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>]
110 [B<-serverinfo types>]
113 [B<-nextprotoneg protocols>]
116 [B<-keylogfile file>]
117 [B<-early_data file>]
122 The B<s_client> command implements a generic SSL/TLS client which connects
123 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
128 In addition to the options below the B<s_client> utility also supports the
129 common and client only options documented in the
130 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
137 Print out a usage message.
139 =item B<-connect host:port>
141 This specifies the host and optional port to connect to. It is possible to
142 select the host and port using the optional target positional argument instead.
143 If neither this nor the target positonal argument are specified then an attempt
144 is made to connect to the local host on port 4433.
146 =item B<-proxy host:port>
148 When used with the B<-connect> flag, the program uses the host and port
149 specified with this flag and issues an HTTP CONNECT command to connect
150 to the desired server.
154 Connect over the specified Unix-domain socket.
164 =item B<-servername name>
166 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
167 the given value. If both this option and the B<-noservername> are not given, the
168 TLS SNI extension is still set to the hostname provided to the B<-connect> option,
169 or "localhost" if B<-connect> has not been supplied. This is default since OpenSSL
172 Even though SNI name should normally be a DNS name and not an IP address, this
173 option will not make the distinction when parsing B<-connect> and will send
174 IP address if one passed.
176 =item B<-noservername>
178 Suppresses sending of the SNI (Server Name Indication) extension in the
179 ClientHello message. Cannot be used in conjunction with the B<-servername> or
180 <-dane_tlsa_domain> options.
182 =item B<-cert certname>
184 The certificate to use, if one is requested by the server. The default is
185 not to use a certificate.
187 =item B<-certform format>
189 The certificate format to use: DER or PEM. PEM is the default.
191 =item B<-key keyfile>
193 The private key to use. If not specified then the certificate file will
196 =item B<-keyform format>
198 The private format to use: DER or PEM. PEM is the default.
202 the private key password source. For more information about the format of B<arg>
203 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
205 =item B<-verify depth>
207 The verify depth to use. This specifies the maximum length of the
208 server certificate chain and turns on server certificate verification.
209 Currently the verify operation continues after errors so all the problems
210 with a certificate chain can be seen. As a side effect the connection
211 will never fail due to a server certificate verify failure.
213 =item B<-verify_return_error>
215 Return verification errors instead of continuing. This will typically
216 abort the handshake with a fatal error.
218 =item B<-nameopt option>
220 Option which determines how the subject or issuer names are displayed. The
221 B<option> argument can be a single option or multiple options separated by
222 commas. Alternatively the B<-nameopt> switch may be used more than once to
223 set multiple options. See the L<x509(1)> manual page for details.
225 =item B<-CApath directory>
227 The directory to use for server certificate verification. This directory
228 must be in "hash format", see B<verify> for more information. These are
229 also used when building the client certificate chain.
231 =item B<-CAfile file>
233 A file containing trusted certificates to use during server authentication
234 and to use when attempting to build the client certificate chain.
238 Do not load the trusted CA certificates from the default file location
242 Do not load the trusted CA certificates from the default directory location
244 =item B<-requestCAfile file>
246 A file containing a list of certificates whose subject names will be sent
247 to the server in the B<certificate_authorities> extension. Only supported
250 =item B<-dane_tlsa_domain domain>
252 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
253 TLSA base domain which becomes the default SNI hint and the primary
254 reference identifier for hostname checks. This must be used in
255 combination with at least one instance of the B<-dane_tlsa_rrdata>
258 When DANE authentication succeeds, the diagnostic output will include
259 the lowest (closest to 0) depth at which a TLSA record authenticated
260 a chain certificate. When that TLSA record is a "2 1 0" trust
261 anchor public key that signed (rather than matched) the top-most
262 certificate of the chain, the result is reported as "TA public key
263 verified". Otherwise, either the TLSA record "matched TA certificate"
264 at a positive depth or else "matched EE certificate" at depth 0.
