5 s_client - SSL/TLS client program
11 [B<-connect host:port>]
15 [B<-verify_return_error>]
17 [B<-certform DER|PEM>]
21 [B<-CApath directory>]
25 [B<-dane_tlsa_domain domain>]
26 [B<-dane_tlsa_rrdata rrdata>]
27 [B<-dane_ee_no_namechecks>]
28 [B<-attime timestamp>]
50 [B<-verify_depth num>]
51 [B<-verify_email email>]
52 [B<-verify_hostname hostname>]
54 [B<-verify_name name>]
86 [B<-cipher cipherlist>]
88 [B<-starttls protocol>]
89 [B<-xmpphost hostname>]
93 [B<-sess_out filename>]
94 [B<-sess_in filename>]
96 [B<-serverinfo types>]
99 [B<-nextprotoneg protocols>]
105 The B<s_client> command implements a generic SSL/TLS client which connects
106 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
111 In addition to the options below the B<s_client> utility also supports the
112 common and client only options documented in the
113 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
120 Print out a usage message.
122 =item B<-connect host:port>
124 This specifies the host and optional port to connect to. If not specified
125 then an attempt is made to connect to the local host on port 4433.
127 =item B<-proxy host:port>
129 When used with the B<-connect> flag, the program uses the host and port
130 specified with this flag and issues an HTTP CONNECT command to connect
131 to the desired server.
133 =item B<-servername name>
135 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
137 =item B<-cert certname>
139 The certificate to use, if one is requested by the server. The default is
140 not to use a certificate.
142 =item B<-certform format>
144 The certificate format to use: DER or PEM. PEM is the default.
146 =item B<-key keyfile>
148 The private key to use. If not specified then the certificate file will
151 =item B<-keyform format>
153 The private format to use: DER or PEM. PEM is the default.
157 the private key password source. For more information about the format of B<arg>
158 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
160 =item B<-verify depth>
162 The verify depth to use. This specifies the maximum length of the
163 server certificate chain and turns on server certificate verification.
164 Currently the verify operation continues after errors so all the problems
165 with a certificate chain can be seen. As a side effect the connection
166 will never fail due to a server certificate verify failure.
168 =item B<-verify_return_error>
170 Return verification errors instead of continuing. This will typically
171 abort the handshake with a fatal error.
173 =item B<-CApath directory>
175 The directory to use for server certificate verification. This directory
176 must be in "hash format", see B<verify> for more information. These are
177 also used when building the client certificate chain.
179 =item B<-CAfile file>
181 A file containing trusted certificates to use during server authentication
182 and to use when attempting to build the client certificate chain.
186 Do not load the trusted CA certificates from the default file location
190 Do not load the trusted CA certificates from the default directory location
192 =item B<-dane_tlsa_domain domain>
194 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
195 TLSA base domain which becomes the default SNI hint and the primary
196 reference identifier for hostname checks. This must be used in
197 combination with at least one instance of the B<-dane_tlsa_rrdata>
200 When DANE authentication succeeds, the diagnostic output will include
201 the lowest (closest to 0) depth at which a TLSA record authenticated
202 a chain certificate. When that TLSA record is a "2 1 0" trust
203 anchor public key that signed (rather than matched) the top-most
204 certificate of the chain, the result is reported as "TA public key
205 verified". Otherwise, either the TLSA record "matched TA certificate"
206 at a positive depth or else "matched EE certificate" at depth 0.
208 =item B<-dane_tlsa_rrdata rrdata>
210 Use one or more times to specify the RRDATA fields of the DANE TLSA
211 RRset associated with the target service. The B<rrdata> value is
212 specied in "presentation form", that is four whitespace separated
213 fields that specify the usage, selector, matching type and associated
214 data, with the last of these encoded in hexadecimal. Optional
215 whitespace is ignored in the associated data field. For example:
217 $ openssl s_client -brief -starttls smtp \
218 -connect smtp.example.com:25 \
219 -dane_tlsa_domain smtp.example.com \
220 -dane_tlsa_rrdata "2 1 1
221 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
222 -dane_tlsa_rrdata "2 1 1
223 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
226 Verified peername: smtp.example.com
227 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
230 =item B<-dane_ee_no_namechecks>
232 This disables server name checks when authenticating via DANE-EE(3) TLSA
234 For some applications, primarily web browsers, it is not safe to disable name
235 checks due to "unknown key share" attacks, in which a malicious server can
236 convince a client that a connection to a victim server is instead a secure
237 connection to the malicious server.
