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<-allow_no_dhe_kex>]
97 [B<-sigalgs sigalglist>]
98 [B<-curves curvelist>]
99 [B<-cipher cipherlist>]
101 [B<-starttls protocol>]
102 [B<-xmpphost hostname>]
106 [B<-sess_out filename>]
107 [B<-sess_in filename>]
109 [B<-serverinfo types>]
112 [B<-nextprotoneg protocols>]
115 [B<-keylogfile file>]
116 [B<-early_data file>]
121 The B<s_client> command implements a generic SSL/TLS client which connects
122 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
127 In addition to the options below the B<s_client> utility also supports the
128 common and client only options documented in the
129 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
136 Print out a usage message.
138 =item B<-connect host:port>
140 This specifies the host and optional port to connect to. It is possible to
141 select the host and port using the optional target positional argument instead.
142 If neither this nor the target positonal argument are specified then an attempt
143 is made to connect to the local host on port 4433.
145 =item B<-proxy host:port>
147 When used with the B<-connect> flag, the program uses the host and port
148 specified with this flag and issues an HTTP CONNECT command to connect
149 to the desired server.
153 Connect over the specified Unix-domain socket.
163 =item B<-servername name>
165 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
166 the given value. If both this option and the B<-noservername> are not given, the
167 TLS SNI extension is still set to the hostname provided to the B<-connect> option,
168 or "localhost" if B<-connect> has not been supplied. This is default since OpenSSL
171 Even though SNI name should normally be a DNS name and not an IP address, this
172 option will not make the distinction when parsing B<-connect> and will send
173 IP address if one passed.
175 =item B<-noservername>
177 Suppresses sending of the SNI (Server Name Indication) extension in the
178 ClientHello message. Cannot be used in conjunction with the B<-servername> or
179 <-dane_tlsa_domain> options.
181 =item B<-cert certname>
183 The certificate to use, if one is requested by the server. The default is
184 not to use a certificate.
186 =item B<-certform format>
188 The certificate format to use: DER or PEM. PEM is the default.
190 =item B<-key keyfile>
192 The private key to use. If not specified then the certificate file will
195 =item B<-keyform format>
197 The private format to use: DER or PEM. PEM is the default.
201 the private key password source. For more information about the format of B<arg>
202 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
204 =item B<-verify depth>
206 The verify depth to use. This specifies the maximum length of the
207 server certificate chain and turns on server certificate verification.
208 Currently the verify operation continues after errors so all the problems
209 with a certificate chain can be seen. As a side effect the connection
210 will never fail due to a server certificate verify failure.
212 =item B<-verify_return_error>
214 Return verification errors instead of continuing. This will typically
215 abort the handshake with a fatal error.
217 =item B<-nameopt option>
219 Option which determines how the subject or issuer names are displayed. The
220 B<option> argument can be a single option or multiple options separated by
221 commas. Alternatively the B<-nameopt> switch may be used more than once to
222 set multiple options. See the L<x509(1)> manual page for details.
224 =item B<-CApath directory>
226 The directory to use for server certificate verification. This directory
227 must be in "hash format", see B<verify> for more information. These are
228 also used when building the client certificate chain.
230 =item B<-CAfile file>
232 A file containing trusted certificates to use during server authentication
233 and to use when attempting to build the client certificate chain.
237 Do not load the trusted CA certificates from the default file location
241 Do not load the trusted CA certificates from the default directory location
243 =item B<-requestCAfile file>
245 A file containing a list of certificates whose subject names will be sent
246 to the server in the B<certificate_authorities> extension. Only supported
249 =item B<-dane_tlsa_domain domain>
251 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
252 TLSA base domain which becomes the default SNI hint and the primary
253 reference identifier for hostname checks. This must be used in
254 combination with at least one instance of the B<-dane_tlsa_rrdata>
257 When DANE authentication succeeds, the diagnostic output will include
258 the lowest (closest to 0) depth at which a TLSA record authenticated
259 a chain certificate. When that TLSA record is a "2 1 0" trust
260 anchor public key that signed (rather than matched) the top-most
261 certificate of the chain, the result is reported as "TA public key
262 verified". Otherwise, either the TLSA record "matched TA certificate"
263 at a positive depth or else "matched EE certificate" at depth 0.
