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>]
27 [B<-CApath directory>]
31 [B<-requestCAfile filename>]
32 [B<-dane_tlsa_domain domain>]
33 [B<-dane_tlsa_rrdata rrdata>]
34 [B<-dane_ee_no_namechecks>]
35 [B<-attime timestamp>]
58 [B<-verify_depth num>]
59 [B<-verify_email email>]
60 [B<-verify_hostname hostname>]
62 [B<-verify_name name>]
74 [B<-psk_identity identity>]
76 [B<-psk_session file>]
101 [B<-allow_no_dhe_kex>]
102 [B<-sigalgs sigalglist>]
103 [B<-curves curvelist>]
104 [B<-cipher cipherlist>]
105 [B<-ciphersuites val>]
107 [B<-starttls protocol>]
108 [B<-xmpphost hostname>]
113 [B<-sess_out filename>]
114 [B<-sess_in filename>]
117 [B<-serverinfo types>]
120 [B<-nextprotoneg protocols>]
124 [B<-keylogfile file>]
125 [B<-early_data file>]
131 The B<s_client> command implements a generic SSL/TLS client which connects
132 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
137 In addition to the options below the B<s_client> utility also supports the
138 common and client only options documented in the
139 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
146 Print out a usage message.
148 =item B<-connect host:port>
150 This specifies the host and optional port to connect to. It is possible to
151 select the host and port using the optional target positional argument instead.
152 If neither this nor the target positional argument are specified then an attempt
153 is made to connect to the local host on port 4433.
155 =item B<-bind host:port>]
157 This specifies the host address and or port to bind as the source for the
158 connection. For Unix-domain sockets the port is ignored and the host is
159 used as the source socket address.
161 =item B<-proxy host:port>
163 When used with the B<-connect> flag, the program uses the host and port
164 specified with this flag and issues an HTTP CONNECT command to connect
165 to the desired server.
169 Connect over the specified Unix-domain socket.
179 =item B<-servername name>
181 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
182 the given value. If both this option and the B<-noservername> are not given, the
183 TLS SNI extension is still set to the hostname provided to the B<-connect> option,
184 or "localhost" if B<-connect> has not been supplied. This is default since OpenSSL
187 Even though SNI name should normally be a DNS name and not an IP address, this
188 option will not make the distinction when parsing B<-connect> and will send
189 IP address if one passed.
191 =item B<-noservername>
193 Suppresses sending of the SNI (Server Name Indication) extension in the
194 ClientHello message. Cannot be used in conjunction with the B<-servername> or
195 <-dane_tlsa_domain> options.
197 =item B<-cert certname>
199 The certificate to use, if one is requested by the server. The default is
200 not to use a certificate.
202 =item B<-certform format>
204 The certificate format to use: DER or PEM. PEM is the default.
206 =item B<-key keyfile>
208 The private key to use. If not specified then the certificate file will
211 =item B<-keyform format>
213 The private format to use: DER or PEM. PEM is the default.
217 the private key password source. For more information about the format of B<arg>
218 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
220 =item B<-verify depth>
222 The verify depth to use. This specifies the maximum length of the
223 server certificate chain and turns on server certificate verification.
224 Currently the verify operation continues after errors so all the problems
225 with a certificate chain can be seen. As a side effect the connection
226 will never fail due to a server certificate verify failure.
228 =item B<-verify_return_error>
230 Return verification errors instead of continuing. This will typically
231 abort the handshake with a fatal error.
233 =item B<-nameopt option>
235 Option which determines how the subject or issuer names are displayed. The
236 B<option> argument can be a single option or multiple options separated by
237 commas. Alternatively the B<-nameopt> switch may be used more than once to
238 set multiple options. See the L<x509(1)> manual page for details.
240 =item B<-CApath directory>
242 The directory to use for server certificate verification. This directory
243 must be in "hash format", see B<verify> for more information. These are
244 also used when building the client certificate chain.
246 =item B<-CAfile file>
248 A file containing trusted certificates to use during server authentication
249 and to use when attempting to build the client certificate chain.
253 Do not load the trusted CA certificates from the default file location
257 Do not load the trusted CA certificates from the default directory location
259 =item B<-requestCAfile file>
261 A file containing a list of certificates whose subject names will be sent
262 to the server in the B<certificate_authorities> extension. Only supported
265 =item B<-dane_tlsa_domain domain>
267 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
268 TLSA base domain which becomes the default SNI hint and the primary
269 reference identifier for hostname checks. This must be used in
270 combination with at least one instance of the B<-dane_tlsa_rrdata>
273 When DANE authentication succeeds, the diagnostic output will include
274 the lowest (closest to 0) depth at which a TLSA record authenticated
275 a chain certificate. When that TLSA record is a "2 1 0" trust
276 anchor public key that signed (rather than matched) the top-most
277 certificate of the chain, the result is reported as "TA public key
278 verified". Otherwise, either the TLSA record "matched TA certificate"
279 at a positive depth or else "matched EE certificate" at depth 0.
