1=pod 2{- OpenSSL::safe::output_do_not_edit_headers(); -} 3 4=head1 NAME 5 6openssl-s_client - SSL/TLS client program 7 8=head1 SYNOPSIS 9 10B<openssl> B<s_client> 11[B<-help>] 12[B<-ssl_config> I<section>] 13[B<-connect> I<host:port>] 14[B<-host> I<hostname>] 15[B<-port> I<port>] 16[B<-bind> I<host:port>] 17[B<-proxy> I<host:port>] 18[B<-proxy_user> I<userid>] 19[B<-proxy_pass> I<arg>] 20[B<-unix> I<path>] 21[B<-4>] 22[B<-6>] 23[B<-servername> I<name>] 24[B<-noservername>] 25[B<-verify> I<depth>] 26[B<-verify_return_error>] 27[B<-verify_quiet>] 28[B<-verifyCAfile> I<filename>] 29[B<-verifyCApath> I<dir>] 30[B<-verifyCAstore> I<uri>] 31[B<-cert> I<filename>] 32[B<-certform> B<DER>|B<PEM>|B<P12>] 33[B<-cert_chain> I<filename>] 34[B<-build_chain>] 35[B<-CRL> I<filename>] 36[B<-CRLform> B<DER>|B<PEM>] 37[B<-crl_download>] 38[B<-key> I<filename>|I<uri>] 39[B<-keyform> B<DER>|B<PEM>|B<P12>|B<ENGINE>] 40[B<-pass> I<arg>] 41[B<-chainCAfile> I<filename>] 42[B<-chainCApath> I<directory>] 43[B<-chainCAstore> I<uri>] 44[B<-requestCAfile> I<filename>] 45[B<-dane_tlsa_domain> I<domain>] 46[B<-dane_tlsa_rrdata> I<rrdata>] 47[B<-dane_ee_no_namechecks>] 48[B<-reconnect>] 49[B<-showcerts>] 50[B<-prexit>] 51[B<-no-interactive>] 52[B<-debug>] 53[B<-trace>] 54[B<-nocommands>] 55[B<-security_debug>] 56[B<-security_debug_verbose>] 57[B<-msg>] 58[B<-timeout>] 59[B<-mtu> I<size>] 60[B<-no_etm>] 61[B<-no_ems>] 62[B<-keymatexport> I<label>] 63[B<-keymatexportlen> I<len>] 64[B<-msgfile> I<filename>] 65[B<-nbio_test>] 66[B<-state>] 67[B<-nbio>] 68[B<-crlf>] 69[B<-ign_eof>] 70[B<-no_ign_eof>] 71[B<-psk_identity> I<identity>] 72[B<-psk> I<key>] 73[B<-psk_session> I<file>] 74[B<-quiet>] 75[B<-sctp>] 76[B<-sctp_label_bug>] 77[B<-fallback_scsv>] 78[B<-async>] 79[B<-maxfraglen> I<len>] 80[B<-max_send_frag>] 81[B<-split_send_frag>] 82[B<-max_pipelines>] 83[B<-read_buf>] 84[B<-ignore_unexpected_eof>] 85[B<-bugs>] 86[B<-comp>] 87[B<-no_comp>] 88[B<-brief>] 89[B<-legacy_server_connect>] 90[B<-no_legacy_server_connect>] 91[B<-allow_no_dhe_kex>] 92[B<-sigalgs> I<sigalglist>] 93[B<-curves> I<curvelist>] 94[B<-cipher> I<cipherlist>] 95[B<-ciphersuites> I<val>] 96[B<-serverpref>] 97[B<-starttls> I<protocol>] 98[B<-name> I<hostname>] 99[B<-xmpphost> I<hostname>] 100[B<-name> I<hostname>] 101[B<-tlsextdebug>] 102[B<-no_ticket>] 103[B<-sess_out> I<filename>] 104[B<-serverinfo> I<types>] 105[B<-sess_in> I<filename>] 106[B<-serverinfo> I<types>] 107[B<-status>] 108[B<-alpn> I<protocols>] 109[B<-nextprotoneg> I<protocols>] 110[B<-ct>] 111[B<-noct>] 112[B<-ctlogfile>] 113[B<-keylogfile> I<file>] 114[B<-early_data> I<file>] 115[B<-enable_pha>] 116[B<-use_srtp> I<value>] 117[B<-srpuser> I<value>] 118[B<-srppass> I<value>] 119[B<-srp_lateuser>] 120[B<-srp_moregroups>] 121[B<-srp_strength> I<number>] 122[B<-ktls>] 123[B<-tfo>] 124{- $OpenSSL::safe::opt_name_synopsis -} 125{- $OpenSSL::safe::opt_version_synopsis -} 126{- $OpenSSL::safe::opt_x_synopsis -} 127{- $OpenSSL::safe::opt_trust_synopsis -} 128{- $OpenSSL::safe::opt_s_synopsis -} 129{- $OpenSSL::safe::opt_r_synopsis -} 130{- $OpenSSL::safe::opt_provider_synopsis -} 131{- $OpenSSL::safe::opt_engine_synopsis -}[B<-ssl_client_engine> I<id>] 132{- $OpenSSL::safe::opt_v_synopsis -} 133[I<host>:I<port>] 134 135=head1 DESCRIPTION 136 137This command implements a generic SSL/TLS client which 138connects to a remote host using SSL/TLS. It is a I<very> useful diagnostic 139tool for SSL servers. 140 141=head1 OPTIONS 142 143In addition to the options below, this command also supports the 144common and client only options documented 145in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)> 146manual page. 147 148=over 4 149 150=item B<-help> 151 152Print out a usage message. 153 154=item B<-ssl_config> I<section> 155 156Use the specified section of the configuration file to configure the B<SSL_CTX> object. 157 158=item B<-connect> I<host>:I<port> 159 160This specifies the host and optional port to connect to. It is possible to 161select the host and port using the optional target positional argument instead. 