6 s_client - SSL/TLS client program
10 B<openssl> B<s_client>
12 [B<-connect host:port>]
15 [B<-proxy_user userid>]
23 [B<-verify_return_error>]
25 [B<-certform DER|PEM>]
28 [B<-cert_chain filename>]
34 [B<-xcertform PEM|DER>]
35 [B<-xkeyform PEM|DER>]
37 [B<-CApath directory>]
39 [B<-chainCApath directory>]
40 [B<-chainCAfile filename>]
43 [B<-requestCAfile filename>]
44 [B<-dane_tlsa_domain domain>]
45 [B<-dane_tlsa_rrdata rrdata>]
46 [B<-dane_ee_no_namechecks>]
47 [B<-attime timestamp>]
70 [B<-verify_depth num>]
71 [B<-verify_email email>]
72 [B<-verify_hostname hostname>]
74 [B<-verify_name name>]
87 [B<-psk_identity identity>]
89 [B<-psk_session file>]
109 [B<-split_send_frag>]
115 [B<-allow_no_dhe_kex>]
116 [B<-sigalgs sigalglist>]
117 [B<-curves curvelist>]
118 [B<-cipher cipherlist>]
119 [B<-ciphersuites val>]
121 [B<-starttls protocol>]
122 [B<-xmpphost hostname>]
127 [B<-sess_out filename>]
128 [B<-sess_in filename>]
131 [B<-serverinfo types>]
134 [B<-nextprotoneg protocols>]
138 [B<-keylogfile file>]
139 [B<-early_data file>]
145 The B<s_client> command implements a generic SSL/TLS client which connects
146 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
151 In addition to the options below the B<s_client> utility also supports the
152 common and client only options documented in the
153 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
160 Print out a usage message.
162 =item B<-connect host:port>
164 This specifies the host and optional port to connect to. It is possible to
165 select the host and port using the optional target positional argument instead.
166 If neither this nor the target positional argument are specified then an attempt
167 is made to connect to the local host on port 4433.
169 =item B<-bind 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 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 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 arg>
192 The proxy password source, used with the B<-proxy_user> flag.
193 For more information about the format of B<arg> see the B<PASS PHRASE ARGUMENTS>
194 section in L<openssl(1)>.
198 Connect over the specified Unix-domain socket.
208 =item B<-servername name>
210 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
211 the given value. If both this option and the B<-noservername> are not given, the
212 TLS SNI extension is still set to the hostname provided to the B<-connect> option,
213 or "localhost" if B<-connect> has not been supplied. This is default since OpenSSL
216 Even though SNI name should normally be a DNS name and not an IP address, this
217 option will not make the distinction when parsing B<-connect> and will send
218 IP address if one passed.
220 =item B<-noservername>
222 Suppresses sending of the SNI (Server Name Indication) extension in the
223 ClientHello message. Cannot be used in conjunction with the B<-servername> or
224 <-dane_tlsa_domain> options.
226 =item B<-cert certname>
228 The certificate to use, if one is requested by the server. The default is
229 not to use a certificate.
231 =item B<-certform format>
233 The certificate format to use: DER or PEM. PEM is the default.
235 =item B<-key keyfile>
237 The private key to use. If not specified then the certificate file will
240 =item B<-keyform format>
242 The private format to use: DER or PEM. PEM is the default.
246 A file containing trusted certificates to use when attempting to build the
247 client/server certificate chain related to the certificate specified via the
250 =item B<-build_chain>
252 Specify whether the application should build the certificate chain to be
253 provided to the server.
255 =item B<-xkey infile>, B<-xcert infile>, B<-xchain>
257 Specify an extra certificate, private key and certificate chain. These behave
258 in the same manner as the B<-cert>, B<-key> and B<-cert_chain> options. When
259 specified, the callback returning the first valid chain will be in use by the
262 =item B<-xchain_build>
264 Specify whether the application should build the certificate chain to be
265 provided to the server for the extra certificates provided via B<-xkey infile>,
266 B<-xcert infile>, B<-xchain> options.
268 =item B<-xcertform PEM|DER>, B<-xkeyform PEM|DER>
270 Extra certificate and private key format respectively.
274 the private key password source. For more information about the format of B<arg>
275 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
277 =item B<-verify depth>
279 The verify depth to use. This specifies the maximum length of the
280 server certificate chain and turns on server certificate verification.
