2 {- OpenSSL::safe::output_do_not_edit_headers(); -}
6 openssl-s_client - SSL/TLS client program
10 B<openssl> B<s_client>
12 [B<-ssl_config> I<section>]
13 [B<-connect> I<host:port>]
14 [B<-host> I<hostname>]
16 [B<-bind> I<host:port>]
17 [B<-proxy> I<host:port>]
18 [B<-proxy_user> I<userid>]
19 [B<-proxy_pass> I<arg>]
23 [B<-servername> I<name>]
26 [B<-verify_return_error>]
28 [B<-verifyCAfile> I<filename>]
29 [B<-verifyCApath> I<dir>]
30 [B<-verifyCAstore> I<uri>]
31 [B<-cert> I<filename>]
32 [B<-certform> B<DER>|B<PEM>]
34 [B<-CRLform> B<DER>|B<PEM>]
37 [B<-keyform> B<DER>|B<PEM>]
38 [B<-cert_chain> I<filename>]
41 [B<-chainCApath> I<directory>]
42 [B<-chainCAfile> I<filename>]
43 [B<-chainCAstore> I<uri>]
44 [B<-requestCAfile> I<filename>]
45 [B<-dane_tlsa_domain> I<domain>]
46 [B<-dane_tlsa_rrdata> I<rrdata>]
47 [B<-dane_ee_no_namechecks>]
56 [B<-security_debug_verbose>]
60 [B<-keymatexport> I<label>]
61 [B<-keymatexportlen> I<len>]
62 [B<-msgfile> I<filename>]
69 [B<-psk_identity> I<identity>]
71 [B<-psk_session> I<file>]
77 [B<-maxfraglen> I<len>]
86 [B<-allow_no_dhe_kex>]
87 [B<-sigalgs> I<sigalglist>]
88 [B<-curves> I<curvelist>]
89 [B<-cipher> I<cipherlist>]
90 [B<-ciphersuites> I<val>]
92 [B<-starttls> I<protocol>]
93 [B<-name> I<hostname>]
94 [B<-xmpphost> I<hostname>]
95 [B<-name> I<hostname>]
98 [B<-sess_out> I<filename>]
99 [B<-serverinfo> I<types>]
100 [B<-sess_in> I<filename>]
101 [B<-serverinfo> I<types>]
103 [B<-alpn> I<protocols>]
104 [B<-nextprotoneg> I<protocols>]
108 [B<-keylogfile> I<file>]
109 [B<-early_data> I<file>]
111 [B<-use_srtp> I<value>]
112 [B<-srpuser> I<value>]
113 [B<-srppass> I<value>]
116 [B<-srp_strength> I<number>]
117 {- $OpenSSL::safe::opt_name_synopsis -}
118 {- $OpenSSL::safe::opt_version_synopsis -}
119 {- $OpenSSL::safe::opt_x_synopsis -}
120 {- $OpenSSL::safe::opt_trust_synopsis -}
121 {- $OpenSSL::safe::opt_s_synopsis -}
122 {- $OpenSSL::safe::opt_r_synopsis -}
123 {- $OpenSSL::safe::opt_provider_synopsis -}
124 {- $OpenSSL::safe::opt_engine_synopsis -}
125 [B<-ssl_client_engine> I<id>]
126 {- $OpenSSL::safe::opt_v_synopsis -}
129 =for openssl ifdef engine ssl_client_engine ct noct ctlogfile
131 =for openssl ifdef ssl3 unix 4 6 use_srtp status trace wdebug nextprotoneg
133 =for openssl ifdef ssl3 tls1 tls1_1 tls1_2 tls1_3 dtls mtu dtls1 dtls1_2
135 =for openssl ifdef sctp_label_bug sctp
137 =for openssl ifdef srpuser srppass srp_lateuser srp_moregroups srp_strength
141 This command implements a generic SSL/TLS client which
142 connects to a remote host using SSL/TLS. It is a I<very> useful diagnostic
143 tool for SSL servers.