281 =item B<-dane_tlsa_rrdata rrdata>
283 Use one or more times to specify the RRDATA fields of the DANE TLSA
284 RRset associated with the target service. The B<rrdata> value is
285 specied in "presentation form", that is four whitespace separated
286 fields that specify the usage, selector, matching type and associated
287 data, with the last of these encoded in hexadecimal. Optional
288 whitespace is ignored in the associated data field. For example:
290 $ openssl s_client -brief -starttls smtp \
291 -connect smtp.example.com:25 \
292 -dane_tlsa_domain smtp.example.com \
293 -dane_tlsa_rrdata "2 1 1
294 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
295 -dane_tlsa_rrdata "2 1 1
296 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
299 Verified peername: smtp.example.com
300 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
303 =item B<-dane_ee_no_namechecks>
305 This disables server name checks when authenticating via DANE-EE(3) TLSA
307 For some applications, primarily web browsers, it is not safe to disable name
308 checks due to "unknown key share" attacks, in which a malicious server can
309 convince a client that a connection to a victim server is instead a secure
310 connection to the malicious server.
311 The malicious server may then be able to violate cross-origin scripting
313 Thus, despite the text of RFC7671, name checks are by default enabled for
314 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
316 In particular, SMTP and XMPP clients should set this option as SRV and MX
317 records already make it possible for a remote domain to redirect client
318 connections to any server of its choice, and in any case SMTP and XMPP clients
319 do not execute scripts downloaded from remote servers.
321 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
322 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
323 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
324 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
325 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
326 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
327 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
329 Set various certificate chain validation options. See the
330 L<verify(1)> manual page for details.
334 Reconnects to the same server 5 times using the same session ID, this can
335 be used as a test that session caching is working.
339 Displays the server certificate list as sent by the server: it only consists of
340 certificates the server has sent (in the order the server has sent them). It is
341 B<not> a verified chain.
345 Print session information when the program exits. This will always attempt
346 to print out information even if the connection fails. Normally information
347 will only be printed out once if the connection succeeds. This option is useful
348 because the cipher in use may be renegotiated or the connection may fail
349 because a client certificate is required or is requested only after an
350 attempt is made to access a certain URL. Note: the output produced by this
351 option is not always accurate because a connection might never have been
356 Prints out the SSL session states.
360 Print extensive debugging information including a hex dump of all traffic.
364 Show all protocol messages with hex dump.
368 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
369 with B<enable-ssl-trace> for this option to work.
373 File to send output of B<-msg> or B<-trace> to, default standard output.
377 Tests non-blocking I/O
381 Turns on non-blocking I/O
385 This option translated a line feed from the terminal into CR+LF as required
390 Inhibit shutting down the connection when end of file is reached in the
395 Inhibit printing of session and certificate information. This implicitly
396 turns on B<-ign_eof> as well.
400 Shut down the connection when end of file is reached in the input.
401 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
403 =item B<-psk_identity identity>
405 Use the PSK identity B<identity> when using a PSK cipher suite.
406 The default value is "Client_identity" (without the quotes).
410 Use the PSK key B<key> when using a PSK cipher suite. The key is
411 given as a hexadecimal number without leading 0x, for example -psk
413 This option must be provided in order to use a PSK cipher.
415 =item B<-psk_session file>
417 Use the pem encoded SSL_SESSION data stored in B<file> as the basis of a PSK.
418 Note that this will only work if TLSv1.3 is negotiated.
420 =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>
422 These options require or disable the use of the specified SSL or TLS protocols.
423 By default B<s_client> will negotiate the highest mutually supported protocol
425 When a specific TLS version is required, only that version will be offered to
426 and accepted from the server.
428 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
430 These options make B<s_client> use DTLS protocols instead of TLS.
431 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
432 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
437 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
438 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
439 available where OpenSSL has support for SCTP enabled.
441 =item B<-fallback_scsv>
443 Send TLS_FALLBACK_SCSV in the ClientHello.
447 Switch on asynchronous mode. Cryptographic operations will be performed
448 asynchronously. This will only have an effect if an asynchronous capable engine
449 is also used via the B<-engine> option. For test purposes the dummy async engine
450 (dasync) can be used (if available).