162If neither this nor the target positional argument are specified then an attempt 163is made to connect to the local host on port 4433. 164 165=item B<-host> I<hostname> 166 167Host to connect to; use B<-connect> instead. 168 169=item B<-port> I<port> 170 171Connect to the specified port; use B<-connect> instead. 172 173=item B<-bind> I<host:port> 174 175This specifies the host address and or port to bind as the source for the 176connection. For Unix-domain sockets the port is ignored and the host is 177used as the source socket address. 178 179=item B<-proxy> I<host:port> 180 181When used with the B<-connect> flag, the program uses the host and port 182specified with this flag and issues an HTTP CONNECT command to connect 183to the desired server. 184 185=item B<-proxy_user> I<userid> 186 187When used with the B<-proxy> flag, the program will attempt to authenticate 188with the specified proxy using basic (base64) authentication. 189NB: Basic authentication is insecure; the credentials are sent to the proxy 190in easily reversible base64 encoding before any TLS/SSL session is established. 191Therefore, these credentials are easily recovered by anyone able to sniff/trace 192the network. Use with caution. 193 194=item B<-proxy_pass> I<arg> 195 196The proxy password source, used with the B<-proxy_user> flag. 197For more information about the format of B<arg> 198see L<openssl-passphrase-options(1)>. 199 200=item B<-unix> I<path> 201 202Connect over the specified Unix-domain socket. 203 204=item B<-4> 205 206Use IPv4 only. 207 208=item B<-6> 209 210Use IPv6 only. 211 212=item B<-servername> I<name> 213 214Set the TLS SNI (Server Name Indication) extension in the ClientHello message to 215the given value. 216If B<-servername> is not provided, the TLS SNI extension will be populated with 217the name given to B<-connect> if it follows a DNS name format. If B<-connect> is 218not provided either, the SNI is set to "localhost". 219This is the default since OpenSSL 1.1.1. 220 221Even though SNI should normally be a DNS name and not an IP address, if 222B<-servername> is provided then that name will be sent, regardless of whether 223it is a DNS name or not. 224 225This option cannot be used in conjunction with B<-noservername>. 226 227=item B<-noservername> 228 229Suppresses sending of the SNI (Server Name Indication) extension in the 230ClientHello message. Cannot be used in conjunction with the B<-servername> or 231B<-dane_tlsa_domain> options. 232 233=item B<-cert> I<filename> 234 235The client certificate to use, if one is requested by the server. 236The default is not to use a certificate. 237 238The chain for the client certificate may be specified using B<-cert_chain>. 239 240=item B<-certform> B<DER>|B<PEM>|B<P12> 241 242The client certificate file format to use; unspecified by default. 243See L<openssl-format-options(1)> for details. 244 245=item B<-cert_chain> 246 247A file or URI of untrusted certificates to use when attempting to build the 248certificate chain related to the certificate specified via the B<-cert> option. 249The input can be in PEM, DER, or PKCS#12 format. 250 251=item B<-build_chain> 252 253Specify whether the application should build the client certificate chain to be 254provided to the server. 255 256=item B<-CRL> I<filename> 257 258CRL file to use to check the server's certificate. 259 260=item B<-CRLform> B<DER>|B<PEM> 261 262The CRL file format; unspecified by default. 263See L<openssl-format-options(1)> for details. 264 265=item B<-crl_download> 266 267Download CRL from distribution points in the certificate. 268 269=item B<-key> I<filename>|I<uri> 270 271The client private key to use. 272If not specified then the certificate file will be used to read also the key. 273 274=item B<-keyform> B<DER>|B<PEM>|B<P12>|B<ENGINE> 275 276The key format; unspecified by default. 277See L<openssl-format-options(1)> for details. 278 279=item B<-pass> I<arg> 280 281the private key and certificate file password source. 