6 s_client - SSL/TLS client program
10 B<openssl> B<s_client>
12 [B<-connect host:port>]
15 [B<-proxy_user userid>]
23 [B<-verify_return_error>]
25 [B<-certform DER|PEM>]
28 [B<-cert_chain filename>]
34 [B<-xcertform PEM|DER>]
35 [B<-xkeyform PEM|DER>]
37 [B<-CApath directory>]
39 [B<-chainCApath directory>]
40 [B<-chainCAfile filename>]
43 [B<-requestCAfile filename>]
44 [B<-dane_tlsa_domain domain>]
45 [B<-dane_tlsa_rrdata rrdata>]
46 [B<-dane_ee_no_namechecks>]
47 [B<-attime timestamp>]
70 [B<-verify_depth num>]
71 [B<-verify_email email>]
72 [B<-verify_hostname hostname>]
74 [B<-verify_name name>]
87 [B<-psk_identity identity>]
89 [B<-psk_session file>]
109 [B<-split_send_frag>]
115 [B<-allow_no_dhe_kex>]
116 [B<-sigalgs sigalglist>]
117 [B<-curves curvelist>]
118 [B<-cipher cipherlist>]
119 [B<-ciphersuites val>]
121 [B<-starttls protocol>]
122 [B<-xmpphost hostname>]
127 [B<-sess_out filename>]
128 [B<-sess_in filename>]
131 [B<-serverinfo types>]
134 [B<-nextprotoneg protocols>]
138 [B<-keylogfile file>]
139 [B<-early_data file>]
145 The B<s_client> command implements a generic SSL/TLS client which connects
146 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
151 In addition to the options below the B<s_client> utility also supports the
152 common and client only options documented in the
153 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
160 Print out a usage message.
162 =item B<-connect host:port>
164 This specifies the host and optional port to connect to. It is possible to
165 select the host and port using the optional target positional argument instead.
166 If neither this nor the target positional argument are specified then an attempt
167 is made to connect to the local host on port 4433.
169 =item B<-bind host:port>]
171 This specifies the host address and or port to bind as the source for the
172 connection. For Unix-domain sockets the port is ignored and the host is
173 used as the source socket address.
175 =item B<-proxy host:port>
177 When used with the B<-connect> flag, the program uses the host and port
178 specified with this flag and issues an HTTP CONNECT command to connect
179 to the desired server.
181 =item B<-proxy_user userid>
183 When used with the B<-proxy> flag, the program will attempt to authenticate
184 with the specified proxy using basic (base64) authentication.
185 NB: Basic authentication is insecure; the credentials are sent to the proxy
186 in easily reversible base64 encoding before any TLS/SSL session is established.
187 Therefore these credentials are easily recovered by anyone able to sniff/trace
188 the network. Use with caution.
190 =item B<-proxy_pass arg>
192 The proxy password source, used with the B<-proxy_user> flag.
193 For more information about the format of B<arg> see the B<PASS PHRASE ARGUMENTS>
194 section in L<openssl(1)>.
198 Connect over the specified Unix-domain socket.
208 =item B<-servername name>
210 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
212 If B<-servername> is not provided, the TLS SNI extension will be populated with
213 the name given to B<-connect> if it follows a DNS name format. If B<-connect> is
214 not provided either, the SNI is set to "localhost".
215 This is the default since OpenSSL 1.1.1.
217 Even though SNI should normally be a DNS name and not an IP address, if
218 B<-servername> is provided then that name will be sent, regardless of whether
219 it is a DNS name or not.
221 This option cannot be used in conjunction with B<-noservername>.
223 =item B<-noservername>
225 Suppresses sending of the SNI (Server Name Indication) extension in the
226 ClientHello message. Cannot be used in conjunction with the B<-servername> or
227 <-dane_tlsa_domain> options.
229 =item B<-cert certname>
231 The certificate to use, if one is requested by the server. The default is
232 not to use a certificate.
234 =item B<-certform format>
236 The certificate format to use: DER or PEM. PEM is the default.
238 =item B<-key keyfile>
240 The private key to use. If not specified then the certificate file will
243 =item B<-keyform format>
245 The private format to use: DER or PEM. PEM is the default.
249 A file containing trusted certificates to use when attempting to build the
250 client/server certificate chain related to the certificate specified via the
253 =item B<-build_chain>
255 Specify whether the application should build the certificate chain to be
256 provided to the server.