452 =item B<-max_send_frag int>
454 The maximum size of data fragment to send.
455 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
457 =item B<-split_send_frag int>
459 The size used to split data for encrypt pipelines. If more data is written in
460 one go than this value then it will be split into multiple pipelines, up to the
461 maximum number of pipelines defined by max_pipelines. This only has an effect if
462 a suitable cipher suite has been negotiated, an engine that supports pipelining
463 has been loaded, and max_pipelines is greater than 1. See
464 L<SSL_CTX_set_split_send_fragment(3)> for further information.
466 =item B<-max_pipelines int>
468 The maximum number of encrypt/decrypt pipelines to be used. This will only have
469 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
470 engine) and a suitable cipher suite has been negotiated. The default value is 1.
471 See L<SSL_CTX_set_max_pipelines(3)> for further information.
473 =item B<-read_buf int>
475 The default read buffer size to be used for connections. This will only have an
476 effect if the buffer size is larger than the size that would otherwise be used
477 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
478 further information).
482 There are several known bug in SSL and TLS implementations. Adding this
483 option enables various workarounds.
487 Enables support for SSL/TLS compression.
488 This option was introduced in OpenSSL 1.1.0.
489 TLS compression is not recommended and is off by default as of
494 Disables support for SSL/TLS compression.
495 TLS compression is not recommended and is off by default as of
500 Only provide a brief summary of connection parameters instead of the
501 normal verbose output.
503 =item B<-sigalgs sigalglist>
505 Specifies the list of signature algorithms that are sent by the client.
506 The server selects one entry in the list based on its preferences.
507 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
509 =item B<-curves curvelist>
511 Specifies the list of supported curves to be sent by the client. The curve is
512 ultimately selected by the server. For a list of all curves, use:
514 $ openssl ecparam -list_curves
516 =item B<-cipher cipherlist>
518 This allows the TLSv1.2 and below cipher list sent by the client to be modified.
519 This list will be combined with any TLSv1.3 ciphersuites that have been
520 configured. Although the server determines which ciphersuite is used it should
521 take the first supported cipher in the list sent by the client. See the
522 B<ciphers> command for more information.
524 =item B<-ciphersuites val>
526 This allows the TLSv1.3 ciphersuites sent by the client to be modified. This
527 list will be combined with any TLSv1.2 and below ciphersuites that have been
528 configured. Although the server determines which cipher suite is used it should
529 take the first supported cipher in the list sent by the client. See the
530 B<ciphers> command for more information. The format for this list is a simple
531 colon (":") separated list of TLSv1.3 ciphersuite names.
533 =item B<-starttls protocol>
535 Send the protocol-specific message(s) to switch to TLS for communication.
536 B<protocol> is a keyword for the intended protocol. Currently, the only
537 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
538 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
540 =item B<-xmpphost hostname>
542 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
543 specifies the host for the "to" attribute of the stream element.
544 If this option is not specified, then the host specified with "-connect"
547 This option is an alias of the B<-name> option for "xmpp" and "xmpp-server".
549 =item B<-name hostname>
551 This option is used to specify hostname information for various protocols
552 used with B<-starttls> option. Currently only "xmpp", "xmpp-server",
553 "smtp" and "lmtp" can utilize this B<-name> option.
555 If this option is used with "-starttls xmpp" or "-starttls xmpp-server",
556 if specifies the host for the "to" attribute of the stream element. If this
557 option is not specified, then the host specified with "-connect" will be used.
559 If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies
560 the name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If
561 this option is not specified, then "mail.example.com" will be used.
563 =item B<-tlsextdebug>
565 Print out a hex dump of any TLS extensions received from the server.
569 Disable RFC4507bis session ticket support.
571 =item B<-sess_out filename>
573 Output SSL session to B<filename>.
575 =item B<-sess_in sess.pem>
577 Load SSL session from B<filename>. The client will attempt to resume a
578 connection from this session.
582 Specifying an engine (by its unique B<id> string) will cause B<s_client>
583 to attempt to obtain a functional reference to the specified engine,
584 thus initialising it if needed. The engine will then be set as the default
585 for all available algorithms.
587 =item B<-rand file...>
589 A file or files containing random data used to seed the random number
591 Multiple files can be specified separated by an OS-dependent character.
592 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
595 =item [B<-writerand file>]
597 Writes random data to the specified I<file> upon exit.
598 This can be used with a subsequent B<-rand> flag.
600 =item B<-serverinfo types>
602 A list of comma-separated TLS Extension Types (numbers between 0 and
603 65535). Each type will be sent as an empty ClientHello TLS Extension.
604 The server's response (if any) will be encoded and displayed as a PEM
609 Sends a certificate status request to the server (OCSP stapling). The server
610 response (if any) is printed out.
612 =item B<-alpn protocols>, B<-nextprotoneg protocols>
614 These flags enable the Enable the Application-Layer Protocol Negotiation
615 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
616 IETF standard and replaces NPN.
617 The B<protocols> list is a comma-separated list of protocol names that
618 the client should advertise support for. The list should contain the most
619 desirable protocols first. Protocol names are printable ASCII strings,
620 for example "http/1.1" or "spdy/3".
