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>]
55 [B<-security_debug_verbose>]
59 [B<-keymatexport> I<label>]
60 [B<-keymatexportlen> I<len>]
61 [B<-msgfile> I<filename>]
68 [B<-psk_identity> I<identity>]
70 [B<-psk_session> I<file>]
76 [B<-maxfraglen> I<len>]
81 [B<-ignore_unexpected_eof>]
86 [B<-legacy_server_connect>]
87 [B<-allow_no_dhe_kex>]
88 [B<-sigalgs> I<sigalglist>]
89 [B<-curves> I<curvelist>]
90 [B<-cipher> I<cipherlist>]
91 [B<-ciphersuites> I<val>]
93 [B<-starttls> I<protocol>]
94 [B<-name> I<hostname>]
95 [B<-xmpphost> I<hostname>]
96 [B<-name> I<hostname>]
99 [B<-sess_out> I<filename>]
100 [B<-serverinfo> I<types>]
101 [B<-sess_in> I<filename>]
102 [B<-serverinfo> I<types>]
104 [B<-alpn> I<protocols>]
105 [B<-nextprotoneg> I<protocols>]
109 [B<-keylogfile> I<file>]
110 [B<-early_data> I<file>]
112 [B<-use_srtp> I<value>]
113 [B<-srpuser> I<value>]
114 [B<-srppass> I<value>]
117 [B<-srp_strength> I<number>]
118 {- $OpenSSL::safe::opt_name_synopsis -}
119 {- $OpenSSL::safe::opt_version_synopsis -}
120 {- $OpenSSL::safe::opt_x_synopsis -}
121 {- $OpenSSL::safe::opt_trust_synopsis -}
122 {- $OpenSSL::safe::opt_s_synopsis -}
123 {- $OpenSSL::safe::opt_r_synopsis -}
124 {- $OpenSSL::safe::opt_provider_synopsis -}
125 {- $OpenSSL::safe::opt_engine_synopsis -}[B<-ssl_client_engine> I<id>]
126 {- $OpenSSL::safe::opt_v_synopsis -}
131 This command implements a generic SSL/TLS client which
132 connects to a remote host using SSL/TLS. It is a I<very> useful diagnostic
133 tool for SSL servers.
137 In addition to the options below, this command also supports the
138 common and client only options documented
139 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
146 Print out a usage message.
148 =item B<-ssl_config> I<section>
150 Use the specified section of the configuration file to configure the B<SSL_CTX> object.
152 =item B<-connect> I<host>:I<port>
154 This specifies the host and optional port to connect to. It is possible to
155 select the host and port using the optional target positional argument instead.
156 If neither this nor the target positional argument are specified then an attempt
157 is made to connect to the local host on port 4433.
159 =item B<-host> I<hostname>
161 Host to connect to; use B<-connect> instead.
163 =item B<-port> I<port>
165 Connect to the specified port; use B<-connect> instead.
167 =item B<-bind> I<host:port>
169 This specifies the host address and or port to bind as the source for the
170 connection. For Unix-domain sockets the port is ignored and the host is
171 used as the source socket address.
173 =item B<-proxy> I<host:port>
175 When used with the B<-connect> flag, the program uses the host and port
176 specified with this flag and issues an HTTP CONNECT command to connect
177 to the desired server.
179 =item B<-proxy_user> I<userid>
181 When used with the B<-proxy> flag, the program will attempt to authenticate
182 with the specified proxy using basic (base64) authentication.
183 NB: Basic authentication is insecure; the credentials are sent to the proxy
184 in easily reversible base64 encoding before any TLS/SSL session is established.
185 Therefore, these credentials are easily recovered by anyone able to sniff/trace
186 the network. Use with caution.
188 =item B<-proxy_pass> I<arg>
190 The proxy password source, used with the B<-proxy_user> flag.
191 For more information about the format of B<arg>
192 see L<openssl-passphrase-options(1)>.
194 =item B<-unix> I<path>
196 Connect over the specified Unix-domain socket.
206 =item B<-servername> I<name>
208 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
210 If B<-servername> is not provided, the TLS SNI extension will be populated with
211 the name given to B<-connect> if it follows a DNS name format. If B<-connect> is
212 not provided either, the SNI is set to "localhost".
