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
194 the given value. If both this option and the B<-noservername> are not given, the
195 TLS SNI extension is still set to the hostname provided to the B<-connect> option,
196 or "localhost" if B<-connect> has not been supplied. This is default since OpenSSL
199 Even though SNI name should normally be a DNS name and not an IP address, this
200 option will not make the distinction when parsing B<-connect> and will send
201 IP address if one passed.
203 =item B<-noservername>
205 Suppresses sending of the SNI (Server Name Indication) extension in the
206 ClientHello message. Cannot be used in conjunction with the B<-servername> or
207 <-dane_tlsa_domain> options.
209 =item B<-cert certname>
211 The certificate to use, if one is requested by the server. The default is
212 not to use a certificate.
214 =item B<-certform format>
216 The certificate format to use: DER or PEM. PEM is the default.
218 =item B<-key keyfile>
220 The private key to use. If not specified then the certificate file will
223 =item B<-keyform format>
225 The private format to use: DER or PEM. PEM is the default.
229 A file containing trusted certificates to use when attempting to build the
230 client/server certificate chain related to the certificate specified via the
233 =item B<-build_chain>
235 Specify whether the application should build the certificate chain to be
236 provided to the server.
238 =item B<-xkey infile>, B<-xcert infile>, B<-xchain>
240 Specify an extra certificate, private key and certificate chain. These behave
241 in the same manner as the B<-cert>, B<-key> and B<-cert_chain> options. When
242 specified, the callback returning the first valid chain will be in use by the
245 =item B<-xchain_build>
247 Specify whether the application should build the certificate chain to be
248 provided to the server for the extra certificates provided via B<-xkey infile>,
249 B<-xcert infile>, B<-xchain> options.
251 =item B<-xcertform PEM|DER>, B<-xkeyform PEM|DER>
253 Extra certificate and private key format respectively.
257 the private key password source. For more information about the format of B<arg>
258 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
260 =item B<-verify depth>
262 The verify depth to use. This specifies the maximum length of the
263 server certificate chain and turns on server certificate verification.
264 Currently the verify operation continues after errors so all the problems
265 with a certificate chain can be seen. As a side effect the connection
266 will never fail due to a server certificate verify failure.
268 =item B<-verify_return_error>
270 Return verification errors instead of continuing. This will typically
271 abort the handshake with a fatal error.
273 =item B<-nameopt option>
275 Option which determines how the subject or issuer names are displayed. The
276 B<option> argument can be a single option or multiple options separated by
277 commas. Alternatively the B<-nameopt> switch may be used more than once to
278 set multiple options. See the L<x509(1)> manual page for details.
280 =item B<-CApath directory>
282 The directory to use for server certificate verification. This directory
283 must be in "hash format", see L<verify(1)> for more information. These are
284 also used when building the client certificate chain.
286 =item B<-CAfile file>
288 A file containing trusted certificates to use during server authentication
289 and to use when attempting to build the client certificate chain.
291 =item B<-chainCApath directory>
293 The directory to use for building the chain provided to the server. This
294 directory must be in "hash format", see L<verify(1)> for more information.
296 =item B<-chainCAfile file>
298 A file containing trusted certificates to use when attempting to build the
299 client certificate chain.
303 Do not load the trusted CA certificates from the default file location
307 Do not load the trusted CA certificates from the default directory location
309 =item B<-requestCAfile file>
311 A file containing a list of certificates whose subject names will be sent
312 to the server in the B<certificate_authorities> extension. Only supported
315 =item B<-dane_tlsa_domain domain>
317 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
318 TLSA base domain which becomes the default SNI hint and the primary
319 reference identifier for hostname checks. This must be used in
320 combination with at least one instance of the B<-dane_tlsa_rrdata>
323 When DANE authentication succeeds, the diagnostic output will include
324 the lowest (closest to 0) depth at which a TLSA record authenticated
325 a chain certificate. When that TLSA record is a "2 1 0" trust
326 anchor public key that signed (rather than matched) the top-most
327 certificate of the chain, the result is reported as "TA public key
328 verified". Otherwise, either the TLSA record "matched TA certificate"
329 at a positive depth or else "matched EE certificate" at depth 0.
