]
 101 [B<-client_sigalgs> I<val>]
 102 [B<-groups> I<val>]
 103 [B<-curves> I<val>]
 104 [B<-named_curve> I<val>]
 105 [B<-cipher> I<val>]
 106 [B<-ciphersuites> I<val>]
 107 [B<-dhparam> I<infile>]
 108 [B<-record_padding> I<val>]
 109 [B<-debug_broken_protocol>]
 110 [B<-policy> I<val>]
 111 [B<-purpose> I<val>]
 112 [B<-verify_name> I<val>]
 113 [B<-verify_depth> I<int>]
 114 [B<-auth_level> I<int>]
 115 [B<-attime> I<intmax>]
 116 [B<-verify_hostname> I<val>]
 117 [B<-verify_email> I<val>]
 118 [B<-verify_ip>]
 119 [B<-ignore_critical>]
 120 [B<-issuer_checks>]
 121 [B<-crl_check>]
 122 [B<-crl_check_all>]
 123 [B<-policy_check>]
 124 [B<-explicit_policy>]
 125 [B<-inhibit_any>]
 126 [B<-inhibit_map>]
 127 [B<-x509_strict>]
 128 [B<-extended_crl>]
 129 [B<-use_deltas>]
 130 [B<-policy_print>]
 131 [B<-check_ss_sig>]
 132 [B<-trusted_first>]
 133 [B<-suiteB_128_only>]
 134 [B<-suiteB_128>]
 135 [B<-suiteB_192>]
 136 [B<-partial_chain>]
 137 [B<-no_alt_chains>]
 138 [B<-no_check_time>]
 139 [B<-allow_proxy_certs>]
 140 [B<-nbio>]
 141 [B<-psk_identity> I<val>]
 142 [B<-psk_hint> I<val>]
 143 [B<-psk> I<val>]
 144 [B<-psk_session> I<file>]
 145 [B<-srpvfile> I<infile>]
 146 [B<-srpuserseed> I<val>]
 147 [B<-timeout>]
 148 [B<-mtu> I<+int>]
 149 [B<-listen>]
 150 [B<-sctp>]
 151 [B<-sctp_label_bug>]
 152 [B<-no_dhe>]
 153 [B<-nextprotoneg> I<val>]
 154 [B<-use_srtp> I<val>]
 155 [B<-alpn> I<val>]
 156 [B<-keylogfile> I<outfile>]
 157 [B<-max_early_data> I<int>]
 158 [B<-early_data>]
 159 [B<-anti_replay>]
 160 [B<-no_anti_replay>]
 161 [B<-http_server_binmode>]
 162 {- $OpenSSL::safe::opt_name_synopsis -}
 163 {- $OpenSSL::safe::opt_version_synopsis -}
 164 {- $OpenSSL::safe::opt_x_synopsis -}
 165 {- $OpenSSL::safe::opt_trust_synopsis -}
 166 {- $OpenSSL::safe::opt_r_synopsis -}
 167 {- $OpenSSL::safe::opt_engine_synopsis -}
 168
 169 =for openssl ifdef unix 4 6 unlink no_dhe nextprotoneg use_srtp engine
 170
 171 =for openssl ifdef status status_verbose status_timeout status_url status_file
 172
 173 =for openssl ifdef psk_hint srpvfile srpuserseed sctp sctp_label_bug
 174
 175 =for openssl ifdef sctp sctp_label_bug trace mtu timeout listen
 176
 177 =for openssl ifdef ssl3 tls1 tls1_1 tls1_2 tls1_3 dtls mtu dtls1 dtls1_2
 178
 179 =head1 DESCRIPTION
 180
 181 This command implements a generic SSL/TLS server which
 182 listens for connections on a given port using SSL/TLS.
 183
 184 =head1 OPTIONS
 185
 186 In addition to the options below, this command also supports
 187 the common and server only options documented
 188 L<SSL_CONF_cmd(3)/Supported Command Line Commands>
 189
 190 =over 4
 191
 192 =item B<-help>
 193
 194 Print out a usage message.
 195
 196 =item B<-port> I<+int>
 197
 198 The TCP port to listen on for connections. If not specified 4433 is used.
 199
 200 =item B<-accept> I<val>
 201
 202 The optional TCP host and port to listen on for connections. If not specified, *:4433 is used.
 203
 204 =item B<-unix> I<val>
 205
 206 Unix domain socket to accept on.
 207
 208 =item B<-4>
 209
 210 Use IPv4 only.
 211
 212 =item B<-6>
 213
 214 Use IPv6 only.
 215
 216 =item B<-unlink>
 217
 218 For -unix, unlink any existing socket first.
 219
 220 =item B<-context> I<val>
 221
 222 Sets the SSL context id. It can be given any string value. If this option
 223 is not present a default value will be used.