213 This is the default since OpenSSL 1.1.1.
215 Even though SNI should normally be a DNS name and not an IP address, if
216 B<-servername> is provided then that name will be sent, regardless of whether
217 it is a DNS name or not.
219 This option cannot be used in conjunction with B<-noservername>.
221 =item B<-noservername>
223 Suppresses sending of the SNI (Server Name Indication) extension in the
224 ClientHello message. Cannot be used in conjunction with the B<-servername> or
225 B<-dane_tlsa_domain> options.
227 =item B<-cert> I<filename>
229 The client certificate to use, if one is requested by the server.
230 The default is not to use a certificate.
232 The chain for the client certificate may be specified using B<-cert_chain>.
234 =item B<-certform> B<DER>|B<PEM>|B<P12>
236 The client certificate file format to use; unspecified by default.
237 See L<openssl-format-options(1)> for details.
241 A file or URI of untrusted certificates to use when attempting to build the
242 certificate chain related to the certificate specified via the B<-cert> option.
243 The input can be in PEM, DER, or PKCS#12 format.
245 =item B<-build_chain>
247 Specify whether the application should build the client certificate chain to be
248 provided to the server.
250 =item B<-CRL> I<filename>
252 CRL file to use to check the server's certificate.
254 =item B<-CRLform> B<DER>|B<PEM>
256 The CRL file format; unspecified by default.
257 See L<openssl-format-options(1)> for details.
259 =item B<-crl_download>
261 Download CRL from distribution points in the certificate.
263 =item B<-key> I<filename>|I<uri>
265 The client private key to use.
266 If not specified then the certificate file will be used to read also the key.
268 =item B<-keyform> B<DER>|B<PEM>|B<P12>|B<ENGINE>
270 The key format; unspecified by default.
271 See L<openssl-format-options(1)> for details.
273 =item B<-pass> I<arg>
275 the private key and certifiate file password source.
276 For more information about the format of I<arg>
277 see L<openssl-passphrase-options(1)>.
279 =item B<-verify> I<depth>
281 The verify depth to use. This specifies the maximum length of the
282 server certificate chain and turns on server certificate verification.
283 Currently the verify operation continues after errors so all the problems
284 with a certificate chain can be seen. As a side effect the connection
285 will never fail due to a server certificate verify failure.
287 =item B<-verify_return_error>
289 Return verification errors instead of continuing. This will typically
290 abort the handshake with a fatal error.
292 =item B<-verify_quiet>
294 Limit verify output to only errors.
296 =item B<-verifyCAfile> I<filename>
298 A file in PEM format containing trusted certificates to use
299 for verifying the server's certificate.
301 =item B<-verifyCApath> I<dir>
303 A directory containing trusted certificates to use
304 for verifying the server's certificate.
305 This directory must be in "hash format",
306 see L<openssl-verify(1)> for more information.
308 =item B<-verifyCAstore> I<uri>
310 The URI of a store containing trusted certificates to use
311 for verifying the server's certificate.
313 =item B<-chainCAfile> I<file>
315 A file in PEM format containing trusted certificates to use
316 when attempting to build the client certificate chain.
318 =item B<-chainCApath> I<directory>
320 A directory containing trusted certificates to use
321 for building the client certificate chain provided to the server.
322 This directory must be in "hash format",
323 see L<openssl-verify(1)> for more information.
325 =item B<-chainCAstore> I<uri>
327 The URI of a store containing trusted certificates to use
328 when attempting to build the client certificate chain.
329 The URI may indicate a single certificate, as well as a collection of them.
330 With URIs in the C<file:> scheme, this acts as B<-chainCAfile> or
331 B<-chainCApath>, depending on if the URI indicates a directory or a
333 See L<ossl_store-file(7)> for more information on the C<file:> scheme.
335 =item B<-requestCAfile> I<file>
337 A file containing a list of certificates whose subject names will be sent
338 to the server in the B<certificate_authorities> extension. Only supported
341 =item B<-dane_tlsa_domain> I<domain>
343 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
344 TLSA base domain which becomes the default SNI hint and the primary
345 reference identifier for hostname checks. This must be used in
346 combination with at least one instance of the B<-dane_tlsa_rrdata>
349 When DANE authentication succeeds, the diagnostic output will include
350 the lowest (closest to 0) depth at which a TLSA record authenticated
351 a chain certificate. When that TLSA record is a "2 1 0" trust
352 anchor public key that signed (rather than matched) the top-most
353 certificate of the chain, the result is reported as "TA public key
354 verified". Otherwise, either the TLSA record "matched TA certificate"
355 at a positive depth or else "matched EE certificate" at depth 0.