266 =item B<-dane_tlsa_rrdata rrdata>
268 Use one or more times to specify the RRDATA fields of the DANE TLSA
269 RRset associated with the target service. The B<rrdata> value is
270 specied in "presentation form", that is four whitespace separated
271 fields that specify the usage, selector, matching type and associated
272 data, with the last of these encoded in hexadecimal. Optional
273 whitespace is ignored in the associated data field. For example:
275 $ openssl s_client -brief -starttls smtp \
276 -connect smtp.example.com:25 \
277 -dane_tlsa_domain smtp.example.com \
278 -dane_tlsa_rrdata "2 1 1
279 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
280 -dane_tlsa_rrdata "2 1 1
281 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
284 Verified peername: smtp.example.com
285 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
288 =item B<-dane_ee_no_namechecks>
290 This disables server name checks when authenticating via DANE-EE(3) TLSA
292 For some applications, primarily web browsers, it is not safe to disable name
293 checks due to "unknown key share" attacks, in which a malicious server can
294 convince a client that a connection to a victim server is instead a secure
295 connection to the malicious server.
296 The malicious server may then be able to violate cross-origin scripting
298 Thus, despite the text of RFC7671, name checks are by default enabled for
299 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
301 In particular, SMTP and XMPP clients should set this option as SRV and MX
302 records already make it possible for a remote domain to redirect client
303 connections to any server of its choice, and in any case SMTP and XMPP clients
304 do not execute scripts downloaded from remote servers.
306 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
307 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
308 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
309 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
310 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
311 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
312 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
314 Set various certificate chain validation options. See the
315 L<verify(1)> manual page for details.
319 Reconnects to the same server 5 times using the same session ID, this can
320 be used as a test that session caching is working.
324 Display the whole server certificate chain: normally only the server
325 certificate itself is displayed.
329 Print session information when the program exits. This will always attempt
330 to print out information even if the connection fails. Normally information
331 will only be printed out once if the connection succeeds. This option is useful
332 because the cipher in use may be renegotiated or the connection may fail
333 because a client certificate is required or is requested only after an
334 attempt is made to access a certain URL. Note: the output produced by this
335 option is not always accurate because a connection might never have been
340 Prints out the SSL session states.
344 Print extensive debugging information including a hex dump of all traffic.
348 Show all protocol messages with hex dump.
352 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
353 with B<enable-ssl-trace> for this option to work.
357 File to send output of B<-msg> or B<-trace> to, default standard output.
361 Tests non-blocking I/O
365 Turns on non-blocking I/O
369 This option translated a line feed from the terminal into CR+LF as required
374 Inhibit shutting down the connection when end of file is reached in the
379 Inhibit printing of session and certificate information. This implicitly
380 turns on B<-ign_eof> as well.
384 Shut down the connection when end of file is reached in the input.
385 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
387 =item B<-psk_identity identity>
389 Use the PSK identity B<identity> when using a PSK cipher suite.
390 The default value is "Client_identity" (without the quotes).
394 Use the PSK key B<key> when using a PSK cipher suite. The key is
395 given as a hexadecimal number without leading 0x, for example -psk
397 This option must be provided in order to use a PSK cipher.
399 =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>
401 These options require or disable the use of the specified SSL or TLS protocols.
402 By default B<s_client> will negotiate the highest mutually supported protocol
404 When a specific TLS version is required, only that version will be offered to
405 and accepted from the server.
407 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
409 These options make B<s_client> use DTLS protocols instead of TLS.
410 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
411 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
416 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
417 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
418 available where OpenSSL has support for SCTP enabled.
420 =item B<-fallback_scsv>
422 Send TLS_FALLBACK_SCSV in the ClientHello.
426 Switch on asynchronous mode. Cryptographic operations will be performed
427 asynchronously. This will only have an effect if an asynchronous capable engine
428 is also used via the B<-engine> option. For test purposes the dummy async engine
429 (dasync) can be used (if available).
