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>]
107 [B<-split_send_frag>]
113 [B<-allow_no_dhe_kex>]
114 [B<-sigalgs sigalglist>]
115 [B<-curves curvelist>]
116 [B<-cipher cipherlist>]
117 [B<-ciphersuites val>]
119 [B<-starttls protocol>]
120 [B<-xmpphost hostname>]
125 [B<-sess_out filename>]
126 [B<-sess_in filename>]
129 [B<-serverinfo types>]
132 [B<-nextprotoneg protocols>]
136 [B<-keylogfile file>]
137 [B<-early_data file>]
143 The B<s_client> command implements a generic SSL/TLS client which connects
144 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
149 In addition to the options below the B<s_client> utility also supports the
150 common and client only options documented in the
151 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
158 Print out a usage message.
160 =item B<-connect host:port>
162 This specifies the host and optional port to connect to. It is possible to
163 select the host and port using the optional target positional argument instead.
164 If neither this nor the target positional argument are specified then an attempt
165 is made to connect to the local host on port 4433.
167 =item B<-bind host:port>]
169 This specifies the host address and or port to bind as the source for the
170 connection. For Unix-domain sockets the port is ignored and the host is
171 used as the source socket address.
173 =item B<-proxy host:port>
175 When used with the B<-connect> flag, the program uses the host and port
176 specified with this flag and issues an HTTP CONNECT command to connect
177 to the desired server.
181 Connect over the specified Unix-domain socket.
191 =item B<-servername name>
193 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
195 If B<-servername> is not provided, the TLS SNI extension will be populated with
196 the name given to B<-connect> if it follows a DNS name format. If B<-connect> is
197 not provided either, the SNI is set to "localhost".
198 This is the default since OpenSSL 1.1.1.
200 Even though SNI should normally be a DNS name and not an IP address, if
201 B<-servername> is provided then that name will be sent, regardless of whether
202 it is a DNS name or not.
204 This option cannot be used in conjunction with B<-noservername>.
206 =item B<-noservername>
208 Suppresses sending of the SNI (Server Name Indication) extension in the
209 ClientHello message. Cannot be used in conjunction with the B<-servername> or
210 <-dane_tlsa_domain> options.
212 =item B<-cert certname>
214 The certificate to use, if one is requested by the server. The default is
215 not to use a certificate.
217 =item B<-certform format>
219 The certificate format to use: DER or PEM. PEM is the default.
221 =item B<-key keyfile>
223 The private key to use. If not specified then the certificate file will
226 =item B<-keyform format>
228 The private format to use: DER or PEM. PEM is the default.
232 A file containing trusted certificates to use when attempting to build the
233 client/server certificate chain related to the certificate specified via the
236 =item B<-build_chain>
238 Specify whether the application should build the certificate chain to be
239 provided to the server.
241 =item B<-xkey infile>, B<-xcert infile>, B<-xchain>
243 Specify an extra certificate, private key and certificate chain. These behave
244 in the same manner as the B<-cert>, B<-key> and B<-cert_chain> options. When
245 specified, the callback returning the first valid chain will be in use by the
248 =item B<-xchain_build>
250 Specify whether the application should build the certificate chain to be
251 provided to the server for the extra certificates provided via B<-xkey infile>,
252 B<-xcert infile>, B<-xchain> options.
254 =item B<-xcertform PEM|DER>, B<-xkeyform PEM|DER>
256 Extra certificate and private key format respectively.
260 the private key password source. For more information about the format of B<arg>
261 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
263 =item B<-verify depth>
265 The verify depth to use. This specifies the maximum length of the
266 server certificate chain and turns on server certificate verification.
267 Currently the verify operation continues after errors so all the problems
268 with a certificate chain can be seen. As a side effect the connection
269 will never fail due to a server certificate verify failure.
271 =item B<-verify_return_error>
273 Return verification errors instead of continuing. This will typically
274 abort the handshake with a fatal error.