357 =item B<-dane_tlsa_rrdata> I<rrdata>
359 Use one or more times to specify the RRDATA fields of the DANE TLSA
360 RRset associated with the target service. The I<rrdata> value is
361 specified in "presentation form", that is four whitespace separated
362 fields that specify the usage, selector, matching type and associated
363 data, with the last of these encoded in hexadecimal. Optional
364 whitespace is ignored in the associated data field. For example:
366 $ openssl s_client -brief -starttls smtp \
367 -connect smtp.example.com:25 \
368 -dane_tlsa_domain smtp.example.com \
369 -dane_tlsa_rrdata "2 1 1
370 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
371 -dane_tlsa_rrdata "2 1 1
372 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
375 Verified peername: smtp.example.com
376 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
379 =item B<-dane_ee_no_namechecks>
381 This disables server name checks when authenticating via DANE-EE(3) TLSA
383 For some applications, primarily web browsers, it is not safe to disable name
384 checks due to "unknown key share" attacks, in which a malicious server can
385 convince a client that a connection to a victim server is instead a secure
386 connection to the malicious server.
387 The malicious server may then be able to violate cross-origin scripting
389 Thus, despite the text of RFC7671, name checks are by default enabled for
390 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
392 In particular, SMTP and XMPP clients should set this option as SRV and MX
393 records already make it possible for a remote domain to redirect client
394 connections to any server of its choice, and in any case SMTP and XMPP clients
395 do not execute scripts downloaded from remote servers.
399 Reconnects to the same server 5 times using the same session ID, this can
400 be used as a test that session caching is working.
404 Displays the server certificate list as sent by the server: it only consists of
405 certificates the server has sent (in the order the server has sent them). It is
406 B<not> a verified chain.
410 Print session information when the program exits. This will always attempt
411 to print out information even if the connection fails. Normally information
412 will only be printed out once if the connection succeeds. This option is useful
413 because the cipher in use may be renegotiated or the connection may fail
414 because a client certificate is required or is requested only after an
415 attempt is made to access a certain URL. Note: the output produced by this
416 option is not always accurate because a connection might never have been
421 Prints out the SSL session states.
425 Print extensive debugging information including a hex dump of all traffic.
429 Do not use interactive command letters.
431 =item B<-security_debug>
433 Enable security debug messages.
435 =item B<-security_debug_verbose>
437 Output more security debug output.
441 Show protocol messages.
445 Enable send/receive timeout on DTLS connections.
447 =item B<-mtu> I<size>
449 Set MTU of the link layer to the specified size.
451 =item B<-keymatexport> I<label>
453 Export keying material using the specified label.
455 =item B<-keymatexportlen> I<len>
457 Export the specified number of bytes of keying material; default is 20.
459 Show all protocol messages with hex dump.
463 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
464 with B<enable-ssl-trace> for this option to work.
466 =item B<-msgfile> I<filename>
468 File to send output of B<-msg> or B<-trace> to, default standard output.
472 Tests nonblocking I/O
476 Turns on nonblocking I/O
480 This option translated a line feed from the terminal into CR+LF as required
485 Inhibit shutting down the connection when end of file is reached in the
490 Inhibit printing of session and certificate information. This implicitly
491 turns on B<-ign_eof> as well.
495 Shut down the connection when end of file is reached in the input.
496 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
498 =item B<-psk_identity> I<identity>
500 Use the PSK identity I<identity> when using a PSK cipher suite.
501 The default value is "Client_identity" (without the quotes).
505 Use the PSK key I<key> when using a PSK cipher suite. The key is
506 given as a hexadecimal number without leading 0x, for example -psk
508 This option must be provided in order to use a PSK cipher.
510 =item B<-psk_session> I<file>
512 Use the pem encoded SSL_SESSION data stored in I<file> as the basis of a PSK.
513 Note that this will only work if TLSv1.3 is negotiated.
517 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
518 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
519 available where OpenSSL has support for SCTP enabled.