331 =item B<-dane_tlsa_rrdata rrdata>
333 Use one or more times to specify the RRDATA fields of the DANE TLSA
334 RRset associated with the target service. The B<rrdata> value is
335 specied in "presentation form", that is four whitespace separated
336 fields that specify the usage, selector, matching type and associated
337 data, with the last of these encoded in hexadecimal. Optional
338 whitespace is ignored in the associated data field. For example:
340 $ openssl s_client -brief -starttls smtp \
341 -connect smtp.example.com:25 \
342 -dane_tlsa_domain smtp.example.com \
343 -dane_tlsa_rrdata "2 1 1
344 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
345 -dane_tlsa_rrdata "2 1 1
346 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
349 Verified peername: smtp.example.com
350 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
353 =item B<-dane_ee_no_namechecks>
355 This disables server name checks when authenticating via DANE-EE(3) TLSA
357 For some applications, primarily web browsers, it is not safe to disable name
358 checks due to "unknown key share" attacks, in which a malicious server can
359 convince a client that a connection to a victim server is instead a secure
360 connection to the malicious server.
361 The malicious server may then be able to violate cross-origin scripting
363 Thus, despite the text of RFC7671, name checks are by default enabled for
364 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
366 In particular, SMTP and XMPP clients should set this option as SRV and MX
367 records already make it possible for a remote domain to redirect client
368 connections to any server of its choice, and in any case SMTP and XMPP clients
369 do not execute scripts downloaded from remote servers.
371 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
372 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
373 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
374 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
375 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
376 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
377 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
379 Set various certificate chain validation options. See the
380 L<verify(1)> manual page for details.
384 Reconnects to the same server 5 times using the same session ID, this can
385 be used as a test that session caching is working.
389 Displays the server certificate list as sent by the server: it only consists of
390 certificates the server has sent (in the order the server has sent them). It is
391 B<not> a verified chain.
395 Print session information when the program exits. This will always attempt
396 to print out information even if the connection fails. Normally information
397 will only be printed out once if the connection succeeds. This option is useful
398 because the cipher in use may be renegotiated or the connection may fail
399 because a client certificate is required or is requested only after an
400 attempt is made to access a certain URL. Note: the output produced by this
401 option is not always accurate because a connection might never have been
406 Prints out the SSL session states.
410 Print extensive debugging information including a hex dump of all traffic.
414 Show all protocol messages with hex dump.
418 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
419 with B<enable-ssl-trace> for this option to work.
423 File to send output of B<-msg> or B<-trace> to, default standard output.
427 Tests non-blocking I/O
431 Turns on non-blocking I/O
435 This option translated a line feed from the terminal into CR+LF as required
440 Inhibit shutting down the connection when end of file is reached in the
445 Inhibit printing of session and certificate information. This implicitly
446 turns on B<-ign_eof> as well.
450 Shut down the connection when end of file is reached in the input.
451 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
453 =item B<-psk_identity identity>
455 Use the PSK identity B<identity> when using a PSK cipher suite.
456 The default value is "Client_identity" (without the quotes).
460 Use the PSK key B<key> when using a PSK cipher suite. The key is
461 given as a hexadecimal number without leading 0x, for example -psk
463 This option must be provided in order to use a PSK cipher.
465 =item B<-psk_session file>
467 Use the pem encoded SSL_SESSION data stored in B<file> as the basis of a PSK.
468 Note that this will only work if TLSv1.3 is negotiated.
470 =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>
472 These options require or disable the use of the specified SSL or TLS protocols.
473 By default B<s_client> will negotiate the highest mutually supported protocol
475 When a specific TLS version is required, only that version will be offered to
476 and accepted from the server.
477 Note that not all protocols and flags may be available, depending on how
480 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
482 These options make B<s_client> use DTLS protocols instead of TLS.
483 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
484 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
489 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
490 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
491 available where OpenSSL has support for SCTP enabled.
493 =item B<-sctp_label_bug>
495 Use the incorrect behaviour of older OpenSSL implementations when computing
496 endpoint-pair shared secrets for DTLS/SCTP. This allows communication with
497 older broken implementations but breaks interoperability with correct
498 implementations. Must be used in conjunction with B<-sctp>. This option is only
499 available where OpenSSL has support for SCTP enabled.
501 =item B<-fallback_scsv>
503 Send TLS_FALLBACK_SCSV in the ClientHello.
507 Switch on asynchronous mode. Cryptographic operations will be performed
508 asynchronously. This will only have an effect if an asynchronous capable engine
509 is also used via the B<-engine> option. For test purposes the dummy async engine
510 (dasync) can be used (if available).
512 =item B<-max_send_frag int>
514 The maximum size of data fragment to send.
515 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
517 =item B<-split_send_frag int>
519 The size used to split data for encrypt pipelines. If more data is written in
520 one go than this value then it will be split into multiple pipelines, up to the
521 maximum number of pipelines defined by max_pipelines. This only has an effect if
522 a suitable cipher suite has been negotiated, an engine that supports pipelining
523 has been loaded, and max_pipelines is greater than 1. See
524 L<SSL_CTX_set_split_send_fragment(3)> for further information.
526 =item B<-max_pipelines int>
528 The maximum number of encrypt/decrypt pipelines to be used. This will only have
529 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
530 engine) and a suitable cipher suite has been negotiated. The default value is 1.
