5 s_client - SSL/TLS client program
11 [B<-connect host:port>]
18 [B<-verify_return_error>]
20 [B<-certform DER|PEM>]
24 [B<-CApath directory>]
28 [B<-requestCAfile filename>]
29 [B<-dane_tlsa_domain domain>]
30 [B<-dane_tlsa_rrdata rrdata>]
31 [B<-dane_ee_no_namechecks>]
32 [B<-attime timestamp>]
55 [B<-verify_depth num>]
56 [B<-verify_email email>]
57 [B<-verify_hostname hostname>]
59 [B<-verify_name name>]
94 [B<-sigalgs sigalglist>]
95 [B<-curves curvelist>]
96 [B<-cipher cipherlist>]
98 [B<-starttls protocol>]
99 [B<-xmpphost hostname>]
103 [B<-sess_out filename>]
104 [B<-sess_in filename>]
106 [B<-serverinfo types>]
109 [B<-nextprotoneg protocols>]
112 [B<-keylogfile file>]
113 [B<-early_data file>]
117 The B<s_client> command implements a generic SSL/TLS client which connects
118 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
123 In addition to the options below the B<s_client> utility also supports the
124 common and client only options documented in the
125 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
132 Print out a usage message.
134 =item B<-connect host:port>
136 This specifies the host and optional port to connect to. If not specified
137 then an attempt is made to connect to the local host on port 4433.
139 =item B<-proxy host:port>
141 When used with the B<-connect> flag, the program uses the host and port
142 specified with this flag and issues an HTTP CONNECT command to connect
143 to the desired server.
147 Connect over the specified Unix-domain socket.
157 =item B<-servername name>
159 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
161 =item B<-cert certname>
163 The certificate to use, if one is requested by the server. The default is
164 not to use a certificate.
166 =item B<-certform format>
168 The certificate format to use: DER or PEM. PEM is the default.
170 =item B<-key keyfile>
172 The private key to use. If not specified then the certificate file will
175 =item B<-keyform format>
177 The private format to use: DER or PEM. PEM is the default.
181 the private key password source. For more information about the format of B<arg>
182 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
184 =item B<-verify depth>
186 The verify depth to use. This specifies the maximum length of the
187 server certificate chain and turns on server certificate verification.
188 Currently the verify operation continues after errors so all the problems
189 with a certificate chain can be seen. As a side effect the connection
190 will never fail due to a server certificate verify failure.
192 =item B<-verify_return_error>
194 Return verification errors instead of continuing. This will typically
195 abort the handshake with a fatal error.
197 =item B<-nameopt option>
199 Option which determines how the subject or issuer names are displayed. The
200 B<option> argument can be a single option or multiple options separated by
201 commas. Alternatively the B<-nameopt> switch may be used more than once to
202 set multiple options. See the L<x509(1)> manual page for details.
204 =item B<-CApath directory>
206 The directory to use for server certificate verification. This directory
207 must be in "hash format", see B<verify> for more information. These are
208 also used when building the client certificate chain.
210 =item B<-CAfile file>
212 A file containing trusted certificates to use during server authentication
213 and to use when attempting to build the client certificate chain.
217 Do not load the trusted CA certificates from the default file location
221 Do not load the trusted CA certificates from the default directory location
223 =item B<-requestCAfile file>
225 A file containing a list of certificates whose subject names will be sent
226 to the server in the B<certificate_authorities> extension. Only supported
229 =item B<-dane_tlsa_domain domain>
231 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
232 TLSA base domain which becomes the default SNI hint and the primary
233 reference identifier for hostname checks. This must be used in
234 combination with at least one instance of the B<-dane_tlsa_rrdata>
237 When DANE authentication succeeds, the diagnostic output will include
238 the lowest (closest to 0) depth at which a TLSA record authenticated
239 a chain certificate. When that TLSA record is a "2 1 0" trust
240 anchor public key that signed (rather than matched) the top-most
241 certificate of the chain, the result is reported as "TA public key
242 verified". Otherwise, either the TLSA record "matched TA certificate"
243 at a positive depth or else "matched EE certificate" at depth 0.
245 =item B<-dane_tlsa_rrdata rrdata>
247 Use one or more times to specify the RRDATA fields of the DANE TLSA
248 RRset associated with the target service. The B<rrdata> value is
249 specied in "presentation form", that is four whitespace separated
250 fields that specify the usage, selector, matching type and associated
251 data, with the last of these encoded in hexadecimal. Optional
252 whitespace is ignored in the associated data field. For example:
254 $ openssl s_client -brief -starttls smtp \
255 -connect smtp.example.com:25 \
256 -dane_tlsa_domain smtp.example.com \
257 -dane_tlsa_rrdata "2 1 1
258 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
259 -dane_tlsa_rrdata "2 1 1
260 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
263 Verified peername: smtp.example.com
264 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
267 =item B<-dane_ee_no_namechecks>
269 This disables server name checks when authenticating via DANE-EE(3) TLSA
271 For some applications, primarily web browsers, it is not safe to disable name
272 checks due to "unknown key share" attacks, in which a malicious server can
273 convince a client that a connection to a victim server is instead a secure
274 connection to the malicious server.
