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>]
95 [B<-sigalgs sigalglist>]
96 [B<-curves curvelist>]
97 [B<-cipher cipherlist>]
99 [B<-starttls protocol>]
100 [B<-xmpphost hostname>]
104 [B<-sess_out filename>]
105 [B<-sess_in filename>]
107 [B<-serverinfo types>]
110 [B<-nextprotoneg protocols>]
113 [B<-keylogfile file>]
114 [B<-early_data file>]
118 The B<s_client> command implements a generic SSL/TLS client which connects
119 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
124 In addition to the options below the B<s_client> utility also supports the
125 common and client only options documented in the
126 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
133 Print out a usage message.
135 =item B<-connect host:port>
137 This specifies the host and optional port to connect to. If not specified
138 then an attempt is made to connect to the local host on port 4433.
140 =item B<-proxy host:port>
142 When used with the B<-connect> flag, the program uses the host and port
143 specified with this flag and issues an HTTP CONNECT command to connect
144 to the desired server.
148 Connect over the specified Unix-domain socket.
158 =item B<-servername name>
160 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
163 =item B<-noservername>
165 Suppresses sending of the SNI (Server Name Indication) extension in the
166 ClientHello message. Cannot be used in conjunction with the B<-servername> or
167 <-dane_tlsa_domain> options. If this option is not given then the hostname
168 provided to the B<-connect> option is used in the SNI extension, or "localhost"
169 if B<-connect> has not been supplied. Note that an SNI name should normally be a
170 DNS name and not an IP address.
172 =item B<-cert certname>
174 The certificate to use, if one is requested by the server. The default is
175 not to use a certificate.
177 =item B<-certform format>
179 The certificate format to use: DER or PEM. PEM is the default.
181 =item B<-key keyfile>
183 The private key to use. If not specified then the certificate file will
186 =item B<-keyform format>
188 The private format to use: DER or PEM. PEM is the default.
192 the private key password source. For more information about the format of B<arg>
193 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
195 =item B<-verify depth>
197 The verify depth to use. This specifies the maximum length of the
198 server certificate chain and turns on server certificate verification.
199 Currently the verify operation continues after errors so all the problems
200 with a certificate chain can be seen. As a side effect the connection
201 will never fail due to a server certificate verify failure.
203 =item B<-verify_return_error>
205 Return verification errors instead of continuing. This will typically
206 abort the handshake with a fatal error.
208 =item B<-nameopt option>
210 Option which determines how the subject or issuer names are displayed. The
211 B<option> argument can be a single option or multiple options separated by
212 commas. Alternatively the B<-nameopt> switch may be used more than once to
213 set multiple options. See the L<x509(1)> manual page for details.
215 =item B<-CApath directory>
217 The directory to use for server certificate verification. This directory
218 must be in "hash format", see B<verify> for more information. These are
219 also used when building the client certificate chain.
221 =item B<-CAfile file>
223 A file containing trusted certificates to use during server authentication
224 and to use when attempting to build the client certificate chain.
228 Do not load the trusted CA certificates from the default file location
232 Do not load the trusted CA certificates from the default directory location
234 =item B<-requestCAfile file>
236 A file containing a list of certificates whose subject names will be sent
237 to the server in the B<certificate_authorities> extension. Only supported
240 =item B<-dane_tlsa_domain domain>
242 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
243 TLSA base domain which becomes the default SNI hint and the primary
244 reference identifier for hostname checks. This must be used in
245 combination with at least one instance of the B<-dane_tlsa_rrdata>
248 When DANE authentication succeeds, the diagnostic output will include
249 the lowest (closest to 0) depth at which a TLSA record authenticated
250 a chain certificate. When that TLSA record is a "2 1 0" trust
251 anchor public key that signed (rather than matched) the top-most
252 certificate of the chain, the result is reported as "TA public key
253 verified". Otherwise, either the TLSA record "matched TA certificate"
254 at a positive depth or else "matched EE certificate" at depth 0.
256 =item B<-dane_tlsa_rrdata rrdata>
258 Use one or more times to specify the RRDATA fields of the DANE TLSA
259 RRset associated with the target service. The B<rrdata> value is
260 specied in "presentation form", that is four whitespace separated
261 fields that specify the usage, selector, matching type and associated
262 data, with the last of these encoded in hexadecimal. Optional
263 whitespace is ignored in the associated data field. For example:
265 $ openssl s_client -brief -starttls smtp \
266 -connect smtp.example.com:25 \
267 -dane_tlsa_domain smtp.example.com \
268 -dane_tlsa_rrdata "2 1 1
269 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
270 -dane_tlsa_rrdata "2 1 1
271 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
274 Verified peername: smtp.example.com
275 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
278 =item B<-dane_ee_no_namechecks>
280 This disables server name checks when authenticating via DANE-EE(3) TLSA
282 For some applications, primarily web browsers, it is not safe to disable name
283 checks due to "unknown key share" attacks, in which a malicious server can
284 convince a client that a connection to a victim server is instead a secure
285 connection to the malicious server.
