2 {- OpenSSL::safe::output_do_not_edit_headers(); -}
6 openssl-s_client - SSL/TLS client program
10 B<openssl> B<s_client>
12 [B<-connect> I<host:port>]
13 [B<-bind> I<host:port>]
14 [B<-proxy> I<host:port>]
15 [B<-proxy_user> I<userid>]
16 [B<-proxy_pass> I<arg>]
20 [B<-servername> I<name>]
23 [B<-verify_return_error>]
24 [B<-cert> I<filename>]
25 [B<-certform> B<DER>|B<PEM>]
26 [B<-CRLform> B<DER>|B<PEM>]
28 [B<-keyform> B<DER>|B<PEM>]
29 [B<-cert_chain> I<filename>]
32 [B<-chainCApath> I<directory>]
33 [B<-chainCAfile> I<filename>]
34 [B<-chainCAstore> I<uri>]
35 [B<-requestCAfile> I<filename>]
36 [B<-dane_tlsa_domain> I<domain>]
37 [B<-dane_tlsa_rrdata> I<rrdata>]
38 [B<-dane_ee_no_namechecks>]
39 [B<-attime> I<timestamp>]
53 [B<-purpose> I<purpose>]
60 [B<-auth_level> I<num>]
61 [B<-verify_depth> I<num>]
62 [B<-verify_email> I<email>]
63 [B<-verify_hostname> I<hostname>]
65 [B<-verify_name> I<name>]
78 [B<-psk_identity> I<identity>]
80 [B<-psk_session> I<file>]
93 [B<-allow_no_dhe_kex>]
94 [B<-sigalgs> I<sigalglist>]
95 [B<-curves> I<curvelist>]
96 [B<-cipher> I<cipherlist>]
97 [B<-ciphersuites> I<val>]
99 [B<-starttls> I<protocol>]
100 [B<-xmpphost> I<hostname>]
101 [B<-name> I<hostname>]
104 [B<-sess_out> I<filename>]
105 [B<-sess_in> I<filename>]
106 [B<-serverinfo> I<types>]
108 [B<-alpn> I<protocols>]
109 [B<-nextprotoneg> I<protocols>]
113 [B<-keylogfile> I<file>]
114 [B<-early_data> I<file>]
116 {- $OpenSSL::safe::opt_name_synopsis -}
117 {- $OpenSSL::safe::opt_version_synopsis -}
118 {- $OpenSSL::safe::opt_x_synopsis -}
119 {- $OpenSSL::safe::opt_trust_synopsis -}
120 {- $OpenSSL::safe::opt_r_synopsis -}
121 {- $OpenSSL::safe::opt_engine_synopsis -}
124 =for openssl ifdef engine ssl_client_engine ct noct ctlogfile
126 =for openssl ifdef ssl3 unix 4 6 use_srtp status trace wdebug nextprotoneg
128 =for openssl ifdef ssl3 tls1 tls1_1 tls1_2 tls1_3 dtls mtu dtls1 dtls1_2
130 =for openssl ifdef sctp_label_bug sctp
132 =for openssl ifdef srpuser srppass srp_lateuser srp_moregroups srp_strength
136 This command implements a generic SSL/TLS client which
137 connects to a remote host using SSL/TLS. It is a I<very> useful diagnostic
138 tool for SSL servers.
142 In addition to the options below, this command also supports the
143 common and client only options documented
144 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
151 Print out a usage message.
153 =item B<-connect> I<host>:I<port>
155 This specifies the host and optional port to connect to. It is possible to
156 select the host and port using the optional target positional argument instead.
157 If neither this nor the target positional argument are specified then an attempt
158 is made to connect to the local host on port 4433.
160 =item B<-bind> I<host:port>
162 This specifies the host address and or port to bind as the source for the
163 connection. For Unix-domain sockets the port is ignored and the host is
164 used as the source socket address.
166 =item B<-proxy> I<host:port>
168 When used with the B<-connect> flag, the program uses the host and port
169 specified with this flag and issues an HTTP CONNECT command to connect
170 to the desired server.
172 =item B<-proxy_user> I<userid>
174 When used with the B<-proxy> flag, the program will attempt to authenticate
175 with the specified proxy using basic (base64) authentication.
176 NB: Basic authentication is insecure; the credentials are sent to the proxy
177 in easily reversible base64 encoding before any TLS/SSL session is established.
178 Therefore these credentials are easily recovered by anyone able to sniff/trace
179 the network. Use with caution.
