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>]
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<-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 client certificate to use, if one is requested by the server.
240 The default is not to use a certificate.
242 The chain for the client certificate may be specified using B<-cert_chain>.
244 =item B<-certform> B<DER>|B<PEM>|B<P12>
246 The client certificate file format to use; the default is B<PEM>.
247 This option has no effect and is retained for backward compatibility only.
251 A file containing untrusted certificates to use when attempting to build the
252 certificate chain related to the certificate specified via the B<-cert> option.
254 =item B<-build_chain>
256 Specify whether the application should build the client certificate chain to be
257 provided to the server.
259 =item B<-CRL> I<filename>
261 CRL file to use to check the server's certificate.
263 =item B<-CRLform> B<DER>|B<PEM>
265 The CRL file format; the default is B<PEM>.
266 See L<openssl(1)/Format Options> for details.
268 =item B<-crl_download>
270 Download CRL from distribution points in the certificate.
272 =item B<-key> I<keyfile>
274 The client private key file to use.
275 If not specified then the certificate file will be used to read also the key.
277 =item B<-keyform> B<DER>|B<PEM>|B<P12>|B<ENGINE>
279 The key format; the default is B<PEM>.
280 The only value with effect is B<ENGINE>; all others have become obsolete.
281 See L<openssl(1)/Format Options> for details.
283 =item B<-pass> I<arg>
285 the private key password source. For more information about the format of I<arg>
286 see L<openssl(1)/Pass phrase options>.
288 =item B<-verify> I<depth>
290 The verify depth to use. This specifies the maximum length of the
291 server certificate chain and turns on server certificate verification.
292 Currently the verify operation continues after errors so all the problems
293 with a certificate chain can be seen. As a side effect the connection
294 will never fail due to a server certificate verify failure.
296 =item B<-verify_return_error>
298 Return verification errors instead of continuing. This will typically
299 abort the handshake with a fatal error.
301 =item B<-verify_quiet>
303 Limit verify output to only errors.
305 =item B<-verifyCAfile> I<filename>
307 A file in PEM format containing trusted certificates to use
308 for verifying the server's certificate.
310 =item B<-verifyCApath> I<dir>
312 A directory containing trusted certificates to use
313 for verifying the server's certificate.
314 This directory must be in "hash format",
315 see L<openssl-verify(1)> for more information.
317 =item B<-verifyCAstore> I<uri>
319 The URI of a store containing trusted certificates to use
320 for verifying the server's certificate.
322 =item B<-chainCAfile> I<file>
324 A file in PEM format containing trusted certificates to use
325 when attempting to build the client certificate chain.
327 =item B<-chainCApath> I<directory>
329 A directory containing trusted certificates to use
330 for building the client certificate chain provided to the server.
331 This directory must be in "hash format",
332 see L<openssl-verify(1)> for more information.
334 =item B<-chainCAstore> I<uri>
336 The URI of a store containing trusted certificates to use
337 when attempting to build the client certificate chain.
338 The URI may indicate a single certificate, as well as a collection of them.
339 With URIs in the C<file:> scheme, this acts as B<-chainCAfile> or
340 B<-chainCApath>, depending on if the URI indicates a directory or a
342 See L<ossl_store-file(7)> for more information on the C<file:> scheme.
344 =item B<-requestCAfile> I<file>
346 A file containing a list of certificates whose subject names will be sent
347 to the server in the B<certificate_authorities> extension. Only supported
350 =item B<-dane_tlsa_domain> I<domain>
352 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
353 TLSA base domain which becomes the default SNI hint and the primary
354 reference identifier for hostname checks. This must be used in
355 combination with at least one instance of the B<-dane_tlsa_rrdata>
358 When DANE authentication succeeds, the diagnostic output will include
359 the lowest (closest to 0) depth at which a TLSA record authenticated
360 a chain certificate. When that TLSA record is a "2 1 0" trust
361 anchor public key that signed (rather than matched) the top-most
362 certificate of the chain, the result is reported as "TA public key
363 verified". Otherwise, either the TLSA record "matched TA certificate"
364 at a positive depth or else "matched EE certificate" at depth 0.
