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<-dane_tlsa_domain domain>]
29 [B<-dane_tlsa_rrdata rrdata>]
30 [B<-dane_ee_no_namechecks>]
31 [B<-attime timestamp>]
54 [B<-verify_depth num>]
55 [B<-verify_email email>]
56 [B<-verify_hostname hostname>]
58 [B<-verify_name name>]
92 [B<-cipher cipherlist>]
94 [B<-starttls protocol>]
95 [B<-xmpphost hostname>]
99 [B<-sess_out filename>]
100 [B<-sess_in filename>]
102 [B<-serverinfo types>]
105 [B<-nextprotoneg protocols>]
111 The B<s_client> command implements a generic SSL/TLS client which connects
112 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
117 In addition to the options below the B<s_client> utility also supports the
118 common and client only options documented in the
119 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
126 Print out a usage message.
128 =item B<-connect host:port>
130 This specifies the host and optional port to connect to. If not specified
131 then an attempt is made to connect to the local host on port 4433.
133 =item B<-proxy host:port>
135 When used with the B<-connect> flag, the program uses the host and port
136 specified with this flag and issues an HTTP CONNECT command to connect
137 to the desired server.
141 Connect over the specified Unix-domain socket.
151 =item B<-servername name>
153 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
155 =item B<-cert certname>
157 The certificate to use, if one is requested by the server. The default is
158 not to use a certificate.
160 =item B<-certform format>
162 The certificate format to use: DER or PEM. PEM is the default.
164 =item B<-key keyfile>
166 The private key to use. If not specified then the certificate file will
169 =item B<-keyform format>
171 The private format to use: DER or PEM. PEM is the default.
175 the private key password source. For more information about the format of B<arg>
176 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
178 =item B<-verify depth>
180 The verify depth to use. This specifies the maximum length of the
181 server certificate chain and turns on server certificate verification.
182 Currently the verify operation continues after errors so all the problems
183 with a certificate chain can be seen. As a side effect the connection
184 will never fail due to a server certificate verify failure.
186 =item B<-verify_return_error>
188 Return verification errors instead of continuing. This will typically
189 abort the handshake with a fatal error.
191 =item B<-nameopt option>
193 option which determines how the subject or issuer names are displayed. The
194 B<option> argument can be a single option or multiple options separated by
195 commas. Alternatively the B<-nameopt> switch may be used more than once to
196 set multiple options. See the L<x509(1)> manual page for details.
198 =item B<-CApath directory>
200 The directory to use for server certificate verification. This directory
201 must be in "hash format", see B<verify> for more information. These are
202 also used when building the client certificate chain.
204 =item B<-CAfile file>
206 A file containing trusted certificates to use during server authentication
207 and to use when attempting to build the client certificate chain.
211 Do not load the trusted CA certificates from the default file location
215 Do not load the trusted CA certificates from the default directory location
217 =item B<-dane_tlsa_domain domain>
219 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
220 TLSA base domain which becomes the default SNI hint and the primary
221 reference identifier for hostname checks. This must be used in
222 combination with at least one instance of the B<-dane_tlsa_rrdata>
225 When DANE authentication succeeds, the diagnostic output will include
226 the lowest (closest to 0) depth at which a TLSA record authenticated
227 a chain certificate. When that TLSA record is a "2 1 0" trust
228 anchor public key that signed (rather than matched) the top-most
229 certificate of the chain, the result is reported as "TA public key
230 verified". Otherwise, either the TLSA record "matched TA certificate"
231 at a positive depth or else "matched EE certificate" at depth 0.
233 =item B<-dane_tlsa_rrdata rrdata>
235 Use one or more times to specify the RRDATA fields of the DANE TLSA
236 RRset associated with the target service. The B<rrdata> value is
237 specied in "presentation form", that is four whitespace separated
238 fields that specify the usage, selector, matching type and associated
239 data, with the last of these encoded in hexadecimal. Optional
240 whitespace is ignored in the associated data field. For example:
242 $ openssl s_client -brief -starttls smtp \
243 -connect smtp.example.com:25 \
244 -dane_tlsa_domain smtp.example.com \
245 -dane_tlsa_rrdata "2 1 1
246 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
247 -dane_tlsa_rrdata "2 1 1
248 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
251 Verified peername: smtp.example.com
252 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
255 =item B<-dane_ee_no_namechecks>
257 This disables server name checks when authenticating via DANE-EE(3) TLSA
259 For some applications, primarily web browsers, it is not safe to disable name
260 checks due to "unknown key share" attacks, in which a malicious server can
261 convince a client that a connection to a victim server is instead a secure
262 connection to the malicious server.