431 =item B<-max_send_frag int>
433 The maximum size of data fragment to send.
434 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
436 =item B<-split_send_frag int>
438 The size used to split data for encrypt pipelines. If more data is written in
439 one go than this value then it will be split into multiple pipelines, up to the
440 maximum number of pipelines defined by max_pipelines. This only has an effect if
441 a suitable cipher suite has been negotiated, an engine that supports pipelining
442 has been loaded, and max_pipelines is greater than 1. See
443 L<SSL_CTX_set_split_send_fragment(3)> for further information.
445 =item B<-max_pipelines int>
447 The maximum number of encrypt/decrypt pipelines to be used. This will only have
448 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
449 engine) and a suitable cipher suite has been negotiated. The default value is 1.
450 See L<SSL_CTX_set_max_pipelines(3)> for further information.
452 =item B<-read_buf int>
454 The default read buffer size to be used for connections. This will only have an
455 effect if the buffer size is larger than the size that would otherwise be used
456 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
457 further information).
461 There are several known bug in SSL and TLS implementations. Adding this
462 option enables various workarounds.
466 Enables support for SSL/TLS compression.
467 This option was introduced in OpenSSL 1.1.0.
468 TLS compression is not recommended and is off by default as of
473 Disables support for SSL/TLS compression.
474 TLS compression is not recommended and is off by default as of
479 Only provide a brief summary of connection parameters instead of the
480 normal verbose output.
482 =item B<-sigalgs sigalglist>
484 Specifies the list of signature algorithms that are sent by the client.
485 The server selects one entry in the list based on its preferences.
486 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
488 =item B<-curves curvelist>
490 Specifies the list of supported curves to be sent by the client. The curve is
491 is ultimately selected by the server. For a list of all curves, use:
493 $ openssl ecparam -list_curves
495 =item B<-cipher cipherlist>
497 This allows the cipher list sent by the client to be modified. Although
498 the server determines which cipher suite is used it should take the first
499 supported cipher in the list sent by the client. See the B<ciphers>
500 command for more information.
502 =item B<-starttls protocol>
504 Send the protocol-specific message(s) to switch to TLS for communication.
505 B<protocol> is a keyword for the intended protocol. Currently, the only
506 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
507 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
509 =item B<-xmpphost hostname>
511 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
512 specifies the host for the "to" attribute of the stream element.
513 If this option is not specified, then the host specified with "-connect"
516 =item B<-tlsextdebug>
518 Print out a hex dump of any TLS extensions received from the server.
522 Disable RFC4507bis session ticket support.
524 =item B<-sess_out filename>
526 Output SSL session to B<filename>.
528 =item B<-sess_in sess.pem>
530 Load SSL session from B<filename>. The client will attempt to resume a
531 connection from this session.
535 Specifying an engine (by its unique B<id> string) will cause B<s_client>
536 to attempt to obtain a functional reference to the specified engine,
537 thus initialising it if needed. The engine will then be set as the default
538 for all available algorithms.
540 =item B<-rand file...>
542 A file or files containing random data used to seed the random number
544 Multiple files can be specified separated by an OS-dependent character.
545 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
548 =item [B<-writerand file>]
550 Writes random data to the specified I<file> upon exit.
551 This can be used with a subsequent B<-rand> flag.
553 =item B<-serverinfo types>
555 A list of comma-separated TLS Extension Types (numbers between 0 and
556 65535). Each type will be sent as an empty ClientHello TLS Extension.
557 The server's response (if any) will be encoded and displayed as a PEM
562 Sends a certificate status request to the server (OCSP stapling). The server
563 response (if any) is printed out.
565 =item B<-alpn protocols>, B<-nextprotoneg protocols>
567 These flags enable the Enable the Application-Layer Protocol Negotiation
568 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
569 IETF standard and replaces NPN.
570 The B<protocols> list is a comma-separated list of protocol names that
571 the client should advertise support for. The list should contain the most
572 desirable protocols first. Protocol names are printable ASCII strings,
573 for example "http/1.1" or "spdy/3".
