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>|B<P12>]
33 [B<-cert_chain> I<filename>]
36 [B<-CRLform> B<DER>|B<PEM>]
38 [B<-key> I<filename>|I<uri>]
39 [B<-keyform> B<DER>|B<PEM>|B<P12>|B<ENGINE>]
41 [B<-chainCAfile> I<filename>]
42 [B<-chainCApath> I<directory>]
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>]
62 [B<-keymatexport> I<label>]
63 [B<-keymatexportlen> I<len>]
64 [B<-msgfile> I<filename>]
71 [B<-psk_identity> I<identity>]
73 [B<-psk_session> I<file>]
79 [B<-maxfraglen> I<len>]
84 [B<-ignore_unexpected_eof>]
89 [B<-legacy_server_connect>]
90 [B<-allow_no_dhe_kex>]
91 [B<-sigalgs> I<sigalglist>]
92 [B<-curves> I<curvelist>]
93 [B<-cipher> I<cipherlist>]
94 [B<-ciphersuites> I<val>]
96 [B<-starttls> I<protocol>]
97 [B<-name> I<hostname>]
98 [B<-xmpphost> I<hostname>]
99 [B<-name> I<hostname>]
102 [B<-sess_out> I<filename>]
103 [B<-serverinfo> I<types>]
104 [B<-sess_in> I<filename>]
105 [B<-serverinfo> I<types>]
107 [B<-alpn> I<protocols>]
108 [B<-nextprotoneg> I<protocols>]
112 [B<-keylogfile> I<file>]
113 [B<-early_data> I<file>]
115 [B<-use_srtp> I<value>]
116 [B<-srpuser> I<value>]
117 [B<-srppass> I<value>]
120 [B<-srp_strength> I<number>]
123 {- $OpenSSL::safe::opt_name_synopsis -}
124 {- $OpenSSL::safe::opt_version_synopsis -}
125 {- $OpenSSL::safe::opt_x_synopsis -}
126 {- $OpenSSL::safe::opt_trust_synopsis -}
127 {- $OpenSSL::safe::opt_s_synopsis -}
128 {- $OpenSSL::safe::opt_r_synopsis -}
129 {- $OpenSSL::safe::opt_provider_synopsis -}
130 {- $OpenSSL::safe::opt_engine_synopsis -}[B<-ssl_client_engine> I<id>]
131 {- $OpenSSL::safe::opt_v_synopsis -}
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<-ssl_config> I<section>
155 Use the specified section of the configuration file to configure the B<SSL_CTX> object.
157 =item B<-connect> I<host>:I<port>
159 This specifies the host and optional port to connect to. It is possible to
160 select the host and port using the optional target positional argument instead.
161 If neither this nor the target positional argument are specified then an attempt
162 is made to connect to the local host on port 4433.
164 =item B<-host> I<hostname>
166 Host to connect to; use B<-connect> instead.
168 =item B<-port> I<port>
170 Connect to the specified port; use B<-connect> instead.
172 =item B<-bind> I<host:port>
174 This specifies the host address and or port to bind as the source for the
175 connection. For Unix-domain sockets the port is ignored and the host is
176 used as the source socket address.
178 =item B<-proxy> I<host:port>
180 When used with the B<-connect> flag, the program uses the host and port
181 specified with this flag and issues an HTTP CONNECT command to connect
182 to the desired server.
184 =item B<-proxy_user> I<userid>
186 When used with the B<-proxy> flag, the program will attempt to authenticate
187 with the specified proxy using basic (base64) authentication.
188 NB: Basic authentication is insecure; the credentials are sent to the proxy
189 in easily reversible base64 encoding before any TLS/SSL session is established.
190 Therefore, these credentials are easily recovered by anyone able to sniff/trace
191 the network. Use with caution.
193 =item B<-proxy_pass> I<arg>
195 The proxy password source, used with the B<-proxy_user> flag.
196 For more information about the format of B<arg>
197 see L<openssl-passphrase-options(1)>.
199 =item B<-unix> I<path>
201 Connect over the specified Unix-domain socket.
211 =item B<-servername> I<name>
213 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
215 If B<-servername> is not provided, the TLS SNI extension will be populated with
216 the name given to B<-connect> if it follows a DNS name format. If B<-connect> is
217 not provided either, the SNI is set to "localhost".