286 The malicious server may then be able to violate cross-origin scripting
288 Thus, despite the text of RFC7671, name checks are by default enabled for
289 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
291 In particular, SMTP and XMPP clients should set this option as SRV and MX
292 records already make it possible for a remote domain to redirect client
293 connections to any server of its choice, and in any case SMTP and XMPP clients
294 do not execute scripts downloaded from remote servers.
296 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
297 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
298 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
299 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
300 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
301 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
302 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
304 Set various certificate chain validation options. See the
305 L<verify(1)> manual page for details.
309 Reconnects to the same server 5 times using the same session ID, this can
310 be used as a test that session caching is working.
314 Display the whole server certificate chain: normally only the server
315 certificate itself is displayed.
319 Print session information when the program exits. This will always attempt
320 to print out information even if the connection fails. Normally information
321 will only be printed out once if the connection succeeds. This option is useful
322 because the cipher in use may be renegotiated or the connection may fail
323 because a client certificate is required or is requested only after an
324 attempt is made to access a certain URL. Note: the output produced by this
325 option is not always accurate because a connection might never have been
330 Prints out the SSL session states.
334 Print extensive debugging information including a hex dump of all traffic.
338 Show all protocol messages with hex dump.
342 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
343 with B<enable-ssl-trace> for this option to work.
347 File to send output of B<-msg> or B<-trace> to, default standard output.
351 Tests non-blocking I/O
355 Turns on non-blocking I/O
359 This option translated a line feed from the terminal into CR+LF as required
364 Inhibit shutting down the connection when end of file is reached in the
369 Inhibit printing of session and certificate information. This implicitly
370 turns on B<-ign_eof> as well.
374 Shut down the connection when end of file is reached in the input.
375 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
377 =item B<-psk_identity identity>
379 Use the PSK identity B<identity> when using a PSK cipher suite.
383 Use the PSK key B<key> when using a PSK cipher suite. The key is
384 given as a hexadecimal number without leading 0x, for example -psk
387 =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>
389 These options require or disable the use of the specified SSL or TLS protocols.
390 By default B<s_client> will negotiate the highest mutually supported protocol
392 When a specific TLS version is required, only that version will be offered to
393 and accepted from the server.
395 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
397 These options make B<s_client> use DTLS protocols instead of TLS.
398 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
399 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
404 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
405 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
406 available where OpenSSL has support for SCTP enabled.
408 =item B<-fallback_scsv>
410 Send TLS_FALLBACK_SCSV in the ClientHello.
414 Switch on asynchronous mode. Cryptographic operations will be performed
415 asynchronously. This will only have an effect if an asynchronous capable engine
416 is also used via the B<-engine> option. For test purposes the dummy async engine
417 (dasync) can be used (if available).
419 =item B<-split_send_frag int>
421 The size used to split data for encrypt pipelines. If more data is written in
422 one go than this value then it will be split into multiple pipelines, up to the
423 maximum number of pipelines defined by max_pipelines. This only has an effect if
424 a suitable cipher suite has been negotiated, an engine that supports pipelining
425 has been loaded, and max_pipelines is greater than 1. See
426 L<SSL_CTX_set_split_send_fragment(3)> for further information.
428 =item B<-max_pipelines int>
430 The maximum number of encrypt/decrypt pipelines to be used. This will only have
431 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
432 engine) and a suitable cipher suite has been negotiated. The default value is 1.
433 See L<SSL_CTX_set_max_pipelines(3)> for further information.
435 =item B<-read_buf int>
437 The default read buffer size to be used for connections. This will only have an
438 effect if the buffer size is larger than the size that would otherwise be used
439 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
440 further information).
444 There are several known bug in SSL and TLS implementations. Adding this
445 option enables various workarounds.
449 Enables support for SSL/TLS compression.
450 This option was introduced in OpenSSL 1.1.0.
451 TLS compression is not recommended and is off by default as of
456 Disables support for SSL/TLS compression.
457 TLS compression is not recommended and is off by default as of
462 Only provide a brief summary of connection parameters instead of the
463 normal verbose output.
465 =item B<-sigalgs sigalglist>
467 Specifies the list of signature algorithms that are sent by the client.
468 The server selects one entry in the list based on its preferences.
469 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
471 =item B<-curves curvelist>
473 Specifies the list of supported curves to be sent by the client. The curve is
474 is ultimately selected by the server. For a list of all curves, use:
476 $ openssl ecparam -list_curves
478 =item B<-cipher cipherlist>
480 This allows the cipher list sent by the client to be modified. Although
481 the server determines which cipher suite is used it should take the first
482 supported cipher in the list sent by the client. See the B<ciphers>
483 command for more information.
485 =item B<-starttls protocol>
487 Send the protocol-specific message(s) to switch to TLS for communication.
488 B<protocol> is a keyword for the intended protocol. Currently, the only
489 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
490 "irc", "postgres", "lmtp", "nntp", "sieve" and "ldap".
