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>]
117 [B<-keylogfile file>]
118 [B<-early_data file>]
123 The B<s_client> command implements a generic SSL/TLS client which connects
124 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
129 In addition to the options below the B<s_client> utility also supports the
130 common and client only options documented in the
131 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
138 Print out a usage message.
140 =item B<-connect host:port>
142 This specifies the host and optional port to connect to. It is possible to
143 select the host and port using the optional target positional argument instead.
144 If neither this nor the target positonal argument are specified then an attempt
145 is made to connect to the local host on port 4433.
147 =item B<-proxy host:port>
149 When used with the B<-connect> flag, the program uses the host and port
150 specified with this flag and issues an HTTP CONNECT command to connect
151 to the desired server.
155 Connect over the specified Unix-domain socket.
165 =item B<-servername name>
167 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
168 the given value. If both this option and the B<-noservername> are not given, the
169 TLS SNI extension is still set to the hostname provided to the B<-connect> option,
170 or "localhost" if B<-connect> has not been supplied. This is default since OpenSSL
173 Even though SNI name should normally be a DNS name and not an IP address, this
174 option will not make the distinction when parsing B<-connect> and will send
175 IP address if one passed.
177 =item B<-noservername>
179 Suppresses sending of the SNI (Server Name Indication) extension in the
180 ClientHello message. Cannot be used in conjunction with the B<-servername> or
181 <-dane_tlsa_domain> options.
183 =item B<-cert certname>
185 The certificate to use, if one is requested by the server. The default is
186 not to use a certificate.
188 =item B<-certform format>
190 The certificate format to use: DER or PEM. PEM is the default.
192 =item B<-key keyfile>
194 The private key to use. If not specified then the certificate file will
197 =item B<-keyform format>
199 The private format to use: DER or PEM. PEM is the default.
203 the private key password source. For more information about the format of B<arg>
204 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
206 =item B<-verify depth>
208 The verify depth to use. This specifies the maximum length of the
209 server certificate chain and turns on server certificate verification.
210 Currently the verify operation continues after errors so all the problems
211 with a certificate chain can be seen. As a side effect the connection
212 will never fail due to a server certificate verify failure.
214 =item B<-verify_return_error>
216 Return verification errors instead of continuing. This will typically
217 abort the handshake with a fatal error.
219 =item B<-nameopt option>
221 Option which determines how the subject or issuer names are displayed. The
222 B<option> argument can be a single option or multiple options separated by
223 commas. Alternatively the B<-nameopt> switch may be used more than once to
224 set multiple options. See the L<x509(1)> manual page for details.
226 =item B<-CApath directory>
228 The directory to use for server certificate verification. This directory
229 must be in "hash format", see B<verify> for more information. These are
230 also used when building the client certificate chain.
232 =item B<-CAfile file>
234 A file containing trusted certificates to use during server authentication
235 and to use when attempting to build the client certificate chain.
239 Do not load the trusted CA certificates from the default file location
243 Do not load the trusted CA certificates from the default directory location
245 =item B<-requestCAfile file>
247 A file containing a list of certificates whose subject names will be sent
248 to the server in the B<certificate_authorities> extension. Only supported
251 =item B<-dane_tlsa_domain domain>
253 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
254 TLSA base domain which becomes the default SNI hint and the primary
255 reference identifier for hostname checks. This must be used in
256 combination with at least one instance of the B<-dane_tlsa_rrdata>
259 When DANE authentication succeeds, the diagnostic output will include
260 the lowest (closest to 0) depth at which a TLSA record authenticated
261 a chain certificate. When that TLSA record is a "2 1 0" trust
262 anchor public key that signed (rather than matched) the top-most
263 certificate of the chain, the result is reported as "TA public key
264 verified". Otherwise, either the TLSA record "matched TA certificate"
265 at a positive depth or else "matched EE certificate" at depth 0.