218 This is the default since OpenSSL 1.1.1.
220 Even though SNI should normally be a DNS name and not an IP address, if
221 B<-servername> is provided then that name will be sent, regardless of whether
222 it is a DNS name or not.
224 This option cannot be used in conjunction with B<-noservername>.
226 =item B<-noservername>
228 Suppresses sending of the SNI (Server Name Indication) extension in the
229 ClientHello message. Cannot be used in conjunction with the B<-servername> or
230 B<-dane_tlsa_domain> options.
232 =item B<-cert> I<filename>
234 The client certificate to use, if one is requested by the server.
235 The default is not to use a certificate.
237 The chain for the client certificate may be specified using B<-cert_chain>.
239 =item B<-certform> B<DER>|B<PEM>|B<P12>
241 The client certificate file format to use; unspecified by default.
242 See L<openssl-format-options(1)> for details.
246 A file or URI of untrusted certificates to use when attempting to build the
247 certificate chain related to the certificate specified via the B<-cert> option.
248 The input can be in PEM, DER, or PKCS#12 format.
250 =item B<-build_chain>
252 Specify whether the application should build the client certificate chain to be
253 provided to the server.
255 =item B<-CRL> I<filename>
257 CRL file to use to check the server's certificate.
259 =item B<-CRLform> B<DER>|B<PEM>
261 The CRL file format; unspecified by default.
262 See L<openssl-format-options(1)> for details.
264 =item B<-crl_download>
266 Download CRL from distribution points in the certificate.
268 =item B<-key> I<filename>|I<uri>
270 The client private key to use.
271 If not specified then the certificate file will be used to read also the key.
273 =item B<-keyform> B<DER>|B<PEM>|B<P12>|B<ENGINE>
275 The key format; unspecified by default.
276 See L<openssl-format-options(1)> for details.
278 =item B<-pass> I<arg>
280 the private key and certificate file password source.
281 For more information about the format of I<arg>
282 see L<openssl-passphrase-options(1)>.
284 =item B<-verify> I<depth>
286 The verify depth to use. This specifies the maximum length of the
287 server certificate chain and turns on server certificate verification.
288 Currently the verify operation continues after errors so all the problems
289 with a certificate chain can be seen. As a side effect the connection
290 will never fail due to a server certificate verify failure.
292 =item B<-verify_return_error>
294 Return verification errors instead of continuing. This will typically
295 abort the handshake with a fatal error.
297 =item B<-verify_quiet>
299 Limit verify output to only errors.
301 =item B<-verifyCAfile> I<filename>
303 A file in PEM format containing trusted certificates to use
304 for verifying the server's certificate.
306 =item B<-verifyCApath> I<dir>
308 A directory containing trusted certificates to use
309 for verifying the server's certificate.
310 This directory must be in "hash format",
311 see L<openssl-verify(1)> for more information.
313 =item B<-verifyCAstore> I<uri>
315 The URI of a store containing trusted certificates to use
316 for verifying the server's certificate.
318 =item B<-chainCAfile> I<file>
320 A file in PEM format containing trusted certificates to use
321 when attempting to build the client certificate chain.
323 =item B<-chainCApath> I<directory>
325 A directory containing trusted certificates to use
326 for building the client certificate chain provided to the server.
327 This directory must be in "hash format",
328 see L<openssl-verify(1)> for more information.
330 =item B<-chainCAstore> I<uri>
332 The URI of a store containing trusted certificates to use
333 when attempting to build the client certificate chain.
334 The URI may indicate a single certificate, as well as a collection of them.
335 With URIs in the C<file:> scheme, this acts as B<-chainCAfile> or
336 B<-chainCApath>, depending on if the URI indicates a directory or a
338 See L<ossl_store-file(7)> for more information on the C<file:> scheme.
340 =item B<-requestCAfile> I<file>
342 A file containing a list of certificates whose subject names will be sent
343 to the server in the B<certificate_authorities> extension. Only supported
346 =item B<-dane_tlsa_domain> I<domain>
348 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
349 TLSA base domain which becomes the default SNI hint and the primary
350 reference identifier for hostname checks. This must be used in
351 combination with at least one instance of the B<-dane_tlsa_rrdata>
354 When DANE authentication succeeds, the diagnostic output will include
355 the lowest (closest to 0) depth at which a TLSA record authenticated
356 a chain certificate. When that TLSA record is a "2 1 0" trust
357 anchor public key that signed (rather than matched) the top-most
358 certificate of the chain, the result is reported as "TA public key
359 verified". Otherwise, either the TLSA record "matched TA certificate"
360 at a positive depth or else "matched EE certificate" at depth 0.