492 =item B<-xmpphost hostname>
494 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
495 specifies the host for the "to" attribute of the stream element.
496 If this option is not specified, then the host specified with "-connect"
499 =item B<-tlsextdebug>
501 Print out a hex dump of any TLS extensions received from the server.
505 Disable RFC4507bis session ticket support.
507 =item B<-sess_out filename>
509 Output SSL session to B<filename>.
511 =item B<-sess_in sess.pem>
513 Load SSL session from B<filename>. The client will attempt to resume a
514 connection from this session.
518 Specifying an engine (by its unique B<id> string) will cause B<s_client>
519 to attempt to obtain a functional reference to the specified engine,
520 thus initialising it if needed. The engine will then be set as the default
521 for all available algorithms.
523 =item B<-rand file(s)>
525 A file or files containing random data used to seed the random number
526 generator, or an EGD socket (see L<RAND_egd(3)>).
527 Multiple files can be specified separated by an OS-dependent character.
528 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
531 =item B<-serverinfo types>
533 A list of comma-separated TLS Extension Types (numbers between 0 and
534 65535). Each type will be sent as an empty ClientHello TLS Extension.
535 The server's response (if any) will be encoded and displayed as a PEM
540 Sends a certificate status request to the server (OCSP stapling). The server
541 response (if any) is printed out.
543 =item B<-alpn protocols>, B<-nextprotoneg protocols>
545 These flags enable the Enable the Application-Layer Protocol Negotiation
546 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
547 IETF standard and replaces NPN.
548 The B<protocols> list is a comma-separated list of protocol names that
549 the client should advertise support for. The list should contain the most
550 desirable protocols first. Protocol names are printable ASCII strings,
551 for example "http/1.1" or "spdy/3".
552 An empty list of protocols is treated specially and will cause the
553 client to advertise support for the TLS extension but disconnect just
554 after receiving ServerHello with a list of server supported protocols.
558 Use one of these two options to control whether Certificate Transparency (CT)
559 is enabled (B<-ct>) or disabled (B<-noct>).
560 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
561 the server and reported at handshake completion.
563 Enabling CT also enables OCSP stapling, as this is one possible delivery method
568 A file containing a list of known Certificate Transparency logs. See
569 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
571 =item B<-keylogfile file>
573 Appends TLS secrets to the specified keylog file such that external programs
574 (like Wireshark) can decrypt TLS connections.
576 =item B<-early_data file>
578 Reads the contents of the specified file and attempts to send it as early data
579 to the server. This will only work with resumed sessions that support early
580 data and when the server accepts the early data.
584 =head1 CONNECTED COMMANDS
586 If a connection is established with an SSL server then any data received
587 from the server is displayed and any key presses will be sent to the
588 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
589 have been given), the session will be renegotiated if the line begins with an
590 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
591 connection will be closed down.
595 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
598 openssl s_client -connect servername:443
600 would typically be used (https uses port 443). If the connection succeeds
601 then an HTTP command can be given such as "GET /" to retrieve a web page.
603 If the handshake fails then there are several possible causes, if it is
604 nothing obvious like no client certificate then the B<-bugs>,
605 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
606 in case it is a buggy server. In particular you should play with these
607 options B<before> submitting a bug report to an OpenSSL mailing list.
609 A frequent problem when attempting to get client certificates working
610 is that a web client complains it has no certificates or gives an empty
611 list to choose from. This is normally because the server is not sending
612 the clients certificate authority in its "acceptable CA list" when it
613 requests a certificate. By using B<s_client> the CA list can be viewed
614 and checked. However some servers only request client authentication
615 after a specific URL is requested. To obtain the list in this case it
616 is necessary to use the B<-prexit> option and send an HTTP request
617 for an appropriate page.
619 If a certificate is specified on the command line using the B<-cert>
620 option it will not be used unless the server specifically requests
621 a client certificate. Therefor merely including a client certificate
622 on the command line is no guarantee that the certificate works.
624 If there are problems verifying a server certificate then the
625 B<-showcerts> option can be used to show the whole chain.
627 The B<s_client> utility is a test tool and is designed to continue the
628 handshake after any certificate verification errors. As a result it will
629 accept any certificate chain (trusted or not) sent by the peer. None test
630 applications should B<not> do this as it makes them vulnerable to a MITM
631 attack. This behaviour can be changed by with the B<-verify_return_error>
632 option: any verify errors are then returned aborting the handshake.
636 Because this program has a lot of options and also because some of the
637 techniques used are rather old, the C source of B<s_client> is rather hard to
638 read and not a model of how things should be done.
639 A typical SSL client program would be much simpler.
641 The B<-prexit> option is a bit of a hack. We should really report
642 information whenever a session is renegotiated.
647 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
651 The -no_alt_chains options was first added to OpenSSL 1.1.0.
655 Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
657 Licensed under the OpenSSL license (the "License"). You may not use
658 this file except in compliance with the License. You can obtain a copy
659 in the file LICENSE in the source distribution or at
660 L<https://www.openssl.org/source/license.html>.