147 In addition to the options below, this command also supports the
148 common and client only options documented
149 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
156 Print out a usage message.
158 =item B<-ssl_config> I<section>
160 Use the specified section of the configuration file to configure the B<SSL_CTX> object.
162 =item B<-connect> I<host>:I<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<-host> I<hostname>
171 Host to connect to; use B<-connect> instead.
173 =item B<-port> I<port>
175 Connect to the specified port; use B<-connect> instead.
177 =item B<-bind> I<host:port>
179 This specifies the host address and or port to bind as the source for the
180 connection. For Unix-domain sockets the port is ignored and the host is
181 used as the source socket address.
183 =item B<-proxy> I<host:port>
185 When used with the B<-connect> flag, the program uses the host and port
186 specified with this flag and issues an HTTP CONNECT command to connect
187 to the desired server.
189 =item B<-proxy_user> I<userid>
191 When used with the B<-proxy> flag, the program will attempt to authenticate
192 with the specified proxy using basic (base64) authentication.
193 NB: Basic authentication is insecure; the credentials are sent to the proxy
194 in easily reversible base64 encoding before any TLS/SSL session is established.
195 Therefore these credentials are easily recovered by anyone able to sniff/trace
196 the network. Use with caution.
198 =item B<-proxy_pass> I<arg>
200 The proxy password source, used with the B<-proxy_user> flag.
201 For more information about the format of B<arg>
202 see L<openssl(1)/Pass Phrase Options>.
204 =item B<-unix> I<path>
206 Connect over the specified Unix-domain socket.
216 =item B<-servername> I<name>
218 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
220 If B<-servername> is not provided, the TLS SNI extension will be populated with
221 the name given to B<-connect> if it follows a DNS name format. If B<-connect> is
222 not provided either, the SNI is set to "localhost".
223 This is the default since OpenSSL 1.1.1.
225 Even though SNI should normally be a DNS name and not an IP address, if
226 B<-servername> is provided then that name will be sent, regardless of whether
227 it is a DNS name or not.
229 This option cannot be used in conjunction with B<-noservername>.
231 =item B<-noservername>
233 Suppresses sending of the SNI (Server Name Indication) extension in the
234 ClientHello message. Cannot be used in conjunction with the B<-servername> or
235 <-dane_tlsa_domain> options.
237 =item B<-cert> I<certname>
239 The certificate to use, if one is requested by the server. The default is
240 not to use a certificate.
242 =item B<-certform> I<format>
244 The certificate format to use: DER or PEM. PEM is the default.
246 =item B<-CRL> I<filename>
248 CRL file to use to check the server's certificate.
250 =item B<-CRLform> B<DER>|B<PEM>
252 The CRL format; the default is B<PEM>.
253 See L<openssl(1)/Format Options> for details.
255 =item B<-crl_download>
257 Download CRL from distribution points in the certificate.
259 =item B<-key> I<keyfile>
261 The private key to use. If not specified then the certificate file will
264 =item B<-keyform> I<format>
266 The key format; the default is B<PEM>.
267 See L<openssl(1)/Format Options> for details.
271 A file containing trusted certificates to use when attempting to build the
272 client/server certificate chain related to the certificate specified via the
275 =item B<-build_chain>
277 Specify whether the application should build the certificate chain to be
278 provided to the server.
280 =item B<-pass> I<arg>
282 the private key password source. For more information about the format of I<arg>
283 see L<openssl(1)/Pass phrase options>.
285 =item B<-verify> I<depth>
287 The verify depth to use. This specifies the maximum length of the
288 server certificate chain and turns on server certificate verification.
289 Currently the verify operation continues after errors so all the problems
290 with a certificate chain can be seen. As a side effect the connection
291 will never fail due to a server certificate verify failure.
293 =item B<-verify_return_error>
295 Return verification errors instead of continuing. This will typically
296 abort the handshake with a fatal error.
298 =item B<-verify_quiet>
300 Limit verify output to only errors.
302 =item B<-verifyCAfile> I<filename>
304 CA file for verifying the server's certificate, in PEM format.
306 =item B<-verifyCApath> I<dir>
308 Use the specified directory as a certificate store path to verify
309 the server's CA certificate.
311 =item B<-verifyCAstore> I<uri>
313 Use the specified URI as a store URI to verify the server's certificate.
316 =item B<-chainCApath> I<directory>
318 The directory to use for building the chain provided to the server. This
319 directory must be in "hash format", see L<openssl-verify(1)> for more
322 =item B<-chainCAfile> I<file>
324 A file containing trusted certificates to use when attempting to build the
325 client certificate chain.