181 =item B<-proxy_pass> I<arg>
183 The proxy password source, used with the B<-proxy_user> flag.
184 For more information about the format of B<arg>
185 see L<openssl(1)/Pass Phrase Options>.
187 =item B<-unix> I<path>
189 Connect over the specified Unix-domain socket.
199 =item B<-servername> I<name>
201 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
203 If B<-servername> is not provided, the TLS SNI extension will be populated with
204 the name given to B<-connect> if it follows a DNS name format. If B<-connect> is
205 not provided either, the SNI is set to "localhost".
206 This is the default since OpenSSL 1.1.1.
208 Even though SNI should normally be a DNS name and not an IP address, if
209 B<-servername> is provided then that name will be sent, regardless of whether
210 it is a DNS name or not.
212 This option cannot be used in conjunction with B<-noservername>.
214 =item B<-noservername>
216 Suppresses sending of the SNI (Server Name Indication) extension in the
217 ClientHello message. Cannot be used in conjunction with the B<-servername> or
218 <-dane_tlsa_domain> options.
220 =item B<-cert> I<certname>
222 The certificate to use, if one is requested by the server. The default is
223 not to use a certificate.
225 =item B<-certform> I<format>
227 The certificate format to use: DER or PEM. PEM is the default.
229 =item B<-CRLform> B<DER>|B<PEM>
231 The CRL format; the default is B<PEM>.
232 See L<openssl(1)/Format Options> for details.
234 =item B<-key> I<keyfile>
236 The private key to use. If not specified then the certificate file will
239 =item B<-keyform> I<format>
241 The key format; the default is B<PEM>.
242 See L<openssl(1)/Format Options> for details.
246 A file containing trusted certificates to use when attempting to build the
247 client/server certificate chain related to the certificate specified via the
250 =item B<-build_chain>
252 Specify whether the application should build the certificate chain to be
253 provided to the server.
255 =item B<-pass> I<arg>
257 the private key password source. For more information about the format of I<arg>
258 see L<openssl(1)/Pass phrase options>.
260 =item B<-verify> I<depth>
262 The verify depth to use. This specifies the maximum length of the
263 server certificate chain and turns on server certificate verification.
264 Currently the verify operation continues after errors so all the problems
265 with a certificate chain can be seen. As a side effect the connection
266 will never fail due to a server certificate verify failure.
268 =item B<-verify_return_error>
270 Return verification errors instead of continuing. This will typically
271 abort the handshake with a fatal error.
273 =item B<-chainCApath> I<directory>
275 The directory to use for building the chain provided to the server. This
276 directory must be in "hash format", see L<openssl-verify(1)> for more
279 =item B<-chainCAfile> I<file>
281 A file containing trusted certificates to use when attempting to build the
282 client certificate chain.
284 =item B<-chainCAstore> I<uri>
286 The URI to use when attempting to build the client certificate chain.
288 =item B<-requestCAfile> I<file>
290 A file containing a list of certificates whose subject names will be sent
291 to the server in the B<certificate_authorities> extension. Only supported
294 =item B<-dane_tlsa_domain> I<domain>
296 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
297 TLSA base domain which becomes the default SNI hint and the primary
298 reference identifier for hostname checks. This must be used in
299 combination with at least one instance of the B<-dane_tlsa_rrdata>
302 When DANE authentication succeeds, the diagnostic output will include
303 the lowest (closest to 0) depth at which a TLSA record authenticated
304 a chain certificate. When that TLSA record is a "2 1 0" trust
305 anchor public key that signed (rather than matched) the top-most
306 certificate of the chain, the result is reported as "TA public key
307 verified". Otherwise, either the TLSA record "matched TA certificate"
308 at a positive depth or else "matched EE certificate" at depth 0.
310 =item B<-dane_tlsa_rrdata> I<rrdata>
312 Use one or more times to specify the RRDATA fields of the DANE TLSA
313 RRset associated with the target service. The I<rrdata> value is
314 specied in "presentation form", that is four whitespace separated
315 fields that specify the usage, selector, matching type and associated
316 data, with the last of these encoded in hexadecimal. Optional
317 whitespace is ignored in the associated data field. For example:
319 $ openssl s_client -brief -starttls smtp \
320 -connect smtp.example.com:25 \
321 -dane_tlsa_domain smtp.example.com \
322 -dane_tlsa_rrdata "2 1 1
323 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
324 -dane_tlsa_rrdata "2 1 1
325 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
328 Verified peername: smtp.example.com
329 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
332 =item B<-dane_ee_no_namechecks>
334 This disables server name checks when authenticating via DANE-EE(3) TLSA
336 For some applications, primarily web browsers, it is not safe to disable name
337 checks due to "unknown key share" attacks, in which a malicious server can
338 convince a client that a connection to a victim server is instead a secure
339 connection to the malicious server.