521 =item B<-sctp_label_bug>
523 Use the incorrect behaviour of older OpenSSL implementations when computing
524 endpoint-pair shared secrets for DTLS/SCTP. This allows communication with
525 older broken implementations but breaks interoperability with correct
526 implementations. Must be used in conjunction with B<-sctp>. This option is only
527 available where OpenSSL has support for SCTP enabled.
529 =item B<-fallback_scsv>
531 Send TLS_FALLBACK_SCSV in the ClientHello.
535 Switch on asynchronous mode. Cryptographic operations will be performed
536 asynchronously. This will only have an effect if an asynchronous capable engine
537 is also used via the B<-engine> option. For test purposes the dummy async engine
538 (dasync) can be used (if available).
540 =item B<-maxfraglen> I<len>
542 Enable Maximum Fragment Length Negotiation; allowed values are
543 C<512>, C<1024>, C<2048>, and C<4096>.
545 =item B<-max_send_frag> I<int>
547 The maximum size of data fragment to send.
548 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
550 =item B<-split_send_frag> I<int>
552 The size used to split data for encrypt pipelines. If more data is written in
553 one go than this value then it will be split into multiple pipelines, up to the
554 maximum number of pipelines defined by max_pipelines. This only has an effect if
555 a suitable cipher suite has been negotiated, an engine that supports pipelining
556 has been loaded, and max_pipelines is greater than 1. See
557 L<SSL_CTX_set_split_send_fragment(3)> for further information.
559 =item B<-max_pipelines> I<int>
561 The maximum number of encrypt/decrypt pipelines to be used. This will only have
562 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
563 engine) and a suitable cipher suite has been negotiated. The default value is 1.
564 See L<SSL_CTX_set_max_pipelines(3)> for further information.
566 =item B<-read_buf> I<int>
568 The default read buffer size to be used for connections. This will only have an
569 effect if the buffer size is larger than the size that would otherwise be used
570 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
571 further information).
573 =item B<-ignore_unexpected_eof>
575 Some TLS implementations do not send the mandatory close_notify alert on
576 shutdown. If the application tries to wait for the close_notify alert but the
577 peer closes the connection without sending it, an error is generated. When this
578 option is enabled the peer does not need to send the close_notify alert and a
579 closed connection will be treated as if the close_notify alert was received.
580 For more information on shutting down a connection, see L<SSL_shutdown(3)>.
584 There are several known bugs in SSL and TLS implementations. Adding this
585 option enables various workarounds.
589 Enables support for SSL/TLS compression.
590 This option was introduced in OpenSSL 1.1.0.
591 TLS compression is not recommended and is off by default as of
596 Disables support for SSL/TLS compression.
597 TLS compression is not recommended and is off by default as of
602 Only provide a brief summary of connection parameters instead of the
603 normal verbose output.
605 =item B<-sigalgs> I<sigalglist>
607 Specifies the list of signature algorithms that are sent by the client.
608 The server selects one entry in the list based on its preferences.
609 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
611 =item B<-curves> I<curvelist>
613 Specifies the list of supported curves to be sent by the client. The curve is
614 ultimately selected by the server. For a list of all curves, use:
616 $ openssl ecparam -list_curves
618 =item B<-cipher> I<cipherlist>
620 This allows the TLSv1.2 and below cipher list sent by the client to be modified.
621 This list will be combined with any TLSv1.3 ciphersuites that have been
622 configured. Although the server determines which ciphersuite is used it should
623 take the first supported cipher in the list sent by the client. See
624 L<openssl-ciphers(1)> for more information.
626 =item B<-ciphersuites> I<val>
628 This allows the TLSv1.3 ciphersuites sent by the client to be modified. This
629 list will be combined with any TLSv1.2 and below ciphersuites that have been
630 configured. Although the server determines which cipher suite is used it should
631 take the first supported cipher in the list sent by the client. See
632 L<openssl-ciphers(1)> for more information. The format for this list is a simple
633 colon (":") separated list of TLSv1.3 ciphersuite names.
635 =item B<-starttls> I<protocol>
637 Send the protocol-specific message(s) to switch to TLS for communication.
638 I<protocol> is a keyword for the intended protocol. Currently, the only
639 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
640 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
642 =item B<-xmpphost> I<hostname>
644 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
645 specifies the host for the "to" attribute of the stream element.