 224
 225 =item B<-verify> I<int>, B<-Verify> I<int>
 226
 227 The verify depth to use. This specifies the maximum length of the
 228 client certificate chain and makes the server request a certificate from
 229 the client. With the B<-verify> option a certificate is requested but the
 230 client does not have to send one, with the B<-Verify> option the client
 231 must supply a certificate or an error occurs.
 232
 233 If the cipher suite cannot request a client certificate (for example an
 234 anonymous cipher suite or PSK) this option has no effect.
 235
 236 =item B<-cert> I<infile>
 237
 238 The certificate to use, most servers cipher suites require the use of a
 239 certificate and some require a certificate with a certain public key type:
 240 for example the DSS cipher suites require a certificate containing a DSS
 241 (DSA) key. If not specified then the filename F<server.pem> will be used.
 242
 243 =item B<-cert_chain>
 244
 245 A file containing trusted certificates to use when attempting to build the
 246 client/server certificate chain related to the certificate specified via the
 247 B<-cert> option.
 248
 249 =item B<-build_chain>
 250
 251 Specify whether the application should build the certificate chain to be
 252 provided to the client.
 253
 254 =item B<-naccept> I<+int>
 255
 256 The server will exit after receiving the specified number of connections,
 257 default unlimited.
 258
 259 =item B<-serverinfo> I<val>
 260
 261 A file containing one or more blocks of PEM data.  Each PEM block
 262 must encode a TLS ServerHello extension (2 bytes type, 2 bytes length,
 263 followed by "length" bytes of extension data).  If the client sends
 264 an empty TLS ClientHello extension matching the type, the corresponding
 265 ServerHello extension will be returned.
 266
 267 =item B<-certform> B<DER>|B<PEM>, B<-CRLForm> B<DER>|B<PEM>
 268
 269 The certificate and CRL format; the default is PEM.
 270 See L<openssl(1)/Format Options> for details.
 271
 272 =item B<-key> I<infile>
 273
 274 The private key to use. If not specified then the certificate file will
 275 be used.
 276
 277 =item B<-keyform> B<DER>|B<PEM>
 278
 279 The key format; the default is B<PEM>.
 280 See L<openssl(1)/Format Options> for details.
 281
 282 =item B<-pass> I<val>
 283
 284 The private key password source.
 285 For more information about the format of I<val>,
 286 see L<openssl(1)/Pass Phrase Options>.
 287
 288 =item B<-dcert> I<infile>, B<-dkey> I<infile>
 289
 290 Specify an additional certificate and private key, these behave in the
 291 same manner as the B<-cert> and B<-key> options except there is no default
 292 if they are not specified (no additional certificate and key is used). As
 293 noted above some cipher suites require a certificate containing a key of
 294 a certain type. Some cipher suites need a certificate carrying an RSA key
 295 and some a DSS (DSA) key. By using RSA and DSS certificates and keys
 296 a server can support clients which only support RSA or DSS cipher suites
 297 by using an appropriate certificate.
 298
 299 =item B<-dcert_chain>
 300
 301 A file containing trusted certificates to use when attempting to build the
 302 server certificate chain when a certificate specified via the B<-dcert> option
 303 is in use.
 304
 305 =item B<-dcertform> B<DER>|B<PEM>, B<-dkeyform> B<DER>|B<PEM>
 306
 307 The format of the certificate and private key; the default is B<PEM>
 308 see L<openssl(1)/Format Options>.
 309
 310 =item B<-dpass> I<val>
 311
 312 The passphrase for the additional private key.
 313 For more information about the format of I<val>,
 314 see L<openssl(1)/Pass Phrase Options>.