282For more information about the format of I<arg> 283see L<openssl-passphrase-options(1)>. 284 285=item B<-verify> I<depth> 286 287The verify depth to use. This specifies the maximum length of the 288server certificate chain and turns on server certificate verification. 289Currently the verify operation continues after errors so all the problems 290with a certificate chain can be seen. As a side effect the connection 291will never fail due to a server certificate verify failure. 292 293=item B<-verify_return_error> 294 295Return verification errors instead of continuing. This will typically 296abort the handshake with a fatal error. 297 298=item B<-verify_quiet> 299 300Limit verify output to only errors. 301 302=item B<-verifyCAfile> I<filename> 303 304A file in PEM format containing trusted certificates to use 305for verifying the server's certificate. 306 307=item B<-verifyCApath> I<dir> 308 309A directory containing trusted certificates to use 310for verifying the server's certificate. 311This directory must be in "hash format", 312see L<openssl-verify(1)> for more information. 313 314=item B<-verifyCAstore> I<uri> 315 316The URI of a store containing trusted certificates to use 317for verifying the server's certificate. 318 319=item B<-chainCAfile> I<file> 320 321A file in PEM format containing trusted certificates to use 322when attempting to build the client certificate chain. 323 324=item B<-chainCApath> I<directory> 325 326A directory containing trusted certificates to use 327for building the client certificate chain provided to the server. 328This directory must be in "hash format", 329see L<openssl-verify(1)> for more information. 330 331=item B<-chainCAstore> I<uri> 332 333The URI of a store containing trusted certificates to use 334when attempting to build the client certificate chain. 335The URI may indicate a single certificate, as well as a collection of them. 336With URIs in the C<file:> scheme, this acts as B<-chainCAfile> or 337B<-chainCApath>, depending on if the URI indicates a directory or a 338single file. 339See L<ossl_store-file(7)> for more information on the C<file:> scheme. 340 341=item B<-requestCAfile> I<file> 342 343A file containing a list of certificates whose subject names will be sent 344to the server in the B<certificate_authorities> extension. Only supported 345for TLS 1.3 346 347=item B<-dane_tlsa_domain> I<domain> 348 349Enable RFC6698/RFC7671 DANE TLSA authentication and specify the 350TLSA base domain which becomes the default SNI hint and the primary 351reference identifier for hostname checks. This must be used in 352combination with at least one instance of the B<-dane_tlsa_rrdata> 353option below. 354 355When DANE authentication succeeds, the diagnostic output will include 356the lowest (closest to 0) depth at which a TLSA record authenticated 357a chain certificate. When that TLSA record is a "2 1 0" trust 358anchor public key that signed (rather than matched) the top-most 359certificate of the chain, the result is reported as "TA public key 360verified". Otherwise, either the TLSA record "matched TA certificate" 361at a positive depth or else "matched EE certificate" at depth 0. 362 363=item B<-dane_tlsa_rrdata> I<rrdata> 364 365Use one or more times to specify the RRDATA fields of the DANE TLSA 366RRset associated with the target service. The I<rrdata> value is 367specified in "presentation form", that is four whitespace separated 368fields that specify the usage, selector, matching type and associated 369data, with the last of these encoded in hexadecimal. Optional 370whitespace is ignored in the associated data field. For example: 371 372 $ openssl s_client -brief -starttls smtp \ 373 -connect smtp.example.com:25 \ 374 -dane_tlsa_domain smtp.example.com \ 375 -dane_tlsa_rrdata "2 1 1 376 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \ 377 -dane_tlsa_rrdata "2 1 1 378 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18" 379 ... 380 Verification: OK 381 Verified peername: smtp.example.com 382 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1 383 ... 