2 {- OpenSSL::safe::output_do_not_edit_headers(); -}
6 openssl-s_client - SSL/TLS client program
10 B<openssl> B<s_client>
12 [B<-ssl_config> I<section>]
13 [B<-connect> I<host:port>]
14 [B<-host> I<hostname>]
16 [B<-bind> I<host:port>]
17 [B<-proxy> I<host:port>]
18 [B<-proxy_user> I<userid>]
19 [B<-proxy_pass> I<arg>]
23 [B<-servername> I<name>]
26 [B<-verify_return_error>]
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>]
36 [B<-CRLform> B<DER>|B<PEM>]
38 [B<-key> I<filename>|I<uri>]
39 [B<-keyform> B<DER>|B<PEM>|B<P12>|B<ENGINE>]
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>]
55 [B<-security_debug_verbose>]
60 [B<-keymatexport> I<label>]
61 [B<-keymatexportlen> I<len>]
62 [B<-msgfile> I<filename>]
69 [B<-psk_identity> I<identity>]
71 [B<-psk_session> I<file>]
77 [B<-maxfraglen> I<len>]
82 [B<-ignore_unexpected_eof>]
87 [B<-legacy_server_connect>]
88 [B<-allow_no_dhe_kex>]
89 [B<-sigalgs> I<sigalglist>]
90 [B<-curves> I<curvelist>]
91 [B<-cipher> I<cipherlist>]
92 [B<-ciphersuites> I<val>]
94 [B<-starttls> I<protocol>]
95 [B<-name> I<hostname>]
96 [B<-xmpphost> I<hostname>]
97 [B<-name> I<hostname>]
100 [B<-sess_out> I<filename>]
101 [B<-serverinfo> I<types>]
102 [B<-sess_in> I<filename>]
103 [B<-serverinfo> I<types>]
105 [B<-alpn> I<protocols>]
106 [B<-nextprotoneg> I<protocols>]
110 [B<-keylogfile> I<file>]
111 [B<-early_data> I<file>]
113 [B<-use_srtp> I<value>]
114 [B<-srpuser> I<value>]
115 [B<-srppass> I<value>]
118 [B<-srp_strength> I<number>]
120 {- $OpenSSL::safe::opt_name_synopsis -}
121 {- $OpenSSL::safe::opt_version_synopsis -}
122 {- $OpenSSL::safe::opt_x_synopsis -}
123 {- $OpenSSL::safe::opt_trust_synopsis -}
124 {- $OpenSSL::safe::opt_s_synopsis -}
125 {- $OpenSSL::safe::opt_r_synopsis -}
126 {- $OpenSSL::safe::opt_provider_synopsis -}
127 {- $OpenSSL::safe::opt_engine_synopsis -}[B<-ssl_client_engine> I<id>]
128 {- $OpenSSL::safe::opt_v_synopsis -}
133 This command implements a generic SSL/TLS client which
134 connects to a remote host using SSL/TLS. It is a I<very> useful diagnostic
135 tool for SSL servers.
139 In addition to the options below, this command also supports the
140 common and client only options documented
141 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
148 Print out a usage message.
150 =item B<-ssl_config> I<section>
152 Use the specified section of the configuration file to configure the B<SSL_CTX> object.
154 =item B<-connect> I<host>:I<port>
156 This specifies the host and optional port to connect to. It is possible to
157 select the host and port using the optional target positional argument instead.
158 If neither this nor the target positional argument are specified then an attempt
159 is made to connect to the local host on port 4433.
161 =item B<-host> I<hostname>
163 Host to connect to; use B<-connect> instead.
165 =item B<-port> I<port>
167 Connect to the specified port; use B<-connect> instead.
169 =item B<-bind> I<host:port>
171 This specifies the host address and or port to bind as the source for the
172 connection. For Unix-domain sockets the port is ignored and the host is
173 used as the source socket address.
175 =item B<-proxy> I<host:port>
177 When used with the B<-connect> flag, the program uses the host and port
178 specified with this flag and issues an HTTP CONNECT command to connect
179 to the desired server.
181 =item B<-proxy_user> I<userid>
183 When used with the B<-proxy> flag, the program will attempt to authenticate
184 with the specified proxy using basic (base64) authentication.
185 NB: Basic authentication is insecure; the credentials are sent to the proxy
186 in easily reversible base64 encoding before any TLS/SSL session is established.