646 If this option is not specified, then the host specified with "-connect"
649 This option is an alias of the B<-name> option for "xmpp" and "xmpp-server".
651 =item B<-name> I<hostname>
653 This option is used to specify hostname information for various protocols
654 used with B<-starttls> option. Currently only "xmpp", "xmpp-server",
655 "smtp" and "lmtp" can utilize this B<-name> option.
657 If this option is used with "-starttls xmpp" or "-starttls xmpp-server",
658 if specifies the host for the "to" attribute of the stream element. If this
659 option is not specified, then the host specified with "-connect" will be used.
661 If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies
662 the name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If
663 this option is not specified, then "mail.example.com" will be used.
665 =item B<-tlsextdebug>
667 Print out a hex dump of any TLS extensions received from the server.
671 Disable RFC4507bis session ticket support.
673 =item B<-sess_out> I<filename>
675 Output SSL session to I<filename>.
677 =item B<-sess_in> I<filename>
679 Load SSL session from I<filename>. The client will attempt to resume a
680 connection from this session.
682 =item B<-serverinfo> I<types>
684 A list of comma-separated TLS Extension Types (numbers between 0 and
685 65535). Each type will be sent as an empty ClientHello TLS Extension.
686 The server's response (if any) will be encoded and displayed as a PEM
691 Sends a certificate status request to the server (OCSP stapling). The server
692 response (if any) is printed out.
694 =item B<-alpn> I<protocols>, B<-nextprotoneg> I<protocols>
696 These flags enable the Enable the Application-Layer Protocol Negotiation
697 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
698 IETF standard and replaces NPN.
699 The I<protocols> list is a comma-separated list of protocol names that
700 the client should advertise support for. The list should contain the most
701 desirable protocols first. Protocol names are printable ASCII strings,
702 for example "http/1.1" or "spdy/3".
703 An empty list of protocols is treated specially and will cause the
704 client to advertise support for the TLS extension but disconnect just
705 after receiving ServerHello with a list of server supported protocols.
706 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
708 =item B<-ct>, B<-noct>
710 Use one of these two options to control whether Certificate Transparency (CT)
711 is enabled (B<-ct>) or disabled (B<-noct>).
712 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
713 the server and reported at handshake completion.
715 Enabling CT also enables OCSP stapling, as this is one possible delivery method
720 A file containing a list of known Certificate Transparency logs. See
721 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
723 =item B<-keylogfile> I<file>
725 Appends TLS secrets to the specified keylog file such that external programs
726 (like Wireshark) can decrypt TLS connections.
728 =item B<-early_data> I<file>
730 Reads the contents of the specified file and attempts to send it as early data
731 to the server. This will only work with resumed sessions that support early
732 data and when the server accepts the early data.
736 For TLSv1.3 only, send the Post-Handshake Authentication extension. This will
737 happen whether or not a certificate has been provided via B<-cert>.
739 =item B<-use_srtp> I<value>
741 Offer SRTP key management, where B<value> is a colon-separated profile list.
743 =item B<-srpuser> I<value>
745 Set the SRP username to the specified value. This option is deprecated.
747 =item B<-srppass> I<value>
749 Set the SRP password to the specified value. This option is deprecated.
751 =item B<-srp_lateuser>
753 SRP username for the second ClientHello message. This option is deprecated.
755 =item B<-srp_moregroups> This option is deprecated.
757 Tolerate other than the known B<g> and B<N> values.
759 =item B<-srp_strength> I<number>
761 Set the minimal acceptable length, in bits, for B<N>. This option is
764 {- $OpenSSL::safe::opt_version_item -}
766 {- $OpenSSL::safe::opt_name_item -}
768 {- $OpenSSL::safe::opt_x_item -}
770 {- $OpenSSL::safe::opt_trust_item -}
772 {- $OpenSSL::safe::opt_s_item -}
774 {- $OpenSSL::safe::opt_r_item -}
776 {- $OpenSSL::safe::opt_provider_item -}
778 {- $OpenSSL::safe::opt_engine_item -}
780 {- output_off() if $disabled{"deprecated-3.0"}; "" -}
781 =item B<-ssl_client_engine> I<id>
783 Specify engine to be used for client certificate operations.
784 {- output_on() if $disabled{"deprecated-3.0"}; "" -}
786 {- $OpenSSL::safe::opt_v_item -}
788 Verification errors are displayed, for debugging, but the command will
789 proceed unless the B<-verify_return_error> option is used.