 315
 316 =item B<-nbio_test>
 317
 318 Tests non blocking I/O.
 319
 320 =item B<-crlf>
 321
 322 This option translated a line feed from the terminal into CR+LF.
 323
 324 =item B<-debug>
 325
 326 Print extensive debugging information including a hex dump of all traffic.
 327
 328 =item B<-msg>
 329
 330 Show all protocol messages with hex dump.
 331
 332 =item B<-msgfile> I<outfile>
 333
 334 File to send output of B<-msg> or B<-trace> to, default standard output.
 335
 336 =item B<-state>
 337
 338 Prints the SSL session states.
 339
 340 =item B<-chainCApath> I<dir>
 341
 342 The directory to use for building the chain provided to the client. This
 343 directory must be in "hash format", see L<openssl-verify(1)> for more
 344 information.
 345
 346 =item B<-chainCAfile> I<file>
 347
 348 A file containing trusted certificates to use when attempting to build the
 349 server certificate chain.
 350
 351 =item B<-chainCAstore> I<uri>
 352
 353 The URI to a store to use for building the chain provided to the client.
 354 The URI may indicate a single certificate, as well as a collection of
 355 them.
 356 With URIs in the C<file:> scheme, this acts as B<-chainCAfile> or
 357 B<-chainCApath>, depending on if the URI indicates a directory or a
 358 single file.
 359 See L<ossl_store-file(7)> for more information on the C<file:> scheme.
 360
 361 =item B<-nocert>
 362
 363 If this option is set then no certificate is used. This restricts the
 364 cipher suites available to the anonymous ones (currently just anonymous
 365 DH).
 366
 367 =item B<-quiet>
 368
 369 Inhibit printing of session and certificate information.
 370
 371 =item B<-www>
 372
 373 Sends a status message back to the client when it connects. This includes
 374 information about the ciphers used and various session parameters.
 375 The output is in HTML format so this option will normally be used with a
 376 web browser. Cannot be used in conjunction with B<-early_data>.
 377
 378 =item B<-WWW>
 379
 380 Emulates a simple web server. Pages will be resolved relative to the
 381 current directory, for example if the URL https://myhost/page.html is
 382 requested the file F<./page.html> will be loaded.
 383 The files loaded are
 384 assumed to contain a complete and correct HTTP response (lines that
 385 are part of the HTTP response line and headers must end with CRLF). Cannot be
 386 used in conjunction with B<-early_data>.
 387 Cannot be used in conjunction
 388 with B<-early_data>.
 389
 390 =item B<-tlsextdebug>
 391
 392 Print a hex dump of any TLS extensions received from the server.
 393
 394 =item B<-id_prefix> I<val>
 395
 396 Generate SSL/TLS session IDs prefixed by I<val>. This is mostly useful
 397 for testing any SSL/TLS code (eg. proxies) that wish to deal with multiple
 398 servers, when each of which might be generating a unique range of session
 399 IDs (eg. with a certain prefix).
 400
 401 =item B<-verify_return_error>
 402
 403 Verification errors normally just print a message but allow the
 404 connection to continue, for debugging purposes.
 405 If this option is used, then verification errors close the connection.
 406
 407 =item B<-status>
 408
 409 Enables certificate status request support (aka OCSP stapling).
 410
 411 =item B<-status_verbose>
 412
 413 Enables certificate status request support (aka OCSP stapling) and gives
 414 a verbose printout of the OCSP response.
 415
 416 =item B<-status_timeout> I<int>
 417
 418 Sets the timeout for OCSP response to I<int> seconds.
 419
 420 =item B<-status_url> I<val>
 421
 422 Sets a fallback responder URL to use if no responder URL is present in the
 423 server certificate. Without this option an error is returned if the server
 424 certificate does not contain a responder address.
 425
 426 =item B<-status_file> I<infile>
 427
 428 Overrides any OCSP responder URLs from the certificate and always provides the
 429 OCSP Response stored in the file. The file must be in DER format.
 430
 431 =item B<-trace>
 432
 433 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
 434 with B<enable-ssl-trace> for this option to work.
 435
 436 =item B<-brief>
 437
 438 Provide a brief summary of connection parameters instead of the normal verbose
 439 output.
 440
 441 =item B<-rev>
 442
 443 Simple test server which just reverses the text received from the client
 444 and sends it back to the server. Also sets B<-brief>. Cannot be used in
 445 conjunction with B<-early_data>.
