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<-sigalgs sigalglist>]
97 [B<-curves curvelist>]
98 [B<-cipher cipherlist>]
100 [B<-starttls protocol>]
101 [B<-xmpphost hostname>]
105 [B<-sess_out filename>]
106 [B<-sess_in filename>]
108 [B<-serverinfo types>]
111 [B<-nextprotoneg protocols>]
114 [B<-keylogfile file>]
115 [B<-early_data file>]
120 The B<s_client> command implements a generic SSL/TLS client which connects
121 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
126 In addition to the options below the B<s_client> utility also supports the
127 common and client only options documented in the
128 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
135 Print out a usage message.
137 =item B<-connect host:port>
139 This specifies the host and optional port to connect to. It is possible to
140 select the host and port using the optional target positional argument instead.
141 If neither this nor the target positonal argument are specified then an attempt
142 is made to connect to the local host on port 4433.
144 =item B<-proxy host:port>
146 When used with the B<-connect> flag, the program uses the host and port
147 specified with this flag and issues an HTTP CONNECT command to connect
148 to the desired server.
152 Connect over the specified Unix-domain socket.
162 =item B<-servername name>
164 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
165 the given value. If both this option and the B<-noservername> are not given, the
166 TLS SNI extension is still set to the hostname provided to the B<-connect> option,
167 or "localhost" if B<-connect> has not been supplied. This is default since OpenSSL
170 Even though SNI name should normally be a DNS name and not an IP address, this
171 option will not make the distinction when parsing B<-connect> and will send
172 IP address if one passed.
174 =item B<-noservername>
176 Suppresses sending of the SNI (Server Name Indication) extension in the
177 ClientHello message. Cannot be used in conjunction with the B<-servername> or
178 <-dane_tlsa_domain> options.
180 =item B<-cert certname>
182 The certificate to use, if one is requested by the server. The default is
183 not to use a certificate.
185 =item B<-certform format>
187 The certificate format to use: DER or PEM. PEM is the default.
189 =item B<-key keyfile>
191 The private key to use. If not specified then the certificate file will
194 =item B<-keyform format>
196 The private format to use: DER or PEM. PEM is the default.
200 the private key password source. For more information about the format of B<arg>
201 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
203 =item B<-verify depth>
205 The verify depth to use. This specifies the maximum length of the
206 server certificate chain and turns on server certificate verification.
207 Currently the verify operation continues after errors so all the problems
208 with a certificate chain can be seen. As a side effect the connection
209 will never fail due to a server certificate verify failure.
211 =item B<-verify_return_error>
213 Return verification errors instead of continuing. This will typically
214 abort the handshake with a fatal error.
216 =item B<-nameopt option>
218 Option which determines how the subject or issuer names are displayed. The
219 B<option> argument can be a single option or multiple options separated by
220 commas. Alternatively the B<-nameopt> switch may be used more than once to
221 set multiple options. See the L<x509(1)> manual page for details.
223 =item B<-CApath directory>
225 The directory to use for server certificate verification. This directory
226 must be in "hash format", see B<verify> for more information. These are
227 also used when building the client certificate chain.
229 =item B<-CAfile file>
231 A file containing trusted certificates to use during server authentication
232 and to use when attempting to build the client certificate chain.
236 Do not load the trusted CA certificates from the default file location
240 Do not load the trusted CA certificates from the default directory location
242 =item B<-requestCAfile file>
244 A file containing a list of certificates whose subject names will be sent
245 to the server in the B<certificate_authorities> extension. Only supported
248 =item B<-dane_tlsa_domain domain>
250 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
251 TLSA base domain which becomes the default SNI hint and the primary
252 reference identifier for hostname checks. This must be used in
253 combination with at least one instance of the B<-dane_tlsa_rrdata>
256 When DANE authentication succeeds, the diagnostic output will include
257 the lowest (closest to 0) depth at which a TLSA record authenticated
258 a chain certificate. When that TLSA record is a "2 1 0" trust
259 anchor public key that signed (rather than matched) the top-most
260 certificate of the chain, the result is reported as "TA public key
261 verified". Otherwise, either the TLSA record "matched TA certificate"
262 at a positive depth or else "matched EE certificate" at depth 0.
