6 s_client - SSL/TLS client program
10 B<openssl> B<s_client>
12 [B<-connect host:port>]
21 [B<-verify_return_error>]
23 [B<-certform DER|PEM>]
26 [B<-cert_chain filename>]
32 [B<-xcertform PEM|DER>]
33 [B<-xkeyform PEM|DER>]
35 [B<-CApath directory>]
37 [B<-chainCApath directory>]
38 [B<-chainCAfile filename>]
41 [B<-requestCAfile filename>]
42 [B<-dane_tlsa_domain domain>]
43 [B<-dane_tlsa_rrdata rrdata>]
44 [B<-dane_ee_no_namechecks>]
45 [B<-attime timestamp>]
68 [B<-verify_depth num>]
69 [B<-verify_email email>]
70 [B<-verify_hostname hostname>]
72 [B<-verify_name name>]
85 [B<-psk_identity identity>]
87 [B<-psk_session file>]
106 [B<-split_send_frag>]
112 [B<-allow_no_dhe_kex>]
113 [B<-sigalgs sigalglist>]
114 [B<-curves curvelist>]
115 [B<-cipher cipherlist>]
116 [B<-ciphersuites val>]
118 [B<-starttls protocol>]
119 [B<-xmpphost hostname>]
124 [B<-sess_out filename>]
125 [B<-sess_in filename>]
128 [B<-serverinfo types>]
131 [B<-nextprotoneg protocols>]
135 [B<-keylogfile file>]
136 [B<-early_data file>]
142 The B<s_client> command implements a generic SSL/TLS client which connects
143 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
148 In addition to the options below the B<s_client> utility also supports the
149 common and client only options documented in the
150 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
157 Print out a usage message.
159 =item B<-connect host:port>
161 This specifies the host and optional port to connect to. It is possible to
162 select the host and port using the optional target positional argument instead.
163 If neither this nor the target positional argument are specified then an attempt
164 is made to connect to the local host on port 4433.
166 =item B<-bind host:port>]
168 This specifies the host address and or port to bind as the source for the
169 connection. For Unix-domain sockets the port is ignored and the host is
170 used as the source socket address.
172 =item B<-proxy host:port>
174 When used with the B<-connect> flag, the program uses the host and port
175 specified with this flag and issues an HTTP CONNECT command to connect
176 to the desired server.
180 Connect over the specified Unix-domain socket.
190 =item B<-servername name>
192 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
193 the given value. If both this option and the B<-noservername> are not given, the
194 TLS SNI extension is still set to the hostname provided to the B<-connect> option,
195 or "localhost" if B<-connect> has not been supplied. This is default since OpenSSL
198 Even though SNI name should normally be a DNS name and not an IP address, this
199 option will not make the distinction when parsing B<-connect> and will send
200 IP address if one passed.
202 =item B<-noservername>
204 Suppresses sending of the SNI (Server Name Indication) extension in the
205 ClientHello message. Cannot be used in conjunction with the B<-servername> or
206 <-dane_tlsa_domain> options.
208 =item B<-cert certname>
210 The certificate to use, if one is requested by the server. The default is
211 not to use a certificate.
213 =item B<-certform format>
215 The certificate format to use: DER or PEM. PEM is the default.
217 =item B<-key keyfile>
219 The private key to use. If not specified then the certificate file will
222 =item B<-keyform format>
224 The private format to use: DER or PEM. PEM is the default.
228 A file containing trusted certificates to use when attempting to build the
229 client/server certificate chain related to the certificate specified via the
232 =item B<-build_chain>
234 Specify whether the application should build the certificate chain to be
235 provided to the server.
237 =item B<-xkey infile>, B<-xcert infile>, B<-xchain>
239 Specify an extra certificate, private key and certificate chain. These behave
240 in the same manner as the B<-cert>, B<-key> and B<-cert_chain> options. When
241 specified, the callback returning the first valid chain will be in use by the
244 =item B<-xchain_build>
246 Specify whether the application should build the certificate chain to be
247 provided to the server for the extra certificates provided via B<-xkey infile>,
248 B<-xcert infile>, B<-xchain> options.
250 =item B<-xcertform PEM|DER>, B<-xkeyform PEM|DER>
252 Extra certificate and private key format respectively.
256 the private key password source. For more information about the format of B<arg>
257 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
259 =item B<-verify depth>
261 The verify depth to use. This specifies the maximum length of the
262 server certificate chain and turns on server certificate verification.
