5 s_client - SSL/TLS client program
11 [B<-connect host:port>]
19 [B<-verify_return_error>]
21 [B<-certform DER|PEM>]
25 [B<-CApath directory>]
29 [B<-requestCAfile filename>]
30 [B<-dane_tlsa_domain domain>]
31 [B<-dane_tlsa_rrdata rrdata>]
32 [B<-dane_ee_no_namechecks>]
33 [B<-attime timestamp>]
56 [B<-verify_depth num>]
57 [B<-verify_email email>]
58 [B<-verify_hostname hostname>]
60 [B<-verify_name name>]
96 [B<-sigalgs sigalglist>]
97 [B<-curves curvelist>]
98 [B<-cipher cipherlist>]
100 [B<-starttls protocol>]
101 [B<-xmpphost hostname>]
105 [B<-sess_out filename>]
106 [B<-sess_in filename>]
108 [B<-serverinfo types>]
111 [B<-nextprotoneg protocols>]
114 [B<-keylogfile file>]
115 [B<-early_data file>]
119 The B<s_client> command implements a generic SSL/TLS client which connects
120 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
125 In addition to the options below the B<s_client> utility also supports the
126 common and client only options documented in the
127 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
134 Print out a usage message.
136 =item B<-connect host:port>
138 This specifies the host and optional port to connect to. If not specified
139 then an attempt is made to connect to the local host on port 4433.
141 =item B<-proxy host:port>
143 When used with the B<-connect> flag, the program uses the host and port
144 specified with this flag and issues an HTTP CONNECT command to connect
145 to the desired server.
149 Connect over the specified Unix-domain socket.
159 =item B<-servername name>
161 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
162 the given value. If both this option and the B<-noservername> are not given, the
163 TLS SNI extension is still set to the hostname provided to the B<-connect> option,
164 or "localhost" if B<-connect> has not been supplied. This is default since OpenSSL
167 Even though SNI name should normally be a DNS name and not an IP address, this
168 option will not make the distinction when parsing B<-connect> and will send
169 IP address if one passed.
171 =item B<-noservername>
173 Suppresses sending of the SNI (Server Name Indication) extension in the
174 ClientHello message. Cannot be used in conjunction with the B<-servername> or
175 <-dane_tlsa_domain> options.
177 =item B<-cert certname>
179 The certificate to use, if one is requested by the server. The default is
180 not to use a certificate.
182 =item B<-certform format>
184 The certificate format to use: DER or PEM. PEM is the default.
186 =item B<-key keyfile>
188 The private key to use. If not specified then the certificate file will
191 =item B<-keyform format>
193 The private format to use: DER or PEM. PEM is the default.
197 the private key password source. For more information about the format of B<arg>
198 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
200 =item B<-verify depth>
202 The verify depth to use. This specifies the maximum length of the
203 server certificate chain and turns on server certificate verification.
204 Currently the verify operation continues after errors so all the problems
205 with a certificate chain can be seen. As a side effect the connection
206 will never fail due to a server certificate verify failure.
208 =item B<-verify_return_error>
210 Return verification errors instead of continuing. This will typically
211 abort the handshake with a fatal error.
213 =item B<-nameopt option>
215 Option which determines how the subject or issuer names are displayed. The
216 B<option> argument can be a single option or multiple options separated by
217 commas. Alternatively the B<-nameopt> switch may be used more than once to
218 set multiple options. See the L<x509(1)> manual page for details.
220 =item B<-CApath directory>
222 The directory to use for server certificate verification. This directory
223 must be in "hash format", see B<verify> for more information. These are
224 also used when building the client certificate chain.
226 =item B<-CAfile file>
228 A file containing trusted certificates to use during server authentication
229 and to use when attempting to build the client certificate chain.