340 The malicious server may then be able to violate cross-origin scripting
342 Thus, despite the text of RFC7671, name checks are by default enabled for
343 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
345 In particular, SMTP and XMPP clients should set this option as SRV and MX
346 records already make it possible for a remote domain to redirect client
347 connections to any server of its choice, and in any case SMTP and XMPP clients
348 do not execute scripts downloaded from remote servers.
350 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
351 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
352 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
353 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
354 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
355 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
356 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
358 Set various certificate chain validation options. See the
359 L<openssl-verify(1)> manual page for details.
363 Reconnects to the same server 5 times using the same session ID, this can
364 be used as a test that session caching is working.
368 Displays the server certificate list as sent by the server: it only consists of
369 certificates the server has sent (in the order the server has sent them). It is
370 B<not> a verified chain.
374 Print session information when the program exits. This will always attempt
375 to print out information even if the connection fails. Normally information
376 will only be printed out once if the connection succeeds. This option is useful
377 because the cipher in use may be renegotiated or the connection may fail
378 because a client certificate is required or is requested only after an
379 attempt is made to access a certain URL. Note: the output produced by this
380 option is not always accurate because a connection might never have been
385 Prints out the SSL session states.
389 Print extensive debugging information including a hex dump of all traffic.
393 Show all protocol messages with hex dump.
397 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
398 with B<enable-ssl-trace> for this option to work.
402 File to send output of B<-msg> or B<-trace> to, default standard output.
406 Tests non-blocking I/O
410 Turns on non-blocking I/O
414 This option translated a line feed from the terminal into CR+LF as required
419 Inhibit shutting down the connection when end of file is reached in the
424 Inhibit printing of session and certificate information. This implicitly
425 turns on B<-ign_eof> as well.
429 Shut down the connection when end of file is reached in the input.
430 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
432 =item B<-psk_identity> I<identity>
434 Use the PSK identity I<identity> when using a PSK cipher suite.
435 The default value is "Client_identity" (without the quotes).
439 Use the PSK key I<key> when using a PSK cipher suite. The key is
440 given as a hexadecimal number without leading 0x, for example -psk
442 This option must be provided in order to use a PSK cipher.
444 =item B<-psk_session> I<file>
446 Use the pem encoded SSL_SESSION data stored in I<file> as the basis of a PSK.
447 Note that this will only work if TLSv1.3 is negotiated.
451 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
452 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
453 available where OpenSSL has support for SCTP enabled.
455 =item B<-sctp_label_bug>
457 Use the incorrect behaviour of older OpenSSL implementations when computing
458 endpoint-pair shared secrets for DTLS/SCTP. This allows communication with
459 older broken implementations but breaks interoperability with correct
460 implementations. Must be used in conjunction with B<-sctp>. This option is only
461 available where OpenSSL has support for SCTP enabled.
463 =item B<-fallback_scsv>
465 Send TLS_FALLBACK_SCSV in the ClientHello.
469 Switch on asynchronous mode. Cryptographic operations will be performed
470 asynchronously. This will only have an effect if an asynchronous capable engine
471 is also used via the B<-engine> option. For test purposes the dummy async engine
472 (dasync) can be used (if available).
474 =item B<-max_send_frag> I<int>
476 The maximum size of data fragment to send.
477 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
479 =item B<-split_send_frag> I<int>
481 The size used to split data for encrypt pipelines. If more data is written in
482 one go than this value then it will be split into multiple pipelines, up to the
483 maximum number of pipelines defined by max_pipelines. This only has an effect if
484 a suitable cipher suite has been negotiated, an engine that supports pipelining
485 has been loaded, and max_pipelines is greater than 1. See
486 L<SSL_CTX_set_split_send_fragment(3)> for further information.
488 =item B<-max_pipelines> I<int>
490 The maximum number of encrypt/decrypt pipelines to be used. This will only have
491 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
492 engine) and a suitable cipher suite has been negotiated. The default value is 1.
493 See L<SSL_CTX_set_max_pipelines(3)> for further information.
495 =item B<-read_buf> I<int>
497 The default read buffer size to be used for connections. This will only have an
498 effect if the buffer size is larger than the size that would otherwise be used
499 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
500 further information).