384 385=item B<-dane_ee_no_namechecks> 386 387This disables server name checks when authenticating via DANE-EE(3) TLSA 388records. 389For some applications, primarily web browsers, it is not safe to disable name 390checks due to "unknown key share" attacks, in which a malicious server can 391convince a client that a connection to a victim server is instead a secure 392connection to the malicious server. 393The malicious server may then be able to violate cross-origin scripting 394restrictions. 395Thus, despite the text of RFC7671, name checks are by default enabled for 396DANE-EE(3) TLSA records, and can be disabled in applications where it is safe 397to do so. 398In particular, SMTP and XMPP clients should set this option as SRV and MX 399records already make it possible for a remote domain to redirect client 400connections to any server of its choice, and in any case SMTP and XMPP clients 401do not execute scripts downloaded from remote servers. 402 403=item B<-reconnect> 404 405Reconnects to the same server 5 times using the same session ID, this can 406be used as a test that session caching is working. 407 408=item B<-showcerts> 409 410Displays the server certificate list as sent by the server: it only consists of 411certificates the server has sent (in the order the server has sent them). It is 412B<not> a verified chain. 413 414=item B<-prexit> 415 416Print session information when the program exits. This will always attempt 417to print out information even if the connection fails. Normally information 418will only be printed out once if the connection succeeds. This option is useful 419because the cipher in use may be renegotiated or the connection may fail 420because a client certificate is required or is requested only after an 421attempt is made to access a certain URL. Note: the output produced by this 422option is not always accurate because a connection might never have been 423established. 424 425=item B<-no-interactive> 426 427This flag can be used to run the client in a non-interactive mode. 428 429=item B<-state> 430 431Prints out the SSL session states. 432 433=item B<-debug> 434 435Print extensive debugging information including a hex dump of all traffic. 436 437=item B<-nocommands> 438 439Do not use interactive command letters. 440 441=item B<-security_debug> 442 443Enable security debug messages. 444 445=item B<-security_debug_verbose> 446 447Output more security debug output. 448 449=item B<-msg> 450 451Show protocol messages. 452 453=item B<-timeout> 454 455Enable send/receive timeout on DTLS connections. 456 457=item B<-mtu> I<size> 458 459Set MTU of the link layer to the specified size. 460 461=item B<-no_etm> 462 463Disable Encrypt-then-MAC negotiation. 464 465=item B<-no_ems> 466 467Disable Extended master secret negotiation. 468 469=item B<-keymatexport> I<label> 470 471Export keying material using the specified label. 472 473=item B<-keymatexportlen> I<len> 474 475Export the specified number of bytes of keying material; default is 20. 476 477Show all protocol messages with hex dump. 478 479=item B<-trace> 480 481Show verbose trace output of protocol messages. 482 483=item B<-msgfile> I<filename> 484 485File to send output of B<-msg> or B<-trace> to, default standard output. 486 487=item B<-nbio_test> 488 489Tests nonblocking I/O 490 491=item B<-nbio> 492 493Turns on nonblocking I/O 494 495=item B<-crlf> 496 497This option translated a line feed from the terminal into CR+LF as required 498by some servers. 499 500=item B<-ign_eof> 501 502Inhibit shutting down the connection when end of file is reached in the 503input. 504 505=item B<-quiet> 506 507Inhibit printing of session and certificate information. This implicitly 508turns on B<-ign_eof> as well. 509 510=item B<-no_ign_eof> 511 512Shut down the connection when end of file is reached in the input. 513Can be used to override the implicit B<-ign_eof> after B<-quiet>. 514 515=item B<-psk_identity> I<identity> 516 517Use the PSK identity I<identity> when using a PSK cipher suite. 518The default value is "Client_identity" (without the quotes). 