366 =item B<-dane_tlsa_rrdata> I<rrdata>
368 Use one or more times to specify the RRDATA fields of the DANE TLSA
369 RRset associated with the target service. The I<rrdata> value is
370 specified in "presentation form", that is four whitespace separated
371 fields that specify the usage, selector, matching type and associated
372 data, with the last of these encoded in hexadecimal. Optional
373 whitespace is ignored in the associated data field. For example:
375 $ openssl s_client -brief -starttls smtp \
376 -connect smtp.example.com:25 \
377 -dane_tlsa_domain smtp.example.com \
378 -dane_tlsa_rrdata "2 1 1
379 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
380 -dane_tlsa_rrdata "2 1 1
381 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
384 Verified peername: smtp.example.com
385 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
388 =item B<-dane_ee_no_namechecks>
390 This disables server name checks when authenticating via DANE-EE(3) TLSA
392 For some applications, primarily web browsers, it is not safe to disable name
393 checks due to "unknown key share" attacks, in which a malicious server can
394 convince a client that a connection to a victim server is instead a secure
395 connection to the malicious server.
396 The malicious server may then be able to violate cross-origin scripting
398 Thus, despite the text of RFC7671, name checks are by default enabled for
399 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
401 In particular, SMTP and XMPP clients should set this option as SRV and MX
402 records already make it possible for a remote domain to redirect client
403 connections to any server of its choice, and in any case SMTP and XMPP clients
404 do not execute scripts downloaded from remote servers.
408 Reconnects to the same server 5 times using the same session ID, this can
409 be used as a test that session caching is working.
413 Displays the server certificate list as sent by the server: it only consists of
414 certificates the server has sent (in the order the server has sent them). It is
415 B<not> a verified chain.
419 Print session information when the program exits. This will always attempt
420 to print out information even if the connection fails. Normally information
421 will only be printed out once if the connection succeeds. This option is useful
422 because the cipher in use may be renegotiated or the connection may fail
423 because a client certificate is required or is requested only after an
424 attempt is made to access a certain URL. Note: the output produced by this
425 option is not always accurate because a connection might never have been
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.
460 =item B<-keymatexport> I<label>
462 Export keying material using the specified label.
464 =item B<-keymatexportlen> I<len>
466 Export the specified number of bytes of keying material; default is 20.
468 Show all protocol messages with hex dump.
472 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
473 with B<enable-ssl-trace> for this option to work.
475 =item B<-msgfile> I<filename>
477 File to send output of B<-msg> or B<-trace> to, default standard output.
481 Tests non-blocking I/O
485 Turns on non-blocking I/O
489 This option translated a line feed from the terminal into CR+LF as required
494 Inhibit shutting down the connection when end of file is reached in the
499 Inhibit printing of session and certificate information. This implicitly
500 turns on B<-ign_eof> as well.
504 Shut down the connection when end of file is reached in the input.
505 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
507 =item B<-psk_identity> I<identity>
509 Use the PSK identity I<identity> when using a PSK cipher suite.
510 The default value is "Client_identity" (without the quotes).
514 Use the PSK key I<key> when using a PSK cipher suite. The key is
515 given as a hexadecimal number without leading 0x, for example -psk
517 This option must be provided in order to use a PSK cipher.
519 =item B<-psk_session> I<file>
521 Use the pem encoded SSL_SESSION data stored in I<file> as the basis of a PSK.
522 Note that this will only work if TLSv1.3 is negotiated.
526 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
527 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
528 available where OpenSSL has support for SCTP enabled.
530 =item B<-sctp_label_bug>
532 Use the incorrect behaviour of older OpenSSL implementations when computing
533 endpoint-pair shared secrets for DTLS/SCTP. This allows communication with
534 older broken implementations but breaks interoperability with correct
535 implementations. Must be used in conjunction with B<-sctp>. This option is only
536 available where OpenSSL has support for SCTP enabled.
