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<-sigalgs sigalglist>]
93 [B<-curves curvelist>]
94 [B<-cipher cipherlist>]
96 [B<-starttls protocol>]
97 [B<-xmpphost hostname>]
101 [B<-sess_out filename>]
102 [B<-sess_in filename>]
104 [B<-serverinfo types>]
107 [B<-nextprotoneg protocols>]
110 [B<-keylogfile file>]
111 [B<-early_data file>]
115 The B<s_client> command implements a generic SSL/TLS client which connects
116 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
121 In addition to the options below the B<s_client> utility also supports the
122 common and client only options documented in the
123 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
130 Print out a usage message.
132 =item B<-connect host:port>
134 This specifies the host and optional port to connect to. If not specified
135 then an attempt is made to connect to the local host on port 4433.
137 =item B<-proxy host:port>
139 When used with the B<-connect> flag, the program uses the host and port
140 specified with this flag and issues an HTTP CONNECT command to connect
141 to the desired server.
145 Connect over the specified Unix-domain socket.
155 =item B<-servername name>
157 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
159 =item B<-cert certname>
161 The certificate to use, if one is requested by the server. The default is
162 not to use a certificate.
164 =item B<-certform format>
166 The certificate format to use: DER or PEM. PEM is the default.
168 =item B<-key keyfile>
170 The private key to use. If not specified then the certificate file will
173 =item B<-keyform format>
175 The private format to use: DER or PEM. PEM is the default.
179 the private key password source. For more information about the format of B<arg>
180 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
182 =item B<-verify depth>
184 The verify depth to use. This specifies the maximum length of the
185 server certificate chain and turns on server certificate verification.
186 Currently the verify operation continues after errors so all the problems
187 with a certificate chain can be seen. As a side effect the connection
188 will never fail due to a server certificate verify failure.
190 =item B<-verify_return_error>
192 Return verification errors instead of continuing. This will typically
193 abort the handshake with a fatal error.
195 =item B<-nameopt option>
197 Option which determines how the subject or issuer names are displayed. The
198 B<option> argument can be a single option or multiple options separated by
199 commas. Alternatively the B<-nameopt> switch may be used more than once to
200 set multiple options. See the L<x509(1)> manual page for details.
202 =item B<-CApath directory>
204 The directory to use for server certificate verification. This directory
205 must be in "hash format", see B<verify> for more information. These are
206 also used when building the client certificate chain.
208 =item B<-CAfile file>
210 A file containing trusted certificates to use during server authentication
211 and to use when attempting to build the client certificate chain.
215 Do not load the trusted CA certificates from the default file location
219 Do not load the trusted CA certificates from the default directory location
221 =item B<-dane_tlsa_domain domain>
223 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
224 TLSA base domain which becomes the default SNI hint and the primary
225 reference identifier for hostname checks. This must be used in
226 combination with at least one instance of the B<-dane_tlsa_rrdata>
229 When DANE authentication succeeds, the diagnostic output will include
230 the lowest (closest to 0) depth at which a TLSA record authenticated
231 a chain certificate. When that TLSA record is a "2 1 0" trust
232 anchor public key that signed (rather than matched) the top-most
233 certificate of the chain, the result is reported as "TA public key
234 verified". Otherwise, either the TLSA record "matched TA certificate"
235 at a positive depth or else "matched EE certificate" at depth 0.
237 =item B<-dane_tlsa_rrdata rrdata>
239 Use one or more times to specify the RRDATA fields of the DANE TLSA
240 RRset associated with the target service. The B<rrdata> value is
241 specied in "presentation form", that is four whitespace separated
242 fields that specify the usage, selector, matching type and associated
243 data, with the last of these encoded in hexadecimal. Optional
244 whitespace is ignored in the associated data field. For example:
246 $ openssl s_client -brief -starttls smtp \
247 -connect smtp.example.com:25 \
248 -dane_tlsa_domain smtp.example.com \
249 -dane_tlsa_rrdata "2 1 1
250 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
251 -dane_tlsa_rrdata "2 1 1
252 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
255 Verified peername: smtp.example.com
256 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
259 =item B<-dane_ee_no_namechecks>
261 This disables server name checks when authenticating via DANE-EE(3) TLSA
263 For some applications, primarily web browsers, it is not safe to disable name
264 checks due to "unknown key share" attacks, in which a malicious server can
265 convince a client that a connection to a victim server is instead a secure
266 connection to the malicious server.
267 The malicious server may then be able to violate cross-origin scripting
269 Thus, despite the text of RFC7671, name checks are by default enabled for
270 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
272 In particular, SMTP and XMPP clients should set this option as SRV and MX
273 records already make it possible for a remote domain to redirect client
274 connections to any server of its choice, and in any case SMTP and XMPP clients
275 do not execute scripts downloaded from remote servers.