327 =item B<-chainCAstore> I<uri>
329 The URI to use when attempting to build the client certificate chain.
331 =item B<-requestCAfile> I<file>
333 A file containing a list of certificates whose subject names will be sent
334 to the server in the B<certificate_authorities> extension. Only supported
337 =item B<-dane_tlsa_domain> I<domain>
339 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
340 TLSA base domain which becomes the default SNI hint and the primary
341 reference identifier for hostname checks. This must be used in
342 combination with at least one instance of the B<-dane_tlsa_rrdata>
345 When DANE authentication succeeds, the diagnostic output will include
346 the lowest (closest to 0) depth at which a TLSA record authenticated
347 a chain certificate. When that TLSA record is a "2 1 0" trust
348 anchor public key that signed (rather than matched) the top-most
349 certificate of the chain, the result is reported as "TA public key
350 verified". Otherwise, either the TLSA record "matched TA certificate"
351 at a positive depth or else "matched EE certificate" at depth 0.
353 =item B<-dane_tlsa_rrdata> I<rrdata>
355 Use one or more times to specify the RRDATA fields of the DANE TLSA
356 RRset associated with the target service. The I<rrdata> value is
357 specified in "presentation form", that is four whitespace separated
358 fields that specify the usage, selector, matching type and associated
359 data, with the last of these encoded in hexadecimal. Optional
360 whitespace is ignored in the associated data field. For example:
362 $ openssl s_client -brief -starttls smtp \
363 -connect smtp.example.com:25 \
364 -dane_tlsa_domain smtp.example.com \
365 -dane_tlsa_rrdata "2 1 1
366 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
367 -dane_tlsa_rrdata "2 1 1
368 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
371 Verified peername: smtp.example.com
372 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
375 =item B<-dane_ee_no_namechecks>
377 This disables server name checks when authenticating via DANE-EE(3) TLSA
379 For some applications, primarily web browsers, it is not safe to disable name
380 checks due to "unknown key share" attacks, in which a malicious server can
381 convince a client that a connection to a victim server is instead a secure
382 connection to the malicious server.
383 The malicious server may then be able to violate cross-origin scripting
385 Thus, despite the text of RFC7671, name checks are by default enabled for
386 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
388 In particular, SMTP and XMPP clients should set this option as SRV and MX
389 records already make it possible for a remote domain to redirect client
390 connections to any server of its choice, and in any case SMTP and XMPP clients
391 do not execute scripts downloaded from remote servers.
395 Reconnects to the same server 5 times using the same session ID, this can
396 be used as a test that session caching is working.
400 Displays the server certificate list as sent by the server: it only consists of
401 certificates the server has sent (in the order the server has sent them). It is
402 B<not> a verified chain.
406 Print session information when the program exits. This will always attempt
407 to print out information even if the connection fails. Normally information
408 will only be printed out once if the connection succeeds. This option is useful
409 because the cipher in use may be renegotiated or the connection may fail
410 because a client certificate is required or is requested only after an
411 attempt is made to access a certain URL. Note: the output produced by this
412 option is not always accurate because a connection might never have been
417 Prints out the SSL session states.
421 Print extensive debugging information including a hex dump of all traffic.
425 Do not use interactive command letters.
427 =item B<-security_debug>
429 Enable security debug messages.
431 =item B<-security_debug_verbose>
433 Output more security debug output.
437 Show protocol messages.
441 Enable send/receive timeout on DTLS connections.
443 =item B<-mtu> I<size>
445 Set MTU of the link layer to the specified size.
447 =item B<-keymatexport> I<label>
449 Export keying material using the specified label.
451 =item B<-keymatexportlen> I<len>
453 Export the specified number of bytes of keying material; default is 20.
455 Show all protocol messages with hex dump.
459 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
460 with B<enable-ssl-trace> for this option to work.
462 =item B<-msgfile> I<filename>
464 File to send output of B<-msg> or B<-trace> to, default standard output.
468 Tests non-blocking I/O
472 Turns on non-blocking I/O
476 This option translated a line feed from the terminal into CR+LF as required
481 Inhibit shutting down the connection when end of file is reached in the
486 Inhibit printing of session and certificate information. This implicitly
487 turns on B<-ign_eof> as well.