362 =item B<-dane_tlsa_rrdata> I<rrdata>
364 Use one or more times to specify the RRDATA fields of the DANE TLSA
365 RRset associated with the target service. The I<rrdata> value is
366 specified in "presentation form", that is four whitespace separated
367 fields that specify the usage, selector, matching type and associated
368 data, with the last of these encoded in hexadecimal. Optional
369 whitespace is ignored in the associated data field. For example:
371 $ openssl s_client -brief -starttls smtp \
372 -connect smtp.example.com:25 \
373 -dane_tlsa_domain smtp.example.com \
374 -dane_tlsa_rrdata "2 1 1
375 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
376 -dane_tlsa_rrdata "2 1 1
377 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
380 Verified peername: smtp.example.com
381 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
384 =item B<-dane_ee_no_namechecks>
386 This disables server name checks when authenticating via DANE-EE(3) TLSA
388 For some applications, primarily web browsers, it is not safe to disable name
389 checks due to "unknown key share" attacks, in which a malicious server can
390 convince a client that a connection to a victim server is instead a secure
391 connection to the malicious server.
392 The malicious server may then be able to violate cross-origin scripting
394 Thus, despite the text of RFC7671, name checks are by default enabled for
395 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
397 In particular, SMTP and XMPP clients should set this option as SRV and MX
398 records already make it possible for a remote domain to redirect client
399 connections to any server of its choice, and in any case SMTP and XMPP clients
400 do not execute scripts downloaded from remote servers.
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
424 =item B<-no-interactive>
426 This flag can be used to run the client in a non-interactive mode.
430 Prints out the SSL session states.
434 Print extensive debugging information including a hex dump of all traffic.
438 Do not use interactive command letters.
440 =item B<-security_debug>
442 Enable security debug messages.
444 =item B<-security_debug_verbose>
446 Output more security debug output.
450 Show protocol messages.
454 Enable send/receive timeout on DTLS connections.
456 =item B<-mtu> I<size>
458 Set MTU of the link layer to the specified size.
462 Disable Encrypt-then-MAC negotiation.
466 Disable Extended master secret negotiation.
468 =item B<-keymatexport> I<label>
470 Export keying material using the specified label.
472 =item B<-keymatexportlen> I<len>
474 Export the specified number of bytes of keying material; default is 20.
476 Show all protocol messages with hex dump.
480 Show verbose trace output of protocol messages.
482 =item B<-msgfile> I<filename>
484 File to send output of B<-msg> or B<-trace> to, default standard output.
488 Tests nonblocking I/O
492 Turns on nonblocking I/O
496 This option translated a line feed from the terminal into CR+LF as required
501 Inhibit shutting down the connection when end of file is reached in the
506 Inhibit printing of session and certificate information. This implicitly
507 turns on B<-ign_eof> as well.
511 Shut down the connection when end of file is reached in the input.
512 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
514 =item B<-psk_identity> I<identity>
516 Use the PSK identity I<identity> when using a PSK cipher suite.
517 The default value is "Client_identity" (without the quotes).
521 Use the PSK key I<key> when using a PSK cipher suite. The key is
522 given as a hexadecimal number without leading 0x, for example -psk
524 This option must be provided in order to use a PSK cipher.
526 =item B<-psk_session> I<file>
528 Use the pem encoded SSL_SESSION data stored in I<file> as the basis of a PSK.
529 Note that this will only work if TLSv1.3 is negotiated.
533 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
534 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
535 available where OpenSSL has support for SCTP enabled.
537 =item B<-sctp_label_bug>
539 Use the incorrect behaviour of older OpenSSL implementations when computing
540 endpoint-pair shared secrets for DTLS/SCTP. This allows communication with
541 older broken implementations but breaks interoperability with correct
542 implementations. Must be used in conjunction with B<-sctp>. This option is only
543 available where OpenSSL has support for SCTP enabled.