258 =item B<-xkey infile>, B<-xcert infile>, B<-xchain>
260 Specify an extra certificate, private key and certificate chain. These behave
261 in the same manner as the B<-cert>, B<-key> and B<-cert_chain> options. When
262 specified, the callback returning the first valid chain will be in use by the
265 =item B<-xchain_build>
267 Specify whether the application should build the certificate chain to be
268 provided to the server for the extra certificates provided via B<-xkey infile>,
269 B<-xcert infile>, B<-xchain> options.
271 =item B<-xcertform PEM|DER>, B<-xkeyform PEM|DER>
273 Extra certificate and private key format respectively.
277 the private key password source. For more information about the format of B<arg>
278 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
280 =item B<-verify depth>
282 The verify depth to use. This specifies the maximum length of the
283 server certificate chain and turns on server certificate verification.
284 Currently the verify operation continues after errors so all the problems
285 with a certificate chain can be seen. As a side effect the connection
286 will never fail due to a server certificate verify failure.
288 =item B<-verify_return_error>
290 Return verification errors instead of continuing. This will typically
291 abort the handshake with a fatal error.
293 =item B<-nameopt option>
295 Option which determines how the subject or issuer names are displayed. The
296 B<option> argument can be a single option or multiple options separated by
297 commas. Alternatively the B<-nameopt> switch may be used more than once to
298 set multiple options. See the L<x509(1)> manual page for details.
300 =item B<-CApath directory>
302 The directory to use for server certificate verification. This directory
303 must be in "hash format", see L<verify(1)> for more information. These are
304 also used when building the client certificate chain.
306 =item B<-CAfile file>
308 A file containing trusted certificates to use during server authentication
309 and to use when attempting to build the client certificate chain.
311 =item B<-chainCApath directory>
313 The directory to use for building the chain provided to the server. This
314 directory must be in "hash format", see L<verify(1)> for more information.
316 =item B<-chainCAfile file>
318 A file containing trusted certificates to use when attempting to build the
319 client certificate chain.
323 Do not load the trusted CA certificates from the default file location
327 Do not load the trusted CA certificates from the default directory location
329 =item B<-requestCAfile file>
331 A file containing a list of certificates whose subject names will be sent
332 to the server in the B<certificate_authorities> extension. Only supported
335 =item B<-dane_tlsa_domain domain>
337 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
338 TLSA base domain which becomes the default SNI hint and the primary
339 reference identifier for hostname checks. This must be used in
340 combination with at least one instance of the B<-dane_tlsa_rrdata>
343 When DANE authentication succeeds, the diagnostic output will include
344 the lowest (closest to 0) depth at which a TLSA record authenticated
345 a chain certificate. When that TLSA record is a "2 1 0" trust
346 anchor public key that signed (rather than matched) the top-most
347 certificate of the chain, the result is reported as "TA public key
348 verified". Otherwise, either the TLSA record "matched TA certificate"
349 at a positive depth or else "matched EE certificate" at depth 0.
351 =item B<-dane_tlsa_rrdata rrdata>
353 Use one or more times to specify the RRDATA fields of the DANE TLSA
354 RRset associated with the target service. The B<rrdata> value is
355 specied in "presentation form", that is four whitespace separated
356 fields that specify the usage, selector, matching type and associated
357 data, with the last of these encoded in hexadecimal. Optional
358 whitespace is ignored in the associated data field. For example:
360 $ openssl s_client -brief -starttls smtp \
361 -connect smtp.example.com:25 \
362 -dane_tlsa_domain smtp.example.com \
363 -dane_tlsa_rrdata "2 1 1
364 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
365 -dane_tlsa_rrdata "2 1 1
366 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
369 Verified peername: smtp.example.com
370 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
373 =item B<-dane_ee_no_namechecks>
375 This disables server name checks when authenticating via DANE-EE(3) TLSA
377 For some applications, primarily web browsers, it is not safe to disable name
378 checks due to "unknown key share" attacks, in which a malicious server can
379 convince a client that a connection to a victim server is instead a secure
380 connection to the malicious server.
381 The malicious server may then be able to violate cross-origin scripting
383 Thus, despite the text of RFC7671, name checks are by default enabled for
384 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
386 In particular, SMTP and XMPP clients should set this option as SRV and MX
387 records already make it possible for a remote domain to redirect client
388 connections to any server of its choice, and in any case SMTP and XMPP clients
389 do not execute scripts downloaded from remote servers.
