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
164 =item B<-noservername>
166 Suppresses sending of the SNI (Server Name Indication) extension in the
167 ClientHello message. Cannot be used in conjunction with the B<-servername> or
168 <-dane_tlsa_domain> options. If this option is not given then the hostname
169 provided to the B<-connect> option is used in the SNI extension, or "localhost"
170 if B<-connect> has not been supplied. Note that an SNI name should normally be a
171 DNS name and not an IP address.
173 =item B<-cert certname>
175 The certificate to use, if one is requested by the server. The default is
176 not to use a certificate.
178 =item B<-certform format>
180 The certificate format to use: DER or PEM. PEM is the default.
182 =item B<-key keyfile>
184 The private key to use. If not specified then the certificate file will
187 =item B<-keyform format>
189 The private format to use: DER or PEM. PEM is the default.
193 the private key password source. For more information about the format of B<arg>
194 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
196 =item B<-verify depth>
198 The verify depth to use. This specifies the maximum length of the
199 server certificate chain and turns on server certificate verification.
200 Currently the verify operation continues after errors so all the problems
201 with a certificate chain can be seen. As a side effect the connection
202 will never fail due to a server certificate verify failure.
204 =item B<-verify_return_error>
206 Return verification errors instead of continuing. This will typically
207 abort the handshake with a fatal error.
209 =item B<-nameopt option>
211 Option which determines how the subject or issuer names are displayed. The
212 B<option> argument can be a single option or multiple options separated by
213 commas. Alternatively the B<-nameopt> switch may be used more than once to
214 set multiple options. See the L<x509(1)> manual page for details.
216 =item B<-CApath directory>
218 The directory to use for server certificate verification. This directory
219 must be in "hash format", see B<verify> for more information. These are
220 also used when building the client certificate chain.
222 =item B<-CAfile file>
224 A file containing trusted certificates to use during server authentication
225 and to use when attempting to build the client certificate chain.
229 Do not load the trusted CA certificates from the default file location
233 Do not load the trusted CA certificates from the default directory location
235 =item B<-requestCAfile file>
237 A file containing a list of certificates whose subject names will be sent
238 to the server in the B<certificate_authorities> extension. Only supported
241 =item B<-dane_tlsa_domain domain>
243 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
244 TLSA base domain which becomes the default SNI hint and the primary
245 reference identifier for hostname checks. This must be used in
246 combination with at least one instance of the B<-dane_tlsa_rrdata>
249 When DANE authentication succeeds, the diagnostic output will include
250 the lowest (closest to 0) depth at which a TLSA record authenticated
251 a chain certificate. When that TLSA record is a "2 1 0" trust
252 anchor public key that signed (rather than matched) the top-most
253 certificate of the chain, the result is reported as "TA public key
254 verified". Otherwise, either the TLSA record "matched TA certificate"
255 at a positive depth or else "matched EE certificate" at depth 0.
257 =item B<-dane_tlsa_rrdata rrdata>
259 Use one or more times to specify the RRDATA fields of the DANE TLSA
260 RRset associated with the target service. The B<rrdata> value is
261 specied in "presentation form", that is four whitespace separated
262 fields that specify the usage, selector, matching type and associated
263 data, with the last of these encoded in hexadecimal. Optional
264 whitespace is ignored in the associated data field. For example:
266 $ openssl s_client -brief -starttls smtp \
267 -connect smtp.example.com:25 \
268 -dane_tlsa_domain smtp.example.com \
269 -dane_tlsa_rrdata "2 1 1
270 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
271 -dane_tlsa_rrdata "2 1 1
272 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
275 Verified peername: smtp.example.com
276 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
279 =item B<-dane_ee_no_namechecks>
281 This disables server name checks when authenticating via DANE-EE(3) TLSA
283 For some applications, primarily web browsers, it is not safe to disable name
284 checks due to "unknown key share" attacks, in which a malicious server can
285 convince a client that a connection to a victim server is instead a secure
286 connection to the malicious server.
287 The malicious server may then be able to violate cross-origin scripting
289 Thus, despite the text of RFC7671, name checks are by default enabled for
290 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
292 In particular, SMTP and XMPP clients should set this option as SRV and MX
293 records already make it possible for a remote domain to redirect client
294 connections to any server of its choice, and in any case SMTP and XMPP clients
295 do not execute scripts downloaded from remote servers.
297 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
298 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
299 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
300 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
301 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
302 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
303 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
305 Set various certificate chain validation options. See the
306 L<verify(1)> manual page for details.
310 Reconnects to the same server 5 times using the same session ID, this can
311 be used as a test that session caching is working.
315 Display the whole server certificate chain: normally only the server
316 certificate itself is displayed.