545 =item B<-fallback_scsv>
547 Send TLS_FALLBACK_SCSV in the ClientHello.
551 Switch on asynchronous mode. Cryptographic operations will be performed
552 asynchronously. This will only have an effect if an asynchronous capable engine
553 is also used via the B<-engine> option. For test purposes the dummy async engine
554 (dasync) can be used (if available).
556 =item B<-maxfraglen> I<len>
558 Enable Maximum Fragment Length Negotiation; allowed values are
559 C<512>, C<1024>, C<2048>, and C<4096>.
561 =item B<-max_send_frag> I<int>
563 The maximum size of data fragment to send.
564 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
566 =item B<-split_send_frag> I<int>
568 The size used to split data for encrypt pipelines. If more data is written in
569 one go than this value then it will be split into multiple pipelines, up to the
570 maximum number of pipelines defined by max_pipelines. This only has an effect if
571 a suitable cipher suite has been negotiated, an engine that supports pipelining
572 has been loaded, and max_pipelines is greater than 1. See
573 L<SSL_CTX_set_split_send_fragment(3)> for further information.
575 =item B<-max_pipelines> I<int>
577 The maximum number of encrypt/decrypt pipelines to be used. This will only have
578 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
579 engine) and a suitable cipher suite has been negotiated. The default value is 1.
580 See L<SSL_CTX_set_max_pipelines(3)> for further information.
582 =item B<-read_buf> I<int>
584 The default read buffer size to be used for connections. This will only have an
585 effect if the buffer size is larger than the size that would otherwise be used
586 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
587 further information).
589 =item B<-ignore_unexpected_eof>
591 Some TLS implementations do not send the mandatory close_notify alert on
592 shutdown. If the application tries to wait for the close_notify alert but the
593 peer closes the connection without sending it, an error is generated. When this
594 option is enabled the peer does not need to send the close_notify alert and a
595 closed connection will be treated as if the close_notify alert was received.
596 For more information on shutting down a connection, see L<SSL_shutdown(3)>.
600 There are several known bugs in SSL and TLS implementations. Adding this
601 option enables various workarounds.
605 Enables support for SSL/TLS compression.
606 This option was introduced in OpenSSL 1.1.0.
607 TLS compression is not recommended and is off by default as of
612 Disables support for SSL/TLS compression.
613 TLS compression is not recommended and is off by default as of
618 Only provide a brief summary of connection parameters instead of the
619 normal verbose output.
621 =item B<-sigalgs> I<sigalglist>
623 Specifies the list of signature algorithms that are sent by the client.
624 The server selects one entry in the list based on its preferences.
625 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
627 =item B<-curves> I<curvelist>
629 Specifies the list of supported curves to be sent by the client. The curve is
630 ultimately selected by the server. For a list of all curves, use:
632 $ openssl ecparam -list_curves
634 =item B<-cipher> I<cipherlist>
636 This allows the TLSv1.2 and below cipher list sent by the client to be modified.
637 This list will be combined with any TLSv1.3 ciphersuites that have been
638 configured. Although the server determines which ciphersuite is used it should
639 take the first supported cipher in the list sent by the client. See
640 L<openssl-ciphers(1)> for more information.
642 =item B<-ciphersuites> I<val>
644 This allows the TLSv1.3 ciphersuites sent by the client to be modified. This
645 list will be combined with any TLSv1.2 and below ciphersuites that have been
646 configured. Although the server determines which cipher suite is used it should
647 take the first supported cipher in the list sent by the client. See
648 L<openssl-ciphers(1)> for more information. The format for this list is a simple
649 colon (":") separated list of TLSv1.3 ciphersuite names.
651 =item B<-starttls> I<protocol>
653 Send the protocol-specific message(s) to switch to TLS for communication.
654 I<protocol> is a keyword for the intended protocol. Currently, the only
655 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
656 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
658 =item B<-xmpphost> I<hostname>
660 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
661 specifies the host for the "to" attribute of the stream element.