791 =item I<host>:I<port>
793 Rather than providing B<-connect>, the target hostname and optional port may
794 be provided as a single positional argument after all options. If neither this
795 nor B<-connect> are provided, falls back to attempting to connect to
796 I<localhost> on port I<4433>.
800 =head1 CONNECTED COMMANDS
802 If a connection is established with an SSL server then any data received
803 from the server is displayed and any key presses will be sent to the
804 server. If end of file is reached then the connection will be closed down. When
805 used interactively (which means neither B<-quiet> nor B<-ign_eof> have been
806 given), then certain commands are also recognized which perform special
807 operations. These commands are a letter which must appear at the start of a
808 line. They are listed below.
814 End the current SSL connection and exit.
818 Renegotiate the SSL session (TLSv1.2 and below only).
822 Send a key update message to the server (TLSv1.3 only)
826 Send a key update message to the server and request one back (TLSv1.3 only)
832 This command can be used to debug SSL servers. To connect to an SSL HTTP
835 openssl s_client -connect servername:443
837 would typically be used (https uses port 443). If the connection succeeds
838 then an HTTP command can be given such as "GET /" to retrieve a web page.
840 If the handshake fails then there are several possible causes, if it is
841 nothing obvious like no client certificate then the B<-bugs>,
842 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
843 in case it is a buggy server. In particular you should play with these
844 options B<before> submitting a bug report to an OpenSSL mailing list.
846 A frequent problem when attempting to get client certificates working
847 is that a web client complains it has no certificates or gives an empty
848 list to choose from. This is normally because the server is not sending
849 the clients certificate authority in its "acceptable CA list" when it
850 requests a certificate. By using this command, the CA list can be viewed
851 and checked. However, some servers only request client authentication
852 after a specific URL is requested. To obtain the list in this case it
853 is necessary to use the B<-prexit> option and send an HTTP request
854 for an appropriate page.
856 If a certificate is specified on the command line using the B<-cert>
857 option it will not be used unless the server specifically requests
858 a client certificate. Therefore, merely including a client certificate
859 on the command line is no guarantee that the certificate works.
861 If there are problems verifying a server certificate then the
862 B<-showcerts> option can be used to show all the certificates sent by the
865 This command is a test tool and is designed to continue the
866 handshake after any certificate verification errors. As a result it will
867 accept any certificate chain (trusted or not) sent by the peer. Non-test
868 applications should B<not> do this as it makes them vulnerable to a MITM
869 attack. This behaviour can be changed by with the B<-verify_return_error>
870 option: any verify errors are then returned aborting the handshake.
872 The B<-bind> option may be useful if the server or a firewall requires
873 connections to come from some particular address and or port.
877 Because this program has a lot of options and also because some of the
878 techniques used are rather old, the C source for this command is rather
879 hard to read and not a model of how things should be done.
880 A typical SSL client program would be much simpler.
882 The B<-prexit> option is a bit of a hack. We should really report
883 information whenever a session is renegotiated.
888 L<openssl-sess_id(1)>,
889 L<openssl-s_server(1)>,
890 L<openssl-ciphers(1)>,
892 L<SSL_CTX_set_max_send_fragment(3)>,
893 L<SSL_CTX_set_split_send_fragment(3)>,
894 L<SSL_CTX_set_max_pipelines(3)>,
895 L<ossl_store-file(7)>
899 The B<-no_alt_chains> option was added in OpenSSL 1.1.0.
900 The B<-name> option was added in OpenSSL 1.1.1.
902 The B<-certform> option has become obsolete in OpenSSL 3.0.0 and has no effect.
904 The B<-engine> option was deprecated in OpenSSL 3.0.
908 Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
910 Licensed under the Apache License 2.0 (the "License"). You may not use
911 this file except in compliance with the License. You can obtain a copy
912 in the file LICENSE in the source distribution or at
913 L<https://www.openssl.org/source/license.html>.