264 =item B<-dane_tlsa_rrdata rrdata>
266 Use one or more times to specify the RRDATA fields of the DANE TLSA
267 RRset associated with the target service. The B<rrdata> value is
268 specied in "presentation form", that is four whitespace separated
269 fields that specify the usage, selector, matching type and associated
270 data, with the last of these encoded in hexadecimal. Optional
271 whitespace is ignored in the associated data field. For example:
273 $ openssl s_client -brief -starttls smtp \
274 -connect smtp.example.com:25 \
275 -dane_tlsa_domain smtp.example.com \
276 -dane_tlsa_rrdata "2 1 1
277 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
278 -dane_tlsa_rrdata "2 1 1
279 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
282 Verified peername: smtp.example.com
283 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
286 =item B<-dane_ee_no_namechecks>
288 This disables server name checks when authenticating via DANE-EE(3) TLSA
290 For some applications, primarily web browsers, it is not safe to disable name
291 checks due to "unknown key share" attacks, in which a malicious server can
292 convince a client that a connection to a victim server is instead a secure
293 connection to the malicious server.
294 The malicious server may then be able to violate cross-origin scripting
296 Thus, despite the text of RFC7671, name checks are by default enabled for
297 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
299 In particular, SMTP and XMPP clients should set this option as SRV and MX
300 records already make it possible for a remote domain to redirect client
301 connections to any server of its choice, and in any case SMTP and XMPP clients
302 do not execute scripts downloaded from remote servers.
304 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
305 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
306 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
307 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
308 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
309 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
310 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
312 Set various certificate chain validation options. See the
313 L<verify(1)> manual page for details.
317 Reconnects to the same server 5 times using the same session ID, this can
318 be used as a test that session caching is working.
322 Display the whole server certificate chain: normally only the server
323 certificate itself is displayed.
327 Print session information when the program exits. This will always attempt
328 to print out information even if the connection fails. Normally information
329 will only be printed out once if the connection succeeds. This option is useful
330 because the cipher in use may be renegotiated or the connection may fail
331 because a client certificate is required or is requested only after an
332 attempt is made to access a certain URL. Note: the output produced by this
333 option is not always accurate because a connection might never have been
338 Prints out the SSL session states.
342 Print extensive debugging information including a hex dump of all traffic.
346 Show all protocol messages with hex dump.
350 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
351 with B<enable-ssl-trace> for this option to work.
355 File to send output of B<-msg> or B<-trace> to, default standard output.
359 Tests non-blocking I/O
363 Turns on non-blocking I/O
367 This option translated a line feed from the terminal into CR+LF as required
372 Inhibit shutting down the connection when end of file is reached in the
377 Inhibit printing of session and certificate information. This implicitly
378 turns on B<-ign_eof> as well.
382 Shut down the connection when end of file is reached in the input.
383 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
385 =item B<-psk_identity identity>
387 Use the PSK identity B<identity> when using a PSK cipher suite.
388 The default value is "Client_identity" (without the quotes).
392 Use the PSK key B<key> when using a PSK cipher suite. The key is
393 given as a hexadecimal number without leading 0x, for example -psk
395 This option must be provided in order to use a PSK cipher.
397 =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>
399 These options require or disable the use of the specified SSL or TLS protocols.
400 By default B<s_client> will negotiate the highest mutually supported protocol
402 When a specific TLS version is required, only that version will be offered to
403 and accepted from the server.
405 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
407 These options make B<s_client> use DTLS protocols instead of TLS.
408 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
409 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
414 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
415 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
416 available where OpenSSL has support for SCTP enabled.