391 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
392 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
393 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
394 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
395 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
396 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
397 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
399 Set various certificate chain validation options. See the
400 L<verify(1)> manual page for details.
404 Reconnects to the same server 5 times using the same session ID, this can
405 be used as a test that session caching is working.
409 Displays the server certificate list as sent by the server: it only consists of
410 certificates the server has sent (in the order the server has sent them). It is
411 B<not> a verified chain.
415 Print session information when the program exits. This will always attempt
416 to print out information even if the connection fails. Normally information
417 will only be printed out once if the connection succeeds. This option is useful
418 because the cipher in use may be renegotiated or the connection may fail
419 because a client certificate is required or is requested only after an
420 attempt is made to access a certain URL. Note: the output produced by this
421 option is not always accurate because a connection might never have been
426 Prints out the SSL session states.
430 Print extensive debugging information including a hex dump of all traffic.
434 Show all protocol messages with hex dump.
438 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
439 with B<enable-ssl-trace> for this option to work.
443 File to send output of B<-msg> or B<-trace> to, default standard output.
447 Tests non-blocking I/O
451 Turns on non-blocking I/O
455 This option translated a line feed from the terminal into CR+LF as required
460 Inhibit shutting down the connection when end of file is reached in the
465 Inhibit printing of session and certificate information. This implicitly
466 turns on B<-ign_eof> as well.
470 Shut down the connection when end of file is reached in the input.
471 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
473 =item B<-psk_identity identity>
475 Use the PSK identity B<identity> when using a PSK cipher suite.
476 The default value is "Client_identity" (without the quotes).
480 Use the PSK key B<key> when using a PSK cipher suite. The key is
481 given as a hexadecimal number without leading 0x, for example -psk
483 This option must be provided in order to use a PSK cipher.
485 =item B<-psk_session file>
487 Use the pem encoded SSL_SESSION data stored in B<file> as the basis of a PSK.
488 Note that this will only work if TLSv1.3 is negotiated.
490 =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>
492 These options require or disable the use of the specified SSL or TLS protocols.
493 By default B<s_client> will negotiate the highest mutually supported protocol
495 When a specific TLS version is required, only that version will be offered to
496 and accepted from the server.
497 Note that not all protocols and flags may be available, depending on how
500 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
502 These options make B<s_client> use DTLS protocols instead of TLS.
503 With B<-dtls>, B<s_client> will negotiate any supported DTLS protocol version,
504 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
509 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
510 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
511 available where OpenSSL has support for SCTP enabled.
513 =item B<-sctp_label_bug>
515 Use the incorrect behaviour of older OpenSSL implementations when computing
516 endpoint-pair shared secrets for DTLS/SCTP. This allows communication with
517 older broken implementations but breaks interoperability with correct
518 implementations. Must be used in conjunction with B<-sctp>. This option is only
519 available where OpenSSL has support for SCTP enabled.
521 =item B<-fallback_scsv>
523 Send TLS_FALLBACK_SCSV in the ClientHello.
527 Switch on asynchronous mode. Cryptographic operations will be performed
528 asynchronously. This will only have an effect if an asynchronous capable engine
529 is also used via the B<-engine> option. For test purposes the dummy async engine
530 (dasync) can be used (if available).
532 =item B<-max_send_frag int>
534 The maximum size of data fragment to send.
535 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
537 =item B<-split_send_frag int>
539 The size used to split data for encrypt pipelines. If more data is written in
540 one go than this value then it will be split into multiple pipelines, up to the
541 maximum number of pipelines defined by max_pipelines. This only has an effect if
542 a suitable cipher suite has been negotiated, an engine that supports pipelining
543 has been loaded, and max_pipelines is greater than 1. See
544 L<SSL_CTX_set_split_send_fragment(3)> for further information.
546 =item B<-max_pipelines int>
548 The maximum number of encrypt/decrypt pipelines to be used. This will only have
549 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
550 engine) and a suitable cipher suite has been negotiated. The default value is 1.
551 See L<SSL_CTX_set_max_pipelines(3)> for further information.
553 =item B<-read_buf int>
555 The default read buffer size to be used for connections. This will only have an
556 effect if the buffer size is larger than the size that would otherwise be used
557 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
558 further information).