519 520=item B<-psk> I<key> 521 522Use the PSK key I<key> when using a PSK cipher suite. The key is 523given as a hexadecimal number without leading 0x, for example -psk 5241a2b3c4d. 525This option must be provided in order to use a PSK cipher. 526 527=item B<-psk_session> I<file> 528 529Use the pem encoded SSL_SESSION data stored in I<file> as the basis of a PSK. 530Note that this will only work if TLSv1.3 is negotiated. 531 532=item B<-sctp> 533 534Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in 535conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only 536available where OpenSSL has support for SCTP enabled. 537 538=item B<-sctp_label_bug> 539 540Use the incorrect behaviour of older OpenSSL implementations when computing 541endpoint-pair shared secrets for DTLS/SCTP. This allows communication with 542older broken implementations but breaks interoperability with correct 543implementations. Must be used in conjunction with B<-sctp>. This option is only 544available where OpenSSL has support for SCTP enabled. 545 546=item B<-fallback_scsv> 547 548Send TLS_FALLBACK_SCSV in the ClientHello. 549 550=item B<-async> 551 552Switch on asynchronous mode. Cryptographic operations will be performed 553asynchronously. This will only have an effect if an asynchronous capable engine 554is also used via the B<-engine> option. For test purposes the dummy async engine 555(dasync) can be used (if available). 556 557=item B<-maxfraglen> I<len> 558 559Enable Maximum Fragment Length Negotiation; allowed values are 560C<512>, C<1024>, C<2048>, and C<4096>. 561 562=item B<-max_send_frag> I<int> 563 564The maximum size of data fragment to send. 565See L<SSL_CTX_set_max_send_fragment(3)> for further information. 566 567=item B<-split_send_frag> I<int> 568 569The size used to split data for encrypt pipelines. If more data is written in 570one go than this value then it will be split into multiple pipelines, up to the 571maximum number of pipelines defined by max_pipelines. This only has an effect if 572a suitable cipher suite has been negotiated, an engine that supports pipelining 573has been loaded, and max_pipelines is greater than 1. See 574L<SSL_CTX_set_split_send_fragment(3)> for further information. 575 576=item B<-max_pipelines> I<int> 577 578The maximum number of encrypt/decrypt pipelines to be used. This will only have 579an effect if an engine has been loaded that supports pipelining (e.g. the dasync 580engine) and a suitable cipher suite has been negotiated. The default value is 1. 581See L<SSL_CTX_set_max_pipelines(3)> for further information. 582 583=item B<-read_buf> I<int> 584 585The default read buffer size to be used for connections. This will only have an 586effect if the buffer size is larger than the size that would otherwise be used 587and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for 588further information). 589 590=item B<-ignore_unexpected_eof> 591 592Some TLS implementations do not send the mandatory close_notify alert on 593shutdown. If the application tries to wait for the close_notify alert but the 594peer closes the connection without sending it, an error is generated. When this 595option is enabled the peer does not need to send the close_notify alert and a 596closed connection will be treated as if the close_notify alert was received. 597For more information on shutting down a connection, see L<SSL_shutdown(3)>. 598 599=item B<-bugs> 600 601There are several known bugs in SSL and TLS implementations. Adding this 602option enables various workarounds. 603 604=item B<-comp> 605 606Enables support for SSL/TLS compression. 607This option was introduced in OpenSSL 1.1.0. 608TLS compression is not recommended and is off by default as of 609OpenSSL 1.1.0. 610 611=item B<-no_comp> 612 613Disables support for SSL/TLS compression. 614TLS compression is not recommended and is off by default as of 615OpenSSL 1.1.0. 616 617=item B<-brief> 618 619Only provide a brief summary of connection parameters instead of the 620normal verbose output. 