320 Print session information when the program exits. This will always attempt
321 to print out information even if the connection fails. Normally information
322 will only be printed out once if the connection succeeds. This option is useful
323 because the cipher in use may be renegotiated or the connection may fail
324 because a client certificate is required or is requested only after an
325 attempt is made to access a certain URL. Note: the output produced by this
326 option is not always accurate because a connection might never have been
331 Prints out the SSL session states.
335 Print extensive debugging information including a hex dump of all traffic.
339 Show all protocol messages with hex dump.
343 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
344 with B<enable-ssl-trace> for this option to work.
348 File to send output of B<-msg> or B<-trace> to, default standard output.
352 Tests non-blocking I/O
356 Turns on non-blocking I/O
360 This option translated a line feed from the terminal into CR+LF as required
365 Inhibit shutting down the connection when end of file is reached in the
370 Inhibit printing of session and certificate information. This implicitly
371 turns on B<-ign_eof> as well.
375 Shut down the connection when end of file is reached in the input.
376 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
378 =item B<-psk_identity identity>
380 Use the PSK identity B<identity> when using a PSK cipher suite.
384 Use the PSK key B<key> when using a PSK cipher suite. The key is
385 given as a hexadecimal number without leading 0x, for example -psk
388 =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>
390 These options require or disable the use of the specified SSL or TLS protocols.
391 By default B<s_client> will negotiate the highest mutually supported protocol
393 When a specific TLS version is required, only that version will be offered to
394 and accepted from the server.
396 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
398 These options make B<s_client> use DTLS protocols instead of TLS.
399 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
400 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
405 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
406 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
407 available where OpenSSL has support for SCTP enabled.
409 =item B<-fallback_scsv>
411 Send TLS_FALLBACK_SCSV in the ClientHello.
415 Switch on asynchronous mode. Cryptographic operations will be performed
416 asynchronously. This will only have an effect if an asynchronous capable engine
417 is also used via the B<-engine> option. For test purposes the dummy async engine
418 (dasync) can be used (if available).
420 =item B<-max_send_frag int>
422 The maximum size of data fragment to send.
423 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
425 =item B<-split_send_frag int>
427 The size used to split data for encrypt pipelines. If more data is written in
428 one go than this value then it will be split into multiple pipelines, up to the
429 maximum number of pipelines defined by max_pipelines. This only has an effect if
430 a suitable cipher suite has been negotiated, an engine that supports pipelining
431 has been loaded, and max_pipelines is greater than 1. See
432 L<SSL_CTX_set_split_send_fragment(3)> for further information.
434 =item B<-max_pipelines int>
436 The maximum number of encrypt/decrypt pipelines to be used. This will only have
437 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
438 engine) and a suitable cipher suite has been negotiated. The default value is 1.
439 See L<SSL_CTX_set_max_pipelines(3)> for further information.
441 =item B<-read_buf int>
443 The default read buffer size to be used for connections. This will only have an
444 effect if the buffer size is larger than the size that would otherwise be used
445 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
446 further information).
450 There are several known bug in SSL and TLS implementations. Adding this
451 option enables various workarounds.
455 Enables support for SSL/TLS compression.
456 This option was introduced in OpenSSL 1.1.0.
457 TLS compression is not recommended and is off by default as of
462 Disables support for SSL/TLS compression.
463 TLS compression is not recommended and is off by default as of
468 Only provide a brief summary of connection parameters instead of the
469 normal verbose output.
471 =item B<-sigalgs sigalglist>
473 Specifies the list of signature algorithms that are sent by the client.
474 The server selects one entry in the list based on its preferences.
475 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
477 =item B<-curves curvelist>
479 Specifies the list of supported curves to be sent by the client. The curve is
480 is ultimately selected by the server. For a list of all curves, use:
482 $ openssl ecparam -list_curves
484 =item B<-cipher cipherlist>
486 This allows the cipher list sent by the client to be modified. Although
487 the server determines which cipher suite is used it should take the first
488 supported cipher in the list sent by the client. See the B<ciphers>
489 command for more information.
491 =item B<-starttls protocol>
493 Send the protocol-specific message(s) to switch to TLS for communication.
494 B<protocol> is a keyword for the intended protocol. Currently, the only
495 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
496 "irc", "postgres", "lmtp", "nntp", "sieve" and "ldap".
498 =item B<-xmpphost hostname>
500 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
501 specifies the host for the "to" attribute of the stream element.
502 If this option is not specified, then the host specified with "-connect"
505 =item B<-tlsextdebug>
507 Print out a hex dump of any TLS extensions received from the server.
511 Disable RFC4507bis session ticket support.
513 =item B<-sess_out filename>
515 Output SSL session to B<filename>.
517 =item B<-sess_in sess.pem>
519 Load SSL session from B<filename>. The client will attempt to resume a
520 connection from this session.