 446
 447 =item B<-async>
 448
 449 Switch on asynchronous mode. Cryptographic operations will be performed
 450 asynchronously. This will only have an effect if an asynchronous capable engine
 451 is also used via the B<-engine> option. For test purposes the dummy async engine
 452 (dasync) can be used (if available).
 453
 454 =item B<-max_send_frag> I<+int>
 455
 456 The maximum size of data fragment to send.
 457 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
 458
 459 =item B<-split_send_frag> I<+int>
 460
 461 The size used to split data for encrypt pipelines. If more data is written in
 462 one go than this value then it will be split into multiple pipelines, up to the
 463 maximum number of pipelines defined by max_pipelines. This only has an effect if
 464 a suitable cipher suite has been negotiated, an engine that supports pipelining
 465 has been loaded, and max_pipelines is greater than 1. See
 466 L<SSL_CTX_set_split_send_fragment(3)> for further information.
 467
 468 =item B<-max_pipelines> I<+int>
 469
 470 The maximum number of encrypt/decrypt pipelines to be used. This will only have
 471 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
 472 engine) and a suitable cipher suite has been negotiated. The default value is 1.
 473 See L<SSL_CTX_set_max_pipelines(3)> for further information.
 474
 475 =item B<-read_buf> I<+int>
 476
 477 The default read buffer size to be used for connections. This will only have an
 478 effect if the buffer size is larger than the size that would otherwise be used
 479 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
 480 further information).
 481
 482 =item B<-bugs>
 483
 484 There are several known bugs in SSL and TLS implementations. Adding this
 485 option enables various workarounds.
 486
 487 =item B<-no_comp>
 488
 489 Disable negotiation of TLS compression.
 490 TLS compression is not recommended and is off by default as of
 491 OpenSSL 1.1.0.
 492
 493 =item B<-comp>
 494
 495 Enable negotiation of TLS compression.
 496 This option was introduced in OpenSSL 1.1.0.
 497 TLS compression is not recommended and is off by default as of
 498 OpenSSL 1.1.0.
 499
 500 =item B<-no_ticket>
 501
 502 Disable RFC4507bis session ticket support. This option has no effect if TLSv1.3
 503 is negotiated. See B<-num_tickets>.
 504
 505 =item B<-num_tickets>
 506
 507 Control the number of tickets that will be sent to the client after a full
 508 handshake in TLSv1.3. The default number of tickets is 2. This option does not
 509 affect the number of tickets sent after a resumption handshake.
 510
 511 =item B<-serverpref>
 512
 513 Use the server's cipher preferences, rather than the client's preferences.
 514
 515 =item B<-prioritize_chacha>
 516
 517 Prioritize ChaCha ciphers when preferred by clients. Requires B<-serverpref>.
 518
 519 =item B<-no_resumption_on_reneg>
 520
 521 Set the B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> option.
 522
 523 =item B<-client_sigalgs> I<val>
 524
 525 Signature algorithms to support for client certificate authentication
 526 (colon-separated list).
 527
 528 =item B<-named_curve> I<val>
 529
 530 Specifies the elliptic curve to use. NOTE: this is single curve, not a list.
 531 For a list of all possible curves, use:
 532
 533     $ openssl ecparam -list_curves
 534
 535 =item B<-cipher> I<val>
 536
 537 This allows the list of TLSv1.2 and below ciphersuites used by the server to be
 538 modified. This list is combined with any TLSv1.3 ciphersuites that have been
 539 configured. When the client sends a list of supported ciphers the first client
 540 cipher also included in the server list is used. Because the client specifies
 541 the preference order, the order of the server cipherlist is irrelevant. See
 542 L<openssl-ciphers(1)> for more information.
 543
 544 =item B<-ciphersuites> I<val>
 545
 546 This allows the list of TLSv1.3 ciphersuites used by the server to be modified.
 547 This list is combined with any TLSv1.2 and below ciphersuites that have been
 548 configured. When the client sends a list of supported ciphers the first client
 549 cipher also included in the server list is used. Because the client specifies
 550 the preference order, the order of the server cipherlist is irrelevant. See
 551 L<openssl-ciphers(1)> command for more information. The format for this list is
 552 a simple colon (":") separated list of TLSv1.3 ciphersuite names.