621 622=item B<-sigalgs> I<sigalglist> 623 624Specifies the list of signature algorithms that are sent by the client. 625The server selects one entry in the list based on its preferences. 626For example strings, see L<SSL_CTX_set1_sigalgs(3)> 627 628=item B<-curves> I<curvelist> 629 630Specifies the list of supported curves to be sent by the client. The curve is 631ultimately selected by the server. For a list of all curves, use: 632 633 $ openssl ecparam -list_curves 634 635=item B<-cipher> I<cipherlist> 636 637This allows the TLSv1.2 and below cipher list sent by the client to be modified. 638This list will be combined with any TLSv1.3 ciphersuites that have been 639configured. Although the server determines which ciphersuite is used it should 640take the first supported cipher in the list sent by the client. See 641L<openssl-ciphers(1)> for more information. 642 643=item B<-ciphersuites> I<val> 644 645This allows the TLSv1.3 ciphersuites sent by the client to be modified. This 646list will be combined with any TLSv1.2 and below ciphersuites that have been 647configured. Although the server determines which cipher suite is used it should 648take the first supported cipher in the list sent by the client. See 649L<openssl-ciphers(1)> for more information. The format for this list is a simple 650colon (":") separated list of TLSv1.3 ciphersuite names. 651 652=item B<-starttls> I<protocol> 653 654Send the protocol-specific message(s) to switch to TLS for communication. 655I<protocol> is a keyword for the intended protocol. Currently, the only 656supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server", 657"irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap". 658 659=item B<-xmpphost> I<hostname> 660 661This option, when used with "-starttls xmpp" or "-starttls xmpp-server", 662specifies the host for the "to" attribute of the stream element. 663If this option is not specified, then the host specified with "-connect" 664will be used. 665 666This option is an alias of the B<-name> option for "xmpp" and "xmpp-server". 667 668=item B<-name> I<hostname> 669 670This option is used to specify hostname information for various protocols 671used with B<-starttls> option. Currently only "xmpp", "xmpp-server", 672"smtp" and "lmtp" can utilize this B<-name> option. 673 674If this option is used with "-starttls xmpp" or "-starttls xmpp-server", 675if specifies the host for the "to" attribute of the stream element. If this 676option is not specified, then the host specified with "-connect" will be used. 677 678If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies 679the name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If 680this option is not specified, then "mail.example.com" will be used. 681 682=item B<-tlsextdebug> 683 684Print out a hex dump of any TLS extensions received from the server. 685 686=item B<-no_ticket> 687 688Disable RFC4507bis session ticket support. 689 690=item B<-sess_out> I<filename> 691 692Output SSL session to I<filename>. 693 694=item B<-sess_in> I<filename> 695 696Load SSL session from I<filename>. The client will attempt to resume a 697connection from this session. 698 699=item B<-serverinfo> I<types> 700 701A list of comma-separated TLS Extension Types (numbers between 0 and 70265535). Each type will be sent as an empty ClientHello TLS Extension. 703The server's response (if any) will be encoded and displayed as a PEM 704file. 705 706=item B<-status> 707 708Sends a certificate status request to the server (OCSP stapling). The server 709response (if any) is printed out. 710 711=item B<-alpn> I<protocols>, B<-nextprotoneg> I<protocols> 712 713These flags enable the Enable the Application-Layer Protocol Negotiation 714or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the 715IETF standard and replaces NPN. 716The I<protocols> list is a comma-separated list of protocol names that 717the client should advertise support for. The list should contain the most 718desirable protocols first. Protocol names are printable ASCII strings, 719for example "http/1.1" or "spdy/3". 