276 =item B<-nameopt option>
278 Option which determines how the subject or issuer names are displayed. The
279 B<option> argument can be a single option or multiple options separated by
280 commas. Alternatively the B<-nameopt> switch may be used more than once to
281 set multiple options. See the L<x509(1)> manual page for details.
283 =item B<-CApath directory>
285 The directory to use for server certificate verification. This directory
286 must be in "hash format", see L<verify(1)> for more information. These are
287 also used when building the client certificate chain.
289 =item B<-CAfile file>
291 A file containing trusted certificates to use during server authentication
292 and to use when attempting to build the client certificate chain.
294 =item B<-chainCApath directory>
296 The directory to use for building the chain provided to the server. This
297 directory must be in "hash format", see L<verify(1)> for more information.
299 =item B<-chainCAfile file>
301 A file containing trusted certificates to use when attempting to build the
302 client certificate chain.
306 Do not load the trusted CA certificates from the default file location
310 Do not load the trusted CA certificates from the default directory location
312 =item B<-requestCAfile file>
314 A file containing a list of certificates whose subject names will be sent
315 to the server in the B<certificate_authorities> extension. Only supported
318 =item B<-dane_tlsa_domain domain>
320 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
321 TLSA base domain which becomes the default SNI hint and the primary
322 reference identifier for hostname checks. This must be used in
323 combination with at least one instance of the B<-dane_tlsa_rrdata>
326 When DANE authentication succeeds, the diagnostic output will include
327 the lowest (closest to 0) depth at which a TLSA record authenticated
328 a chain certificate. When that TLSA record is a "2 1 0" trust
329 anchor public key that signed (rather than matched) the top-most
330 certificate of the chain, the result is reported as "TA public key
331 verified". Otherwise, either the TLSA record "matched TA certificate"
332 at a positive depth or else "matched EE certificate" at depth 0.
334 =item B<-dane_tlsa_rrdata rrdata>
336 Use one or more times to specify the RRDATA fields of the DANE TLSA
337 RRset associated with the target service. The B<rrdata> value is
338 specied in "presentation form", that is four whitespace separated
339 fields that specify the usage, selector, matching type and associated
340 data, with the last of these encoded in hexadecimal. Optional
341 whitespace is ignored in the associated data field. For example:
343 $ openssl s_client -brief -starttls smtp \
344 -connect smtp.example.com:25 \
345 -dane_tlsa_domain smtp.example.com \
346 -dane_tlsa_rrdata "2 1 1
347 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
348 -dane_tlsa_rrdata "2 1 1
349 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
352 Verified peername: smtp.example.com
353 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
356 =item B<-dane_ee_no_namechecks>
358 This disables server name checks when authenticating via DANE-EE(3) TLSA
360 For some applications, primarily web browsers, it is not safe to disable name
361 checks due to "unknown key share" attacks, in which a malicious server can
362 convince a client that a connection to a victim server is instead a secure
363 connection to the malicious server.
364 The malicious server may then be able to violate cross-origin scripting
366 Thus, despite the text of RFC7671, name checks are by default enabled for
367 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
369 In particular, SMTP and XMPP clients should set this option as SRV and MX
370 records already make it possible for a remote domain to redirect client
371 connections to any server of its choice, and in any case SMTP and XMPP clients
372 do not execute scripts downloaded from remote servers.
374 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
375 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
376 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
377 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
378 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
379 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
380 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
382 Set various certificate chain validation options. See the
383 L<verify(1)> manual page for details.
387 Reconnects to the same server 5 times using the same session ID, this can
388 be used as a test that session caching is working.
392 Displays the server certificate list as sent by the server: it only consists of
393 certificates the server has sent (in the order the server has sent them). It is
394 B<not> a verified chain.
398 Print session information when the program exits. This will always attempt
399 to print out information even if the connection fails. Normally information
400 will only be printed out once if the connection succeeds. This option is useful
401 because the cipher in use may be renegotiated or the connection may fail
402 because a client certificate is required or is requested only after an
403 attempt is made to access a certain URL. Note: the output produced by this
404 option is not always accurate because a connection might never have been
409 Prints out the SSL session states.
413 Print extensive debugging information including a hex dump of all traffic.
417 Show all protocol messages with hex dump.
421 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
422 with B<enable-ssl-trace> for this option to work.