662 If this option is not specified, then the host specified with "-connect"
665 This option is an alias of the B<-name> option for "xmpp" and "xmpp-server".
667 =item B<-name> I<hostname>
669 This option is used to specify hostname information for various protocols
670 used with B<-starttls> option. Currently only "xmpp", "xmpp-server",
671 "smtp" and "lmtp" can utilize this B<-name> option.
673 If this option is used with "-starttls xmpp" or "-starttls xmpp-server",
674 if specifies the host for the "to" attribute of the stream element. If this
675 option is not specified, then the host specified with "-connect" will be used.
677 If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies
678 the name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If
679 this option is not specified, then "mail.example.com" will be used.
681 =item B<-tlsextdebug>
683 Print out a hex dump of any TLS extensions received from the server.
687 Disable RFC4507bis session ticket support.
689 =item B<-sess_out> I<filename>
691 Output SSL session to I<filename>.
693 =item B<-sess_in> I<filename>
695 Load SSL session from I<filename>. The client will attempt to resume a
696 connection from this session.
698 =item B<-serverinfo> I<types>
700 A list of comma-separated TLS Extension Types (numbers between 0 and
701 65535). Each type will be sent as an empty ClientHello TLS Extension.
702 The server's response (if any) will be encoded and displayed as a PEM
707 Sends a certificate status request to the server (OCSP stapling). The server
708 response (if any) is printed out.
710 =item B<-alpn> I<protocols>, B<-nextprotoneg> I<protocols>
712 These flags enable the Enable the Application-Layer Protocol Negotiation
713 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
714 IETF standard and replaces NPN.
715 The I<protocols> list is a comma-separated list of protocol names that
716 the client should advertise support for. The list should contain the most
717 desirable protocols first. Protocol names are printable ASCII strings,
718 for example "http/1.1" or "spdy/3".
719 An empty list of protocols is treated specially and will cause the
720 client to advertise support for the TLS extension but disconnect just
721 after receiving ServerHello with a list of server supported protocols.
722 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
724 =item B<-ct>, B<-noct>
726 Use one of these two options to control whether Certificate Transparency (CT)
727 is enabled (B<-ct>) or disabled (B<-noct>).
728 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
729 the server and reported at handshake completion.
731 Enabling CT also enables OCSP stapling, as this is one possible delivery method
736 A file containing a list of known Certificate Transparency logs. See
737 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
739 =item B<-keylogfile> I<file>
741 Appends TLS secrets to the specified keylog file such that external programs
742 (like Wireshark) can decrypt TLS connections.
744 =item B<-early_data> I<file>
746 Reads the contents of the specified file and attempts to send it as early data
747 to the server. This will only work with resumed sessions that support early
748 data and when the server accepts the early data.
752 For TLSv1.3 only, send the Post-Handshake Authentication extension. This will
753 happen whether or not a certificate has been provided via B<-cert>.
755 =item B<-use_srtp> I<value>
757 Offer SRTP key management, where B<value> is a colon-separated profile list.
759 =item B<-srpuser> I<value>
761 Set the SRP username to the specified value. This option is deprecated.
763 =item B<-srppass> I<value>
765 Set the SRP password to the specified value. This option is deprecated.
767 =item B<-srp_lateuser>
769 SRP username for the second ClientHello message. This option is deprecated.
771 =item B<-srp_moregroups> This option is deprecated.
773 Tolerate other than the known B<g> and B<N> values.
775 =item B<-srp_strength> I<number>
777 Set the minimal acceptable length, in bits, for B<N>. This option is
782 Enable Kernel TLS for sending and receiving.
783 This option was introduced in OpenSSL 3.1.0.
784 Kernel TLS is off by default as of OpenSSL 3.1.0.
788 Enable creation of connections via TCP fast open (RFC7413).
790 {- $OpenSSL::safe::opt_version_item -}
792 {- $OpenSSL::safe::opt_name_item -}
794 {- $OpenSSL::safe::opt_x_item -}
796 {- $OpenSSL::safe::opt_trust_item -}
798 {- $OpenSSL::safe::opt_s_item -}
800 {- $OpenSSL::safe::opt_r_item -}
802 {- $OpenSSL::safe::opt_provider_item -}
804 {- $OpenSSL::safe::opt_engine_item -}
806 {- output_off() if $disabled{"deprecated-3.0"}; "" -}
807 =item B<-ssl_client_engine> I<id>
809 Specify engine to be used for client certificate operations.
810 {- output_on() if $disabled{"deprecated-3.0"}; "" -}
812 {- $OpenSSL::safe::opt_v_item -}
814 Verification errors are displayed, for debugging, but the command will
815 proceed unless the B<-verify_return_error> option is used.