562 There are several known bugs in SSL and TLS implementations. Adding this
563 option enables various workarounds.
567 Enables support for SSL/TLS compression.
568 This option was introduced in OpenSSL 1.1.0.
569 TLS compression is not recommended and is off by default as of
574 Disables support for SSL/TLS compression.
575 TLS compression is not recommended and is off by default as of
580 Only provide a brief summary of connection parameters instead of the
581 normal verbose output.
583 =item B<-sigalgs sigalglist>
585 Specifies the list of signature algorithms that are sent by the client.
586 The server selects one entry in the list based on its preferences.
587 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
589 =item B<-curves curvelist>
591 Specifies the list of supported curves to be sent by the client. The curve is
592 ultimately selected by the server. For a list of all curves, use:
594 $ openssl ecparam -list_curves
596 =item B<-cipher cipherlist>
598 This allows the TLSv1.2 and below cipher list sent by the client to be modified.
599 This list will be combined with any TLSv1.3 ciphersuites that have been
600 configured. Although the server determines which ciphersuite is used it should
601 take the first supported cipher in the list sent by the client. See the
602 B<ciphers> command for more information.
604 =item B<-ciphersuites val>
606 This allows the TLSv1.3 ciphersuites sent by the client to be modified. This
607 list will be combined with any TLSv1.2 and below ciphersuites that have been
608 configured. Although the server determines which cipher suite is used it should
609 take the first supported cipher in the list sent by the client. See the
610 B<ciphers> command for more information. The format for this list is a simple
611 colon (":") separated list of TLSv1.3 ciphersuite names.
613 =item B<-starttls protocol>
615 Send the protocol-specific message(s) to switch to TLS for communication.
616 B<protocol> is a keyword for the intended protocol. Currently, the only
617 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
618 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
620 =item B<-xmpphost hostname>
622 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
623 specifies the host for the "to" attribute of the stream element.
624 If this option is not specified, then the host specified with "-connect"
627 This option is an alias of the B<-name> option for "xmpp" and "xmpp-server".
629 =item B<-name hostname>
631 This option is used to specify hostname information for various protocols
632 used with B<-starttls> option. Currently only "xmpp", "xmpp-server",
633 "smtp" and "lmtp" can utilize this B<-name> option.
635 If this option is used with "-starttls xmpp" or "-starttls xmpp-server",
636 if specifies the host for the "to" attribute of the stream element. If this
637 option is not specified, then the host specified with "-connect" will be used.
639 If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies
640 the name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If
641 this option is not specified, then "mail.example.com" will be used.
643 =item B<-tlsextdebug>
645 Print out a hex dump of any TLS extensions received from the server.
649 Disable RFC4507bis session ticket support.
651 =item B<-sess_out filename>
653 Output SSL session to B<filename>.
655 =item B<-sess_in sess.pem>
657 Load SSL session from B<filename>. The client will attempt to resume a
658 connection from this session.
662 Specifying an engine (by its unique B<id> string) will cause B<s_client>
663 to attempt to obtain a functional reference to the specified engine,
664 thus initialising it if needed. The engine will then be set as the default
665 for all available algorithms.
667 =item B<-rand file...>
669 A file or files containing random data used to seed the random number
671 Multiple files can be specified separated by an OS-dependent character.
672 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
675 =item [B<-writerand file>]
677 Writes random data to the specified I<file> upon exit.
678 This can be used with a subsequent B<-rand> flag.
680 =item B<-serverinfo types>
682 A list of comma-separated TLS Extension Types (numbers between 0 and
683 65535). Each type will be sent as an empty ClientHello TLS Extension.
684 The server's response (if any) will be encoded and displayed as a PEM
689 Sends a certificate status request to the server (OCSP stapling). The server
690 response (if any) is printed out.
692 =item B<-alpn protocols>, B<-nextprotoneg protocols>
694 These flags enable the Enable the Application-Layer Protocol Negotiation
695 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
696 IETF standard and replaces NPN.
697 The B<protocols> list is a comma-separated list of protocol names that
698 the client should advertise support for. The list should contain the most
699 desirable protocols first. Protocol names are printable ASCII strings,
700 for example "http/1.1" or "spdy/3".
701 An empty list of protocols is treated specially and will cause the
702 client to advertise support for the TLS extension but disconnect just
703 after receiving ServerHello with a list of server supported protocols.