524 Specifying an engine (by its unique B<id> string) will cause B<s_client>
525 to attempt to obtain a functional reference to the specified engine,
526 thus initialising it if needed. The engine will then be set as the default
527 for all available algorithms.
529 =item B<-rand file(s)>
531 A file or files containing random data used to seed the random number
532 generator, or an EGD socket (see L<RAND_egd(3)>).
533 Multiple files can be specified separated by an OS-dependent character.
534 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
537 =item B<-serverinfo types>
539 A list of comma-separated TLS Extension Types (numbers between 0 and
540 65535). Each type will be sent as an empty ClientHello TLS Extension.
541 The server's response (if any) will be encoded and displayed as a PEM
546 Sends a certificate status request to the server (OCSP stapling). The server
547 response (if any) is printed out.
549 =item B<-alpn protocols>, B<-nextprotoneg protocols>
551 These flags enable the Enable the Application-Layer Protocol Negotiation
552 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
553 IETF standard and replaces NPN.
554 The B<protocols> list is a comma-separated list of protocol names that
555 the client should advertise support for. The list should contain the most
556 desirable protocols first. Protocol names are printable ASCII strings,
557 for example "http/1.1" or "spdy/3".
558 An empty list of protocols is treated specially and will cause the
559 client to advertise support for the TLS extension but disconnect just
560 after receiving ServerHello with a list of server supported protocols.
564 Use one of these two options to control whether Certificate Transparency (CT)
565 is enabled (B<-ct>) or disabled (B<-noct>).
566 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
567 the server and reported at handshake completion.
569 Enabling CT also enables OCSP stapling, as this is one possible delivery method
574 A file containing a list of known Certificate Transparency logs. See
575 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
577 =item B<-keylogfile file>
579 Appends TLS secrets to the specified keylog file such that external programs
580 (like Wireshark) can decrypt TLS connections.
582 =item B<-early_data file>
584 Reads the contents of the specified file and attempts to send it as early data
585 to the server. This will only work with resumed sessions that support early
586 data and when the server accepts the early data.
590 =head1 CONNECTED COMMANDS
592 If a connection is established with an SSL server then any data received
593 from the server is displayed and any key presses will be sent to the
594 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
595 have been given), the session will be renegotiated if the line begins with an
596 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
597 connection will be closed down.
601 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
604 openssl s_client -connect servername:443
606 would typically be used (https uses port 443). If the connection succeeds
607 then an HTTP command can be given such as "GET /" to retrieve a web page.
609 If the handshake fails then there are several possible causes, if it is
610 nothing obvious like no client certificate then the B<-bugs>,
611 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
612 in case it is a buggy server. In particular you should play with these
613 options B<before> submitting a bug report to an OpenSSL mailing list.
615 A frequent problem when attempting to get client certificates working
616 is that a web client complains it has no certificates or gives an empty
617 list to choose from. This is normally because the server is not sending
618 the clients certificate authority in its "acceptable CA list" when it
619 requests a certificate. By using B<s_client> the CA list can be viewed
620 and checked. However some servers only request client authentication
621 after a specific URL is requested. To obtain the list in this case it
622 is necessary to use the B<-prexit> option and send an HTTP request
623 for an appropriate page.
625 If a certificate is specified on the command line using the B<-cert>
626 option it will not be used unless the server specifically requests
627 a client certificate. Therefor merely including a client certificate
628 on the command line is no guarantee that the certificate works.
630 If there are problems verifying a server certificate then the
631 B<-showcerts> option can be used to show the whole chain.
633 The B<s_client> utility is a test tool and is designed to continue the
634 handshake after any certificate verification errors. As a result it will
635 accept any certificate chain (trusted or not) sent by the peer. None test
636 applications should B<not> do this as it makes them vulnerable to a MITM
637 attack. This behaviour can be changed by with the B<-verify_return_error>
638 option: any verify errors are then returned aborting the handshake.
642 Because this program has a lot of options and also because some of the
643 techniques used are rather old, the C source of B<s_client> is rather hard to
644 read and not a model of how things should be done.
645 A typical SSL client program would be much simpler.
647 The B<-prexit> option is a bit of a hack. We should really report
648 information whenever a session is renegotiated.
652 L<SSL_CONF_cmd(3)>, L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>,
653 L<SSL_CTX_set_max_send_fragment(3)>, L<SSL_CTX_set_split_send_fragment(3)>
654 L<SSL_CTX_set_max_pipelines(3)>
658 The -no_alt_chains options was first added to OpenSSL 1.1.0.
662 Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
664 Licensed under the OpenSSL license (the "License"). You may not use
665 this file except in compliance with the License. You can obtain a copy
666 in the file LICENSE in the source distribution or at
667 L<https://www.openssl.org/source/license.html>.