538 =item B<-fallback_scsv>
540 Send TLS_FALLBACK_SCSV in the ClientHello.
544 Switch on asynchronous mode. Cryptographic operations will be performed
545 asynchronously. This will only have an effect if an asynchronous capable engine
546 is also used via the B<-engine> option. For test purposes the dummy async engine
547 (dasync) can be used (if available).
549 =item B<-maxfraglen> I<len>
551 Enable Maximum Fragment Length Negotiation; allowed values are
552 C<512>, C<1024>, C<2048>, and C<4096>.
554 =item B<-max_send_frag> I<int>
556 The maximum size of data fragment to send.
557 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
559 =item B<-split_send_frag> I<int>
561 The size used to split data for encrypt pipelines. If more data is written in
562 one go than this value then it will be split into multiple pipelines, up to the
563 maximum number of pipelines defined by max_pipelines. This only has an effect if
564 a suitable cipher suite has been negotiated, an engine that supports pipelining
565 has been loaded, and max_pipelines is greater than 1. See
566 L<SSL_CTX_set_split_send_fragment(3)> for further information.
568 =item B<-max_pipelines> I<int>
570 The maximum number of encrypt/decrypt pipelines to be used. This will only have
571 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
572 engine) and a suitable cipher suite has been negotiated. The default value is 1.
573 See L<SSL_CTX_set_max_pipelines(3)> for further information.
575 =item B<-read_buf> I<int>
577 The default read buffer size to be used for connections. This will only have an
578 effect if the buffer size is larger than the size that would otherwise be used
579 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
580 further information).
582 =item B<-ignore_unexpected_eof>
584 Some TLS implementations do not send the mandatory close_notify alert on
585 shutdown. If the application tries to wait for the close_notify alert but the
586 peer closes the connection without sending it, an error is generated. When this
587 option is enabled the peer does not need to send the close_notify alert and a
588 closed connection will be treated as if the close_notify alert was received.
589 For more information on shutting down a connection, see L<SSL_shutdown(3)>.
593 There are several known bugs in SSL and TLS implementations. Adding this
594 option enables various workarounds.
598 Enables support for SSL/TLS compression.
599 This option was introduced in OpenSSL 1.1.0.
600 TLS compression is not recommended and is off by default as of
605 Disables support for SSL/TLS compression.
606 TLS compression is not recommended and is off by default as of
611 Only provide a brief summary of connection parameters instead of the
612 normal verbose output.
614 =item B<-sigalgs> I<sigalglist>
616 Specifies the list of signature algorithms that are sent by the client.
617 The server selects one entry in the list based on its preferences.
618 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
620 =item B<-curves> I<curvelist>
622 Specifies the list of supported curves to be sent by the client. The curve is
623 ultimately selected by the server. For a list of all curves, use:
625 $ openssl ecparam -list_curves
627 =item B<-cipher> I<cipherlist>
629 This allows the TLSv1.2 and below cipher list sent by the client to be modified.
630 This list will be combined with any TLSv1.3 ciphersuites that have been
631 configured. Although the server determines which ciphersuite is used it should
632 take the first supported cipher in the list sent by the client. See
633 L<openssl-ciphers(1)> for more information.
635 =item B<-ciphersuites> I<val>
637 This allows the TLSv1.3 ciphersuites sent by the client to be modified. This
638 list will be combined with any TLSv1.2 and below ciphersuites that have been
639 configured. Although the server determines which cipher suite is used it should
640 take the first supported cipher in the list sent by the client. See
641 L<openssl-ciphers(1)> for more information. The format for this list is a simple
642 colon (":") separated list of TLSv1.3 ciphersuite names.
644 =item B<-starttls> I<protocol>
646 Send the protocol-specific message(s) to switch to TLS for communication.
647 I<protocol> is a keyword for the intended protocol. Currently, the only
648 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
649 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
651 =item B<-xmpphost> I<hostname>
653 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
654 specifies the host for the "to" attribute of the stream element.