704 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
706 =item B<-ct>, B<-noct>
708 Use one of these two options to control whether Certificate Transparency (CT)
709 is enabled (B<-ct>) or disabled (B<-noct>).
710 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
711 the server and reported at handshake completion.
713 Enabling CT also enables OCSP stapling, as this is one possible delivery method
718 A file containing a list of known Certificate Transparency logs. See
719 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
721 =item B<-keylogfile file>
723 Appends TLS secrets to the specified keylog file such that external programs
724 (like Wireshark) can decrypt TLS connections.
726 =item B<-early_data file>
728 Reads the contents of the specified file and attempts to send it as early data
729 to the server. This will only work with resumed sessions that support early
730 data and when the server accepts the early data.
734 For TLSv1.3 only, send the Post-Handshake Authentication extension. This will
735 happen whether or not a certificate has been provided via B<-cert>.
739 Rather than providing B<-connect>, the target hostname and optional port may
740 be provided as a single positional argument after all options. If neither this
741 nor B<-connect> are provided, falls back to attempting to connect to localhost
746 =head1 CONNECTED COMMANDS
748 If a connection is established with an SSL server then any data received
749 from the server is displayed and any key presses will be sent to the
750 server. If end of file is reached then the connection will be closed down. When
751 used interactively (which means neither B<-quiet> nor B<-ign_eof> have been
752 given), then certain commands are also recognized which perform special
753 operations. These commands are a letter which must appear at the start of a
754 line. They are listed below.
760 End the current SSL connection and exit.
764 Renegotiate the SSL session (TLSv1.2 and below only).
768 Send a key update message to the server (TLSv1.3 only)
772 Send a key update message to the server and request one back (TLSv1.3 only)
778 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
781 openssl s_client -connect servername:443
783 would typically be used (https uses port 443). If the connection succeeds
784 then an HTTP command can be given such as "GET /" to retrieve a web page.
786 If the handshake fails then there are several possible causes, if it is
787 nothing obvious like no client certificate then the B<-bugs>,
788 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
789 in case it is a buggy server. In particular you should play with these
790 options B<before> submitting a bug report to an OpenSSL mailing list.
792 A frequent problem when attempting to get client certificates working
793 is that a web client complains it has no certificates or gives an empty
794 list to choose from. This is normally because the server is not sending
795 the clients certificate authority in its "acceptable CA list" when it
796 requests a certificate. By using B<s_client> the CA list can be viewed
797 and checked. However some servers only request client authentication
798 after a specific URL is requested. To obtain the list in this case it
799 is necessary to use the B<-prexit> option and send an HTTP request
800 for an appropriate page.
802 If a certificate is specified on the command line using the B<-cert>
803 option it will not be used unless the server specifically requests
804 a client certificate. Therefor merely including a client certificate
805 on the command line is no guarantee that the certificate works.
807 If there are problems verifying a server certificate then the
808 B<-showcerts> option can be used to show all the certificates sent by the
811 The B<s_client> utility is a test tool and is designed to continue the
812 handshake after any certificate verification errors. As a result it will
813 accept any certificate chain (trusted or not) sent by the peer. None test
814 applications should B<not> do this as it makes them vulnerable to a MITM
815 attack. This behaviour can be changed by with the B<-verify_return_error>
816 option: any verify errors are then returned aborting the handshake.
818 The B<-bind> option may be useful if the server or a firewall requires
819 connections to come from some particular address and or port.
823 Because this program has a lot of options and also because some of the
824 techniques used are rather old, the C source of B<s_client> is rather hard to
825 read and not a model of how things should be done.
826 A typical SSL client program would be much simpler.
828 The B<-prexit> option is a bit of a hack. We should really report
829 information whenever a session is renegotiated.
833 L<SSL_CONF_cmd(3)>, L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>,
834 L<SSL_CTX_set_max_send_fragment(3)>, L<SSL_CTX_set_split_send_fragment(3)>,
835 L<SSL_CTX_set_max_pipelines(3)>
839 The B<-no_alt_chains> option was added in OpenSSL 1.1.0.
840 The B<-name> option was added in OpenSSL 1.1.1.
844 Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
846 Licensed under the Apache License 2.0 (the "License"). You may not use
847 this file except in compliance with the License. You can obtain a copy
848 in the file LICENSE in the source distribution or at
849 L<https://www.openssl.org/source/license.html>.