263 Currently the verify operation continues after errors so all the problems
264 with a certificate chain can be seen. As a side effect the connection
265 will never fail due to a server certificate verify failure.
267 =item B<-verify_return_error>
269 Return verification errors instead of continuing. This will typically
270 abort the handshake with a fatal error.
272 =item B<-nameopt option>
274 Option which determines how the subject or issuer names are displayed. The
275 B<option> argument can be a single option or multiple options separated by
276 commas. Alternatively the B<-nameopt> switch may be used more than once to
277 set multiple options. See the L<x509(1)> manual page for details.
279 =item B<-CApath directory>
281 The directory to use for server certificate verification. This directory
282 must be in "hash format", see L<verify(1)> for more information. These are
283 also used when building the client certificate chain.
285 =item B<-CAfile file>
287 A file containing trusted certificates to use during server authentication
288 and to use when attempting to build the client certificate chain.
290 =item B<-chainCApath directory>
292 The directory to use for building the chain provided to the server. This
293 directory must be in "hash format", see L<verify(1)> for more information.
295 =item B<-chainCAfile file>
297 A file containing trusted certificates to use when attempting to build the
298 client certificate chain.
302 Do not load the trusted CA certificates from the default file location
306 Do not load the trusted CA certificates from the default directory location
308 =item B<-requestCAfile file>
310 A file containing a list of certificates whose subject names will be sent
311 to the server in the B<certificate_authorities> extension. Only supported
314 =item B<-dane_tlsa_domain domain>
316 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
317 TLSA base domain which becomes the default SNI hint and the primary
318 reference identifier for hostname checks. This must be used in
319 combination with at least one instance of the B<-dane_tlsa_rrdata>
322 When DANE authentication succeeds, the diagnostic output will include
323 the lowest (closest to 0) depth at which a TLSA record authenticated
324 a chain certificate. When that TLSA record is a "2 1 0" trust
325 anchor public key that signed (rather than matched) the top-most
326 certificate of the chain, the result is reported as "TA public key
327 verified". Otherwise, either the TLSA record "matched TA certificate"
328 at a positive depth or else "matched EE certificate" at depth 0.
330 =item B<-dane_tlsa_rrdata rrdata>
332 Use one or more times to specify the RRDATA fields of the DANE TLSA
333 RRset associated with the target service. The B<rrdata> value is
334 specied in "presentation form", that is four whitespace separated
335 fields that specify the usage, selector, matching type and associated
336 data, with the last of these encoded in hexadecimal. Optional
337 whitespace is ignored in the associated data field. For example:
339 $ openssl s_client -brief -starttls smtp \
340 -connect smtp.example.com:25 \
341 -dane_tlsa_domain smtp.example.com \
342 -dane_tlsa_rrdata "2 1 1
343 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
344 -dane_tlsa_rrdata "2 1 1
345 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
348 Verified peername: smtp.example.com
349 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
352 =item B<-dane_ee_no_namechecks>
354 This disables server name checks when authenticating via DANE-EE(3) TLSA
356 For some applications, primarily web browsers, it is not safe to disable name
357 checks due to "unknown key share" attacks, in which a malicious server can
358 convince a client that a connection to a victim server is instead a secure
359 connection to the malicious server.
360 The malicious server may then be able to violate cross-origin scripting
362 Thus, despite the text of RFC7671, name checks are by default enabled for
363 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
365 In particular, SMTP and XMPP clients should set this option as SRV and MX
366 records already make it possible for a remote domain to redirect client
367 connections to any server of its choice, and in any case SMTP and XMPP clients
368 do not execute scripts downloaded from remote servers.
370 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
371 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
372 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
373 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
374 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
375 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
376 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
378 Set various certificate chain validation options. See the
379 L<verify(1)> manual page for details.
383 Reconnects to the same server 5 times using the same session ID, this can
384 be used as a test that session caching is working.