263 The malicious server may then be able to violate cross-origin scripting
265 Thus, despite the text of RFC7671, name checks are by default enabled for
266 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
268 In particular, SMTP and XMPP clients should set this option as SRV and MX
269 records already make it possible for a remote domain to redirect client
270 connections to any server of its choice, and in any case SMTP and XMPP clients
271 do not execute scripts downloaded from remote servers.
273 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
274 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
275 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
276 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
277 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
278 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
279 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
281 Set various certificate chain validation options. See the
282 L<verify(1)> manual page for details.
286 reconnects to the same server 5 times using the same session ID, this can
287 be used as a test that session caching is working.
291 display the whole server certificate chain: normally only the server
292 certificate itself is displayed.
296 print session information when the program exits. This will always attempt
297 to print out information even if the connection fails. Normally information
298 will only be printed out once if the connection succeeds. This option is useful
299 because the cipher in use may be renegotiated or the connection may fail
300 because a client certificate is required or is requested only after an
301 attempt is made to access a certain URL. Note: the output produced by this
302 option is not always accurate because a connection might never have been
307 prints out the SSL session states.
311 print extensive debugging information including a hex dump of all traffic.
315 show all protocol messages with hex dump.
319 show verbose trace output of protocol messages. OpenSSL needs to be compiled
320 with B<enable-ssl-trace> for this option to work.
324 file to send output of B<-msg> or B<-trace> to, default standard output.
328 tests non-blocking I/O
332 turns on non-blocking I/O
336 this option translated a line feed from the terminal into CR+LF as required
341 inhibit shutting down the connection when end of file is reached in the
346 inhibit printing of session and certificate information. This implicitly
347 turns on B<-ign_eof> as well.
351 shut down the connection when end of file is reached in the input.
352 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
354 =item B<-psk_identity identity>
356 Use the PSK identity B<identity> when using a PSK cipher suite.
360 Use the PSK key B<key> when using a PSK cipher suite. The key is
361 given as a hexadecimal number without leading 0x, for example -psk
364 =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>
366 These options require or disable the use of the specified SSL or TLS protocols.
367 By default B<s_client> will negotiate the highest mutually supported protocol
369 When a specific TLS version is required, only that version will be offered to
370 and accepted from the server.
372 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
374 These options make B<s_client> use DTLS protocols instead of TLS.
375 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
376 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
379 =item B<-fallback_scsv>
381 Send TLS_FALLBACK_SCSV in the ClientHello.
385 switch on asynchronous mode. Cryptographic operations will be performed
386 asynchronously. This will only have an effect if an asynchronous capable engine
387 is also used via the B<-engine> option. For test purposes the dummy async engine
388 (dasync) can be used (if available).
390 =item B<-split_send_frag int>
392 The size used to split data for encrypt pipelines. If more data is written in
393 one go than this value then it will be split into multiple pipelines, up to the
394 maximum number of pipelines defined by max_pipelines. This only has an effect if
395 a suitable ciphersuite has been negotiated, an engine that supports pipelining
396 has been loaded, and max_pipelines is greater than 1. See
397 L<SSL_CTX_set_split_send_fragment(3)> for further information.
399 =item B<-max_pipelines int>
401 The maximum number of encrypt/decrypt pipelines to be used. This will only have
402 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
403 engine) and a suitable ciphersuite has been negotiated. The default value is 1.
404 See L<SSL_CTX_set_max_pipelines(3)> for further information.
406 =item B<-read_buf int>
408 The default read buffer size to be used for connections. This will only have an
409 effect if the buffer size is larger than the size that would otherwise be used
410 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
411 further information).
415 there are several known bug in SSL and TLS implementations. Adding this
416 option enables various workarounds.
420 Enables support for SSL/TLS compression.
421 This option was introduced in OpenSSL 1.1.0.
422 TLS compression is not recommended and is off by default as of
427 Disables support for SSL/TLS compression.
428 TLS compression is not recommended and is off by default as of
433 only provide a brief summary of connection parameters instead of the
434 normal verbose output.
436 =item B<-cipher cipherlist>
438 this allows the cipher list sent by the client to be modified. Although
439 the server determines which cipher suite is used it should take the first
440 supported cipher in the list sent by the client. See the B<ciphers>
441 command for more information.
443 =item B<-starttls protocol>
445 send the protocol-specific message(s) to switch to TLS for communication.
446 B<protocol> is a keyword for the intended protocol. Currently, the only
447 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
448 "irc", "postgres", "lmtp", "nntp" and "sieve".
450 =item B<-xmpphost hostname>
452 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
453 specifies the host for the "to" attribute of the stream element.
454 If this option is not specified, then the host specified with "-connect"
457 =item B<-tlsextdebug>
459 print out a hex dump of any TLS extensions received from the server.