275 The malicious server may then be able to violate cross-origin scripting
277 Thus, despite the text of RFC7671, name checks are by default enabled for
278 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
280 In particular, SMTP and XMPP clients should set this option as SRV and MX
281 records already make it possible for a remote domain to redirect client
282 connections to any server of its choice, and in any case SMTP and XMPP clients
283 do not execute scripts downloaded from remote servers.
285 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
286 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
287 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
288 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
289 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
290 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
291 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
293 Set various certificate chain validation options. See the
294 L<verify(1)> manual page for details.
298 Reconnects to the same server 5 times using the same session ID, this can
299 be used as a test that session caching is working.
303 Display the whole server certificate chain: normally only the server
304 certificate itself is displayed.
308 Print session information when the program exits. This will always attempt
309 to print out information even if the connection fails. Normally information
310 will only be printed out once if the connection succeeds. This option is useful
311 because the cipher in use may be renegotiated or the connection may fail
312 because a client certificate is required or is requested only after an
313 attempt is made to access a certain URL. Note: the output produced by this
314 option is not always accurate because a connection might never have been
319 Prints out the SSL session states.
323 Print extensive debugging information including a hex dump of all traffic.
327 Show all protocol messages with hex dump.
331 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
332 with B<enable-ssl-trace> for this option to work.
336 File to send output of B<-msg> or B<-trace> to, default standard output.
340 Tests non-blocking I/O
344 Turns on non-blocking I/O
348 This option translated a line feed from the terminal into CR+LF as required
353 Inhibit shutting down the connection when end of file is reached in the
358 Inhibit printing of session and certificate information. This implicitly
359 turns on B<-ign_eof> as well.
363 Shut down the connection when end of file is reached in the input.
364 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
366 =item B<-psk_identity identity>
368 Use the PSK identity B<identity> when using a PSK cipher suite.
372 Use the PSK key B<key> when using a PSK cipher suite. The key is
373 given as a hexadecimal number without leading 0x, for example -psk
376 =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>
378 These options require or disable the use of the specified SSL or TLS protocols.
379 By default B<s_client> will negotiate the highest mutually supported protocol
381 When a specific TLS version is required, only that version will be offered to
382 and accepted from the server.
384 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
386 These options make B<s_client> use DTLS protocols instead of TLS.
387 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
388 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
393 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
394 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
395 available where OpenSSL has support for SCTP enabled.
397 =item B<-fallback_scsv>
399 Send TLS_FALLBACK_SCSV in the ClientHello.
403 Switch on asynchronous mode. Cryptographic operations will be performed
404 asynchronously. This will only have an effect if an asynchronous capable engine
405 is also used via the B<-engine> option. For test purposes the dummy async engine
406 (dasync) can be used (if available).
408 =item B<-split_send_frag int>
410 The size used to split data for encrypt pipelines. If more data is written in
411 one go than this value then it will be split into multiple pipelines, up to the
412 maximum number of pipelines defined by max_pipelines. This only has an effect if
413 a suitable cipher suite has been negotiated, an engine that supports pipelining
414 has been loaded, and max_pipelines is greater than 1. See
415 L<SSL_CTX_set_split_send_fragment(3)> for further information.
417 =item B<-max_pipelines int>
419 The maximum number of encrypt/decrypt pipelines to be used. This will only have
420 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
421 engine) and a suitable cipher suite has been negotiated. The default value is 1.
422 See L<SSL_CTX_set_max_pipelines(3)> for further information.
424 =item B<-read_buf int>
426 The default read buffer size to be used for connections. This will only have an
427 effect if the buffer size is larger than the size that would otherwise be used
428 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
429 further information).
433 There are several known bug in SSL and TLS implementations. Adding this
434 option enables various workarounds.
438 Enables support for SSL/TLS compression.
439 This option was introduced in OpenSSL 1.1.0.
440 TLS compression is not recommended and is off by default as of
445 Disables support for SSL/TLS compression.
446 TLS compression is not recommended and is off by default as of
451 Only provide a brief summary of connection parameters instead of the
452 normal verbose output.
454 =item B<-sigalgs sigalglist>
456 Specifies the list of signature algorithms that are sent by the client.
457 The server selects one entry in the list based on its preferences.
458 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
460 =item B<-curves curvelist>
462 Specifies the list of supported curves to be sent by the client. The curve is
463 is ultimately selected by the server. For a list of all curves, use:
465 $ openssl ecparam -list_curves
467 =item B<-cipher cipherlist>
469 This allows the cipher list sent by the client to be modified. Although
470 the server determines which cipher suite is used it should take the first
471 supported cipher in the list sent by the client. See the B<ciphers>
472 command for more information.
474 =item B<-starttls protocol>
476 Send the protocol-specific message(s) to switch to TLS for communication.
477 B<protocol> is a keyword for the intended protocol. Currently, the only
478 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
479 "irc", "postgres", "lmtp", "nntp", "sieve" and "ldap".