267 =item B<-dane_tlsa_rrdata rrdata>
269 Use one or more times to specify the RRDATA fields of the DANE TLSA
270 RRset associated with the target service. The B<rrdata> value is
271 specied in "presentation form", that is four whitespace separated
272 fields that specify the usage, selector, matching type and associated
273 data, with the last of these encoded in hexadecimal. Optional
274 whitespace is ignored in the associated data field. For example:
276 $ openssl s_client -brief -starttls smtp \
277 -connect smtp.example.com:25 \
278 -dane_tlsa_domain smtp.example.com \
279 -dane_tlsa_rrdata "2 1 1
280 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
281 -dane_tlsa_rrdata "2 1 1
282 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
285 Verified peername: smtp.example.com
286 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
289 =item B<-dane_ee_no_namechecks>
291 This disables server name checks when authenticating via DANE-EE(3) TLSA
293 For some applications, primarily web browsers, it is not safe to disable name
294 checks due to "unknown key share" attacks, in which a malicious server can
295 convince a client that a connection to a victim server is instead a secure
296 connection to the malicious server.
297 The malicious server may then be able to violate cross-origin scripting
299 Thus, despite the text of RFC7671, name checks are by default enabled for
300 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
302 In particular, SMTP and XMPP clients should set this option as SRV and MX
303 records already make it possible for a remote domain to redirect client
304 connections to any server of its choice, and in any case SMTP and XMPP clients
305 do not execute scripts downloaded from remote servers.
307 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
308 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
309 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
310 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
311 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
312 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
313 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
315 Set various certificate chain validation options. See the
316 L<verify(1)> manual page for details.
320 Reconnects to the same server 5 times using the same session ID, this can
321 be used as a test that session caching is working.
325 Display the whole server certificate chain: normally only the server
326 certificate itself is displayed.
330 Print session information when the program exits. This will always attempt
331 to print out information even if the connection fails. Normally information
332 will only be printed out once if the connection succeeds. This option is useful
333 because the cipher in use may be renegotiated or the connection may fail
334 because a client certificate is required or is requested only after an
335 attempt is made to access a certain URL. Note: the output produced by this
336 option is not always accurate because a connection might never have been
341 Prints out the SSL session states.
345 Print extensive debugging information including a hex dump of all traffic.
349 Show all protocol messages with hex dump.
353 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
354 with B<enable-ssl-trace> for this option to work.
358 File to send output of B<-msg> or B<-trace> to, default standard output.
362 Tests non-blocking I/O
366 Turns on non-blocking I/O
370 This option translated a line feed from the terminal into CR+LF as required
375 Inhibit shutting down the connection when end of file is reached in the
380 Inhibit printing of session and certificate information. This implicitly
381 turns on B<-ign_eof> as well.
385 Shut down the connection when end of file is reached in the input.
386 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
388 =item B<-psk_identity identity>
390 Use the PSK identity B<identity> when using a PSK cipher suite.
391 The default value is "Client_identity" (without the quotes).
395 Use the PSK key B<key> when using a PSK cipher suite. The key is
396 given as a hexadecimal number without leading 0x, for example -psk
398 This option must be provided in order to use a PSK cipher.
400 =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>
402 These options require or disable the use of the specified SSL or TLS protocols.
403 By default B<s_client> will negotiate the highest mutually supported protocol
405 When a specific TLS version is required, only that version will be offered to
406 and accepted from the server.
408 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
410 These options make B<s_client> use DTLS protocols instead of TLS.
411 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
412 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
417 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
418 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
419 available where OpenSSL has support for SCTP enabled.
421 =item B<-fallback_scsv>
423 Send TLS_FALLBACK_SCSV in the ClientHello.
427 Switch on asynchronous mode. Cryptographic operations will be performed
428 asynchronously. This will only have an effect if an asynchronous capable engine
429 is also used via the B<-engine> option. For test purposes the dummy async engine
430 (dasync) can be used (if available).