265 =item B<-dane_tlsa_rrdata rrdata>
267 Use one or more times to specify the RRDATA fields of the DANE TLSA
268 RRset associated with the target service. The B<rrdata> value is
269 specied in "presentation form", that is four whitespace separated
270 fields that specify the usage, selector, matching type and associated
271 data, with the last of these encoded in hexadecimal. Optional
272 whitespace is ignored in the associated data field. For example:
274 $ openssl s_client -brief -starttls smtp \
275 -connect smtp.example.com:25 \
276 -dane_tlsa_domain smtp.example.com \
277 -dane_tlsa_rrdata "2 1 1
278 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
279 -dane_tlsa_rrdata "2 1 1
280 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
283 Verified peername: smtp.example.com
284 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
287 =item B<-dane_ee_no_namechecks>
289 This disables server name checks when authenticating via DANE-EE(3) TLSA
291 For some applications, primarily web browsers, it is not safe to disable name
292 checks due to "unknown key share" attacks, in which a malicious server can
293 convince a client that a connection to a victim server is instead a secure
294 connection to the malicious server.
295 The malicious server may then be able to violate cross-origin scripting
297 Thus, despite the text of RFC7671, name checks are by default enabled for
298 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
300 In particular, SMTP and XMPP clients should set this option as SRV and MX
301 records already make it possible for a remote domain to redirect client
302 connections to any server of its choice, and in any case SMTP and XMPP clients
303 do not execute scripts downloaded from remote servers.
305 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
306 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
307 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
308 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
309 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
310 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
311 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
313 Set various certificate chain validation options. See the
314 L<verify(1)> manual page for details.
318 Reconnects to the same server 5 times using the same session ID, this can
319 be used as a test that session caching is working.
323 Display the whole server certificate chain: normally only the server
324 certificate itself is displayed.
328 Print session information when the program exits. This will always attempt
329 to print out information even if the connection fails. Normally information
330 will only be printed out once if the connection succeeds. This option is useful
331 because the cipher in use may be renegotiated or the connection may fail
332 because a client certificate is required or is requested only after an
333 attempt is made to access a certain URL. Note: the output produced by this
334 option is not always accurate because a connection might never have been
339 Prints out the SSL session states.
343 Print extensive debugging information including a hex dump of all traffic.
347 Show all protocol messages with hex dump.
351 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
352 with B<enable-ssl-trace> for this option to work.
356 File to send output of B<-msg> or B<-trace> to, default standard output.
360 Tests non-blocking I/O
364 Turns on non-blocking I/O
368 This option translated a line feed from the terminal into CR+LF as required
373 Inhibit shutting down the connection when end of file is reached in the
378 Inhibit printing of session and certificate information. This implicitly
379 turns on B<-ign_eof> as well.
383 Shut down the connection when end of file is reached in the input.
384 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
386 =item B<-psk_identity identity>
388 Use the PSK identity B<identity> when using a PSK cipher suite.
389 The default value is "Client_identity" (without the quotes).
393 Use the PSK key B<key> when using a PSK cipher suite. The key is
394 given as a hexadecimal number without leading 0x, for example -psk
396 This option must be provided in order to use a PSK cipher.
398 =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>
400 These options require or disable the use of the specified SSL or TLS protocols.
401 By default B<s_client> will negotiate the highest mutually supported protocol
403 When a specific TLS version is required, only that version will be offered to
404 and accepted from the server.
406 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
408 These options make B<s_client> use DTLS protocols instead of TLS.
409 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
410 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
415 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
416 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
417 available where OpenSSL has support for SCTP enabled.