388 Displays the server certificate list as sent by the server: it only consists of
389 certificates the server has sent (in the order the server has sent them). It is
390 B<not> a verified chain.
394 Print session information when the program exits. This will always attempt
395 to print out information even if the connection fails. Normally information
396 will only be printed out once if the connection succeeds. This option is useful
397 because the cipher in use may be renegotiated or the connection may fail
398 because a client certificate is required or is requested only after an
399 attempt is made to access a certain URL. Note: the output produced by this
400 option is not always accurate because a connection might never have been
405 Prints out the SSL session states.
409 Print extensive debugging information including a hex dump of all traffic.
413 Show all protocol messages with hex dump.
417 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
418 with B<enable-ssl-trace> for this option to work.
422 File to send output of B<-msg> or B<-trace> to, default standard output.
426 Tests non-blocking I/O
430 Turns on non-blocking I/O
434 This option translated a line feed from the terminal into CR+LF as required
439 Inhibit shutting down the connection when end of file is reached in the
444 Inhibit printing of session and certificate information. This implicitly
445 turns on B<-ign_eof> as well.
449 Shut down the connection when end of file is reached in the input.
450 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
452 =item B<-psk_identity identity>
454 Use the PSK identity B<identity> when using a PSK cipher suite.
455 The default value is "Client_identity" (without the quotes).
459 Use the PSK key B<key> when using a PSK cipher suite. The key is
460 given as a hexadecimal number without leading 0x, for example -psk
462 This option must be provided in order to use a PSK cipher.
464 =item B<-psk_session file>
466 Use the pem encoded SSL_SESSION data stored in B<file> as the basis of a PSK.
467 Note that this will only work if TLSv1.3 is negotiated.
469 =item B<-ssl3>, B<-tls1>, B<-tls1_1>, B<-tls1_2>, B<-tls1_3>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>, B<-no_tls1_3>
471 These options require or disable the use of the specified SSL or TLS protocols.
472 By default B<s_client> will negotiate the highest mutually supported protocol
474 When a specific TLS version is required, only that version will be offered to
475 and accepted from the server.
476 Note that not all protocols and flags may be available, depending on how
479 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
481 These options make B<s_client> use DTLS protocols instead of TLS.
482 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
483 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
488 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
489 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
490 available where OpenSSL has support for SCTP enabled.
492 =item B<-fallback_scsv>
494 Send TLS_FALLBACK_SCSV in the ClientHello.
498 Switch on asynchronous mode. Cryptographic operations will be performed
499 asynchronously. This will only have an effect if an asynchronous capable engine
500 is also used via the B<-engine> option. For test purposes the dummy async engine
501 (dasync) can be used (if available).
503 =item B<-max_send_frag int>
505 The maximum size of data fragment to send.
506 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
508 =item B<-split_send_frag int>
510 The size used to split data for encrypt pipelines. If more data is written in
511 one go than this value then it will be split into multiple pipelines, up to the
512 maximum number of pipelines defined by max_pipelines. This only has an effect if
513 a suitable cipher suite has been negotiated, an engine that supports pipelining
514 has been loaded, and max_pipelines is greater than 1. See
515 L<SSL_CTX_set_split_send_fragment(3)> for further information.
517 =item B<-max_pipelines int>
519 The maximum number of encrypt/decrypt pipelines to be used. This will only have
520 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
521 engine) and a suitable cipher suite has been negotiated. The default value is 1.
522 See L<SSL_CTX_set_max_pipelines(3)> for further information.
524 =item B<-read_buf int>
526 The default read buffer size to be used for connections. This will only have an
527 effect if the buffer size is larger than the size that would otherwise be used
528 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
529 further information).
533 There are several known bug in SSL and TLS implementations. Adding this
534 option enables various workarounds.
538 Enables support for SSL/TLS compression.
539 This option was introduced in OpenSSL 1.1.0.
540 TLS compression is not recommended and is off by default as of
545 Disables support for SSL/TLS compression.
546 TLS compression is not recommended and is off by default as of
551 Only provide a brief summary of connection parameters instead of the
552 normal verbose output.