504 There are several known bugs in SSL and TLS implementations. Adding this
505 option enables various workarounds.
509 Enables support for SSL/TLS compression.
510 This option was introduced in OpenSSL 1.1.0.
511 TLS compression is not recommended and is off by default as of
516 Disables support for SSL/TLS compression.
517 TLS compression is not recommended and is off by default as of
522 Only provide a brief summary of connection parameters instead of the
523 normal verbose output.
525 =item B<-sigalgs> I<sigalglist>
527 Specifies the list of signature algorithms that are sent by the client.
528 The server selects one entry in the list based on its preferences.
529 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
531 =item B<-curves> I<curvelist>
533 Specifies the list of supported curves to be sent by the client. The curve is
534 ultimately selected by the server. For a list of all curves, use:
536 $ openssl ecparam -list_curves
538 =item B<-cipher> I<cipherlist>
540 This allows the TLSv1.2 and below cipher list sent by the client to be modified.
541 This list will be combined with any TLSv1.3 ciphersuites that have been
542 configured. Although the server determines which ciphersuite is used it should
543 take the first supported cipher in the list sent by the client. See
544 L<openssl-ciphers(1)> for more information.
546 =item B<-ciphersuites> I<val>
548 This allows the TLSv1.3 ciphersuites sent by the client to be modified. This
549 list will be combined with any TLSv1.2 and below ciphersuites that have been
550 configured. Although the server determines which cipher suite is used it should
551 take the first supported cipher in the list sent by the client. See
552 L<openssl-ciphers(1)> for more information. The format for this list is a simple
553 colon (":") separated list of TLSv1.3 ciphersuite names.
555 =item B<-starttls> I<protocol>
557 Send the protocol-specific message(s) to switch to TLS for communication.
558 I<protocol> is a keyword for the intended protocol. Currently, the only
559 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
560 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
562 =item B<-xmpphost> I<hostname>
564 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
565 specifies the host for the "to" attribute of the stream element.
566 If this option is not specified, then the host specified with "-connect"
569 This option is an alias of the B<-name> option for "xmpp" and "xmpp-server".
571 =item B<-name> I<hostname>
573 This option is used to specify hostname information for various protocols
574 used with B<-starttls> option. Currently only "xmpp", "xmpp-server",
575 "smtp" and "lmtp" can utilize this B<-name> option.
577 If this option is used with "-starttls xmpp" or "-starttls xmpp-server",
578 if specifies the host for the "to" attribute of the stream element. If this
579 option is not specified, then the host specified with "-connect" will be used.
581 If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies
582 the name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If
583 this option is not specified, then "mail.example.com" will be used.
585 =item B<-tlsextdebug>
587 Print out a hex dump of any TLS extensions received from the server.
591 Disable RFC4507bis session ticket support.
593 =item B<-sess_out> I<filename>
595 Output SSL session to I<filename>.
597 =item B<-sess_in> I<filename>
599 Load SSL session from I<filename>. The client will attempt to resume a
600 connection from this session.
602 =item B<-serverinfo> I<types>
604 A list of comma-separated TLS Extension Types (numbers between 0 and
605 65535). Each type will be sent as an empty ClientHello TLS Extension.
606 The server's response (if any) will be encoded and displayed as a PEM
611 Sends a certificate status request to the server (OCSP stapling). The server
612 response (if any) is printed out.
614 =item B<-alpn> I<protocols>, B<-nextprotoneg> I<protocols>
616 These flags enable the Enable the Application-Layer Protocol Negotiation
617 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
618 IETF standard and replaces NPN.
619 The I<protocols> list is a comma-separated list of protocol names that
620 the client should advertise support for. The list should contain the most
621 desirable protocols first. Protocol names are printable ASCII strings,
622 for example "http/1.1" or "spdy/3".
623 An empty list of protocols is treated specially and will cause the
624 client to advertise support for the TLS extension but disconnect just
625 after receiving ServerHello with a list of server supported protocols.
626 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
628 =item B<-ct>, B<-noct>
630 Use one of these two options to control whether Certificate Transparency (CT)
631 is enabled (B<-ct>) or disabled (B<-noct>).
632 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
633 the server and reported at handshake completion.
635 Enabling CT also enables OCSP stapling, as this is one possible delivery method
640 A file containing a list of known Certificate Transparency logs. See
641 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
643 =item B<-keylogfile> I<file>
645 Appends TLS secrets to the specified keylog file such that external programs
646 (like Wireshark) can decrypt TLS connections.