574 An empty list of protocols is treated specially and will cause the
575 client to advertise support for the TLS extension but disconnect just
576 after receiving ServerHello with a list of server supported protocols.
577 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
581 Use one of these two options to control whether Certificate Transparency (CT)
582 is enabled (B<-ct>) or disabled (B<-noct>).
583 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
584 the server and reported at handshake completion.
586 Enabling CT also enables OCSP stapling, as this is one possible delivery method
591 A file containing a list of known Certificate Transparency logs. See
592 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
594 =item B<-keylogfile file>
596 Appends TLS secrets to the specified keylog file such that external programs
597 (like Wireshark) can decrypt TLS connections.
599 =item B<-early_data file>
601 Reads the contents of the specified file and attempts to send it as early data
602 to the server. This will only work with resumed sessions that support early
603 data and when the server accepts the early data.
607 Rather than providing B<-connect>, the target hostname and optional port may
608 be provided as a single positional argument after all options. If neither this
609 nor B<-connect> are provided, falls back to attempting to connect to localhost
614 =head1 CONNECTED COMMANDS
616 If a connection is established with an SSL server then any data received
617 from the server is displayed and any key presses will be sent to the
618 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
619 have been given), the session will be renegotiated if the line begins with an
620 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
621 connection will be closed down.
625 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
628 openssl s_client -connect servername:443
630 would typically be used (https uses port 443). If the connection succeeds
631 then an HTTP command can be given such as "GET /" to retrieve a web page.
633 If the handshake fails then there are several possible causes, if it is
634 nothing obvious like no client certificate then the B<-bugs>,
635 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
636 in case it is a buggy server. In particular you should play with these
637 options B<before> submitting a bug report to an OpenSSL mailing list.
639 A frequent problem when attempting to get client certificates working
640 is that a web client complains it has no certificates or gives an empty
641 list to choose from. This is normally because the server is not sending
642 the clients certificate authority in its "acceptable CA list" when it
643 requests a certificate. By using B<s_client> the CA list can be viewed
644 and checked. However some servers only request client authentication
645 after a specific URL is requested. To obtain the list in this case it
646 is necessary to use the B<-prexit> option and send an HTTP request
647 for an appropriate page.
649 If a certificate is specified on the command line using the B<-cert>
650 option it will not be used unless the server specifically requests
651 a client certificate. Therefor merely including a client certificate
652 on the command line is no guarantee that the certificate works.
654 If there are problems verifying a server certificate then the
655 B<-showcerts> option can be used to show the whole chain.
657 The B<s_client> utility is a test tool and is designed to continue the
658 handshake after any certificate verification errors. As a result it will
659 accept any certificate chain (trusted or not) sent by the peer. None test
660 applications should B<not> do this as it makes them vulnerable to a MITM
661 attack. This behaviour can be changed by with the B<-verify_return_error>
662 option: any verify errors are then returned aborting the handshake.
666 Because this program has a lot of options and also because some of the
667 techniques used are rather old, the C source of B<s_client> is rather hard to
668 read and not a model of how things should be done.
669 A typical SSL client program would be much simpler.
671 The B<-prexit> option is a bit of a hack. We should really report
672 information whenever a session is renegotiated.
676 L<SSL_CONF_cmd(3)>, L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>,
677 L<SSL_CTX_set_max_send_fragment(3)>, L<SSL_CTX_set_split_send_fragment(3)>
678 L<SSL_CTX_set_max_pipelines(3)>
682 The -no_alt_chains options was first added to OpenSSL 1.1.0.
686 Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
688 Licensed under the OpenSSL license (the "License"). You may not use
689 this file except in compliance with the License. You can obtain a copy
690 in the file LICENSE in the source distribution or at
691 L<https://www.openssl.org/source/license.html>.