554 =item B<-sigalgs sigalglist>
556 Specifies the list of signature algorithms that are sent by the client.
557 The server selects one entry in the list based on its preferences.
558 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
560 =item B<-curves curvelist>
562 Specifies the list of supported curves to be sent by the client. The curve is
563 ultimately selected by the server. For a list of all curves, use:
565 $ openssl ecparam -list_curves
567 =item B<-cipher cipherlist>
569 This allows the TLSv1.2 and below cipher list sent by the client to be modified.
570 This list will be combined with any TLSv1.3 ciphersuites that have been
571 configured. Although the server determines which ciphersuite is used it should
572 take the first supported cipher in the list sent by the client. See the
573 B<ciphers> command for more information.
575 =item B<-ciphersuites val>
577 This allows the TLSv1.3 ciphersuites sent by the client to be modified. This
578 list will be combined with any TLSv1.2 and below ciphersuites that have been
579 configured. Although the server determines which cipher suite is used it should
580 take the first supported cipher in the list sent by the client. See the
581 B<ciphers> command for more information. The format for this list is a simple
582 colon (":") separated list of TLSv1.3 ciphersuite names.
584 =item B<-starttls protocol>
586 Send the protocol-specific message(s) to switch to TLS for communication.
587 B<protocol> is a keyword for the intended protocol. Currently, the only
588 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
589 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
591 =item B<-xmpphost hostname>
593 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
594 specifies the host for the "to" attribute of the stream element.
595 If this option is not specified, then the host specified with "-connect"
598 This option is an alias of the B<-name> option for "xmpp" and "xmpp-server".
600 =item B<-name hostname>
602 This option is used to specify hostname information for various protocols
603 used with B<-starttls> option. Currently only "xmpp", "xmpp-server",
604 "smtp" and "lmtp" can utilize this B<-name> option.
606 If this option is used with "-starttls xmpp" or "-starttls xmpp-server",
607 if specifies the host for the "to" attribute of the stream element. If this
608 option is not specified, then the host specified with "-connect" will be used.
610 If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies
611 the name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If
612 this option is not specified, then "mail.example.com" will be used.
614 =item B<-tlsextdebug>
616 Print out a hex dump of any TLS extensions received from the server.
620 Disable RFC4507bis session ticket support.
622 =item B<-sess_out filename>
624 Output SSL session to B<filename>.
626 =item B<-sess_in sess.pem>
628 Load SSL session from B<filename>. The client will attempt to resume a
629 connection from this session.
633 Specifying an engine (by its unique B<id> string) will cause B<s_client>
634 to attempt to obtain a functional reference to the specified engine,
635 thus initialising it if needed. The engine will then be set as the default
636 for all available algorithms.
638 =item B<-rand file...>
640 A file or files containing random data used to seed the random number
642 Multiple files can be specified separated by an OS-dependent character.
643 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
646 =item [B<-writerand file>]
648 Writes random data to the specified I<file> upon exit.
649 This can be used with a subsequent B<-rand> flag.
651 =item B<-serverinfo types>
653 A list of comma-separated TLS Extension Types (numbers between 0 and
654 65535). Each type will be sent as an empty ClientHello TLS Extension.
655 The server's response (if any) will be encoded and displayed as a PEM
660 Sends a certificate status request to the server (OCSP stapling). The server
661 response (if any) is printed out.
663 =item B<-alpn protocols>, B<-nextprotoneg protocols>
665 These flags enable the Enable the Application-Layer Protocol Negotiation
666 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
667 IETF standard and replaces NPN.
668 The B<protocols> list is a comma-separated list of protocol names that
669 the client should advertise support for. The list should contain the most
670 desirable protocols first. Protocol names are printable ASCII strings,
671 for example "http/1.1" or "spdy/3".
672 An empty list of protocols is treated specially and will cause the
673 client to advertise support for the TLS extension but disconnect just
674 after receiving ServerHello with a list of server supported protocols.
675 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
677 =item B<-ct>, B<-noct>
679 Use one of these two options to control whether Certificate Transparency (CT)
680 is enabled (B<-ct>) or disabled (B<-noct>).
681 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
682 the server and reported at handshake completion.