187 Therefore, these credentials are easily recovered by anyone able to sniff/trace
188 the network. Use with caution.
190 =item B<-proxy_pass> I<arg>
192 The proxy password source, used with the B<-proxy_user> flag.
193 For more information about the format of B<arg>
194 see L<openssl-passphrase-options(1)>.
196 =item B<-unix> I<path>
198 Connect over the specified Unix-domain socket.
208 =item B<-servername> I<name>
210 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
212 If B<-servername> is not provided, the TLS SNI extension will be populated with
213 the name given to B<-connect> if it follows a DNS name format. If B<-connect> is
214 not provided either, the SNI is set to "localhost".
215 This is the default since OpenSSL 1.1.1.
217 Even though SNI should normally be a DNS name and not an IP address, if
218 B<-servername> is provided then that name will be sent, regardless of whether
219 it is a DNS name or not.
221 This option cannot be used in conjunction with B<-noservername>.
223 =item B<-noservername>
225 Suppresses sending of the SNI (Server Name Indication) extension in the
226 ClientHello message. Cannot be used in conjunction with the B<-servername> or
227 B<-dane_tlsa_domain> options.
229 =item B<-cert> I<filename>
231 The client certificate to use, if one is requested by the server.
232 The default is not to use a certificate.
234 The chain for the client certificate may be specified using B<-cert_chain>.
236 =item B<-certform> B<DER>|B<PEM>|B<P12>
238 The client certificate file format to use; unspecified by default.
239 See L<openssl-format-options(1)> for details.
243 A file or URI of untrusted certificates to use when attempting to build the
244 certificate chain related to the certificate specified via the B<-cert> option.
245 The input can be in PEM, DER, or PKCS#12 format.
247 =item B<-build_chain>
249 Specify whether the application should build the client certificate chain to be
250 provided to the server.
252 =item B<-CRL> I<filename>
254 CRL file to use to check the server's certificate.
256 =item B<-CRLform> B<DER>|B<PEM>
258 The CRL file format; unspecified by default.
259 See L<openssl-format-options(1)> for details.
261 =item B<-crl_download>
263 Download CRL from distribution points in the certificate.
265 =item B<-key> I<filename>|I<uri>
267 The client private key to use.
268 If not specified then the certificate file will be used to read also the key.
270 =item B<-keyform> B<DER>|B<PEM>|B<P12>|B<ENGINE>
272 The key format; unspecified by default.
273 See L<openssl-format-options(1)> for details.
275 =item B<-pass> I<arg>
277 the private key and certificate file password source.
278 For more information about the format of I<arg>
279 see L<openssl-passphrase-options(1)>.
281 =item B<-verify> I<depth>
283 The verify depth to use. This specifies the maximum length of the
284 server certificate chain and turns on server certificate verification.
285 Currently the verify operation continues after errors so all the problems
286 with a certificate chain can be seen. As a side effect the connection
287 will never fail due to a server certificate verify failure.
289 =item B<-verify_return_error>
291 Return verification errors instead of continuing. This will typically
292 abort the handshake with a fatal error.
294 =item B<-verify_quiet>
296 Limit verify output to only errors.
298 =item B<-verifyCAfile> I<filename>
300 A file in PEM format containing trusted certificates to use
301 for verifying the server's certificate.
303 =item B<-verifyCApath> I<dir>
305 A directory containing trusted certificates to use
306 for verifying the server's certificate.
307 This directory must be in "hash format",
308 see L<openssl-verify(1)> for more information.
310 =item B<-verifyCAstore> I<uri>
312 The URI of a store containing trusted certificates to use
313 for verifying the server's certificate.
315 =item B<-chainCAfile> I<file>
317 A file in PEM format containing trusted certificates to use
318 when attempting to build the client certificate chain.
320 =item B<-chainCApath> I<directory>
322 A directory containing trusted certificates to use
323 for building the client certificate chain provided to the server.
324 This directory must be in "hash format",
325 see L<openssl-verify(1)> for more information.
327 =item B<-chainCAstore> I<uri>
329 The URI of a store containing trusted certificates to use
330 when attempting to build the client certificate chain.