621 An empty list of protocols is treated specially and will cause the
622 client to advertise support for the TLS extension but disconnect just
623 after receiving ServerHello with a list of server supported protocols.
624 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
626 =item B<-ct>, B<-noct>
628 Use one of these two options to control whether Certificate Transparency (CT)
629 is enabled (B<-ct>) or disabled (B<-noct>).
630 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
631 the server and reported at handshake completion.
633 Enabling CT also enables OCSP stapling, as this is one possible delivery method
638 A file containing a list of known Certificate Transparency logs. See
639 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
641 =item B<-keylogfile file>
643 Appends TLS secrets to the specified keylog file such that external programs
644 (like Wireshark) can decrypt TLS connections.
646 =item B<-early_data file>
648 Reads the contents of the specified file and attempts to send it as early data
649 to the server. This will only work with resumed sessions that support early
650 data and when the server accepts the early data.
654 For TLSv1.3 only, always send the Post-Handshake Authentication extension,
655 whether or not a certificate has been provided via B<-cert>.
659 Rather than providing B<-connect>, the target hostname and optional port may
660 be provided as a single positional argument after all options. If neither this
661 nor B<-connect> are provided, falls back to attempting to connect to localhost
666 =head1 CONNECTED COMMANDS
668 If a connection is established with an SSL server then any data received
669 from the server is displayed and any key presses will be sent to the
670 server. If end of file is reached then the connection will be closed down. When
671 used interactively (which means neither B<-quiet> nor B<-ign_eof> have been
672 given), then certain commands are also recognized which perform special
673 operations. These commands are a letter which must appear at the start of a
674 line. They are listed below.
680 End the current SSL connection and exit.
684 Renegotiate the SSL session (TLSv1.2 and below only).
688 Send a heartbeat message to the server (DTLS only)
692 Send a key update message to the server (TLSv1.3 only)
696 Send a key update message to the server and request one back (TLSv1.3 only)
702 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
705 openssl s_client -connect servername:443
707 would typically be used (https uses port 443). If the connection succeeds
708 then an HTTP command can be given such as "GET /" to retrieve a web page.
710 If the handshake fails then there are several possible causes, if it is
711 nothing obvious like no client certificate then the B<-bugs>,
712 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
713 in case it is a buggy server. In particular you should play with these
714 options B<before> submitting a bug report to an OpenSSL mailing list.
716 A frequent problem when attempting to get client certificates working
717 is that a web client complains it has no certificates or gives an empty
718 list to choose from. This is normally because the server is not sending
719 the clients certificate authority in its "acceptable CA list" when it
720 requests a certificate. By using B<s_client> the CA list can be viewed
721 and checked. However some servers only request client authentication
722 after a specific URL is requested. To obtain the list in this case it
723 is necessary to use the B<-prexit> option and send an HTTP request
724 for an appropriate page.
726 If a certificate is specified on the command line using the B<-cert>
727 option it will not be used unless the server specifically requests
728 a client certificate. Therefor merely including a client certificate
729 on the command line is no guarantee that the certificate works.
731 If there are problems verifying a server certificate then the
732 B<-showcerts> option can be used to show all the certificates sent by the
735 The B<s_client> utility is a test tool and is designed to continue the
736 handshake after any certificate verification errors. As a result it will
737 accept any certificate chain (trusted or not) sent by the peer. None test
738 applications should B<not> do this as it makes them vulnerable to a MITM
739 attack. This behaviour can be changed by with the B<-verify_return_error>
740 option: any verify errors are then returned aborting the handshake.
742 The B<-bind> option may be useful if the server or a firewall requires
743 connections to come from some particular address and or port.
747 Because this program has a lot of options and also because some of the
748 techniques used are rather old, the C source of B<s_client> is rather hard to
749 read and not a model of how things should be done.
750 A typical SSL client program would be much simpler.
752 The B<-prexit> option is a bit of a hack. We should really report
753 information whenever a session is renegotiated.
757 L<SSL_CONF_cmd(3)>, L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>,
758 L<SSL_CTX_set_max_send_fragment(3)>, L<SSL_CTX_set_split_send_fragment(3)>
759 L<SSL_CTX_set_max_pipelines(3)>
763 The B<-no_alt_chains> option was first added to OpenSSL 1.1.0.
764 The B<-name> option was added in OpenSSL 1.1.1.
768 Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
770 Licensed under the OpenSSL license (the "License"). You may not use
771 this file except in compliance with the License. You can obtain a copy
772 in the file LICENSE in the source distribution or at
773 L<https://www.openssl.org/source/license.html>.