655 If this option is not specified, then the host specified with "-connect"
658 This option is an alias of the B<-name> option for "xmpp" and "xmpp-server".
660 =item B<-name> I<hostname>
662 This option is used to specify hostname information for various protocols
663 used with B<-starttls> option. Currently only "xmpp", "xmpp-server",
664 "smtp" and "lmtp" can utilize this B<-name> option.
666 If this option is used with "-starttls xmpp" or "-starttls xmpp-server",
667 if specifies the host for the "to" attribute of the stream element. If this
668 option is not specified, then the host specified with "-connect" will be used.
670 If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies
671 the name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If
672 this option is not specified, then "mail.example.com" will be used.
674 =item B<-tlsextdebug>
676 Print out a hex dump of any TLS extensions received from the server.
680 Disable RFC4507bis session ticket support.
682 =item B<-sess_out> I<filename>
684 Output SSL session to I<filename>.
686 =item B<-sess_in> I<filename>
688 Load SSL session from I<filename>. The client will attempt to resume a
689 connection from this session.
691 =item B<-serverinfo> I<types>
693 A list of comma-separated TLS Extension Types (numbers between 0 and
694 65535). Each type will be sent as an empty ClientHello TLS Extension.
695 The server's response (if any) will be encoded and displayed as a PEM
700 Sends a certificate status request to the server (OCSP stapling). The server
701 response (if any) is printed out.
703 =item B<-alpn> I<protocols>, B<-nextprotoneg> I<protocols>
705 These flags enable the Enable the Application-Layer Protocol Negotiation
706 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
707 IETF standard and replaces NPN.
708 The I<protocols> list is a comma-separated list of protocol names that
709 the client should advertise support for. The list should contain the most
710 desirable protocols first. Protocol names are printable ASCII strings,
711 for example "http/1.1" or "spdy/3".
712 An empty list of protocols is treated specially and will cause the
713 client to advertise support for the TLS extension but disconnect just
714 after receiving ServerHello with a list of server supported protocols.
715 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
717 =item B<-ct>, B<-noct>
719 Use one of these two options to control whether Certificate Transparency (CT)
720 is enabled (B<-ct>) or disabled (B<-noct>).
721 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
722 the server and reported at handshake completion.
724 Enabling CT also enables OCSP stapling, as this is one possible delivery method
729 A file containing a list of known Certificate Transparency logs. See
730 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
732 =item B<-keylogfile> I<file>
734 Appends TLS secrets to the specified keylog file such that external programs
735 (like Wireshark) can decrypt TLS connections.
737 =item B<-early_data> I<file>
739 Reads the contents of the specified file and attempts to send it as early data
740 to the server. This will only work with resumed sessions that support early
741 data and when the server accepts the early data.
745 For TLSv1.3 only, send the Post-Handshake Authentication extension. This will
746 happen whether or not a certificate has been provided via B<-cert>.
748 =item B<-use_srtp> I<value>
750 Offer SRTP key management, where B<value> is a colon-separated profile list.
752 =item B<-srpuser> I<value>
754 Set the SRP username to the specified value.
756 =item B<-srppass> I<value>
758 Set the SRP password to the specified value.
760 =item B<-srp_lateuser>
762 SRP username for the second ClientHello message.
764 =item B<-srp_moregroups>
766 Tolerate other than the known B<g> and B<N> values.
768 =item B<-srp_strength> I<number>
770 Set the minimal acceptable length, in bits, for B<N>.
772 {- $OpenSSL::safe::opt_version_item -}
774 {- $OpenSSL::safe::opt_name_item -}
776 {- $OpenSSL::safe::opt_x_item -}
778 {- $OpenSSL::safe::opt_trust_item -}
780 {- $OpenSSL::safe::opt_s_item -}
782 {- $OpenSSL::safe::opt_r_item -}
784 {- $OpenSSL::safe::opt_provider_item -}
786 {- $OpenSSL::safe::opt_engine_item -}
788 =item B<-ssl_client_engine> I<id>
790 Specify engine to be used for client certificate operations.
792 {- $OpenSSL::safe::opt_v_item -}
794 Verification errors are displayed, for debugging, but the command will
795 proceed unless the B<-verify_return_error> option is used.