418 =item B<-fallback_scsv>
420 Send TLS_FALLBACK_SCSV in the ClientHello.
424 Switch on asynchronous mode. Cryptographic operations will be performed
425 asynchronously. This will only have an effect if an asynchronous capable engine
426 is also used via the B<-engine> option. For test purposes the dummy async engine
427 (dasync) can be used (if available).
429 =item B<-max_send_frag int>
431 The maximum size of data fragment to send.
432 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
434 =item B<-split_send_frag int>
436 The size used to split data for encrypt pipelines. If more data is written in
437 one go than this value then it will be split into multiple pipelines, up to the
438 maximum number of pipelines defined by max_pipelines. This only has an effect if
439 a suitable cipher suite has been negotiated, an engine that supports pipelining
440 has been loaded, and max_pipelines is greater than 1. See
441 L<SSL_CTX_set_split_send_fragment(3)> for further information.
443 =item B<-max_pipelines int>
445 The maximum number of encrypt/decrypt pipelines to be used. This will only have
446 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
447 engine) and a suitable cipher suite has been negotiated. The default value is 1.
448 See L<SSL_CTX_set_max_pipelines(3)> for further information.
450 =item B<-read_buf int>
452 The default read buffer size to be used for connections. This will only have an
453 effect if the buffer size is larger than the size that would otherwise be used
454 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
455 further information).
459 There are several known bug in SSL and TLS implementations. Adding this
460 option enables various workarounds.
464 Enables support for SSL/TLS compression.
465 This option was introduced in OpenSSL 1.1.0.
466 TLS compression is not recommended and is off by default as of
471 Disables support for SSL/TLS compression.
472 TLS compression is not recommended and is off by default as of
477 Only provide a brief summary of connection parameters instead of the
478 normal verbose output.
480 =item B<-sigalgs sigalglist>
482 Specifies the list of signature algorithms that are sent by the client.
483 The server selects one entry in the list based on its preferences.
484 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
486 =item B<-curves curvelist>
488 Specifies the list of supported curves to be sent by the client. The curve is
489 is ultimately selected by the server. For a list of all curves, use:
491 $ openssl ecparam -list_curves
493 =item B<-cipher cipherlist>
495 This allows the cipher list sent by the client to be modified. Although
496 the server determines which cipher suite is used it should take the first
497 supported cipher in the list sent by the client. See the B<ciphers>
498 command for more information.
500 =item B<-starttls protocol>
502 Send the protocol-specific message(s) to switch to TLS for communication.
503 B<protocol> is a keyword for the intended protocol. Currently, the only
504 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
505 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
507 =item B<-xmpphost hostname>
509 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
510 specifies the host for the "to" attribute of the stream element.
511 If this option is not specified, then the host specified with "-connect"
514 =item B<-tlsextdebug>
516 Print out a hex dump of any TLS extensions received from the server.
520 Disable RFC4507bis session ticket support.
522 =item B<-sess_out filename>
524 Output SSL session to B<filename>.
526 =item B<-sess_in sess.pem>
528 Load SSL session from B<filename>. The client will attempt to resume a
529 connection from this session.
533 Specifying an engine (by its unique B<id> string) will cause B<s_client>
534 to attempt to obtain a functional reference to the specified engine,
535 thus initialising it if needed. The engine will then be set as the default
536 for all available algorithms.
538 =item B<-rand file(s)>
540 A file or files containing random data used to seed the random number
541 generator, or an EGD socket (see L<RAND_egd(3)>).
542 Multiple files can be specified separated by an OS-dependent character.
543 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
546 =item B<-serverinfo types>
548 A list of comma-separated TLS Extension Types (numbers between 0 and
549 65535). Each type will be sent as an empty ClientHello TLS Extension.
550 The server's response (if any) will be encoded and displayed as a PEM
555 Sends a certificate status request to the server (OCSP stapling). The server
556 response (if any) is printed out.
558 =item B<-alpn protocols>, B<-nextprotoneg protocols>
560 These flags enable the Enable the Application-Layer Protocol Negotiation
561 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
562 IETF standard and replaces NPN.
563 The B<protocols> list is a comma-separated list of protocol names that
564 the client should advertise support for. The list should contain the most
565 desirable protocols first. Protocol names are printable ASCII strings,
566 for example "http/1.1" or "spdy/3".