277 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
278 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
279 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
280 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
281 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
282 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
283 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
285 Set various certificate chain validation options. See the
286 L<verify(1)> manual page for details.
290 Reconnects to the same server 5 times using the same session ID, this can
291 be used as a test that session caching is working.
295 Display the whole server certificate chain: normally only the server
296 certificate itself is displayed.
300 Print session information when the program exits. This will always attempt
301 to print out information even if the connection fails. Normally information
302 will only be printed out once if the connection succeeds. This option is useful
303 because the cipher in use may be renegotiated or the connection may fail
304 because a client certificate is required or is requested only after an
305 attempt is made to access a certain URL. Note: the output produced by this
306 option is not always accurate because a connection might never have been
311 Prints out the SSL session states.
315 Print extensive debugging information including a hex dump of all traffic.
319 Show all protocol messages with hex dump.
323 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
324 with B<enable-ssl-trace> for this option to work.
328 File to send output of B<-msg> or B<-trace> to, default standard output.
332 Tests non-blocking I/O
336 Turns on non-blocking I/O
340 This option translated a line feed from the terminal into CR+LF as required
345 Inhibit shutting down the connection when end of file is reached in the
350 Inhibit printing of session and certificate information. This implicitly
351 turns on B<-ign_eof> as well.
355 Shut down the connection when end of file is reached in the input.
356 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
358 =item B<-psk_identity identity>
360 Use the PSK identity B<identity> when using a PSK cipher suite.
364 Use the PSK key B<key> when using a PSK cipher suite. The key is
365 given as a hexadecimal number without leading 0x, for example -psk
368 =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>
370 These options require or disable the use of the specified SSL or TLS protocols.
371 By default B<s_client> will negotiate the highest mutually supported protocol
373 When a specific TLS version is required, only that version will be offered to
374 and accepted from the server.
376 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
378 These options make B<s_client> use DTLS protocols instead of TLS.
379 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
380 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
383 =item B<-fallback_scsv>
385 Send TLS_FALLBACK_SCSV in the ClientHello.
389 Switch on asynchronous mode. Cryptographic operations will be performed
390 asynchronously. This will only have an effect if an asynchronous capable engine
391 is also used via the B<-engine> option. For test purposes the dummy async engine
392 (dasync) can be used (if available).
394 =item B<-split_send_frag int>
396 The size used to split data for encrypt pipelines. If more data is written in
397 one go than this value then it will be split into multiple pipelines, up to the
398 maximum number of pipelines defined by max_pipelines. This only has an effect if
399 a suitable cipher suite has been negotiated, an engine that supports pipelining
400 has been loaded, and max_pipelines is greater than 1. See
401 L<SSL_CTX_set_split_send_fragment(3)> for further information.
403 =item B<-max_pipelines int>
405 The maximum number of encrypt/decrypt pipelines to be used. This will only have
406 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
407 engine) and a suitable cipher suite has been negotiated. The default value is 1.
408 See L<SSL_CTX_set_max_pipelines(3)> for further information.
410 =item B<-read_buf int>
412 The default read buffer size to be used for connections. This will only have an
413 effect if the buffer size is larger than the size that would otherwise be used
414 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
415 further information).
419 There are several known bug in SSL and TLS implementations. Adding this
420 option enables various workarounds.
424 Enables support for SSL/TLS compression.
425 This option was introduced in OpenSSL 1.1.0.
426 TLS compression is not recommended and is off by default as of
431 Disables support for SSL/TLS compression.
432 TLS compression is not recommended and is off by default as of
437 Only provide a brief summary of connection parameters instead of the
438 normal verbose output.
440 =item B<-sigalgs sigalglist>
442 Specifies the list of signature algorithms that are sent by the client.
443 The server selects one entry in the list based on its preferences.
444 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
446 =item B<-curves curvelist>
448 Specifies the list of supported curves to be sent by the client. The curve is
449 is ultimately selected by the server. For a list of all curves, use:
451 $ openssl ecparam -list_curves
453 =item B<-cipher cipherlist>
455 This allows the cipher list sent by the client to be modified. Although
456 the server determines which cipher suite is used it should take the first
457 supported cipher in the list sent by the client. See the B<ciphers>
458 command for more information.
460 =item B<-starttls protocol>
462 Send the protocol-specific message(s) to switch to TLS for communication.
463 B<protocol> is a keyword for the intended protocol. Currently, the only
464 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
465 "irc", "postgres", "lmtp", "nntp", "sieve" and "ldap".
467 =item B<-xmpphost hostname>
469 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
470 specifies the host for the "to" attribute of the stream element.