648 =item B<-early_data> I<file>
650 Reads the contents of the specified file and attempts to send it as early data
651 to the server. This will only work with resumed sessions that support early
652 data and when the server accepts the early data.
656 For TLSv1.3 only, send the Post-Handshake Authentication extension. This will
657 happen whether or not a certificate has been provided via B<-cert>.
659 {- $OpenSSL::safe::opt_version_item -}
661 {- $OpenSSL::safe::opt_name_item -}
663 {- $OpenSSL::safe::opt_x_item -}
665 {- $OpenSSL::safe::opt_trust_item -}
667 {- $OpenSSL::safe::opt_r_item -}
669 {- $OpenSSL::safe::opt_engine_item -}
671 =item I<host>:I<port>
673 Rather than providing B<-connect>, the target hostname and optional port may
674 be provided as a single positional argument after all options. If neither this
675 nor B<-connect> are provided, falls back to attempting to connect to
676 I<localhost> on port I<4433>.
680 =head1 CONNECTED COMMANDS
682 If a connection is established with an SSL server then any data received
683 from the server is displayed and any key presses will be sent to the
684 server. If end of file is reached then the connection will be closed down. When
685 used interactively (which means neither B<-quiet> nor B<-ign_eof> have been
686 given), then certain commands are also recognized which perform special
687 operations. These commands are a letter which must appear at the start of a
688 line. They are listed below.
694 End the current SSL connection and exit.
698 Renegotiate the SSL session (TLSv1.2 and below only).
702 Send a key update message to the server (TLSv1.3 only)
706 Send a key update message to the server and request one back (TLSv1.3 only)
712 This command can be used to debug SSL servers. To connect to an SSL HTTP
715 openssl s_client -connect servername:443
717 would typically be used (https uses port 443). If the connection succeeds
718 then an HTTP command can be given such as "GET /" to retrieve a web page.
720 If the handshake fails then there are several possible causes, if it is
721 nothing obvious like no client certificate then the B<-bugs>,
722 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
723 in case it is a buggy server. In particular you should play with these
724 options B<before> submitting a bug report to an OpenSSL mailing list.
726 A frequent problem when attempting to get client certificates working
727 is that a web client complains it has no certificates or gives an empty
728 list to choose from. This is normally because the server is not sending
729 the clients certificate authority in its "acceptable CA list" when it
730 requests a certificate. By using this command, the CA list can be viewed
731 and checked. However some servers only request client authentication
732 after a specific URL is requested. To obtain the list in this case it
733 is necessary to use the B<-prexit> option and send an HTTP request
734 for an appropriate page.
736 If a certificate is specified on the command line using the B<-cert>
737 option it will not be used unless the server specifically requests
738 a client certificate. Therefor merely including a client certificate
739 on the command line is no guarantee that the certificate works.
741 If there are problems verifying a server certificate then the
742 B<-showcerts> option can be used to show all the certificates sent by the
745 This command is a test tool and is designed to continue the
746 handshake after any certificate verification errors. As a result it will
747 accept any certificate chain (trusted or not) sent by the peer. None test
748 applications should B<not> do this as it makes them vulnerable to a MITM
749 attack. This behaviour can be changed by with the B<-verify_return_error>
750 option: any verify errors are then returned aborting the handshake.
752 The B<-bind> option may be useful if the server or a firewall requires
753 connections to come from some particular address and or port.
757 Because this program has a lot of options and also because some of the
758 techniques used are rather old, the C source for this command is rather
759 hard to read and not a model of how things should be done.
760 A typical SSL client program would be much simpler.
762 The B<-prexit> option is a bit of a hack. We should really report
763 information whenever a session is renegotiated.
768 L<openssl-sess_id(1)>,
769 L<openssl-s_server(1)>,
770 L<openssl-ciphers(1)>,
772 L<SSL_CTX_set_max_send_fragment(3)>,
773 L<SSL_CTX_set_split_send_fragment(3)>,
774 L<SSL_CTX_set_max_pipelines(3)>,
775 L<ossl_store-file(7)>
779 The B<-no_alt_chains> option was added in OpenSSL 1.1.0.
780 The B<-name> option was added in OpenSSL 1.1.1.
784 Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.
786 Licensed under the Apache License 2.0 (the "License"). You may not use
787 this file except in compliance with the License. You can obtain a copy
788 in the file LICENSE in the source distribution or at
789 L<https://www.openssl.org/source/license.html>.