684 Enabling CT also enables OCSP stapling, as this is one possible delivery method
689 A file containing a list of known Certificate Transparency logs. See
690 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
692 =item B<-keylogfile file>
694 Appends TLS secrets to the specified keylog file such that external programs
695 (like Wireshark) can decrypt TLS connections.
697 =item B<-early_data file>
699 Reads the contents of the specified file and attempts to send it as early data
700 to the server. This will only work with resumed sessions that support early
701 data and when the server accepts the early data.
705 For TLSv1.3 only, send the Post-Handshake Authentication extension. This will
706 happen whether or not a certificate has been provided via B<-cert>.
710 Rather than providing B<-connect>, the target hostname and optional port may
711 be provided as a single positional argument after all options. If neither this
712 nor B<-connect> are provided, falls back to attempting to connect to localhost
717 =head1 CONNECTED COMMANDS
719 If a connection is established with an SSL server then any data received
720 from the server is displayed and any key presses will be sent to the
721 server. If end of file is reached then the connection will be closed down. When
722 used interactively (which means neither B<-quiet> nor B<-ign_eof> have been
723 given), then certain commands are also recognized which perform special
724 operations. These commands are a letter which must appear at the start of a
725 line. They are listed below.
731 End the current SSL connection and exit.
735 Renegotiate the SSL session (TLSv1.2 and below only).
739 Send a heartbeat message to the server (DTLS only)
743 Send a key update message to the server (TLSv1.3 only)
747 Send a key update message to the server and request one back (TLSv1.3 only)
753 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
756 openssl s_client -connect servername:443
758 would typically be used (https uses port 443). If the connection succeeds
759 then an HTTP command can be given such as "GET /" to retrieve a web page.
761 If the handshake fails then there are several possible causes, if it is
762 nothing obvious like no client certificate then the B<-bugs>,
763 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
764 in case it is a buggy server. In particular you should play with these
765 options B<before> submitting a bug report to an OpenSSL mailing list.
767 A frequent problem when attempting to get client certificates working
768 is that a web client complains it has no certificates or gives an empty
769 list to choose from. This is normally because the server is not sending
770 the clients certificate authority in its "acceptable CA list" when it
771 requests a certificate. By using B<s_client> the CA list can be viewed
772 and checked. However some servers only request client authentication
773 after a specific URL is requested. To obtain the list in this case it
774 is necessary to use the B<-prexit> option and send an HTTP request
775 for an appropriate page.
777 If a certificate is specified on the command line using the B<-cert>
778 option it will not be used unless the server specifically requests
779 a client certificate. Therefor merely including a client certificate
780 on the command line is no guarantee that the certificate works.
782 If there are problems verifying a server certificate then the
783 B<-showcerts> option can be used to show all the certificates sent by the
786 The B<s_client> utility is a test tool and is designed to continue the
787 handshake after any certificate verification errors. As a result it will
788 accept any certificate chain (trusted or not) sent by the peer. None test
789 applications should B<not> do this as it makes them vulnerable to a MITM
790 attack. This behaviour can be changed by with the B<-verify_return_error>
791 option: any verify errors are then returned aborting the handshake.
793 The B<-bind> option may be useful if the server or a firewall requires
794 connections to come from some particular address and or port.
798 Because this program has a lot of options and also because some of the
799 techniques used are rather old, the C source of B<s_client> is rather hard to
800 read and not a model of how things should be done.
801 A typical SSL client program would be much simpler.
803 The B<-prexit> option is a bit of a hack. We should really report
804 information whenever a session is renegotiated.
808 L<SSL_CONF_cmd(3)>, L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>,
809 L<SSL_CTX_set_max_send_fragment(3)>, L<SSL_CTX_set_split_send_fragment(3)>,
810 L<SSL_CTX_set_max_pipelines(3)>
814 The B<-no_alt_chains> option was added in OpenSSL 1.1.0.
815 The B<-name> option was added in OpenSSL 1.1.1.
819 Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
821 Licensed under the OpenSSL license (the "License"). You may not use
822 this file except in compliance with the License. You can obtain a copy
823 in the file LICENSE in the source distribution or at
824 L<https://www.openssl.org/source/license.html>.