567 An empty list of protocols is treated specially and will cause the
568 client to advertise support for the TLS extension but disconnect just
569 after receiving ServerHello with a list of server supported protocols.
570 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
574 Use one of these two options to control whether Certificate Transparency (CT)
575 is enabled (B<-ct>) or disabled (B<-noct>).
576 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
577 the server and reported at handshake completion.
579 Enabling CT also enables OCSP stapling, as this is one possible delivery method
584 A file containing a list of known Certificate Transparency logs. See
585 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
587 =item B<-keylogfile file>
589 Appends TLS secrets to the specified keylog file such that external programs
590 (like Wireshark) can decrypt TLS connections.
592 =item B<-early_data file>
594 Reads the contents of the specified file and attempts to send it as early data
595 to the server. This will only work with resumed sessions that support early
596 data and when the server accepts the early data.
600 Rather than providing B<-connect>, the target hostname and optional port may
601 be provided as a single positional argument after all options. If neither this
602 nor B<-connect> are provided, falls back to attempting to connect to localhost
607 =head1 CONNECTED COMMANDS
609 If a connection is established with an SSL server then any data received
610 from the server is displayed and any key presses will be sent to the
611 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
612 have been given), the session will be renegotiated if the line begins with an
613 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
614 connection will be closed down.
618 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
621 openssl s_client -connect servername:443
623 would typically be used (https uses port 443). If the connection succeeds
624 then an HTTP command can be given such as "GET /" to retrieve a web page.
626 If the handshake fails then there are several possible causes, if it is
627 nothing obvious like no client certificate then the B<-bugs>,
628 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
629 in case it is a buggy server. In particular you should play with these
630 options B<before> submitting a bug report to an OpenSSL mailing list.
632 A frequent problem when attempting to get client certificates working
633 is that a web client complains it has no certificates or gives an empty
634 list to choose from. This is normally because the server is not sending
635 the clients certificate authority in its "acceptable CA list" when it
636 requests a certificate. By using B<s_client> the CA list can be viewed
637 and checked. However some servers only request client authentication
638 after a specific URL is requested. To obtain the list in this case it
639 is necessary to use the B<-prexit> option and send an HTTP request
640 for an appropriate page.
642 If a certificate is specified on the command line using the B<-cert>
643 option it will not be used unless the server specifically requests
644 a client certificate. Therefor merely including a client certificate
645 on the command line is no guarantee that the certificate works.
647 If there are problems verifying a server certificate then the
648 B<-showcerts> option can be used to show the whole chain.
650 The B<s_client> utility is a test tool and is designed to continue the
651 handshake after any certificate verification errors. As a result it will
652 accept any certificate chain (trusted or not) sent by the peer. None test
653 applications should B<not> do this as it makes them vulnerable to a MITM
654 attack. This behaviour can be changed by with the B<-verify_return_error>
655 option: any verify errors are then returned aborting the handshake.
659 Because this program has a lot of options and also because some of the
660 techniques used are rather old, the C source of B<s_client> is rather hard to
661 read and not a model of how things should be done.
662 A typical SSL client program would be much simpler.
664 The B<-prexit> option is a bit of a hack. We should really report
665 information whenever a session is renegotiated.
669 L<SSL_CONF_cmd(3)>, L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>,
670 L<SSL_CTX_set_max_send_fragment(3)>, L<SSL_CTX_set_split_send_fragment(3)>
671 L<SSL_CTX_set_max_pipelines(3)>
675 The -no_alt_chains options was first added to OpenSSL 1.1.0.
679 Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
681 Licensed under the OpenSSL license (the "License"). You may not use
682 this file except in compliance with the License. You can obtain a copy
683 in the file LICENSE in the source distribution or at
684 L<https://www.openssl.org/source/license.html>.