720An empty list of protocols is treated specially and will cause the 721client to advertise support for the TLS extension but disconnect just 722after receiving ServerHello with a list of server supported protocols. 723The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used. 724 725=item B<-ct>, B<-noct> 726 727Use one of these two options to control whether Certificate Transparency (CT) 728is enabled (B<-ct>) or disabled (B<-noct>). 729If CT is enabled, signed certificate timestamps (SCTs) will be requested from 730the server and reported at handshake completion. 731 732Enabling CT also enables OCSP stapling, as this is one possible delivery method 733for SCTs. 734 735=item B<-ctlogfile> 736 737A file containing a list of known Certificate Transparency logs. See 738L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format. 739 740=item B<-keylogfile> I<file> 741 742Appends TLS secrets to the specified keylog file such that external programs 743(like Wireshark) can decrypt TLS connections. 744 745=item B<-early_data> I<file> 746 747Reads the contents of the specified file and attempts to send it as early data 748to the server. This will only work with resumed sessions that support early 749data and when the server accepts the early data. 750 751=item B<-enable_pha> 752 753For TLSv1.3 only, send the Post-Handshake Authentication extension. This will 754happen whether or not a certificate has been provided via B<-cert>. 755 756=item B<-use_srtp> I<value> 757 758Offer SRTP key management, where B<value> is a colon-separated profile list. 759 760=item B<-srpuser> I<value> 761 762Set the SRP username to the specified value. This option is deprecated. 763 764=item B<-srppass> I<value> 765 766Set the SRP password to the specified value. This option is deprecated. 767 768=item B<-srp_lateuser> 769 770SRP username for the second ClientHello message. This option is deprecated. 771 772=item B<-srp_moregroups> This option is deprecated. 773 774Tolerate other than the known B<g> and B<N> values. 775 776=item B<-srp_strength> I<number> 777 778Set the minimal acceptable length, in bits, for B<N>. This option is 779deprecated. 780 781=item B<-ktls> 782 783Enable Kernel TLS for sending and receiving. 784This option was introduced in OpenSSL 3.1.0. 785Kernel TLS is off by default as of OpenSSL 3.1.0. 786 787=item B<-tfo> 788 789Enable creation of connections via TCP fast open (RFC7413). 790 791{- $OpenSSL::safe::opt_version_item -} 792 793{- $OpenSSL::safe::opt_name_item -} 794 795{- $OpenSSL::safe::opt_x_item -} 796 797{- $OpenSSL::safe::opt_trust_item -} 798 799{- $OpenSSL::safe::opt_s_item -} 800 801{- $OpenSSL::safe::opt_r_item -} 802 803{- $OpenSSL::safe::opt_provider_item -} 804 805{- $OpenSSL::safe::opt_engine_item -} 806 807{- output_off() if $disabled{"deprecated-3.0"}; "" -} 808=item B<-ssl_client_engine> I<id> 809 810Specify engine to be used for client certificate operations. 811{- output_on() if $disabled{"deprecated-3.0"}; "" -} 812 813{- $OpenSSL::safe::opt_v_item -} 814 815Verification errors are displayed, for debugging, but the command will 816proceed unless the B<-verify_return_error> option is used. 817 818=item I<host>:I<port> 819 820Rather than providing B<-connect>, the target hostname and optional port may 821be provided as a single positional argument after all options. If neither this 822nor B<-connect> are provided, falls back to attempting to connect to 823I<localhost> on port I<4433>. 824 825=back 826 827=head1 CONNECTED COMMANDS 828 829If a connection is established with an SSL server then any data received 830from the server is displayed and any key presses will be sent to the 831server. If end of file is reached then the connection will be closed down. When 832used interactively (which means neither B<-quiet> nor B<-ign_eof> have been 833given), then certain commands are also recognized which perform special 834operations. These commands are a letter which must appear at the start of a 835line. They are listed below. 