281 Currently the verify operation continues after errors so all the problems
282 with a certificate chain can be seen. As a side effect the connection
283 will never fail due to a server certificate verify failure.
285 =item B<-verify_return_error>
287 Return verification errors instead of continuing. This will typically
288 abort the handshake with a fatal error.
290 =item B<-nameopt option>
292 Option which determines how the subject or issuer names are displayed. The
293 B<option> argument can be a single option or multiple options separated by
294 commas. Alternatively the B<-nameopt> switch may be used more than once to
295 set multiple options. See the L<x509(1)> manual page for details.
297 =item B<-CApath directory>
299 The directory to use for server certificate verification. This directory
300 must be in "hash format", see L<verify(1)> for more information. These are
301 also used when building the client certificate chain.
303 =item B<-CAfile file>
305 A file containing trusted certificates to use during server authentication
306 and to use when attempting to build the client certificate chain.
308 =item B<-chainCApath directory>
310 The directory to use for building the chain provided to the server. This
311 directory must be in "hash format", see L<verify(1)> for more information.
313 =item B<-chainCAfile file>
315 A file containing trusted certificates to use when attempting to build the
316 client certificate chain.
320 Do not load the trusted CA certificates from the default file location
324 Do not load the trusted CA certificates from the default directory location
326 =item B<-requestCAfile file>
328 A file containing a list of certificates whose subject names will be sent
329 to the server in the B<certificate_authorities> extension. Only supported
332 =item B<-dane_tlsa_domain domain>
334 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
335 TLSA base domain which becomes the default SNI hint and the primary
336 reference identifier for hostname checks. This must be used in
337 combination with at least one instance of the B<-dane_tlsa_rrdata>
340 When DANE authentication succeeds, the diagnostic output will include
341 the lowest (closest to 0) depth at which a TLSA record authenticated
342 a chain certificate. When that TLSA record is a "2 1 0" trust
343 anchor public key that signed (rather than matched) the top-most
344 certificate of the chain, the result is reported as "TA public key
345 verified". Otherwise, either the TLSA record "matched TA certificate"
346 at a positive depth or else "matched EE certificate" at depth 0.
348 =item B<-dane_tlsa_rrdata rrdata>
350 Use one or more times to specify the RRDATA fields of the DANE TLSA
351 RRset associated with the target service. The B<rrdata> value is
352 specied in "presentation form", that is four whitespace separated
353 fields that specify the usage, selector, matching type and associated
354 data, with the last of these encoded in hexadecimal. Optional
355 whitespace is ignored in the associated data field. For example:
357 $ openssl s_client -brief -starttls smtp \
358 -connect smtp.example.com:25 \
359 -dane_tlsa_domain smtp.example.com \
360 -dane_tlsa_rrdata "2 1 1
361 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
362 -dane_tlsa_rrdata "2 1 1
363 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
366 Verified peername: smtp.example.com
367 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
370 =item B<-dane_ee_no_namechecks>
372 This disables server name checks when authenticating via DANE-EE(3) TLSA
374 For some applications, primarily web browsers, it is not safe to disable name
375 checks due to "unknown key share" attacks, in which a malicious server can
376 convince a client that a connection to a victim server is instead a secure
377 connection to the malicious server.
378 The malicious server may then be able to violate cross-origin scripting
380 Thus, despite the text of RFC7671, name checks are by default enabled for
381 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
383 In particular, SMTP and XMPP clients should set this option as SRV and MX
384 records already make it possible for a remote domain to redirect client
385 connections to any server of its choice, and in any case SMTP and XMPP clients
386 do not execute scripts downloaded from remote servers.