331 The URI may indicate a single certificate, as well as a collection of them.
332 With URIs in the C<file:> scheme, this acts as B<-chainCAfile> or
333 B<-chainCApath>, depending on if the URI indicates a directory or a
335 See L<ossl_store-file(7)> for more information on the C<file:> scheme.
337 =item B<-requestCAfile> I<file>
339 A file containing a list of certificates whose subject names will be sent
340 to the server in the B<certificate_authorities> extension. Only supported
343 =item B<-dane_tlsa_domain> I<domain>
345 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
346 TLSA base domain which becomes the default SNI hint and the primary
347 reference identifier for hostname checks. This must be used in
348 combination with at least one instance of the B<-dane_tlsa_rrdata>
351 When DANE authentication succeeds, the diagnostic output will include
352 the lowest (closest to 0) depth at which a TLSA record authenticated
353 a chain certificate. When that TLSA record is a "2 1 0" trust
354 anchor public key that signed (rather than matched) the top-most
355 certificate of the chain, the result is reported as "TA public key
356 verified". Otherwise, either the TLSA record "matched TA certificate"
357 at a positive depth or else "matched EE certificate" at depth 0.
359 =item B<-dane_tlsa_rrdata> I<rrdata>
361 Use one or more times to specify the RRDATA fields of the DANE TLSA
362 RRset associated with the target service. The I<rrdata> value is
363 specified in "presentation form", that is four whitespace separated
364 fields that specify the usage, selector, matching type and associated
365 data, with the last of these encoded in hexadecimal. Optional
366 whitespace is ignored in the associated data field. For example:
368 $ openssl s_client -brief -starttls smtp \
369 -connect smtp.example.com:25 \
370 -dane_tlsa_domain smtp.example.com \
371 -dane_tlsa_rrdata "2 1 1
372 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
373 -dane_tlsa_rrdata "2 1 1
374 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
377 Verified peername: smtp.example.com
378 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
381 =item B<-dane_ee_no_namechecks>
383 This disables server name checks when authenticating via DANE-EE(3) TLSA
385 For some applications, primarily web browsers, it is not safe to disable name
386 checks due to "unknown key share" attacks, in which a malicious server can
387 convince a client that a connection to a victim server is instead a secure
388 connection to the malicious server.
389 The malicious server may then be able to violate cross-origin scripting
391 Thus, despite the text of RFC7671, name checks are by default enabled for
392 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
394 In particular, SMTP and XMPP clients should set this option as SRV and MX
395 records already make it possible for a remote domain to redirect client
396 connections to any server of its choice, and in any case SMTP and XMPP clients
397 do not execute scripts downloaded from remote servers.
401 Reconnects to the same server 5 times using the same session ID, this can
402 be used as a test that session caching is working.
406 Displays the server certificate list as sent by the server: it only consists of
407 certificates the server has sent (in the order the server has sent them). It is
408 B<not> a verified chain.
412 Print session information when the program exits. This will always attempt
413 to print out information even if the connection fails. Normally information
414 will only be printed out once if the connection succeeds. This option is useful
415 because the cipher in use may be renegotiated or the connection may fail
416 because a client certificate is required or is requested only after an
417 attempt is made to access a certain URL. Note: the output produced by this
418 option is not always accurate because a connection might never have been
423 Prints out the SSL session states.
427 Print extensive debugging information including a hex dump of all traffic.
431 Do not use interactive command letters.
433 =item B<-security_debug>
435 Enable security debug messages.
437 =item B<-security_debug_verbose>
439 Output more security debug output.
443 Show protocol messages.
447 Enable send/receive timeout on DTLS connections.
449 =item B<-mtu> I<size>
451 Set MTU of the link layer to the specified size.
455 Disable Encrypt-then-MAC negotiation.
457 =item B<-keymatexport> I<label>
459 Export keying material using the specified label.
461 =item B<-keymatexportlen> I<len>
463 Export the specified number of bytes of keying material; default is 20.
465 Show all protocol messages with hex dump.
469 Show verbose trace output of protocol messages.
471 =item B<-msgfile> I<filename>
473 File to send output of B<-msg> or B<-trace> to, default standard output.
477 Tests nonblocking I/O
481 Turns on nonblocking I/O
485 This option translated a line feed from the terminal into CR+LF as required
490 Inhibit shutting down the connection when end of file is reached in the
495 Inhibit printing of session and certificate information. This implicitly
496 turns on B<-ign_eof> as well.