233 Do not load the trusted CA certificates from the default file location
237 Do not load the trusted CA certificates from the default directory location
239 =item B<-requestCAfile file>
241 A file containing a list of certificates whose subject names will be sent
242 to the server in the B<certificate_authorities> extension. Only supported
245 =item B<-dane_tlsa_domain domain>
247 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
248 TLSA base domain which becomes the default SNI hint and the primary
249 reference identifier for hostname checks. This must be used in
250 combination with at least one instance of the B<-dane_tlsa_rrdata>
253 When DANE authentication succeeds, the diagnostic output will include
254 the lowest (closest to 0) depth at which a TLSA record authenticated
255 a chain certificate. When that TLSA record is a "2 1 0" trust
256 anchor public key that signed (rather than matched) the top-most
257 certificate of the chain, the result is reported as "TA public key
258 verified". Otherwise, either the TLSA record "matched TA certificate"
259 at a positive depth or else "matched EE certificate" at depth 0.
261 =item B<-dane_tlsa_rrdata rrdata>
263 Use one or more times to specify the RRDATA fields of the DANE TLSA
264 RRset associated with the target service. The B<rrdata> value is
265 specied in "presentation form", that is four whitespace separated
266 fields that specify the usage, selector, matching type and associated
267 data, with the last of these encoded in hexadecimal. Optional
268 whitespace is ignored in the associated data field. For example:
270 $ openssl s_client -brief -starttls smtp \
271 -connect smtp.example.com:25 \
272 -dane_tlsa_domain smtp.example.com \
273 -dane_tlsa_rrdata "2 1 1
274 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
275 -dane_tlsa_rrdata "2 1 1
276 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
279 Verified peername: smtp.example.com
280 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
283 =item B<-dane_ee_no_namechecks>
285 This disables server name checks when authenticating via DANE-EE(3) TLSA
287 For some applications, primarily web browsers, it is not safe to disable name
288 checks due to "unknown key share" attacks, in which a malicious server can
289 convince a client that a connection to a victim server is instead a secure
290 connection to the malicious server.
291 The malicious server may then be able to violate cross-origin scripting
293 Thus, despite the text of RFC7671, name checks are by default enabled for
294 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
296 In particular, SMTP and XMPP clients should set this option as SRV and MX
297 records already make it possible for a remote domain to redirect client
298 connections to any server of its choice, and in any case SMTP and XMPP clients
299 do not execute scripts downloaded from remote servers.
301 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
302 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
303 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
304 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
305 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
306 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
307 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
309 Set various certificate chain validation options. See the
310 L<verify(1)> manual page for details.
314 Reconnects to the same server 5 times using the same session ID, this can
315 be used as a test that session caching is working.
319 Display the whole server certificate chain: normally only the server
320 certificate itself is displayed.
324 Print session information when the program exits. This will always attempt
325 to print out information even if the connection fails. Normally information
326 will only be printed out once if the connection succeeds. This option is useful
327 because the cipher in use may be renegotiated or the connection may fail
328 because a client certificate is required or is requested only after an
329 attempt is made to access a certain URL. Note: the output produced by this
330 option is not always accurate because a connection might never have been
335 Prints out the SSL session states.
339 Print extensive debugging information including a hex dump of all traffic.
343 Show all protocol messages with hex dump.
347 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
348 with B<enable-ssl-trace> for this option to work.
352 File to send output of B<-msg> or B<-trace> to, default standard output.
356 Tests non-blocking I/O
360 Turns on non-blocking I/O
364 This option translated a line feed from the terminal into CR+LF as required
369 Inhibit shutting down the connection when end of file is reached in the
374 Inhibit printing of session and certificate information. This implicitly
375 turns on B<-ign_eof> as well.
379 Shut down the connection when end of file is reached in the input.
380 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
382 =item B<-psk_identity identity>
384 Use the PSK identity B<identity> when using a PSK cipher suite.
385 The default value is "Client_identity" (without the quotes).
389 Use the PSK key B<key> when using a PSK cipher suite. The key is
390 given as a hexadecimal number without leading 0x, for example -psk
392 This option must be provided in order to use a PSK cipher.
394 =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>
396 These options require or disable the use of the specified SSL or TLS protocols.
397 By default B<s_client> will negotiate the highest mutually supported protocol
399 When a specific TLS version is required, only that version will be offered to
400 and accepted from the server.