388 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
389 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
390 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
391 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
392 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
393 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
394 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
396 Set various certificate chain validation options. See the
397 L<verify(1)> manual page for details.
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 Show all protocol messages with hex dump.
435 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
436 with B<enable-ssl-trace> for this option to work.
440 File to send output of B<-msg> or B<-trace> to, default standard output.
444 Tests non-blocking I/O
448 Turns on non-blocking I/O
452 This option translated a line feed from the terminal into CR+LF as required
457 Inhibit shutting down the connection when end of file is reached in the
462 Inhibit printing of session and certificate information. This implicitly
463 turns on B<-ign_eof> as well.
467 Shut down the connection when end of file is reached in the input.
468 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
470 =item B<-psk_identity identity>
472 Use the PSK identity B<identity> when using a PSK cipher suite.
473 The default value is "Client_identity" (without the quotes).
477 Use the PSK key B<key> when using a PSK cipher suite. The key is
478 given as a hexadecimal number without leading 0x, for example -psk
480 This option must be provided in order to use a PSK cipher.
482 =item B<-psk_session file>
484 Use the pem encoded SSL_SESSION data stored in B<file> as the basis of a PSK.
485 Note that this will only work if TLSv1.3 is negotiated.
487 =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>
489 These options require or disable the use of the specified SSL or TLS protocols.
490 By default B<s_client> will negotiate the highest mutually supported protocol
492 When a specific TLS version is required, only that version will be offered to
493 and accepted from the server.
494 Note that not all protocols and flags may be available, depending on how
497 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
499 These options make B<s_client> use DTLS protocols instead of TLS.
500 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
501 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
506 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
507 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
508 available where OpenSSL has support for SCTP enabled.
510 =item B<-sctp_label_bug>
512 Use the incorrect behaviour of older OpenSSL implementations when computing
513 endpoint-pair shared secrets for DTLS/SCTP. This allows communication with
514 older broken implementations but breaks interoperability with correct
515 implementations. Must be used in conjunction with B<-sctp>. This option is only
516 available where OpenSSL has support for SCTP enabled.
518 =item B<-fallback_scsv>
520 Send TLS_FALLBACK_SCSV in the ClientHello.
524 Switch on asynchronous mode. Cryptographic operations will be performed
525 asynchronously. This will only have an effect if an asynchronous capable engine
526 is also used via the B<-engine> option. For test purposes the dummy async engine
527 (dasync) can be used (if available).
529 =item B<-max_send_frag int>
531 The maximum size of data fragment to send.
532 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
534 =item B<-split_send_frag int>
536 The size used to split data for encrypt pipelines. If more data is written in
537 one go than this value then it will be split into multiple pipelines, up to the
538 maximum number of pipelines defined by max_pipelines. This only has an effect if
539 a suitable cipher suite has been negotiated, an engine that supports pipelining
540 has been loaded, and max_pipelines is greater than 1. See
541 L<SSL_CTX_set_split_send_fragment(3)> for further information.
543 =item B<-max_pipelines int>
545 The maximum number of encrypt/decrypt pipelines to be used. This will only have
546 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
547 engine) and a suitable cipher suite has been negotiated. The default value is 1.
548 See L<SSL_CTX_set_max_pipelines(3)> for further information.
550 =item B<-read_buf int>
552 The default read buffer size to be used for connections. This will only have an
553 effect if the buffer size is larger than the size that would otherwise be used
554 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
555 further information).
559 There are several known bug in SSL and TLS implementations. Adding this
560 option enables various workarounds.
564 Enables support for SSL/TLS compression.
565 This option was introduced in OpenSSL 1.1.0.
566 TLS compression is not recommended and is off by default as of
571 Disables support for SSL/TLS compression.
572 TLS compression is not recommended and is off by default as of
577 Only provide a brief summary of connection parameters instead of the
578 normal verbose output.