238 The malicious server may then be able to violate cross-origin scripting
240 Thus, despite the text of RFC7671, name checks are by default enabled for
241 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
243 In particular, SMTP and XMPP clients should set this option as SRV and MX
244 records already make it possible for a remote domain to redirect client
245 connections to any server of its choice, and in any case SMTP and XMPP clients
246 do not execute scripts downloaded from remote servers.
248 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
249 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
250 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
251 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
252 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
253 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
254 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
256 Set various certificate chain validation options. See the
257 L<verify(1)> manual page for details.
261 reconnects to the same server 5 times using the same session ID, this can
262 be used as a test that session caching is working.
266 display the whole server certificate chain: normally only the server
267 certificate itself is displayed.
271 print session information when the program exits. This will always attempt
272 to print out information even if the connection fails. Normally information
273 will only be printed out once if the connection succeeds. This option is useful
274 because the cipher in use may be renegotiated or the connection may fail
275 because a client certificate is required or is requested only after an
276 attempt is made to access a certain URL. Note: the output produced by this
277 option is not always accurate because a connection might never have been
282 prints out the SSL session states.
286 print extensive debugging information including a hex dump of all traffic.
290 show all protocol messages with hex dump.
294 show verbose trace output of protocol messages. OpenSSL needs to be compiled
295 with B<enable-ssl-trace> for this option to work.
299 file to send output of B<-msg> or B<-trace> to, default standard output.
303 tests non-blocking I/O
307 turns on non-blocking I/O
311 this option translated a line feed from the terminal into CR+LF as required
316 inhibit shutting down the connection when end of file is reached in the
321 inhibit printing of session and certificate information. This implicitly
322 turns on B<-ign_eof> as well.
326 shut down the connection when end of file is reached in the input.
327 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
329 =item B<-psk_identity identity>
331 Use the PSK identity B<identity> when using a PSK cipher suite.
335 Use the PSK key B<key> when using a PSK cipher suite. The key is
336 given as a hexadecimal number without leading 0x, for example -psk
339 =item B<-ssl3>, B<-tls1>, B<-tls1_1>, B<-tls1_2>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>
341 These options require or disable the use of the specified SSL or TLS protocols.
342 By default B<s_client> will negotiate the highest mutually supported protocol
344 When a specific TLS version is required, only that version will be offered to
345 and accepted from the server.
347 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
349 These options make B<s_client> use DTLS protocols instead of TLS.
350 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
351 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
354 =item B<-fallback_scsv>
356 Send TLS_FALLBACK_SCSV in the ClientHello.
360 switch on asynchronous mode. Cryptographic operations will be performed
361 asynchronously. This will only have an effect if an asynchronous capable engine
362 is also used via the B<-engine> option. For test purposes the dummy async engine
363 (dasync) can be used (if available).
365 =item B<-split_send_frag int>
367 The size used to split data for encrypt pipelines. If more data is written in
368 one go than this value then it will be split into multiple pipelines, up to the
369 maximum number of pipelines defined by max_pipelines. This only has an effect if
370 a suitable ciphersuite has been negotiated, an engine that supports pipelining
371 has been loaded, and max_pipelines is greater than 1. See
372 L<SSL_CTX_set_split_send_fragment(3)> for further information.
374 =item B<-max_pipelines int>
376 The maximum number of encrypt/decrypt pipelines to be used. This will only have
377 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
378 engine) and a suitable ciphersuite has been negotiated. The default value is 1.
379 See L<SSL_CTX_set_max_pipelines(3)> for further information.
381 =item B<-read_buf int>
383 The default read buffer size to be used for connections. This will only have an
384 effect if the buffer size is larger than the size that would otherwise be used
385 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
386 further information).
390 there are several known bug in SSL and TLS implementations. Adding this
391 option enables various workarounds.
395 Enables support for SSL/TLS compression.
396 This option was introduced in OpenSSL 1.1.0.
397 TLS compression is not recommended and is off by default as of
402 Disables support for SSL/TLS compression.
403 TLS compression is not recommended and is off by default as of
408 only provide a brief summary of connection parameters instead of the
409 normal verbose output.
411 =item B<-cipher cipherlist>
413 this allows the cipher list sent by the client to be modified. Although
414 the server determines which cipher suite is used it should take the first
415 supported cipher in the list sent by the client. See the B<ciphers>
416 command for more information.
418 =item B<-starttls protocol>
420 send the protocol-specific message(s) to switch to TLS for communication.
421 B<protocol> is a keyword for the intended protocol. Currently, the only
422 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
425 =item B<-xmpphost hostname>
427 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
428 specifies the host for the "to" attribute of the stream element.