402 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
404 These options make B<s_client> use DTLS protocols instead of TLS.
405 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
406 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
411 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
412 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
413 available where OpenSSL has support for SCTP enabled.
415 =item B<-fallback_scsv>
417 Send TLS_FALLBACK_SCSV in the ClientHello.
421 Switch on asynchronous mode. Cryptographic operations will be performed
422 asynchronously. This will only have an effect if an asynchronous capable engine
423 is also used via the B<-engine> option. For test purposes the dummy async engine
424 (dasync) can be used (if available).
426 =item B<-max_send_frag int>
428 The maximum size of data fragment to send.
429 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
431 =item B<-split_send_frag int>
433 The size used to split data for encrypt pipelines. If more data is written in
434 one go than this value then it will be split into multiple pipelines, up to the
435 maximum number of pipelines defined by max_pipelines. This only has an effect if
436 a suitable cipher suite has been negotiated, an engine that supports pipelining
437 has been loaded, and max_pipelines is greater than 1. See
438 L<SSL_CTX_set_split_send_fragment(3)> for further information.
440 =item B<-max_pipelines int>
442 The maximum number of encrypt/decrypt pipelines to be used. This will only have
443 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
444 engine) and a suitable cipher suite has been negotiated. The default value is 1.
445 See L<SSL_CTX_set_max_pipelines(3)> for further information.
447 =item B<-read_buf int>
449 The default read buffer size to be used for connections. This will only have an
450 effect if the buffer size is larger than the size that would otherwise be used
451 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
452 further information).
456 There are several known bug in SSL and TLS implementations. Adding this
457 option enables various workarounds.
461 Enables support for SSL/TLS compression.
462 This option was introduced in OpenSSL 1.1.0.
463 TLS compression is not recommended and is off by default as of
468 Disables support for SSL/TLS compression.
469 TLS compression is not recommended and is off by default as of
474 Only provide a brief summary of connection parameters instead of the
475 normal verbose output.
477 =item B<-sigalgs sigalglist>
479 Specifies the list of signature algorithms that are sent by the client.
480 The server selects one entry in the list based on its preferences.
481 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
483 =item B<-curves curvelist>
485 Specifies the list of supported curves to be sent by the client. The curve is
486 is ultimately selected by the server. For a list of all curves, use:
488 $ openssl ecparam -list_curves
490 =item B<-cipher cipherlist>
492 This allows the cipher list sent by the client to be modified. Although
493 the server determines which cipher suite is used it should take the first
494 supported cipher in the list sent by the client. See the B<ciphers>
495 command for more information.
497 =item B<-starttls protocol>
499 Send the protocol-specific message(s) to switch to TLS for communication.
500 B<protocol> is a keyword for the intended protocol. Currently, the only
501 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
502 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
504 =item B<-xmpphost hostname>
506 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
507 specifies the host for the "to" attribute of the stream element.
508 If this option is not specified, then the host specified with "-connect"
511 =item B<-tlsextdebug>
513 Print out a hex dump of any TLS extensions received from the server.
517 Disable RFC4507bis session ticket support.
519 =item B<-sess_out filename>
521 Output SSL session to B<filename>.
523 =item B<-sess_in sess.pem>
525 Load SSL session from B<filename>. The client will attempt to resume a
526 connection from this session.
530 Specifying an engine (by its unique B<id> string) will cause B<s_client>
531 to attempt to obtain a functional reference to the specified engine,
532 thus initialising it if needed. The engine will then be set as the default
533 for all available algorithms.
535 =item B<-rand file(s)>
537 A file or files containing random data used to seed the random number
538 generator, or an EGD socket (see L<RAND_egd(3)>).
539 Multiple files can be specified separated by an OS-dependent character.
540 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
543 =item B<-serverinfo types>
545 A list of comma-separated TLS Extension Types (numbers between 0 and
546 65535). Each type will be sent as an empty ClientHello TLS Extension.
547 The server's response (if any) will be encoded and displayed as a PEM
552 Sends a certificate status request to the server (OCSP stapling). The server
553 response (if any) is printed out.