426 File to send output of B<-msg> or B<-trace> to, default standard output.
430 Tests non-blocking I/O
434 Turns on non-blocking I/O
438 This option translated a line feed from the terminal into CR+LF as required
443 Inhibit shutting down the connection when end of file is reached in the
448 Inhibit printing of session and certificate information. This implicitly
449 turns on B<-ign_eof> as well.
453 Shut down the connection when end of file is reached in the input.
454 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
456 =item B<-psk_identity identity>
458 Use the PSK identity B<identity> when using a PSK cipher suite.
459 The default value is "Client_identity" (without the quotes).
463 Use the PSK key B<key> when using a PSK cipher suite. The key is
464 given as a hexadecimal number without leading 0x, for example -psk
466 This option must be provided in order to use a PSK cipher.
468 =item B<-psk_session file>
470 Use the pem encoded SSL_SESSION data stored in B<file> as the basis of a PSK.
471 Note that this will only work if TLSv1.3 is negotiated.
473 =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>
475 These options require or disable the use of the specified SSL or TLS protocols.
476 By default B<s_client> will negotiate the highest mutually supported protocol
478 When a specific TLS version is required, only that version will be offered to
479 and accepted from the server.
480 Note that not all protocols and flags may be available, depending on how
483 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
485 These options make B<s_client> use DTLS protocols instead of TLS.
486 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
487 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
492 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
493 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
494 available where OpenSSL has support for SCTP enabled.
496 =item B<-sctp_label_bug>
498 Use the incorrect behaviour of older OpenSSL implementations when computing
499 endpoint-pair shared secrets for DTLS/SCTP. This allows communication with
500 older broken implementations but breaks interoperability with correct
501 implementations. Must be used in conjunction with B<-sctp>. This option is only
502 available where OpenSSL has support for SCTP enabled.
504 =item B<-fallback_scsv>
506 Send TLS_FALLBACK_SCSV in the ClientHello.
510 Switch on asynchronous mode. Cryptographic operations will be performed
511 asynchronously. This will only have an effect if an asynchronous capable engine
512 is also used via the B<-engine> option. For test purposes the dummy async engine
513 (dasync) can be used (if available).
515 =item B<-max_send_frag int>
517 The maximum size of data fragment to send.
518 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
520 =item B<-split_send_frag int>
522 The size used to split data for encrypt pipelines. If more data is written in
523 one go than this value then it will be split into multiple pipelines, up to the
524 maximum number of pipelines defined by max_pipelines. This only has an effect if
525 a suitable cipher suite has been negotiated, an engine that supports pipelining
526 has been loaded, and max_pipelines is greater than 1. See
527 L<SSL_CTX_set_split_send_fragment(3)> for further information.
529 =item B<-max_pipelines int>
531 The maximum number of encrypt/decrypt pipelines to be used. This will only have
532 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
533 engine) and a suitable cipher suite has been negotiated. The default value is 1.
534 See L<SSL_CTX_set_max_pipelines(3)> for further information.
536 =item B<-read_buf int>
538 The default read buffer size to be used for connections. This will only have an
539 effect if the buffer size is larger than the size that would otherwise be used
540 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
541 further information).
545 There are several known bugs in SSL and TLS implementations. Adding this
546 option enables various workarounds.
550 Enables support for SSL/TLS compression.
551 This option was introduced in OpenSSL 1.1.0.
552 TLS compression is not recommended and is off by default as of
557 Disables support for SSL/TLS compression.
558 TLS compression is not recommended and is off by default as of
563 Only provide a brief summary of connection parameters instead of the
564 normal verbose output.