531 See L<SSL_CTX_set_max_pipelines(3)> for further information.
533 =item B<-read_buf int>
535 The default read buffer size to be used for connections. This will only have an
536 effect if the buffer size is larger than the size that would otherwise be used
537 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
538 further information).
542 There are several known bug in SSL and TLS implementations. Adding this
543 option enables various workarounds.
547 Enables support for SSL/TLS compression.
548 This option was introduced in OpenSSL 1.1.0.
549 TLS compression is not recommended and is off by default as of
554 Disables support for SSL/TLS compression.
555 TLS compression is not recommended and is off by default as of
560 Only provide a brief summary of connection parameters instead of the
561 normal verbose output.
563 =item B<-sigalgs sigalglist>
565 Specifies the list of signature algorithms that are sent by the client.
566 The server selects one entry in the list based on its preferences.
567 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
569 =item B<-curves curvelist>
571 Specifies the list of supported curves to be sent by the client. The curve is
572 ultimately selected by the server. For a list of all curves, use:
574 $ openssl ecparam -list_curves
576 =item B<-cipher cipherlist>
578 This allows the TLSv1.2 and below cipher list sent by the client to be modified.
579 This list will be combined with any TLSv1.3 ciphersuites that have been
580 configured. Although the server determines which ciphersuite is used it should
581 take the first supported cipher in the list sent by the client. See the
582 B<ciphers> command for more information.
584 =item B<-ciphersuites val>
586 This allows the TLSv1.3 ciphersuites sent by the client to be modified. This
587 list will be combined with any TLSv1.2 and below ciphersuites that have been
588 configured. Although the server determines which cipher suite is used it should
589 take the first supported cipher in the list sent by the client. See the
590 B<ciphers> command for more information. The format for this list is a simple
591 colon (":") separated list of TLSv1.3 ciphersuite names.
593 =item B<-starttls protocol>
595 Send the protocol-specific message(s) to switch to TLS for communication.
596 B<protocol> is a keyword for the intended protocol. Currently, the only
597 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
598 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
600 =item B<-xmpphost hostname>
602 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
603 specifies the host for the "to" attribute of the stream element.
604 If this option is not specified, then the host specified with "-connect"
607 This option is an alias of the B<-name> option for "xmpp" and "xmpp-server".
609 =item B<-name hostname>
611 This option is used to specify hostname information for various protocols
612 used with B<-starttls> option. Currently only "xmpp", "xmpp-server",
613 "smtp" and "lmtp" can utilize this B<-name> option.
615 If this option is used with "-starttls xmpp" or "-starttls xmpp-server",
616 if specifies the host for the "to" attribute of the stream element. If this
617 option is not specified, then the host specified with "-connect" will be used.
619 If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies
620 the name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If
621 this option is not specified, then "mail.example.com" will be used.
623 =item B<-tlsextdebug>
625 Print out a hex dump of any TLS extensions received from the server.
629 Disable RFC4507bis session ticket support.
631 =item B<-sess_out filename>
633 Output SSL session to B<filename>.
635 =item B<-sess_in sess.pem>
637 Load SSL session from B<filename>. The client will attempt to resume a
638 connection from this session.
642 Specifying an engine (by its unique B<id> string) will cause B<s_client>
643 to attempt to obtain a functional reference to the specified engine,
644 thus initialising it if needed. The engine will then be set as the default
645 for all available algorithms.
647 =item B<-rand file...>
649 A file or files containing random data used to seed the random number
651 Multiple files can be specified separated by an OS-dependent character.
652 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
655 =item [B<-writerand file>]
657 Writes random data to the specified I<file> upon exit.
658 This can be used with a subsequent B<-rand> flag.
660 =item B<-serverinfo types>
662 A list of comma-separated TLS Extension Types (numbers between 0 and
663 65535). Each type will be sent as an empty ClientHello TLS Extension.
664 The server's response (if any) will be encoded and displayed as a PEM
669 Sends a certificate status request to the server (OCSP stapling). The server
670 response (if any) is printed out.
672 =item B<-alpn protocols>, B<-nextprotoneg protocols>
674 These flags enable the Enable the Application-Layer Protocol Negotiation
675 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
676 IETF standard and replaces NPN.
677 The B<protocols> list is a comma-separated list of protocol names that
678 the client should advertise support for. The list should contain the most
679 desirable protocols first. Protocol names are printable ASCII strings,
680 for example "http/1.1" or "spdy/3".