 553
 554 =item B<-dhparam> I<infile>
 555
 556 The DH parameter file to use. The ephemeral DH cipher suites generate keys
 557 using a set of DH parameters. If not specified then an attempt is made to
 558 load the parameters from the server certificate file.
 559 If this fails then a static set of parameters hard coded into this command
 560 will be used.
 561
 562 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
 563 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
 564 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
 565 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
 566 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
 567 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
 568 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
 569
 570 Set different peer certificate verification options.
 571 See the L<openssl-verify(1)> manual page for details.
 572
 573 =item B<-crl_check>, B<-crl_check_all>
 574
 575 Check the peer certificate has not been revoked by its CA.
 576 The CRL(s) are appended to the certificate file. With the B<-crl_check_all>
 577 option all CRLs of all CAs in the chain are checked.
 578
 579 =item B<-nbio>
 580
 581 Turns on non blocking I/O.
 582
 583 =item B<-psk_identity> I<val>
 584
 585 Expect the client to send PSK identity I<val> when using a PSK
 586 cipher suite, and warn if they do not.  By default, the expected PSK
 587 identity is the string "Client_identity".
 588
 589 =item B<-psk_hint> I<val>
 590
 591 Use the PSK identity hint I<val> when using a PSK cipher suite.
 592
 593 =item B<-psk> I<val>
 594
 595 Use the PSK key I<val> when using a PSK cipher suite. The key is
 596 given as a hexadecimal number without leading 0x, for example -psk
 597 1a2b3c4d.
 598 This option must be provided in order to use a PSK cipher.
 599
 600 =item B<-psk_session> I<file>
 601
 602 Use the pem encoded SSL_SESSION data stored in I<file> as the basis of a PSK.
 603 Note that this will only work if TLSv1.3 is negotiated.
 604
 605 =item B<-listen>
 606
 607 This option can only be used in conjunction with one of the DTLS options above.
 608 With this option, this command will listen on a UDP port for incoming
 609 connections.
 610 Any ClientHellos that arrive will be checked to see if they have a cookie in
 611 them or not.
 612 Any without a cookie will be responded to with a HelloVerifyRequest.
 613 If a ClientHello with a cookie is received then this command will
 614 connect to that peer and complete the handshake.
 615
 616 =item B<-sctp>
 617
 618 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
 619 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
 620 available where OpenSSL has support for SCTP enabled.
 621
 622 =item B<-sctp_label_bug>
 623
 624 Use the incorrect behaviour of older OpenSSL implementations when computing
 625 endpoint-pair shared secrets for DTLS/SCTP. This allows communication with
 626 older broken implementations but breaks interoperability with correct
 627 implementations. Must be used in conjunction with B<-sctp>. This option is only
 628 available where OpenSSL has support for SCTP enabled.
 629
 630 =item B<-no_dhe>
 631
 632 If this option is set then no DH parameters will be loaded effectively
 633 disabling the ephemeral DH cipher suites.
 634
 635 =item B<-alpn> I<val>, B<-nextprotoneg> I<val>
 636
 637 These flags enable the Enable the Application-Layer Protocol Negotiation
 638 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
 639 IETF standard and replaces NPN.
 640 The I<val> list is a comma-separated list of supported protocol
 641 names.  The list should contain the most desirable protocols first.
 642 Protocol names are printable ASCII strings, for example "http/1.1" or
 643 "spdy/3".
 644 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
 645
 646 =item B<-keylogfile> I<outfile>
 647
 648 Appends TLS secrets to the specified keylog file such that external programs
 649 (like Wireshark) can decrypt TLS connections.
 650
 651 =item B<-max_early_data> I<int>
 652
 653 Change the default maximum early data bytes that are specified for new sessions
 654 and any incoming early data (when used in conjunction with the B<-early_data>
 655 flag). The default value is approximately 16k. The argument must be an integer
 656 greater than or equal to 0.
 657
 658 =item B<-early_data>
 659
 660 Accept early data where possible. Cannot be used in conjunction with B<-www>,
 661 B<-WWW>, B<-HTTP> or B<-rev>.
 662
 663 =item B<-anti_replay>, B<-no_anti_replay>
 664
 665 Switches replay protection on or off, respectively. Replay protection is on by
 666 default unless overridden by a configuration file. When it is on, OpenSSL will
 667 automatically detect if a session ticket has been used more than once, TLSv1.3
 668 has been negotiated, and early data is enabled on the server. A full handshake
 669 is forced if a session ticket is used a second or subsequent time. Any early
 670 data that was sent will be rejected.