580 =item B<-sigalgs sigalglist>
582 Specifies the list of signature algorithms that are sent by the client.
583 The server selects one entry in the list based on its preferences.
584 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
586 =item B<-curves curvelist>
588 Specifies the list of supported curves to be sent by the client. The curve is
589 ultimately selected by the server. For a list of all curves, use:
591 $ openssl ecparam -list_curves
593 =item B<-cipher cipherlist>
595 This allows the TLSv1.2 and below cipher list sent by the client to be modified.
596 This list will be combined with any TLSv1.3 ciphersuites that have been
597 configured. Although the server determines which ciphersuite is used it should
598 take the first supported cipher in the list sent by the client. See the
599 B<ciphers> command for more information.
601 =item B<-ciphersuites val>
603 This allows the TLSv1.3 ciphersuites sent by the client to be modified. This
604 list will be combined with any TLSv1.2 and below ciphersuites that have been
605 configured. Although the server determines which cipher suite is used it should
606 take the first supported cipher in the list sent by the client. See the
607 B<ciphers> command for more information. The format for this list is a simple
608 colon (":") separated list of TLSv1.3 ciphersuite names.
610 =item B<-starttls protocol>
612 Send the protocol-specific message(s) to switch to TLS for communication.
613 B<protocol> is a keyword for the intended protocol. Currently, the only
614 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
615 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
617 =item B<-xmpphost hostname>
619 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
620 specifies the host for the "to" attribute of the stream element.
621 If this option is not specified, then the host specified with "-connect"
624 This option is an alias of the B<-name> option for "xmpp" and "xmpp-server".
626 =item B<-name hostname>
628 This option is used to specify hostname information for various protocols
629 used with B<-starttls> option. Currently only "xmpp", "xmpp-server",
630 "smtp" and "lmtp" can utilize this B<-name> option.
632 If this option is used with "-starttls xmpp" or "-starttls xmpp-server",
633 if specifies the host for the "to" attribute of the stream element. If this
634 option is not specified, then the host specified with "-connect" will be used.
636 If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies
637 the name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If
638 this option is not specified, then "mail.example.com" will be used.
640 =item B<-tlsextdebug>
642 Print out a hex dump of any TLS extensions received from the server.
646 Disable RFC4507bis session ticket support.
648 =item B<-sess_out filename>
650 Output SSL session to B<filename>.
652 =item B<-sess_in sess.pem>
654 Load SSL session from B<filename>. The client will attempt to resume a
655 connection from this session.
659 Specifying an engine (by its unique B<id> string) will cause B<s_client>
660 to attempt to obtain a functional reference to the specified engine,
661 thus initialising it if needed. The engine will then be set as the default
662 for all available algorithms.
664 =item B<-rand file...>
666 A file or files containing random data used to seed the random number
668 Multiple files can be specified separated by an OS-dependent character.
669 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
672 =item [B<-writerand file>]
674 Writes random data to the specified I<file> upon exit.
675 This can be used with a subsequent B<-rand> flag.
677 =item B<-serverinfo types>
679 A list of comma-separated TLS Extension Types (numbers between 0 and
680 65535). Each type will be sent as an empty ClientHello TLS Extension.
681 The server's response (if any) will be encoded and displayed as a PEM
686 Sends a certificate status request to the server (OCSP stapling). The server
687 response (if any) is printed out.
689 =item B<-alpn protocols>, B<-nextprotoneg protocols>
691 These flags enable the Enable the Application-Layer Protocol Negotiation
692 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
693 IETF standard and replaces NPN.
694 The B<protocols> list is a comma-separated list of protocol names that
695 the client should advertise support for. The list should contain the most
696 desirable protocols first. Protocol names are printable ASCII strings,
697 for example "http/1.1" or "spdy/3".
698 An empty list of protocols is treated specially and will cause the
699 client to advertise support for the TLS extension but disconnect just
700 after receiving ServerHello with a list of server supported protocols.
701 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
703 =item B<-ct>, B<-noct>
705 Use one of these two options to control whether Certificate Transparency (CT)
706 is enabled (B<-ct>) or disabled (B<-noct>).
707 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
708 the server and reported at handshake completion.