491 Shut down the connection when end of file is reached in the input.
492 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
494 =item B<-psk_identity> I<identity>
496 Use the PSK identity I<identity> when using a PSK cipher suite.
497 The default value is "Client_identity" (without the quotes).
501 Use the PSK key I<key> when using a PSK cipher suite. The key is
502 given as a hexadecimal number without leading 0x, for example -psk
504 This option must be provided in order to use a PSK cipher.
506 =item B<-psk_session> I<file>
508 Use the pem encoded SSL_SESSION data stored in I<file> as the basis of a PSK.
509 Note that this will only work if TLSv1.3 is negotiated.
513 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
514 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
515 available where OpenSSL has support for SCTP enabled.
517 =item B<-sctp_label_bug>
519 Use the incorrect behaviour of older OpenSSL implementations when computing
520 endpoint-pair shared secrets for DTLS/SCTP. This allows communication with
521 older broken implementations but breaks interoperability with correct
522 implementations. Must be used in conjunction with B<-sctp>. This option is only
523 available where OpenSSL has support for SCTP enabled.
525 =item B<-fallback_scsv>
527 Send TLS_FALLBACK_SCSV in the ClientHello.
531 Switch on asynchronous mode. Cryptographic operations will be performed
532 asynchronously. This will only have an effect if an asynchronous capable engine
533 is also used via the B<-engine> option. For test purposes the dummy async engine
534 (dasync) can be used (if available).
536 =item B<-maxfraglen> I<len>
538 Enable Maximum Fragment Length Negotiation; allowed values are
539 C<512>, C<1024>, C<2048>, and C<4096>.
541 =item B<-max_send_frag> I<int>
543 The maximum size of data fragment to send.
544 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
546 =item B<-split_send_frag> I<int>
548 The size used to split data for encrypt pipelines. If more data is written in
549 one go than this value then it will be split into multiple pipelines, up to the
550 maximum number of pipelines defined by max_pipelines. This only has an effect if
551 a suitable cipher suite has been negotiated, an engine that supports pipelining
552 has been loaded, and max_pipelines is greater than 1. See
553 L<SSL_CTX_set_split_send_fragment(3)> for further information.
555 =item B<-max_pipelines> I<int>
557 The maximum number of encrypt/decrypt pipelines to be used. This will only have
558 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
559 engine) and a suitable cipher suite has been negotiated. The default value is 1.
560 See L<SSL_CTX_set_max_pipelines(3)> for further information.
562 =item B<-read_buf> I<int>
564 The default read buffer size to be used for connections. This will only have an
565 effect if the buffer size is larger than the size that would otherwise be used
566 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
567 further information).
571 There are several known bugs in SSL and TLS implementations. Adding this
572 option enables various workarounds.
576 Enables support for SSL/TLS compression.
577 This option was introduced in OpenSSL 1.1.0.
578 TLS compression is not recommended and is off by default as of
583 Disables support for SSL/TLS compression.
584 TLS compression is not recommended and is off by default as of
589 Only provide a brief summary of connection parameters instead of the
590 normal verbose output.
592 =item B<-sigalgs> I<sigalglist>
594 Specifies the list of signature algorithms that are sent by the client.
595 The server selects one entry in the list based on its preferences.
596 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
598 =item B<-curves> I<curvelist>
600 Specifies the list of supported curves to be sent by the client. The curve is
601 ultimately selected by the server. For a list of all curves, use:
603 $ openssl ecparam -list_curves
605 =item B<-cipher> I<cipherlist>
607 This allows the TLSv1.2 and below cipher list sent by the client to be modified.
608 This list will be combined with any TLSv1.3 ciphersuites that have been
609 configured. Although the server determines which ciphersuite is used it should
610 take the first supported cipher in the list sent by the client. See
611 L<openssl-ciphers(1)> for more information.
613 =item B<-ciphersuites> I<val>
615 This allows the TLSv1.3 ciphersuites sent by the client to be modified. This
616 list will be combined with any TLSv1.2 and below ciphersuites that have been
617 configured. Although the server determines which cipher suite is used it should
618 take the first supported cipher in the list sent by the client. See
619 L<openssl-ciphers(1)> for more information. The format for this list is a simple
620 colon (":") separated list of TLSv1.3 ciphersuite names.