419 =item B<-fallback_scsv>
421 Send TLS_FALLBACK_SCSV in the ClientHello.
425 Switch on asynchronous mode. Cryptographic operations will be performed
426 asynchronously. This will only have an effect if an asynchronous capable engine
427 is also used via the B<-engine> option. For test purposes the dummy async engine
428 (dasync) can be used (if available).
430 =item B<-max_send_frag int>
432 The maximum size of data fragment to send.
433 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
435 =item B<-split_send_frag int>
437 The size used to split data for encrypt pipelines. If more data is written in
438 one go than this value then it will be split into multiple pipelines, up to the
439 maximum number of pipelines defined by max_pipelines. This only has an effect if
440 a suitable cipher suite has been negotiated, an engine that supports pipelining
441 has been loaded, and max_pipelines is greater than 1. See
442 L<SSL_CTX_set_split_send_fragment(3)> for further information.
444 =item B<-max_pipelines int>
446 The maximum number of encrypt/decrypt pipelines to be used. This will only have
447 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
448 engine) and a suitable cipher suite has been negotiated. The default value is 1.
449 See L<SSL_CTX_set_max_pipelines(3)> for further information.
451 =item B<-read_buf int>
453 The default read buffer size to be used for connections. This will only have an
454 effect if the buffer size is larger than the size that would otherwise be used
455 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
456 further information).
460 There are several known bug in SSL and TLS implementations. Adding this
461 option enables various workarounds.
465 Enables support for SSL/TLS compression.
466 This option was introduced in OpenSSL 1.1.0.
467 TLS compression is not recommended and is off by default as of
472 Disables support for SSL/TLS compression.
473 TLS compression is not recommended and is off by default as of
478 Only provide a brief summary of connection parameters instead of the
479 normal verbose output.
481 =item B<-sigalgs sigalglist>
483 Specifies the list of signature algorithms that are sent by the client.
484 The server selects one entry in the list based on its preferences.
485 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
487 =item B<-curves curvelist>
489 Specifies the list of supported curves to be sent by the client. The curve is
490 is ultimately selected by the server. For a list of all curves, use:
492 $ openssl ecparam -list_curves
494 =item B<-cipher cipherlist>
496 This allows the cipher list sent by the client to be modified. Although
497 the server determines which cipher suite is used it should take the first
498 supported cipher in the list sent by the client. See the B<ciphers>
499 command for more information.
501 =item B<-starttls protocol>
503 Send the protocol-specific message(s) to switch to TLS for communication.
504 B<protocol> is a keyword for the intended protocol. Currently, the only
505 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
506 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
508 =item B<-xmpphost hostname>
510 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
511 specifies the host for the "to" attribute of the stream element.
512 If this option is not specified, then the host specified with "-connect"
515 =item B<-tlsextdebug>
517 Print out a hex dump of any TLS extensions received from the server.
521 Disable RFC4507bis session ticket support.
523 =item B<-sess_out filename>
525 Output SSL session to B<filename>.
527 =item B<-sess_in sess.pem>
529 Load SSL session from B<filename>. The client will attempt to resume a
530 connection from this session.
534 Specifying an engine (by its unique B<id> string) will cause B<s_client>
535 to attempt to obtain a functional reference to the specified engine,
536 thus initialising it if needed. The engine will then be set as the default
537 for all available algorithms.
539 =item B<-rand file(s)>
541 A file or files containing random data used to seed the random number
542 generator, or an EGD socket (see L<RAND_egd(3)>).
543 Multiple files can be specified separated by an OS-dependent character.
544 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
547 =item B<-serverinfo types>
549 A list of comma-separated TLS Extension Types (numbers between 0 and
550 65535). Each type will be sent as an empty ClientHello TLS Extension.
551 The server's response (if any) will be encoded and displayed as a PEM
556 Sends a certificate status request to the server (OCSP stapling). The server
557 response (if any) is printed out.