481 =item B<-xmpphost hostname>
483 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
484 specifies the host for the "to" attribute of the stream element.
485 If this option is not specified, then the host specified with "-connect"
488 =item B<-tlsextdebug>
490 Print out a hex dump of any TLS extensions received from the server.
494 Disable RFC4507bis session ticket support.
496 =item B<-sess_out filename>
498 Output SSL session to B<filename>.
500 =item B<-sess_in sess.pem>
502 Load SSL session from B<filename>. The client will attempt to resume a
503 connection from this session.
507 Specifying an engine (by its unique B<id> string) will cause B<s_client>
508 to attempt to obtain a functional reference to the specified engine,
509 thus initialising it if needed. The engine will then be set as the default
510 for all available algorithms.
512 =item B<-rand file(s)>
514 A file or files containing random data used to seed the random number
515 generator, or an EGD socket (see L<RAND_egd(3)>).
516 Multiple files can be specified separated by an OS-dependent character.
517 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
520 =item B<-serverinfo types>
522 A list of comma-separated TLS Extension Types (numbers between 0 and
523 65535). Each type will be sent as an empty ClientHello TLS Extension.
524 The server's response (if any) will be encoded and displayed as a PEM
529 Sends a certificate status request to the server (OCSP stapling). The server
530 response (if any) is printed out.
532 =item B<-alpn protocols>, B<-nextprotoneg protocols>
534 These flags enable the Enable the Application-Layer Protocol Negotiation
535 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
536 IETF standard and replaces NPN.
537 The B<protocols> list is a comma-separated list of protocol names that
538 the client should advertise support for. The list should contain the most
539 desirable protocols first. Protocol names are printable ASCII strings,
540 for example "http/1.1" or "spdy/3".
541 An empty list of protocols is treated specially and will cause the
542 client to advertise support for the TLS extension but disconnect just
543 after receiving ServerHello with a list of server supported protocols.
547 Use one of these two options to control whether Certificate Transparency (CT)
548 is enabled (B<-ct>) or disabled (B<-noct>).
549 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
550 the server and reported at handshake completion.
552 Enabling CT also enables OCSP stapling, as this is one possible delivery method
557 A file containing a list of known Certificate Transparency logs. See
558 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
560 =item B<-keylogfile file>
562 Appends TLS secrets to the specified keylog file such that external programs
563 (like Wireshark) can decrypt TLS connections.
565 =item B<-early_data file>
567 Reads the contents of the specified file and attempts to send it as early data
568 to the server. This will only work with resumed sessions that support early
569 data and when the server accepts the early data.
573 =head1 CONNECTED COMMANDS
575 If a connection is established with an SSL server then any data received
576 from the server is displayed and any key presses will be sent to the
577 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
578 have been given), the session will be renegotiated if the line begins with an
579 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
580 connection will be closed down.
584 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
587 openssl s_client -connect servername:443
589 would typically be used (https uses port 443). If the connection succeeds
590 then an HTTP command can be given such as "GET /" to retrieve a web page.
592 If the handshake fails then there are several possible causes, if it is
593 nothing obvious like no client certificate then the B<-bugs>,
594 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
595 in case it is a buggy server. In particular you should play with these
596 options B<before> submitting a bug report to an OpenSSL mailing list.
598 A frequent problem when attempting to get client certificates working
599 is that a web client complains it has no certificates or gives an empty
600 list to choose from. This is normally because the server is not sending
601 the clients certificate authority in its "acceptable CA list" when it
602 requests a certificate. By using B<s_client> the CA list can be viewed
603 and checked. However some servers only request client authentication
604 after a specific URL is requested. To obtain the list in this case it
605 is necessary to use the B<-prexit> option and send an HTTP request
606 for an appropriate page.
608 If a certificate is specified on the command line using the B<-cert>
609 option it will not be used unless the server specifically requests
610 a client certificate. Therefor merely including a client certificate
611 on the command line is no guarantee that the certificate works.
613 If there are problems verifying a server certificate then the
614 B<-showcerts> option can be used to show the whole chain.
616 The B<s_client> utility is a test tool and is designed to continue the
617 handshake after any certificate verification errors. As a result it will
618 accept any certificate chain (trusted or not) sent by the peer. None test
619 applications should B<not> do this as it makes them vulnerable to a MITM
620 attack. This behaviour can be changed by with the B<-verify_return_error>
621 option: any verify errors are then returned aborting the handshake.
625 Because this program has a lot of options and also because some of the
626 techniques used are rather old, the C source of B<s_client> is rather hard to
627 read and not a model of how things should be done.
628 A typical SSL client program would be much simpler.
630 The B<-prexit> option is a bit of a hack. We should really report
631 information whenever a session is renegotiated.
636 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
640 The -no_alt_chains options was first added to OpenSSL 1.1.0.
644 Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
646 Licensed under the OpenSSL license (the "License"). You may not use
647 this file except in compliance with the License. You can obtain a copy
648 in the file LICENSE in the source distribution or at
649 L<https://www.openssl.org/source/license.html>.