500 Shut down the connection when end of file is reached in the input.
501 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
503 =item B<-psk_identity> I<identity>
505 Use the PSK identity I<identity> when using a PSK cipher suite.
506 The default value is "Client_identity" (without the quotes).
510 Use the PSK key I<key> when using a PSK cipher suite. The key is
511 given as a hexadecimal number without leading 0x, for example -psk
513 This option must be provided in order to use a PSK cipher.
515 =item B<-psk_session> I<file>
517 Use the pem encoded SSL_SESSION data stored in I<file> as the basis of a PSK.
518 Note that this will only work if TLSv1.3 is negotiated.
522 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
523 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
524 available where OpenSSL has support for SCTP enabled.
526 =item B<-sctp_label_bug>
528 Use the incorrect behaviour of older OpenSSL implementations when computing
529 endpoint-pair shared secrets for DTLS/SCTP. This allows communication with
530 older broken implementations but breaks interoperability with correct
531 implementations. Must be used in conjunction with B<-sctp>. This option is only
532 available where OpenSSL has support for SCTP enabled.
534 =item B<-fallback_scsv>
536 Send TLS_FALLBACK_SCSV in the ClientHello.
540 Switch on asynchronous mode. Cryptographic operations will be performed
541 asynchronously. This will only have an effect if an asynchronous capable engine
542 is also used via the B<-engine> option. For test purposes the dummy async engine
543 (dasync) can be used (if available).
545 =item B<-maxfraglen> I<len>
547 Enable Maximum Fragment Length Negotiation; allowed values are
548 C<512>, C<1024>, C<2048>, and C<4096>.
550 =item B<-max_send_frag> I<int>
552 The maximum size of data fragment to send.
553 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
555 =item B<-split_send_frag> I<int>
557 The size used to split data for encrypt pipelines. If more data is written in
558 one go than this value then it will be split into multiple pipelines, up to the
559 maximum number of pipelines defined by max_pipelines. This only has an effect if
560 a suitable cipher suite has been negotiated, an engine that supports pipelining
561 has been loaded, and max_pipelines is greater than 1. See
562 L<SSL_CTX_set_split_send_fragment(3)> for further information.
564 =item B<-max_pipelines> I<int>
566 The maximum number of encrypt/decrypt pipelines to be used. This will only have
567 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
568 engine) and a suitable cipher suite has been negotiated. The default value is 1.
569 See L<SSL_CTX_set_max_pipelines(3)> for further information.
571 =item B<-read_buf> I<int>
573 The default read buffer size to be used for connections. This will only have an
574 effect if the buffer size is larger than the size that would otherwise be used
575 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
576 further information).
578 =item B<-ignore_unexpected_eof>
580 Some TLS implementations do not send the mandatory close_notify alert on
581 shutdown. If the application tries to wait for the close_notify alert but the
582 peer closes the connection without sending it, an error is generated. When this
583 option is enabled the peer does not need to send the close_notify alert and a
584 closed connection will be treated as if the close_notify alert was received.
585 For more information on shutting down a connection, see L<SSL_shutdown(3)>.
589 There are several known bugs in SSL and TLS implementations. Adding this
590 option enables various workarounds.
594 Enables support for SSL/TLS compression.
595 This option was introduced in OpenSSL 1.1.0.
596 TLS compression is not recommended and is off by default as of
601 Disables support for SSL/TLS compression.
602 TLS compression is not recommended and is off by default as of
607 Only provide a brief summary of connection parameters instead of the
608 normal verbose output.
610 =item B<-sigalgs> I<sigalglist>
612 Specifies the list of signature algorithms that are sent by the client.
613 The server selects one entry in the list based on its preferences.
614 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
616 =item B<-curves> I<curvelist>
618 Specifies the list of supported curves to be sent by the client. The curve is
619 ultimately selected by the server. For a list of all curves, use:
621 $ openssl ecparam -list_curves
623 =item B<-cipher> I<cipherlist>
625 This allows the TLSv1.2 and below cipher list sent by the client to be modified.
626 This list will be combined with any TLSv1.3 ciphersuites that have been
627 configured. Although the server determines which ciphersuite is used it should
628 take the first supported cipher in the list sent by the client. See
629 L<openssl-ciphers(1)> for more information.
631 =item B<-ciphersuites> I<val>
633 This allows the TLSv1.3 ciphersuites sent by the client to be modified. This
634 list will be combined with any TLSv1.2 and below ciphersuites that have been
635 configured. Although the server determines which cipher suite is used it should
636 take the first supported cipher in the list sent by the client. See
637 L<openssl-ciphers(1)> for more information. The format for this list is a simple
638 colon (":") separated list of TLSv1.3 ciphersuite names.