559 =item B<-alpn protocols>, B<-nextprotoneg protocols>
561 These flags enable the Enable the Application-Layer Protocol Negotiation
562 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
563 IETF standard and replaces NPN.
564 The B<protocols> list is a comma-separated list of protocol names that
565 the client should advertise support for. The list should contain the most
566 desirable protocols first. Protocol names are printable ASCII strings,
567 for example "http/1.1" or "spdy/3".
568 An empty list of protocols is treated specially and will cause the
569 client to advertise support for the TLS extension but disconnect just
570 after receiving ServerHello with a list of server supported protocols.
571 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
575 Use one of these two options to control whether Certificate Transparency (CT)
576 is enabled (B<-ct>) or disabled (B<-noct>).
577 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
578 the server and reported at handshake completion.
580 Enabling CT also enables OCSP stapling, as this is one possible delivery method
585 A file containing a list of known Certificate Transparency logs. See
586 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
588 =item B<-keylogfile file>
590 Appends TLS secrets to the specified keylog file such that external programs
591 (like Wireshark) can decrypt TLS connections.
593 =item B<-early_data file>
595 Reads the contents of the specified file and attempts to send it as early data
596 to the server. This will only work with resumed sessions that support early
597 data and when the server accepts the early data.
601 Rather than providing B<-connect>, the target hostname and optional port may
602 be provided as a single positional argument after all options. If neither this
603 nor B<-connect> are provided, falls back to attempting to connect to localhost
608 =head1 CONNECTED COMMANDS
610 If a connection is established with an SSL server then any data received
611 from the server is displayed and any key presses will be sent to the
612 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
613 have been given), the session will be renegotiated if the line begins with an
614 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
615 connection will be closed down.
619 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
622 openssl s_client -connect servername:443
624 would typically be used (https uses port 443). If the connection succeeds
625 then an HTTP command can be given such as "GET /" to retrieve a web page.
627 If the handshake fails then there are several possible causes, if it is
628 nothing obvious like no client certificate then the B<-bugs>,
629 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
630 in case it is a buggy server. In particular you should play with these
631 options B<before> submitting a bug report to an OpenSSL mailing list.
633 A frequent problem when attempting to get client certificates working
634 is that a web client complains it has no certificates or gives an empty
635 list to choose from. This is normally because the server is not sending
636 the clients certificate authority in its "acceptable CA list" when it
637 requests a certificate. By using B<s_client> the CA list can be viewed
638 and checked. However some servers only request client authentication
639 after a specific URL is requested. To obtain the list in this case it
640 is necessary to use the B<-prexit> option and send an HTTP request
641 for an appropriate page.
643 If a certificate is specified on the command line using the B<-cert>
644 option it will not be used unless the server specifically requests
645 a client certificate. Therefor merely including a client certificate
646 on the command line is no guarantee that the certificate works.
648 If there are problems verifying a server certificate then the
649 B<-showcerts> option can be used to show the whole chain.
651 The B<s_client> utility is a test tool and is designed to continue the
652 handshake after any certificate verification errors. As a result it will
653 accept any certificate chain (trusted or not) sent by the peer. None test
654 applications should B<not> do this as it makes them vulnerable to a MITM
655 attack. This behaviour can be changed by with the B<-verify_return_error>
656 option: any verify errors are then returned aborting the handshake.
660 Because this program has a lot of options and also because some of the
661 techniques used are rather old, the C source of B<s_client> is rather hard to
662 read and not a model of how things should be done.
663 A typical SSL client program would be much simpler.
665 The B<-prexit> option is a bit of a hack. We should really report
666 information whenever a session is renegotiated.
670 L<SSL_CONF_cmd(3)>, L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>,
671 L<SSL_CTX_set_max_send_fragment(3)>, L<SSL_CTX_set_split_send_fragment(3)>
672 L<SSL_CTX_set_max_pipelines(3)>
676 The -no_alt_chains options was first added to OpenSSL 1.1.0.
680 Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
682 Licensed under the OpenSSL license (the "License"). You may not use
683 this file except in compliance with the License. You can obtain a copy
684 in the file LICENSE in the source distribution or at
685 L<https://www.openssl.org/source/license.html>.