710 Enabling CT also enables OCSP stapling, as this is one possible delivery method
715 A file containing a list of known Certificate Transparency logs. See
716 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
718 =item B<-keylogfile file>
720 Appends TLS secrets to the specified keylog file such that external programs
721 (like Wireshark) can decrypt TLS connections.
723 =item B<-early_data file>
725 Reads the contents of the specified file and attempts to send it as early data
726 to the server. This will only work with resumed sessions that support early
727 data and when the server accepts the early data.
731 For TLSv1.3 only, send the Post-Handshake Authentication extension. This will
732 happen whether or not a certificate has been provided via B<-cert>.
736 Rather than providing B<-connect>, the target hostname and optional port may
737 be provided as a single positional argument after all options. If neither this
738 nor B<-connect> are provided, falls back to attempting to connect to localhost
743 =head1 CONNECTED COMMANDS
745 If a connection is established with an SSL server then any data received
746 from the server is displayed and any key presses will be sent to the
747 server. If end of file is reached then the connection will be closed down. When
748 used interactively (which means neither B<-quiet> nor B<-ign_eof> have been
749 given), then certain commands are also recognized which perform special
750 operations. These commands are a letter which must appear at the start of a
751 line. They are listed below.
757 End the current SSL connection and exit.
761 Renegotiate the SSL session (TLSv1.2 and below only).
765 Send a heartbeat message to the server (DTLS only)
769 Send a key update message to the server (TLSv1.3 only)
773 Send a key update message to the server and request one back (TLSv1.3 only)
779 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
782 openssl s_client -connect servername:443
784 would typically be used (https uses port 443). If the connection succeeds
785 then an HTTP command can be given such as "GET /" to retrieve a web page.
787 If the handshake fails then there are several possible causes, if it is
788 nothing obvious like no client certificate then the B<-bugs>,
789 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
790 in case it is a buggy server. In particular you should play with these
791 options B<before> submitting a bug report to an OpenSSL mailing list.
793 A frequent problem when attempting to get client certificates working
794 is that a web client complains it has no certificates or gives an empty
795 list to choose from. This is normally because the server is not sending
796 the clients certificate authority in its "acceptable CA list" when it
797 requests a certificate. By using B<s_client> the CA list can be viewed
798 and checked. However some servers only request client authentication
799 after a specific URL is requested. To obtain the list in this case it
800 is necessary to use the B<-prexit> option and send an HTTP request
801 for an appropriate page.
803 If a certificate is specified on the command line using the B<-cert>
804 option it will not be used unless the server specifically requests
805 a client certificate. Therefor merely including a client certificate
806 on the command line is no guarantee that the certificate works.
808 If there are problems verifying a server certificate then the
809 B<-showcerts> option can be used to show all the certificates sent by the
812 The B<s_client> utility is a test tool and is designed to continue the
813 handshake after any certificate verification errors. As a result it will
814 accept any certificate chain (trusted or not) sent by the peer. None test
815 applications should B<not> do this as it makes them vulnerable to a MITM
816 attack. This behaviour can be changed by with the B<-verify_return_error>
817 option: any verify errors are then returned aborting the handshake.
819 The B<-bind> option may be useful if the server or a firewall requires
820 connections to come from some particular address and or port.
824 Because this program has a lot of options and also because some of the
825 techniques used are rather old, the C source of B<s_client> is rather hard to
826 read and not a model of how things should be done.
827 A typical SSL client program would be much simpler.
829 The B<-prexit> option is a bit of a hack. We should really report
830 information whenever a session is renegotiated.
834 L<SSL_CONF_cmd(3)>, L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>,
835 L<SSL_CTX_set_max_send_fragment(3)>, L<SSL_CTX_set_split_send_fragment(3)>,
836 L<SSL_CTX_set_max_pipelines(3)>
840 The B<-no_alt_chains> option was added in OpenSSL 1.1.0.
841 The B<-name> option was added in OpenSSL 1.1.1.
845 Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
847 Licensed under the Apache License 2.0 (the "License"). You may not use
848 this file except in compliance with the License. You can obtain a copy
849 in the file LICENSE in the source distribution or at
850 L<https://www.openssl.org/source/license.html>.