566 =item B<-sigalgs sigalglist>
568 Specifies the list of signature algorithms that are sent by the client.
569 The server selects one entry in the list based on its preferences.
570 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
572 =item B<-curves curvelist>
574 Specifies the list of supported curves to be sent by the client. The curve is
575 ultimately selected by the server. For a list of all curves, use:
577 $ openssl ecparam -list_curves
579 =item B<-cipher cipherlist>
581 This allows the TLSv1.2 and below cipher list sent by the client to be modified.
582 This list will be combined with any TLSv1.3 ciphersuites that have been
583 configured. Although the server determines which ciphersuite is used it should
584 take the first supported cipher in the list sent by the client. See the
585 B<ciphers> command for more information.
587 =item B<-ciphersuites val>
589 This allows the TLSv1.3 ciphersuites sent by the client to be modified. This
590 list will be combined with any TLSv1.2 and below ciphersuites that have been
591 configured. Although the server determines which cipher suite is used it should
592 take the first supported cipher in the list sent by the client. See the
593 B<ciphers> command for more information. The format for this list is a simple
594 colon (":") separated list of TLSv1.3 ciphersuite names.
596 =item B<-starttls protocol>
598 Send the protocol-specific message(s) to switch to TLS for communication.
599 B<protocol> is a keyword for the intended protocol. Currently, the only
600 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
601 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
603 =item B<-xmpphost hostname>
605 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
606 specifies the host for the "to" attribute of the stream element.
607 If this option is not specified, then the host specified with "-connect"
610 This option is an alias of the B<-name> option for "xmpp" and "xmpp-server".
612 =item B<-name hostname>
614 This option is used to specify hostname information for various protocols
615 used with B<-starttls> option. Currently only "xmpp", "xmpp-server",
616 "smtp" and "lmtp" can utilize this B<-name> option.
618 If this option is used with "-starttls xmpp" or "-starttls xmpp-server",
619 if specifies the host for the "to" attribute of the stream element. If this
620 option is not specified, then the host specified with "-connect" will be used.
622 If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies
623 the name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If
624 this option is not specified, then "mail.example.com" will be used.
626 =item B<-tlsextdebug>
628 Print out a hex dump of any TLS extensions received from the server.
632 Disable RFC4507bis session ticket support.
634 =item B<-sess_out filename>
636 Output SSL session to B<filename>.
638 =item B<-sess_in sess.pem>
640 Load SSL session from B<filename>. The client will attempt to resume a
641 connection from this session.
645 Specifying an engine (by its unique B<id> string) will cause B<s_client>
646 to attempt to obtain a functional reference to the specified engine,
647 thus initialising it if needed. The engine will then be set as the default
648 for all available algorithms.
650 =item B<-rand file...>
652 A file or files containing random data used to seed the random number
654 Multiple files can be specified separated by an OS-dependent character.
655 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
658 =item [B<-writerand file>]
660 Writes random data to the specified I<file> upon exit.
661 This can be used with a subsequent B<-rand> flag.
663 =item B<-serverinfo types>
665 A list of comma-separated TLS Extension Types (numbers between 0 and
666 65535). Each type will be sent as an empty ClientHello TLS Extension.
667 The server's response (if any) will be encoded and displayed as a PEM
672 Sends a certificate status request to the server (OCSP stapling). The server
673 response (if any) is printed out.
675 =item B<-alpn protocols>, B<-nextprotoneg protocols>
677 These flags enable the Enable the Application-Layer Protocol Negotiation
678 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
679 IETF standard and replaces NPN.
680 The B<protocols> list is a comma-separated list of protocol names that
681 the client should advertise support for. The list should contain the most
682 desirable protocols first. Protocol names are printable ASCII strings,
683 for example "http/1.1" or "spdy/3".
684 An empty list of protocols is treated specially and will cause the
685 client to advertise support for the TLS extension but disconnect just
686 after receiving ServerHello with a list of server supported protocols.
687 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
689 =item B<-ct>, B<-noct>
691 Use one of these two options to control whether Certificate Transparency (CT)
692 is enabled (B<-ct>) or disabled (B<-noct>).
693 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
694 the server and reported at handshake completion.
