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