622 =item B<-starttls> I<protocol>
624 Send the protocol-specific message(s) to switch to TLS for communication.
625 I<protocol> is a keyword for the intended protocol. Currently, the only
626 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
627 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
629 =item B<-xmpphost> I<hostname>
631 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
632 specifies the host for the "to" attribute of the stream element.
633 If this option is not specified, then the host specified with "-connect"
636 This option is an alias of the B<-name> option for "xmpp" and "xmpp-server".
638 =item B<-name> I<hostname>
640 This option is used to specify hostname information for various protocols
641 used with B<-starttls> option. Currently only "xmpp", "xmpp-server",
642 "smtp" and "lmtp" can utilize this B<-name> option.
644 If this option is used with "-starttls xmpp" or "-starttls xmpp-server",
645 if specifies the host for the "to" attribute of the stream element. If this
646 option is not specified, then the host specified with "-connect" will be used.
648 If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies
649 the name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If
650 this option is not specified, then "mail.example.com" will be used.
652 =item B<-tlsextdebug>
654 Print out a hex dump of any TLS extensions received from the server.
658 Disable RFC4507bis session ticket support.
660 =item B<-sess_out> I<filename>
662 Output SSL session to I<filename>.
664 =item B<-sess_in> I<filename>
666 Load SSL session from I<filename>. The client will attempt to resume a
667 connection from this session.
669 =item B<-serverinfo> I<types>
671 A list of comma-separated TLS Extension Types (numbers between 0 and
672 65535). Each type will be sent as an empty ClientHello TLS Extension.
673 The server's response (if any) will be encoded and displayed as a PEM
678 Sends a certificate status request to the server (OCSP stapling). The server
679 response (if any) is printed out.
681 =item B<-alpn> I<protocols>, B<-nextprotoneg> I<protocols>
683 These flags enable the Enable the Application-Layer Protocol Negotiation
684 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
685 IETF standard and replaces NPN.
686 The I<protocols> list is a comma-separated list of protocol names that
687 the client should advertise support for. The list should contain the most
688 desirable protocols first. Protocol names are printable ASCII strings,
689 for example "http/1.1" or "spdy/3".
690 An empty list of protocols is treated specially and will cause the
691 client to advertise support for the TLS extension but disconnect just
692 after receiving ServerHello with a list of server supported protocols.
693 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
695 =item B<-ct>, B<-noct>
697 Use one of these two options to control whether Certificate Transparency (CT)
698 is enabled (B<-ct>) or disabled (B<-noct>).
699 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
700 the server and reported at handshake completion.
702 Enabling CT also enables OCSP stapling, as this is one possible delivery method
707 A file containing a list of known Certificate Transparency logs. See
708 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
710 =item B<-keylogfile> I<file>
712 Appends TLS secrets to the specified keylog file such that external programs
713 (like Wireshark) can decrypt TLS connections.
715 =item B<-early_data> I<file>
717 Reads the contents of the specified file and attempts to send it as early data
718 to the server. This will only work with resumed sessions that support early
719 data and when the server accepts the early data.
723 For TLSv1.3 only, send the Post-Handshake Authentication extension. This will
724 happen whether or not a certificate has been provided via B<-cert>.
726 =item B<-use_srtp> I<value>
728 Offer SRTP key management, where B<value> is a colon-separated profile list.
730 =item B<-srpuser> I<value>
732 Set the SRP username to the specified value.
734 =item B<-srppass> I<value>
736 Set the SRP password to the specified value.
738 =item B<-srp_lateuser>
740 SRP username for the second ClientHello message.
742 =item B<-srp_moregroups>
744 Tolerate other than the known B<g> and B<N> values.
746 =item B<-srp_strength> I<number>
748 Set the minimal acceptable length, in bits, for B<N>.
750 {- $OpenSSL::safe::opt_version_item -}
752 {- $OpenSSL::safe::opt_name_item -}
754 {- $OpenSSL::safe::opt_x_item -}
756 {- $OpenSSL::safe::opt_trust_item -}
758 {- $OpenSSL::safe::opt_s_item -}
760 {- $OpenSSL::safe::opt_r_item -}
762 {- $OpenSSL::safe::opt_provider_item -}
764 {- $OpenSSL::safe::opt_engine_item -}
766 =item B<-ssl_client_engine> I<id>
768 Specify engine to be used for client certificate operations.
770 {- $OpenSSL::safe::opt_v_item -}
772 Verification errors are displayed, for debugging, but the command will
773 proceed unless the B<-verify_return_error> option is used.