432 =item B<-max_send_frag int>
434 The maximum size of data fragment to send.
435 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
437 =item B<-split_send_frag int>
439 The size used to split data for encrypt pipelines. If more data is written in
440 one go than this value then it will be split into multiple pipelines, up to the
441 maximum number of pipelines defined by max_pipelines. This only has an effect if
442 a suitable cipher suite has been negotiated, an engine that supports pipelining
443 has been loaded, and max_pipelines is greater than 1. See
444 L<SSL_CTX_set_split_send_fragment(3)> for further information.
446 =item B<-max_pipelines int>
448 The maximum number of encrypt/decrypt pipelines to be used. This will only have
449 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
450 engine) and a suitable cipher suite has been negotiated. The default value is 1.
451 See L<SSL_CTX_set_max_pipelines(3)> for further information.
453 =item B<-read_buf int>
455 The default read buffer size to be used for connections. This will only have an
456 effect if the buffer size is larger than the size that would otherwise be used
457 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
458 further information).
462 There are several known bug in SSL and TLS implementations. Adding this
463 option enables various workarounds.
467 Enables support for SSL/TLS compression.
468 This option was introduced in OpenSSL 1.1.0.
469 TLS compression is not recommended and is off by default as of
474 Disables support for SSL/TLS compression.
475 TLS compression is not recommended and is off by default as of
480 Only provide a brief summary of connection parameters instead of the
481 normal verbose output.
483 =item B<-sigalgs sigalglist>
485 Specifies the list of signature algorithms that are sent by the client.
486 The server selects one entry in the list based on its preferences.
487 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
489 =item B<-curves curvelist>
491 Specifies the list of supported curves to be sent by the client. The curve is
492 is ultimately selected by the server. For a list of all curves, use:
494 $ openssl ecparam -list_curves
496 =item B<-cipher cipherlist>
498 This allows the cipher list sent by the client to be modified. Although
499 the server determines which cipher suite is used it should take the first
500 supported cipher in the list sent by the client. See the B<ciphers>
501 command for more information.
503 =item B<-starttls protocol>
505 Send the protocol-specific message(s) to switch to TLS for communication.
506 B<protocol> is a keyword for the intended protocol. Currently, the only
507 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
508 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
510 =item B<-xmpphost hostname>
512 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
513 specifies the host for the "to" attribute of the stream element.
514 If this option is not specified, then the host specified with "-connect"
517 =item B<-tlsextdebug>
519 Print out a hex dump of any TLS extensions received from the server.
523 Disable RFC4507bis session ticket support.
525 =item B<-sess_out filename>
527 Output SSL session to B<filename>.
529 =item B<-sess_in sess.pem>
531 Load SSL session from B<filename>. The client will attempt to resume a
532 connection from this session.
536 Specifying an engine (by its unique B<id> string) will cause B<s_client>
537 to attempt to obtain a functional reference to the specified engine,
538 thus initialising it if needed. The engine will then be set as the default
539 for all available algorithms.
541 =item B<-rand file...>
543 A file or files containing random data used to seed the random number
545 Multiple files can be specified separated by an OS-dependent character.
546 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
549 =item [B<-writerand file>]
551 Writes random data to the specified I<file> upon exit.
552 This can be used with a subsequent B<-rand> flag.
554 =item B<-serverinfo types>
556 A list of comma-separated TLS Extension Types (numbers between 0 and
557 65535). Each type will be sent as an empty ClientHello TLS Extension.
558 The server's response (if any) will be encoded and displayed as a PEM
563 Sends a certificate status request to the server (OCSP stapling). The server
564 response (if any) is printed out.
566 =item B<-alpn protocols>, B<-nextprotoneg protocols>
568 These flags enable the Enable the Application-Layer Protocol Negotiation
569 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
570 IETF standard and replaces NPN.
571 The B<protocols> list is a comma-separated list of protocol names that
572 the client should advertise support for. The list should contain the most
573 desirable protocols first. Protocol names are printable ASCII strings,
574 for example "http/1.1" or "spdy/3".