681 An empty list of protocols is treated specially and will cause the
682 client to advertise support for the TLS extension but disconnect just
683 after receiving ServerHello with a list of server supported protocols.
684 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
686 =item B<-ct>, B<-noct>
688 Use one of these two options to control whether Certificate Transparency (CT)
689 is enabled (B<-ct>) or disabled (B<-noct>).
690 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
691 the server and reported at handshake completion.
693 Enabling CT also enables OCSP stapling, as this is one possible delivery method
698 A file containing a list of known Certificate Transparency logs. See
699 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
701 =item B<-keylogfile file>
703 Appends TLS secrets to the specified keylog file such that external programs
704 (like Wireshark) can decrypt TLS connections.
706 =item B<-early_data file>
708 Reads the contents of the specified file and attempts to send it as early data
709 to the server. This will only work with resumed sessions that support early
710 data and when the server accepts the early data.
714 For TLSv1.3 only, send the Post-Handshake Authentication extension. This will
715 happen whether or not a certificate has been provided via B<-cert>.
719 Rather than providing B<-connect>, the target hostname and optional port may
720 be provided as a single positional argument after all options. If neither this
721 nor B<-connect> are provided, falls back to attempting to connect to localhost
726 =head1 CONNECTED COMMANDS
728 If a connection is established with an SSL server then any data received
729 from the server is displayed and any key presses will be sent to the
730 server. If end of file is reached then the connection will be closed down. When
731 used interactively (which means neither B<-quiet> nor B<-ign_eof> have been
732 given), then certain commands are also recognized which perform special
733 operations. These commands are a letter which must appear at the start of a
734 line. They are listed below.
740 End the current SSL connection and exit.
744 Renegotiate the SSL session (TLSv1.2 and below only).
748 Send a heartbeat message to the server (DTLS only)
752 Send a key update message to the server (TLSv1.3 only)
756 Send a key update message to the server and request one back (TLSv1.3 only)
762 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
765 openssl s_client -connect servername:443
767 would typically be used (https uses port 443). If the connection succeeds
768 then an HTTP command can be given such as "GET /" to retrieve a web page.
770 If the handshake fails then there are several possible causes, if it is
771 nothing obvious like no client certificate then the B<-bugs>,
772 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
773 in case it is a buggy server. In particular you should play with these
774 options B<before> submitting a bug report to an OpenSSL mailing list.
776 A frequent problem when attempting to get client certificates working
777 is that a web client complains it has no certificates or gives an empty
778 list to choose from. This is normally because the server is not sending
779 the clients certificate authority in its "acceptable CA list" when it
780 requests a certificate. By using B<s_client> the CA list can be viewed
781 and checked. However some servers only request client authentication
782 after a specific URL is requested. To obtain the list in this case it
783 is necessary to use the B<-prexit> option and send an HTTP request
784 for an appropriate page.
786 If a certificate is specified on the command line using the B<-cert>
787 option it will not be used unless the server specifically requests
788 a client certificate. Therefor merely including a client certificate
789 on the command line is no guarantee that the certificate works.
791 If there are problems verifying a server certificate then the
792 B<-showcerts> option can be used to show all the certificates sent by the
795 The B<s_client> utility is a test tool and is designed to continue the
796 handshake after any certificate verification errors. As a result it will
797 accept any certificate chain (trusted or not) sent by the peer. None test
798 applications should B<not> do this as it makes them vulnerable to a MITM
799 attack. This behaviour can be changed by with the B<-verify_return_error>
800 option: any verify errors are then returned aborting the handshake.
802 The B<-bind> option may be useful if the server or a firewall requires
803 connections to come from some particular address and or port.
807 Because this program has a lot of options and also because some of the
808 techniques used are rather old, the C source of B<s_client> is rather hard to
809 read and not a model of how things should be done.
810 A typical SSL client program would be much simpler.
812 The B<-prexit> option is a bit of a hack. We should really report
813 information whenever a session is renegotiated.
817 L<SSL_CONF_cmd(3)>, L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>,
818 L<SSL_CTX_set_max_send_fragment(3)>, L<SSL_CTX_set_split_send_fragment(3)>,
819 L<SSL_CTX_set_max_pipelines(3)>
823 The B<-no_alt_chains> option was added in OpenSSL 1.1.0.
824 The B<-name> option was added in OpenSSL 1.1.1.
828 Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
830 Licensed under the OpenSSL license (the "License"). You may not use
831 this file except in compliance with the License. You can obtain a copy
832 in the file LICENSE in the source distribution or at
833 L<https://www.openssl.org/source/license.html>.