471 If this option is not specified, then the host specified with "-connect"
474 =item B<-tlsextdebug>
476 Print out a hex dump of any TLS extensions received from the server.
480 Disable RFC4507bis session ticket support.
482 =item B<-sess_out filename>
484 Output SSL session to B<filename>.
486 =item B<-sess_in sess.pem>
488 Load SSL session from B<filename>. The client will attempt to resume a
489 connection from this session.
493 Specifying an engine (by its unique B<id> string) will cause B<s_client>
494 to attempt to obtain a functional reference to the specified engine,
495 thus initialising it if needed. The engine will then be set as the default
496 for all available algorithms.
498 =item B<-rand file(s)>
500 A file or files containing random data used to seed the random number
501 generator, or an EGD socket (see L<RAND_egd(3)>).
502 Multiple files can be specified separated by an OS-dependent character.
503 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
506 =item B<-serverinfo types>
508 A list of comma-separated TLS Extension Types (numbers between 0 and
509 65535). Each type will be sent as an empty ClientHello TLS Extension.
510 The server's response (if any) will be encoded and displayed as a PEM
515 Sends a certificate status request to the server (OCSP stapling). The server
516 response (if any) is printed out.
518 =item B<-alpn protocols>, B<-nextprotoneg protocols>
520 These flags enable the Enable the Application-Layer Protocol Negotiation
521 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
522 IETF standard and replaces NPN.
523 The B<protocols> list is a comma-separated list of protocol names that
524 the client should advertise support for. The list should contain the most
525 desirable protocols first. Protocol names are printable ASCII strings,
526 for example "http/1.1" or "spdy/3".
527 An empty list of protocols is treated specially and will cause the
528 client to advertise support for the TLS extension but disconnect just
529 after receiving ServerHello with a list of server supported protocols.
533 Use one of these two options to control whether Certificate Transparency (CT)
534 is enabled (B<-ct>) or disabled (B<-noct>).
535 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
536 the server and reported at handshake completion.
538 Enabling CT also enables OCSP stapling, as this is one possible delivery method
543 A file containing a list of known Certificate Transparency logs. See
544 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
546 =item B<-keylogfile file>
548 Appends TLS secrets to the specified keylog file such that external programs
549 (like Wireshark) can decrypt TLS connections.
551 =item B<-early_data file>
553 Reads the contents of the specified file and attempts to send it as early data
554 to the server. This will only work with resumed sessions that support early
555 data and when the server accepts the early data.
559 =head1 CONNECTED COMMANDS
561 If a connection is established with an SSL server then any data received
562 from the server is displayed and any key presses will be sent to the
563 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
564 have been given), the session will be renegotiated if the line begins with an
565 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
566 connection will be closed down.
570 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
573 openssl s_client -connect servername:443
575 would typically be used (https uses port 443). If the connection succeeds
576 then an HTTP command can be given such as "GET /" to retrieve a web page.
578 If the handshake fails then there are several possible causes, if it is
579 nothing obvious like no client certificate then the B<-bugs>,
580 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
581 in case it is a buggy server. In particular you should play with these
582 options B<before> submitting a bug report to an OpenSSL mailing list.
584 A frequent problem when attempting to get client certificates working
585 is that a web client complains it has no certificates or gives an empty
586 list to choose from. This is normally because the server is not sending
587 the clients certificate authority in its "acceptable CA list" when it
588 requests a certificate. By using B<s_client> the CA list can be viewed
589 and checked. However some servers only request client authentication
590 after a specific URL is requested. To obtain the list in this case it
591 is necessary to use the B<-prexit> option and send an HTTP request
592 for an appropriate page.
594 If a certificate is specified on the command line using the B<-cert>
595 option it will not be used unless the server specifically requests
596 a client certificate. Therefor merely including a client certificate
597 on the command line is no guarantee that the certificate works.
599 If there are problems verifying a server certificate then the
600 B<-showcerts> option can be used to show the whole chain.
602 The B<s_client> utility is a test tool and is designed to continue the
603 handshake after any certificate verification errors. As a result it will
604 accept any certificate chain (trusted or not) sent by the peer. None test
605 applications should B<not> do this as it makes them vulnerable to a MITM
606 attack. This behaviour can be changed by with the B<-verify_return_error>
607 option: any verify errors are then returned aborting the handshake.
611 Because this program has a lot of options and also because some of the
612 techniques used are rather old, the C source of B<s_client> is rather hard to
613 read and not a model of how things should be done.
614 A typical SSL client program would be much simpler.
616 The B<-prexit> option is a bit of a hack. We should really report
617 information whenever a session is renegotiated.
622 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
626 The -no_alt_chains options was first added to OpenSSL 1.1.0.
630 Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
632 Licensed under the OpenSSL license (the "License"). You may not use
633 this file except in compliance with the License. You can obtain a copy
634 in the file LICENSE in the source distribution or at
635 L<https://www.openssl.org/source/license.html>.