 671
 672 =item B<-http_server_binmode>
 673
 674 When acting as web-server (using option B<-WWW> or B<-HTTP>) open files requested
 675 by the client in binary mode.
 676
 677 {- $OpenSSL::safe::opt_name_item -}
 678
 679 {- $OpenSSL::safe::opt_version_item -}
 680
 681 {- $OpenSSL::safe::opt_x_item -}
 682
 683 {- $OpenSSL::safe::opt_trust_item -}
 684
 685 {- $OpenSSL::safe::opt_r_item -}
 686
 687 {- $OpenSSL::safe::opt_engine_item -}
 688
 689 =back
 690
 691 =head1 CONNECTED COMMANDS
 692
 693 If a connection request is established with an SSL client and neither the
 694 B<-www> nor the B<-WWW> option has been used then normally any data received
 695 from the client is displayed and any key presses will be sent to the client.
 696
 697 Certain commands are also recognized which perform special operations. These
 698 commands are a letter which must appear at the start of a line. They are listed
 699 below.
 700
 701 =over 4
 702
 703 =item B<q>
 704
 705 End the current SSL connection but still accept new connections.
 706
 707 =item B<Q>
 708
 709 End the current SSL connection and exit.
 710
 711 =item B<r>
 712
 713 Renegotiate the SSL session (TLSv1.2 and below only).
 714
 715 =item B<R>
 716
 717 Renegotiate the SSL session and request a client certificate (TLSv1.2 and below
 718 only).
 719
 720 =item B<P>
 721
 722 Send some plain text down the underlying TCP connection: this should
 723 cause the client to disconnect due to a protocol violation.
 724
 725 =item B<S>
 726
 727 Print out some session cache status information.
 728
 729 =item B<k>
 730
 731 Send a key update message to the client (TLSv1.3 only)
 732
 733 =item B<K>
 734
 735 Send a key update message to the client and request one back (TLSv1.3 only)
 736
 737 =item B<c>
 738
 739 Send a certificate request to the client (TLSv1.3 only)
 740
 741 =back
 742
 743 =head1 NOTES
 744
 745 This command can be used to debug SSL clients. To accept connections
 746 from a web browser the command:
 747
 748  openssl s_server -accept 443 -www
 749
 750 can be used for example.
 751
 752 Although specifying an empty list of CAs when requesting a client certificate
 753 is strictly speaking a protocol violation, some SSL clients interpret this to
 754 mean any CA is acceptable. This is useful for debugging purposes.
 755
 756 The session parameters can printed out using the L<openssl-sess_id(1)> command.
 757
 758 =head1 BUGS
 759
 760 Because this program has a lot of options and also because some of the
 761 techniques used are rather old, the C source for this command is rather
 762 hard to read and not a model of how things should be done.
 763 A typical SSL server program would be much simpler.
 764
 765 The output of common ciphers is wrong: it just gives the list of ciphers that
 766 OpenSSL recognizes and the client supports.
 767
 768 There should be a way for this command to print out details
 769 of any unknown cipher suites a client says it supports.
 770
 771 =head1 SEE ALSO
 772
 773 L<openssl(1)>,
 774 L<openssl-sess_id(1)>,
 775 L<openssl-s_client(1)>,
 776 L<openssl-ciphers(1)>,
 777 L<SSL_CONF_cmd(3)>,
 778 L<SSL_CTX_set_max_send_fragment(3)>,
 779 L<SSL_CTX_set_split_send_fragment(3)>,
 780 L<SSL_CTX_set_max_pipelines(3)>,
 781 L<ossl_store-file(7)>
 782
 783 =head1 HISTORY
 784
 785 The -no_alt_chains option was added in OpenSSL 1.1.0.
 786
 787 The
 788 -allow-no-dhe-kex and -prioritize_chacha options were added in OpenSSL 1.1.1.
 789
 790 =head1 COPYRIGHT
 791
 792 Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.
 793
 794 Licensed under the Apache License 2.0 (the "License").  You may not use
 795 this file except in compliance with the License.  You can obtain a copy
 796 in the file LICENSE in the source distribution or at
 797 L<https://www.openssl.org/source/license.html>.
 798
 799 =cut