836 837=over 4 838 839=item B<Q> 840 841End the current SSL connection and exit. 842 843=item B<R> 844 845Renegotiate the SSL session (TLSv1.2 and below only). 846 847=item B<k> 848 849Send a key update message to the server (TLSv1.3 only) 850 851=item B<K> 852 853Send a key update message to the server and request one back (TLSv1.3 only) 854 855=back 856 857=head1 NOTES 858 859This command can be used to debug SSL servers. To connect to an SSL HTTP 860server the command: 861 862 openssl s_client -connect servername:443 863 864would typically be used (https uses port 443). If the connection succeeds 865then an HTTP command can be given such as "GET /" to retrieve a web page. 866 867If the handshake fails then there are several possible causes, if it is 868nothing obvious like no client certificate then the B<-bugs>, 869B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried 870in case it is a buggy server. In particular you should play with these 871options B<before> submitting a bug report to an OpenSSL mailing list. 872 873A frequent problem when attempting to get client certificates working 874is that a web client complains it has no certificates or gives an empty 875list to choose from. This is normally because the server is not sending 876the clients certificate authority in its "acceptable CA list" when it 877requests a certificate. By using this command, the CA list can be viewed 878and checked. However, some servers only request client authentication 879after a specific URL is requested. To obtain the list in this case it 880is necessary to use the B<-prexit> option and send an HTTP request 881for an appropriate page. 882 883If a certificate is specified on the command line using the B<-cert> 884option it will not be used unless the server specifically requests 885a client certificate. Therefore, merely including a client certificate 886on the command line is no guarantee that the certificate works. 887 888If there are problems verifying a server certificate then the 889B<-showcerts> option can be used to show all the certificates sent by the 890server. 891 892This command is a test tool and is designed to continue the 893handshake after any certificate verification errors. As a result it will 894accept any certificate chain (trusted or not) sent by the peer. Non-test 895applications should B<not> do this as it makes them vulnerable to a MITM 896attack. This behaviour can be changed by with the B<-verify_return_error> 897option: any verify errors are then returned aborting the handshake. 898 899The B<-bind> option may be useful if the server or a firewall requires 900connections to come from some particular address and or port. 901 902=head1 BUGS 903 904Because this program has a lot of options and also because some of the 905techniques used are rather old, the C source for this command is rather 906hard to read and not a model of how things should be done. 907A typical SSL client program would be much simpler. 908 909The B<-prexit> option is a bit of a hack. We should really report 910information whenever a session is renegotiated. 911 912=head1 SEE ALSO 913 914L<openssl(1)>, 915L<openssl-sess_id(1)>, 916L<openssl-s_server(1)>, 917L<openssl-ciphers(1)>, 918L<SSL_CONF_cmd(3)>, 919L<SSL_CTX_set_max_send_fragment(3)>, 920L<SSL_CTX_set_split_send_fragment(3)>, 921L<SSL_CTX_set_max_pipelines(3)>, 922L<ossl_store-file(7)> 923 924=head1 HISTORY 925 926The B<-no_alt_chains> option was added in OpenSSL 1.1.0. 927The B<-name> option was added in OpenSSL 1.1.1. 928 929The B<-certform> option has become obsolete in OpenSSL 3.0.0 and has no effect. 930 931The B<-engine> option was deprecated in OpenSSL 3.0. 932 933The -tfo option was added in OpenSSL 3.1. 934 935=head1 COPYRIGHT 936 937Copyright 2000-2022 The OpenSSL Project Authors. All Rights Reserved. 938 939Licensed under the Apache License 2.0 (the "License"). You may not use 940this file except in compliance with the License. You can obtain a copy 941in the file LICENSE in the source distribution or at 942L<https://www.openssl.org/source/license.html>. 943 944=cut 945