817 =item I<host>:I<port>
819 Rather than providing B<-connect>, the target hostname and optional port may
820 be provided as a single positional argument after all options. If neither this
821 nor B<-connect> are provided, falls back to attempting to connect to
822 I<localhost> on port I<4433>.
826 =head1 CONNECTED COMMANDS
828 If a connection is established with an SSL server then any data received
829 from the server is displayed and any key presses will be sent to the
830 server. If end of file is reached then the connection will be closed down. When
831 used interactively (which means neither B<-quiet> nor B<-ign_eof> have been
832 given), then certain commands are also recognized which perform special
833 operations. These commands are a letter which must appear at the start of a
834 line. They are listed below.
840 End the current SSL connection and exit.
844 Renegotiate the SSL session (TLSv1.2 and below only).
848 Send a key update message to the server (TLSv1.3 only)
852 Send a key update message to the server and request one back (TLSv1.3 only)
858 This command can be used to debug SSL servers. To connect to an SSL HTTP
861 openssl s_client -connect servername:443
863 would typically be used (https uses port 443). If the connection succeeds
864 then an HTTP command can be given such as "GET /" to retrieve a web page.
866 If the handshake fails then there are several possible causes, if it is
867 nothing obvious like no client certificate then the B<-bugs>,
868 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
869 in case it is a buggy server. In particular you should play with these
870 options B<before> submitting a bug report to an OpenSSL mailing list.
872 A frequent problem when attempting to get client certificates working
873 is that a web client complains it has no certificates or gives an empty
874 list to choose from. This is normally because the server is not sending
875 the clients certificate authority in its "acceptable CA list" when it
876 requests a certificate. By using this command, the CA list can be viewed
877 and checked. However, some servers only request client authentication
878 after a specific URL is requested. To obtain the list in this case it
879 is necessary to use the B<-prexit> option and send an HTTP request
880 for an appropriate page.
882 If a certificate is specified on the command line using the B<-cert>
883 option it will not be used unless the server specifically requests
884 a client certificate. Therefore, merely including a client certificate
885 on the command line is no guarantee that the certificate works.
887 If there are problems verifying a server certificate then the
888 B<-showcerts> option can be used to show all the certificates sent by the
891 This command is a test tool and is designed to continue the
892 handshake after any certificate verification errors. As a result it will
893 accept any certificate chain (trusted or not) sent by the peer. Non-test
894 applications should B<not> do this as it makes them vulnerable to a MITM
895 attack. This behaviour can be changed by with the B<-verify_return_error>
896 option: any verify errors are then returned aborting the handshake.
898 The B<-bind> option may be useful if the server or a firewall requires
899 connections to come from some particular address and or port.
903 Because this program has a lot of options and also because some of the
904 techniques used are rather old, the C source for this command is rather
905 hard to read and not a model of how things should be done.
906 A typical SSL client program would be much simpler.
908 The B<-prexit> option is a bit of a hack. We should really report
909 information whenever a session is renegotiated.
914 L<openssl-sess_id(1)>,
915 L<openssl-s_server(1)>,
916 L<openssl-ciphers(1)>,
918 L<SSL_CTX_set_max_send_fragment(3)>,
919 L<SSL_CTX_set_split_send_fragment(3)>,
920 L<SSL_CTX_set_max_pipelines(3)>,
921 L<ossl_store-file(7)>
925 The B<-no_alt_chains> option was added in OpenSSL 1.1.0.
926 The B<-name> option was added in OpenSSL 1.1.1.
928 The B<-certform> option has become obsolete in OpenSSL 3.0.0 and has no effect.
930 The B<-engine> option was deprecated in OpenSSL 3.0.
932 The -tfo option was added in OpenSSL 3.1.
936 Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
938 Licensed under the Apache License 2.0 (the "License"). You may not use
939 this file except in compliance with the License. You can obtain a copy
940 in the file LICENSE in the source distribution or at
941 L<https://www.openssl.org/source/license.html>.