640 =item B<-starttls> I<protocol>
642 Send the protocol-specific message(s) to switch to TLS for communication.
643 I<protocol> is a keyword for the intended protocol. Currently, the only
644 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
645 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
647 =item B<-xmpphost> I<hostname>
649 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
650 specifies the host for the "to" attribute of the stream element.
651 If this option is not specified, then the host specified with "-connect"
654 This option is an alias of the B<-name> option for "xmpp" and "xmpp-server".
656 =item B<-name> I<hostname>
658 This option is used to specify hostname information for various protocols
659 used with B<-starttls> option. Currently only "xmpp", "xmpp-server",
660 "smtp" and "lmtp" can utilize this B<-name> option.
662 If this option is used with "-starttls xmpp" or "-starttls xmpp-server",
663 if specifies the host for the "to" attribute of the stream element. If this
664 option is not specified, then the host specified with "-connect" will be used.
666 If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies
667 the name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If
668 this option is not specified, then "mail.example.com" will be used.
670 =item B<-tlsextdebug>
672 Print out a hex dump of any TLS extensions received from the server.
676 Disable RFC4507bis session ticket support.
678 =item B<-sess_out> I<filename>
680 Output SSL session to I<filename>.
682 =item B<-sess_in> I<filename>
684 Load SSL session from I<filename>. The client will attempt to resume a
685 connection from this session.
687 =item B<-serverinfo> I<types>
689 A list of comma-separated TLS Extension Types (numbers between 0 and
690 65535). Each type will be sent as an empty ClientHello TLS Extension.
691 The server's response (if any) will be encoded and displayed as a PEM
696 Sends a certificate status request to the server (OCSP stapling). The server
697 response (if any) is printed out.
699 =item B<-alpn> I<protocols>, B<-nextprotoneg> I<protocols>
701 These flags enable the Enable the Application-Layer Protocol Negotiation
702 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
703 IETF standard and replaces NPN.
704 The I<protocols> list is a comma-separated list of protocol names that
705 the client should advertise support for. The list should contain the most
706 desirable protocols first. Protocol names are printable ASCII strings,
707 for example "http/1.1" or "spdy/3".
708 An empty list of protocols is treated specially and will cause the
709 client to advertise support for the TLS extension but disconnect just
710 after receiving ServerHello with a list of server supported protocols.
711 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
713 =item B<-ct>, B<-noct>
715 Use one of these two options to control whether Certificate Transparency (CT)
716 is enabled (B<-ct>) or disabled (B<-noct>).
717 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
718 the server and reported at handshake completion.
720 Enabling CT also enables OCSP stapling, as this is one possible delivery method
725 A file containing a list of known Certificate Transparency logs. See
726 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
728 =item B<-keylogfile> I<file>
730 Appends TLS secrets to the specified keylog file such that external programs
731 (like Wireshark) can decrypt TLS connections.
733 =item B<-early_data> I<file>
735 Reads the contents of the specified file and attempts to send it as early data
736 to the server. This will only work with resumed sessions that support early
737 data and when the server accepts the early data.
741 For TLSv1.3 only, send the Post-Handshake Authentication extension. This will
742 happen whether or not a certificate has been provided via B<-cert>.
744 =item B<-use_srtp> I<value>
746 Offer SRTP key management, where B<value> is a colon-separated profile list.
748 =item B<-srpuser> I<value>
750 Set the SRP username to the specified value. This option is deprecated.
752 =item B<-srppass> I<value>
754 Set the SRP password to the specified value. This option is deprecated.
756 =item B<-srp_lateuser>
758 SRP username for the second ClientHello message. This option is deprecated.
760 =item B<-srp_moregroups> This option is deprecated.
762 Tolerate other than the known B<g> and B<N> values.
764 =item B<-srp_strength> I<number>
766 Set the minimal acceptable length, in bits, for B<N>. This option is
771 Enable Kernel TLS for sending and receiving.
772 This option was introduced in OpenSSL 3.1.0.
773 Kernel TLS is off by default as of OpenSSL 3.1.0.
775 {- $OpenSSL::safe::opt_version_item -}
777 {- $OpenSSL::safe::opt_name_item -}
779 {- $OpenSSL::safe::opt_x_item -}
781 {- $OpenSSL::safe::opt_trust_item -}
783 {- $OpenSSL::safe::opt_s_item -}
785 {- $OpenSSL::safe::opt_r_item -}
787 {- $OpenSSL::safe::opt_provider_item -}
789 {- $OpenSSL::safe::opt_engine_item -}
791 {- output_off() if $disabled{"deprecated-3.0"}; "" -}
792 =item B<-ssl_client_engine> I<id>
794 Specify engine to be used for client certificate operations.
795 {- output_on() if $disabled{"deprecated-3.0"}; "" -}
797 {- $OpenSSL::safe::opt_v_item -}
799 Verification errors are displayed, for debugging, but the command will
800 proceed unless the B<-verify_return_error> option is used.