696 Enabling CT also enables OCSP stapling, as this is one possible delivery method
701 A file containing a list of known Certificate Transparency logs. See
702 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
704 =item B<-keylogfile file>
706 Appends TLS secrets to the specified keylog file such that external programs
707 (like Wireshark) can decrypt TLS connections.
709 =item B<-early_data file>
711 Reads the contents of the specified file and attempts to send it as early data
712 to the server. This will only work with resumed sessions that support early
713 data and when the server accepts the early data.
717 For TLSv1.3 only, send the Post-Handshake Authentication extension. This will
718 happen whether or not a certificate has been provided via B<-cert>.
722 Rather than providing B<-connect>, the target hostname and optional port may
723 be provided as a single positional argument after all options. If neither this
724 nor B<-connect> are provided, falls back to attempting to connect to localhost
729 =head1 CONNECTED COMMANDS
731 If a connection is established with an SSL server then any data received
732 from the server is displayed and any key presses will be sent to the
733 server. If end of file is reached then the connection will be closed down. When
734 used interactively (which means neither B<-quiet> nor B<-ign_eof> have been
735 given), then certain commands are also recognized which perform special
736 operations. These commands are a letter which must appear at the start of a
737 line. They are listed below.
743 End the current SSL connection and exit.
747 Renegotiate the SSL session (TLSv1.2 and below only).
751 Send a heartbeat message to the server (DTLS only)
755 Send a key update message to the server (TLSv1.3 only)
759 Send a key update message to the server and request one back (TLSv1.3 only)
765 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
768 openssl s_client -connect servername:443
770 would typically be used (https uses port 443). If the connection succeeds
771 then an HTTP command can be given such as "GET /" to retrieve a web page.
773 If the handshake fails then there are several possible causes, if it is
774 nothing obvious like no client certificate then the B<-bugs>,
775 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
776 in case it is a buggy server. In particular you should play with these
777 options B<before> submitting a bug report to an OpenSSL mailing list.
779 A frequent problem when attempting to get client certificates working
780 is that a web client complains it has no certificates or gives an empty
781 list to choose from. This is normally because the server is not sending
782 the clients certificate authority in its "acceptable CA list" when it
783 requests a certificate. By using B<s_client> the CA list can be viewed
784 and checked. However some servers only request client authentication
785 after a specific URL is requested. To obtain the list in this case it
786 is necessary to use the B<-prexit> option and send an HTTP request
787 for an appropriate page.
789 If a certificate is specified on the command line using the B<-cert>
790 option it will not be used unless the server specifically requests
791 a client certificate. Therefor merely including a client certificate
792 on the command line is no guarantee that the certificate works.
794 If there are problems verifying a server certificate then the
795 B<-showcerts> option can be used to show all the certificates sent by the
798 The B<s_client> utility is a test tool and is designed to continue the
799 handshake after any certificate verification errors. As a result it will
800 accept any certificate chain (trusted or not) sent by the peer. None test
801 applications should B<not> do this as it makes them vulnerable to a MITM
802 attack. This behaviour can be changed by with the B<-verify_return_error>
803 option: any verify errors are then returned aborting the handshake.
805 The B<-bind> option may be useful if the server or a firewall requires
806 connections to come from some particular address and or port.
810 Because this program has a lot of options and also because some of the
811 techniques used are rather old, the C source of B<s_client> is rather hard to
812 read and not a model of how things should be done.
813 A typical SSL client program would be much simpler.
815 The B<-prexit> option is a bit of a hack. We should really report
816 information whenever a session is renegotiated.
820 L<SSL_CONF_cmd(3)>, L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>,
821 L<SSL_CTX_set_max_send_fragment(3)>, L<SSL_CTX_set_split_send_fragment(3)>,
822 L<SSL_CTX_set_max_pipelines(3)>
826 The B<-no_alt_chains> option was added in OpenSSL 1.1.0.
827 The B<-name> option was added in OpenSSL 1.1.1.
831 Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.
833 Licensed under the OpenSSL license (the "License"). You may not use
834 this file except in compliance with the License. You can obtain a copy
835 in the file LICENSE in the source distribution or at
836 L<https://www.openssl.org/source/license.html>.