575 An empty list of protocols is treated specially and will cause the
576 client to advertise support for the TLS extension but disconnect just
577 after receiving ServerHello with a list of server supported protocols.
578 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
580 =item B<-ct>, B<-noct>
582 Use one of these two options to control whether Certificate Transparency (CT)
583 is enabled (B<-ct>) or disabled (B<-noct>).
584 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
585 the server and reported at handshake completion.
587 Enabling CT also enables OCSP stapling, as this is one possible delivery method
592 A file containing a list of known Certificate Transparency logs. See
593 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
595 =item B<-keylogfile file>
597 Appends TLS secrets to the specified keylog file such that external programs
598 (like Wireshark) can decrypt TLS connections.
600 =item B<-early_data file>
602 Reads the contents of the specified file and attempts to send it as early data
603 to the server. This will only work with resumed sessions that support early
604 data and when the server accepts the early data.
608 Rather than providing B<-connect>, the target hostname and optional port may
609 be provided as a single positional argument after all options. If neither this
610 nor B<-connect> are provided, falls back to attempting to connect to localhost
615 =head1 CONNECTED COMMANDS
617 If a connection is established with an SSL server then any data received
618 from the server is displayed and any key presses will be sent to the
619 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
620 have been given), the session will be renegotiated if the line begins with an
621 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
622 connection will be closed down.
626 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
629 openssl s_client -connect servername:443
631 would typically be used (https uses port 443). If the connection succeeds
632 then an HTTP command can be given such as "GET /" to retrieve a web page.
634 If the handshake fails then there are several possible causes, if it is
635 nothing obvious like no client certificate then the B<-bugs>,
636 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
637 in case it is a buggy server. In particular you should play with these
638 options B<before> submitting a bug report to an OpenSSL mailing list.
640 A frequent problem when attempting to get client certificates working
641 is that a web client complains it has no certificates or gives an empty
642 list to choose from. This is normally because the server is not sending
643 the clients certificate authority in its "acceptable CA list" when it
644 requests a certificate. By using B<s_client> the CA list can be viewed
645 and checked. However some servers only request client authentication
646 after a specific URL is requested. To obtain the list in this case it
647 is necessary to use the B<-prexit> option and send an HTTP request
648 for an appropriate page.
650 If a certificate is specified on the command line using the B<-cert>
651 option it will not be used unless the server specifically requests
652 a client certificate. Therefor merely including a client certificate
653 on the command line is no guarantee that the certificate works.
655 If there are problems verifying a server certificate then the
656 B<-showcerts> option can be used to show the whole chain.
658 The B<s_client> utility is a test tool and is designed to continue the
659 handshake after any certificate verification errors. As a result it will
660 accept any certificate chain (trusted or not) sent by the peer. None test
661 applications should B<not> do this as it makes them vulnerable to a MITM
662 attack. This behaviour can be changed by with the B<-verify_return_error>
663 option: any verify errors are then returned aborting the handshake.
667 Because this program has a lot of options and also because some of the
668 techniques used are rather old, the C source of B<s_client> is rather hard to
669 read and not a model of how things should be done.
670 A typical SSL client program would be much simpler.
672 The B<-prexit> option is a bit of a hack. We should really report
673 information whenever a session is renegotiated.
677 L<SSL_CONF_cmd(3)>, L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>,
678 L<SSL_CTX_set_max_send_fragment(3)>, L<SSL_CTX_set_split_send_fragment(3)>
679 L<SSL_CTX_set_max_pipelines(3)>
683 The -no_alt_chains options was first added to OpenSSL 1.1.0.
687 Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
689 Licensed under the OpenSSL license (the "License"). You may not use
690 this file except in compliance with the License. You can obtain a copy
691 in the file LICENSE in the source distribution or at
692 L<https://www.openssl.org/source/license.html>.