802 =item I<host>:I<port>
804 Rather than providing B<-connect>, the target hostname and optional port may
805 be provided as a single positional argument after all options. If neither this
806 nor B<-connect> are provided, falls back to attempting to connect to
807 I<localhost> on port I<4433>.
811 =head1 CONNECTED COMMANDS
813 If a connection is established with an SSL server then any data received
814 from the server is displayed and any key presses will be sent to the
815 server. If end of file is reached then the connection will be closed down. When
816 used interactively (which means neither B<-quiet> nor B<-ign_eof> have been
817 given), then certain commands are also recognized which perform special
818 operations. These commands are a letter which must appear at the start of a
819 line. They are listed below.
825 End the current SSL connection and exit.
829 Renegotiate the SSL session (TLSv1.2 and below only).
833 Send a key update message to the server (TLSv1.3 only)
837 Send a key update message to the server and request one back (TLSv1.3 only)
843 This command can be used to debug SSL servers. To connect to an SSL HTTP
846 openssl s_client -connect servername:443
848 would typically be used (https uses port 443). If the connection succeeds
849 then an HTTP command can be given such as "GET /" to retrieve a web page.
851 If the handshake fails then there are several possible causes, if it is
852 nothing obvious like no client certificate then the B<-bugs>,
853 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
854 in case it is a buggy server. In particular you should play with these
855 options B<before> submitting a bug report to an OpenSSL mailing list.
857 A frequent problem when attempting to get client certificates working
858 is that a web client complains it has no certificates or gives an empty
859 list to choose from. This is normally because the server is not sending
860 the clients certificate authority in its "acceptable CA list" when it
861 requests a certificate. By using this command, the CA list can be viewed
862 and checked. However, some servers only request client authentication
863 after a specific URL is requested. To obtain the list in this case it
864 is necessary to use the B<-prexit> option and send an HTTP request
865 for an appropriate page.
867 If a certificate is specified on the command line using the B<-cert>
868 option it will not be used unless the server specifically requests
869 a client certificate. Therefore, merely including a client certificate
870 on the command line is no guarantee that the certificate works.
872 If there are problems verifying a server certificate then the
873 B<-showcerts> option can be used to show all the certificates sent by the
876 This command is a test tool and is designed to continue the
877 handshake after any certificate verification errors. As a result it will
878 accept any certificate chain (trusted or not) sent by the peer. Non-test
879 applications should B<not> do this as it makes them vulnerable to a MITM
880 attack. This behaviour can be changed by with the B<-verify_return_error>
881 option: any verify errors are then returned aborting the handshake.
883 The B<-bind> option may be useful if the server or a firewall requires
884 connections to come from some particular address and or port.
888 Because this program has a lot of options and also because some of the
889 techniques used are rather old, the C source for this command is rather
890 hard to read and not a model of how things should be done.
891 A typical SSL client program would be much simpler.
893 The B<-prexit> option is a bit of a hack. We should really report
894 information whenever a session is renegotiated.
899 L<openssl-sess_id(1)>,
900 L<openssl-s_server(1)>,
901 L<openssl-ciphers(1)>,
903 L<SSL_CTX_set_max_send_fragment(3)>,
904 L<SSL_CTX_set_split_send_fragment(3)>,
905 L<SSL_CTX_set_max_pipelines(3)>,
906 L<ossl_store-file(7)>
910 The B<-no_alt_chains> option was added in OpenSSL 1.1.0.
911 The B<-name> option was added in OpenSSL 1.1.1.
913 The B<-certform> option has become obsolete in OpenSSL 3.0.0 and has no effect.
915 The B<-engine> option was deprecated in OpenSSL 3.0.
919 Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
921 Licensed under the Apache License 2.0 (the "License"). You may not use
922 this file except in compliance with the License. You can obtain a copy
923 in the file LICENSE in the source distribution or at
924 L<https://www.openssl.org/source/license.html>.