429 If this option is not specified, then the host specified with "-connect"
432 =item B<-tlsextdebug>
434 print out a hex dump of any TLS extensions received from the server.
438 disable RFC4507bis session ticket support.
440 =item B<-sess_out filename>
442 output SSL session to B<filename>
444 =item B<-sess_in sess.pem>
446 load SSL session from B<filename>. The client will attempt to resume a
447 connection from this session.
451 specifying an engine (by its unique B<id> string) will cause B<s_client>
452 to attempt to obtain a functional reference to the specified engine,
453 thus initialising it if needed. The engine will then be set as the default
454 for all available algorithms.
456 =item B<-rand file(s)>
458 a file or files containing random data used to seed the random number
459 generator, or an EGD socket (see L<RAND_egd(3)>).
460 Multiple files can be specified separated by an OS-dependent character.
461 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
464 =item B<-serverinfo types>
466 a list of comma-separated TLS Extension Types (numbers between 0 and
467 65535). Each type will be sent as an empty ClientHello TLS Extension.
468 The server's response (if any) will be encoded and displayed as a PEM
473 sends a certificate status request to the server (OCSP stapling). The server
474 response (if any) is printed out.
476 =item B<-alpn protocols>, B<-nextprotoneg protocols>
478 these flags enable the
479 Enable the Application-Layer Protocol Negotiation or Next Protocol
480 Negotiation extension, respectively. ALPN is the IETF standard and
482 The B<protocols> list is a
483 comma-separated protocol names that the client should advertise
484 support for. The list should contain most wanted protocols first.
485 Protocol names are printable ASCII strings, for example "http/1.1" or
487 Empty list of protocols is treated specially and will cause the client to
488 advertise support for the TLS extension but disconnect just after
489 receiving ServerHello with a list of server supported protocols.
493 Use one of these two options to control whether Certificate Transparency (CT)
494 is enabled (B<-ct>) or disabled (B<-noct>).
495 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
496 the server and reported at handshake completion.
498 Enabling CT also enables OCSP stapling, as this is one possible delivery method
503 A file containing a list of known Certificate Transparency logs. See
504 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
508 =head1 CONNECTED COMMANDS
510 If a connection is established with an SSL server then any data received
511 from the server is displayed and any key presses will be sent to the
512 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
513 have been given), the session will be renegotiated if the line begins with an
514 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
515 connection will be closed down.
519 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
522 openssl s_client -connect servername:443
524 would typically be used (https uses port 443). If the connection succeeds
525 then an HTTP command can be given such as "GET /" to retrieve a web page.
527 If the handshake fails then there are several possible causes, if it is
528 nothing obvious like no client certificate then the B<-bugs>,
529 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
530 in case it is a buggy server. In particular you should play with these
531 options B<before> submitting a bug report to an OpenSSL mailing list.
533 A frequent problem when attempting to get client certificates working
534 is that a web client complains it has no certificates or gives an empty
535 list to choose from. This is normally because the server is not sending
536 the clients certificate authority in its "acceptable CA list" when it
537 requests a certificate. By using B<s_client> the CA list can be viewed
538 and checked. However some servers only request client authentication
539 after a specific URL is requested. To obtain the list in this case it
540 is necessary to use the B<-prexit> option and send an HTTP request
541 for an appropriate page.
543 If a certificate is specified on the command line using the B<-cert>
544 option it will not be used unless the server specifically requests
545 a client certificate. Therefor merely including a client certificate
546 on the command line is no guarantee that the certificate works.
548 If there are problems verifying a server certificate then the
549 B<-showcerts> option can be used to show the whole chain.
551 The B<s_client> utility is a test tool and is designed to continue the
552 handshake after any certificate verification errors. As a result it will
553 accept any certificate chain (trusted or not) sent by the peer. None test
554 applications should B<not> do this as it makes them vulnerable to a MITM
555 attack. This behaviour can be changed by with the B<-verify_return_error>
556 option: any verify errors are then returned aborting the handshake.
560 Because this program has a lot of options and also because some of the
561 techniques used are rather old, the C source of B<s_client> is rather hard to
562 read and not a model of how things should be done.
563 A typical SSL client program would be much simpler.
565 The B<-prexit> option is a bit of a hack. We should really report
566 information whenever a session is renegotiated.
571 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
575 The -no_alt_chains options was first added to OpenSSL 1.1.0.
579 Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
581 Licensed under the OpenSSL license (the "License"). You may not use
582 this file except in compliance with the License. You can obtain a copy
583 in the file LICENSE in the source distribution or at
584 L<https://www.openssl.org/source/license.html>.