463 disable RFC4507bis session ticket support.
465 =item B<-sess_out filename>
467 output SSL session to B<filename>
469 =item B<-sess_in sess.pem>
471 load SSL session from B<filename>. The client will attempt to resume a
472 connection from this session.
476 specifying an engine (by its unique B<id> string) will cause B<s_client>
477 to attempt to obtain a functional reference to the specified engine,
478 thus initialising it if needed. The engine will then be set as the default
479 for all available algorithms.
481 =item B<-rand file(s)>
483 a file or files containing random data used to seed the random number
484 generator, or an EGD socket (see L<RAND_egd(3)>).
485 Multiple files can be specified separated by an OS-dependent character.
486 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
489 =item B<-serverinfo types>
491 a list of comma-separated TLS Extension Types (numbers between 0 and
492 65535). Each type will be sent as an empty ClientHello TLS Extension.
493 The server's response (if any) will be encoded and displayed as a PEM
498 sends a certificate status request to the server (OCSP stapling). The server
499 response (if any) is printed out.
501 =item B<-alpn protocols>, B<-nextprotoneg protocols>
503 these flags enable the
504 Enable the Application-Layer Protocol Negotiation or Next Protocol
505 Negotiation extension, respectively. ALPN is the IETF standard and
507 The B<protocols> list is a
508 comma-separated protocol names that the client should advertise
509 support for. The list should contain most wanted protocols first.
510 Protocol names are printable ASCII strings, for example "http/1.1" or
512 Empty list of protocols is treated specially and will cause the client to
513 advertise support for the TLS extension but disconnect just after
514 receiving ServerHello with a list of server supported protocols.
518 Use one of these two options to control whether Certificate Transparency (CT)
519 is enabled (B<-ct>) or disabled (B<-noct>).
520 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
521 the server and reported at handshake completion.
523 Enabling CT also enables OCSP stapling, as this is one possible delivery method
528 A file containing a list of known Certificate Transparency logs. See
529 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
531 =item B<-keylogfile path>
533 Appends TLS secrets to the specified keylog file such that external programs
534 (like Wireshark) can decrypt TLS connections.
538 =head1 CONNECTED COMMANDS
540 If a connection is established with an SSL server then any data received
541 from the server is displayed and any key presses will be sent to the
542 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
543 have been given), the session will be renegotiated if the line begins with an
544 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
545 connection will be closed down.
549 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
552 openssl s_client -connect servername:443
554 would typically be used (https uses port 443). If the connection succeeds
555 then an HTTP command can be given such as "GET /" to retrieve a web page.
557 If the handshake fails then there are several possible causes, if it is
558 nothing obvious like no client certificate then the B<-bugs>,
559 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
560 in case it is a buggy server. In particular you should play with these
561 options B<before> submitting a bug report to an OpenSSL mailing list.
563 A frequent problem when attempting to get client certificates working
564 is that a web client complains it has no certificates or gives an empty
565 list to choose from. This is normally because the server is not sending
566 the clients certificate authority in its "acceptable CA list" when it
567 requests a certificate. By using B<s_client> the CA list can be viewed
568 and checked. However some servers only request client authentication
569 after a specific URL is requested. To obtain the list in this case it
570 is necessary to use the B<-prexit> option and send an HTTP request
571 for an appropriate page.
573 If a certificate is specified on the command line using the B<-cert>
574 option it will not be used unless the server specifically requests
575 a client certificate. Therefor merely including a client certificate
576 on the command line is no guarantee that the certificate works.
578 If there are problems verifying a server certificate then the
579 B<-showcerts> option can be used to show the whole chain.
581 The B<s_client> utility is a test tool and is designed to continue the
582 handshake after any certificate verification errors. As a result it will
583 accept any certificate chain (trusted or not) sent by the peer. None test
584 applications should B<not> do this as it makes them vulnerable to a MITM
585 attack. This behaviour can be changed by with the B<-verify_return_error>
586 option: any verify errors are then returned aborting the handshake.
590 Because this program has a lot of options and also because some of the
591 techniques used are rather old, the C source of B<s_client> is rather hard to
592 read and not a model of how things should be done.
593 A typical SSL client program would be much simpler.
595 The B<-prexit> option is a bit of a hack. We should really report
596 information whenever a session is renegotiated.
601 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
605 The -no_alt_chains options was first added to OpenSSL 1.1.0.
609 Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
611 Licensed under the OpenSSL license (the "License"). You may not use
612 this file except in compliance with the License. You can obtain a copy
613 in the file LICENSE in the source distribution or at
614 L<https://www.openssl.org/source/license.html>.