797 =item I<host>:I<port>
799 Rather than providing B<-connect>, the target hostname and optional port may
800 be provided as a single positional argument after all options. If neither this
801 nor B<-connect> are provided, falls back to attempting to connect to
802 I<localhost> on port I<4433>.
806 =head1 CONNECTED COMMANDS
808 If a connection is established with an SSL server then any data received
809 from the server is displayed and any key presses will be sent to the
810 server. If end of file is reached then the connection will be closed down. When
811 used interactively (which means neither B<-quiet> nor B<-ign_eof> have been
812 given), then certain commands are also recognized which perform special
813 operations. These commands are a letter which must appear at the start of a
814 line. They are listed below.
820 End the current SSL connection and exit.
824 Renegotiate the SSL session (TLSv1.2 and below only).
828 Send a key update message to the server (TLSv1.3 only)
832 Send a key update message to the server and request one back (TLSv1.3 only)
838 This command can be used to debug SSL servers. To connect to an SSL HTTP
841 openssl s_client -connect servername:443
843 would typically be used (https uses port 443). If the connection succeeds
844 then an HTTP command can be given such as "GET /" to retrieve a web page.
846 If the handshake fails then there are several possible causes, if it is
847 nothing obvious like no client certificate then the B<-bugs>,
848 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
849 in case it is a buggy server. In particular you should play with these
850 options B<before> submitting a bug report to an OpenSSL mailing list.
852 A frequent problem when attempting to get client certificates working
853 is that a web client complains it has no certificates or gives an empty
854 list to choose from. This is normally because the server is not sending
855 the clients certificate authority in its "acceptable CA list" when it
856 requests a certificate. By using this command, the CA list can be viewed
857 and checked. However some servers only request client authentication
858 after a specific URL is requested. To obtain the list in this case it
859 is necessary to use the B<-prexit> option and send an HTTP request
860 for an appropriate page.
862 If a certificate is specified on the command line using the B<-cert>
863 option it will not be used unless the server specifically requests
864 a client certificate. Therefore merely including a client certificate
865 on the command line is no guarantee that the certificate works.
867 If there are problems verifying a server certificate then the
868 B<-showcerts> option can be used to show all the certificates sent by the
871 This command is a test tool and is designed to continue the
872 handshake after any certificate verification errors. As a result it will
873 accept any certificate chain (trusted or not) sent by the peer. None test
874 applications should B<not> do this as it makes them vulnerable to a MITM
875 attack. This behaviour can be changed by with the B<-verify_return_error>
876 option: any verify errors are then returned aborting the handshake.
878 The B<-bind> option may be useful if the server or a firewall requires
879 connections to come from some particular address and or port.
883 Because this program has a lot of options and also because some of the
884 techniques used are rather old, the C source for this command is rather
885 hard to read and not a model of how things should be done.
886 A typical SSL client program would be much simpler.
888 The B<-prexit> option is a bit of a hack. We should really report
889 information whenever a session is renegotiated.
894 L<openssl-sess_id(1)>,
895 L<openssl-s_server(1)>,
896 L<openssl-ciphers(1)>,
898 L<SSL_CTX_set_max_send_fragment(3)>,
899 L<SSL_CTX_set_split_send_fragment(3)>,
900 L<SSL_CTX_set_max_pipelines(3)>,
901 L<ossl_store-file(7)>
905 The B<-no_alt_chains> option was added in OpenSSL 1.1.0.
906 The B<-name> option was added in OpenSSL 1.1.1.
908 The B<-certform> option has become obsolete in OpenSSL 3.0.0 and has no effect.
910 All B<-keyform> values except B<ENGINE> have become obsolete in OpenSSL 3.0.0
915 Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
917 Licensed under the Apache License 2.0 (the "License"). You may not use
918 this file except in compliance with the License. You can obtain a copy
919 in the file LICENSE in the source distribution or at
920 L<https://www.openssl.org/source/license.html>.