775 =item I<host>:I<port>
777 Rather than providing B<-connect>, the target hostname and optional port may
778 be provided as a single positional argument after all options. If neither this
779 nor B<-connect> are provided, falls back to attempting to connect to
780 I<localhost> on port I<4433>.
784 =head1 CONNECTED COMMANDS
786 If a connection is established with an SSL server then any data received
787 from the server is displayed and any key presses will be sent to the
788 server. If end of file is reached then the connection will be closed down. When
789 used interactively (which means neither B<-quiet> nor B<-ign_eof> have been
790 given), then certain commands are also recognized which perform special
791 operations. These commands are a letter which must appear at the start of a
792 line. They are listed below.
798 End the current SSL connection and exit.
802 Renegotiate the SSL session (TLSv1.2 and below only).
806 Send a key update message to the server (TLSv1.3 only)
810 Send a key update message to the server and request one back (TLSv1.3 only)
816 This command can be used to debug SSL servers. To connect to an SSL HTTP
819 openssl s_client -connect servername:443
821 would typically be used (https uses port 443). If the connection succeeds
822 then an HTTP command can be given such as "GET /" to retrieve a web page.
824 If the handshake fails then there are several possible causes, if it is
825 nothing obvious like no client certificate then the B<-bugs>,
826 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
827 in case it is a buggy server. In particular you should play with these
828 options B<before> submitting a bug report to an OpenSSL mailing list.
830 A frequent problem when attempting to get client certificates working
831 is that a web client complains it has no certificates or gives an empty
832 list to choose from. This is normally because the server is not sending
833 the clients certificate authority in its "acceptable CA list" when it
834 requests a certificate. By using this command, the CA list can be viewed
835 and checked. However some servers only request client authentication
836 after a specific URL is requested. To obtain the list in this case it
837 is necessary to use the B<-prexit> option and send an HTTP request
838 for an appropriate page.
840 If a certificate is specified on the command line using the B<-cert>
841 option it will not be used unless the server specifically requests
842 a client certificate. Therefor merely including a client certificate
843 on the command line is no guarantee that the certificate works.
845 If there are problems verifying a server certificate then the
846 B<-showcerts> option can be used to show all the certificates sent by the
849 This command is a test tool and is designed to continue the
850 handshake after any certificate verification errors. As a result it will
851 accept any certificate chain (trusted or not) sent by the peer. None test
852 applications should B<not> do this as it makes them vulnerable to a MITM
853 attack. This behaviour can be changed by with the B<-verify_return_error>
854 option: any verify errors are then returned aborting the handshake.
856 The B<-bind> option may be useful if the server or a firewall requires
857 connections to come from some particular address and or port.
861 Because this program has a lot of options and also because some of the
862 techniques used are rather old, the C source for this command is rather
863 hard to read and not a model of how things should be done.
864 A typical SSL client program would be much simpler.
866 The B<-prexit> option is a bit of a hack. We should really report
867 information whenever a session is renegotiated.
872 L<openssl-sess_id(1)>,
873 L<openssl-s_server(1)>,
874 L<openssl-ciphers(1)>,
876 L<SSL_CTX_set_max_send_fragment(3)>,
877 L<SSL_CTX_set_split_send_fragment(3)>,
878 L<SSL_CTX_set_max_pipelines(3)>,
879 L<ossl_store-file(7)>
883 The B<-no_alt_chains> option was added in OpenSSL 1.1.0.
884 The B<-name> option was added in OpenSSL 1.1.1.
888 Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.
890 Licensed under the Apache License 2.0 (the "License"). You may not use
891 this file except in compliance with the License. You can obtain a copy
892 in the file LICENSE in the source distribution or at
893 L<https://www.openssl.org/source/license.html>.