555 =item B<-alpn protocols>, B<-nextprotoneg protocols>
557 These flags enable the Enable the Application-Layer Protocol Negotiation
558 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
559 IETF standard and replaces NPN.
560 The B<protocols> list is a comma-separated list of protocol names that
561 the client should advertise support for. The list should contain the most
562 desirable protocols first. Protocol names are printable ASCII strings,
563 for example "http/1.1" or "spdy/3".
564 An empty list of protocols is treated specially and will cause the
565 client to advertise support for the TLS extension but disconnect just
566 after receiving ServerHello with a list of server supported protocols.
567 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
571 Use one of these two options to control whether Certificate Transparency (CT)
572 is enabled (B<-ct>) or disabled (B<-noct>).
573 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
574 the server and reported at handshake completion.
576 Enabling CT also enables OCSP stapling, as this is one possible delivery method
581 A file containing a list of known Certificate Transparency logs. See
582 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
584 =item B<-keylogfile file>
586 Appends TLS secrets to the specified keylog file such that external programs
587 (like Wireshark) can decrypt TLS connections.
589 =item B<-early_data file>
591 Reads the contents of the specified file and attempts to send it as early data
592 to the server. This will only work with resumed sessions that support early
593 data and when the server accepts the early data.
597 =head1 CONNECTED COMMANDS
599 If a connection is established with an SSL server then any data received
600 from the server is displayed and any key presses will be sent to the
601 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
602 have been given), the session will be renegotiated if the line begins with an
603 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
604 connection will be closed down.
608 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
611 openssl s_client -connect servername:443
613 would typically be used (https uses port 443). If the connection succeeds
614 then an HTTP command can be given such as "GET /" to retrieve a web page.
616 If the handshake fails then there are several possible causes, if it is
617 nothing obvious like no client certificate then the B<-bugs>,
618 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
619 in case it is a buggy server. In particular you should play with these
620 options B<before> submitting a bug report to an OpenSSL mailing list.
622 A frequent problem when attempting to get client certificates working
623 is that a web client complains it has no certificates or gives an empty
624 list to choose from. This is normally because the server is not sending
625 the clients certificate authority in its "acceptable CA list" when it
626 requests a certificate. By using B<s_client> the CA list can be viewed
627 and checked. However some servers only request client authentication
628 after a specific URL is requested. To obtain the list in this case it
629 is necessary to use the B<-prexit> option and send an HTTP request
630 for an appropriate page.
632 If a certificate is specified on the command line using the B<-cert>
633 option it will not be used unless the server specifically requests
634 a client certificate. Therefor merely including a client certificate
635 on the command line is no guarantee that the certificate works.
637 If there are problems verifying a server certificate then the
638 B<-showcerts> option can be used to show the whole chain.
640 The B<s_client> utility is a test tool and is designed to continue the
641 handshake after any certificate verification errors. As a result it will
642 accept any certificate chain (trusted or not) sent by the peer. None test
643 applications should B<not> do this as it makes them vulnerable to a MITM
644 attack. This behaviour can be changed by with the B<-verify_return_error>
645 option: any verify errors are then returned aborting the handshake.
649 Because this program has a lot of options and also because some of the
650 techniques used are rather old, the C source of B<s_client> is rather hard to
651 read and not a model of how things should be done.
652 A typical SSL client program would be much simpler.
654 The B<-prexit> option is a bit of a hack. We should really report
655 information whenever a session is renegotiated.
659 L<SSL_CONF_cmd(3)>, L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>,
660 L<SSL_CTX_set_max_send_fragment(3)>, L<SSL_CTX_set_split_send_fragment(3)>
661 L<SSL_CTX_set_max_pipelines(3)>
665 The -no_alt_chains options was first added to OpenSSL 1.1.0.
669 Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
671 Licensed under the OpenSSL license (the "License"). You may not use
672 this file except in compliance with the License. You can obtain a copy
673 in the file LICENSE in the source distribution or at
674 L<https://www.openssl.org/source/license.html>.