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>]
91 [B<-legacy_server_connect>]
92 [B<-no_legacy_server_connect>]
93 [B<-allow_no_dhe_kex>]
94 [B<-sigalgs> I<sigalglist>]
95 [B<-curves> I<curvelist>]
96 [B<-cipher> I<cipherlist>]
97 [B<-ciphersuites> I<val>]
99 [B<-starttls> I<protocol>]
100 [B<-name> I<hostname>]
101 [B<-xmpphost> I<hostname>]
102 [B<-name> I<hostname>]
105 [B<-sess_out> I<filename>]
106 [B<-serverinfo> I<types>]
107 [B<-sess_in> I<filename>]
108 [B<-serverinfo> I<types>]
110 [B<-alpn> I<protocols>]
111 [B<-nextprotoneg> I<protocols>]
115 [B<-keylogfile> I<file>]
116 [B<-early_data> I<file>]
118 [B<-use_srtp> I<value>]
119 [B<-srpuser> I<value>]
120 [B<-srppass> I<value>]
123 [B<-srp_strength> I<number>]
126 {- $OpenSSL::safe::opt_name_synopsis -}
127 {- $OpenSSL::safe::opt_version_synopsis -}
128 {- $OpenSSL::safe::opt_x_synopsis -}
129 {- $OpenSSL::safe::opt_trust_synopsis -}
130 {- $OpenSSL::safe::opt_s_synopsis -}
131 {- $OpenSSL::safe::opt_r_synopsis -}
132 {- $OpenSSL::safe::opt_provider_synopsis -}
133 {- $OpenSSL::safe::opt_engine_synopsis -}[B<-ssl_client_engine> I<id>]
134 {- $OpenSSL::safe::opt_v_synopsis -}
135 [B<-enable_server_rpk>]
136 [B<-enable_client_rpk>]
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-passphrase-options(1)>.
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 B<-dane_tlsa_domain> options.
237 =item B<-cert> I<filename>
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; unspecified by default.
247 See L<openssl-format-options(1)> for details.
251 A file or URI of untrusted certificates to use when attempting to build the
252 certificate chain related to the certificate specified via the B<-cert> option.
253 The input can be in PEM, DER, or PKCS#12 format.
255 =item B<-build_chain>
257 Specify whether the application should build the client certificate chain to be
258 provided to the server.
260 =item B<-CRL> I<filename>
262 CRL file to use to check the server's certificate.
264 =item B<-CRLform> B<DER>|B<PEM>
266 The CRL file format; unspecified by default.
267 See L<openssl-format-options(1)> for details.
269 =item B<-crl_download>
271 Download CRL from distribution points in the certificate.
273 =item B<-key> I<filename>|I<uri>
275 The client private key to use.
276 If not specified then the certificate file will be used to read also the key.
278 =item B<-keyform> B<DER>|B<PEM>|B<P12>|B<ENGINE>
280 The key format; unspecified by default.
281 See L<openssl-format-options(1)> for details.
283 =item B<-pass> I<arg>
285 the private key and certificate file password source.
286 For more information about the format of I<arg>
287 see L<openssl-passphrase-options(1)>.
289 =item B<-verify> I<depth>
291 The verify depth to use. This specifies the maximum length of the
292 server certificate chain and turns on server certificate verification.
293 Currently the verify operation continues after errors so all the problems
294 with a certificate chain can be seen. As a side effect the connection
295 will never fail due to a server certificate verify failure.
297 =item B<-verify_return_error>
299 Return verification errors instead of continuing. This will typically
300 abort the handshake with a fatal error.
302 =item B<-verify_quiet>
304 Limit verify output to only errors.
306 =item B<-verifyCAfile> I<filename>
308 A file in PEM format containing trusted certificates to use
309 for verifying the server's certificate.
311 =item B<-verifyCApath> I<dir>
313 A directory containing trusted certificates to use
314 for verifying the server's certificate.
315 This directory must be in "hash format",
316 see L<openssl-verify(1)> for more information.
318 =item B<-verifyCAstore> I<uri>
320 The URI of a store containing trusted certificates to use
321 for verifying the server's certificate.
323 =item B<-chainCAfile> I<file>
325 A file in PEM format containing trusted certificates to use
326 when attempting to build the client certificate chain.
328 =item B<-chainCApath> I<directory>
330 A directory containing trusted certificates to use
331 for building the client certificate chain provided to the server.
332 This directory must be in "hash format",
333 see L<openssl-verify(1)> for more information.
335 =item B<-chainCAstore> I<uri>
337 The URI of a store containing trusted certificates to use
338 when attempting to build the client certificate chain.
339 The URI may indicate a single certificate, as well as a collection of them.
340 With URIs in the C<file:> scheme, this acts as B<-chainCAfile> or
341 B<-chainCApath>, depending on if the URI indicates a directory or a
343 See L<ossl_store-file(7)> for more information on the C<file:> scheme.
345 =item B<-requestCAfile> I<file>
347 A file containing a list of certificates whose subject names will be sent
348 to the server in the B<certificate_authorities> extension. Only supported
351 =item B<-dane_tlsa_domain> I<domain>
353 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
354 TLSA base domain which becomes the default SNI hint and the primary
355 reference identifier for hostname checks. This must be used in
356 combination with at least one instance of the B<-dane_tlsa_rrdata>
359 When DANE authentication succeeds, the diagnostic output will include
360 the lowest (closest to 0) depth at which a TLSA record authenticated
361 a chain certificate. When that TLSA record is a "2 1 0" trust
362 anchor public key that signed (rather than matched) the top-most
363 certificate of the chain, the result is reported as "TA public key
364 verified". Otherwise, either the TLSA record "matched TA certificate"
365 at a positive depth or else "matched EE certificate" at depth 0.
367 =item B<-dane_tlsa_rrdata> I<rrdata>
369 Use one or more times to specify the RRDATA fields of the DANE TLSA
370 RRset associated with the target service. The I<rrdata> value is
371 specified in "presentation form", that is four whitespace separated
372 fields that specify the usage, selector, matching type and associated
373 data, with the last of these encoded in hexadecimal. Optional
374 whitespace is ignored in the associated data field. For example:
376 $ openssl s_client -brief -starttls smtp \
377 -connect smtp.example.com:25 \
378 -dane_tlsa_domain smtp.example.com \
379 -dane_tlsa_rrdata "2 1 1
380 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
381 -dane_tlsa_rrdata "2 1 1
382 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
385 Verified peername: smtp.example.com
386 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
389 =item B<-dane_ee_no_namechecks>
391 This disables server name checks when authenticating via DANE-EE(3) TLSA
393 For some applications, primarily web browsers, it is not safe to disable name
394 checks due to "unknown key share" attacks, in which a malicious server can
395 convince a client that a connection to a victim server is instead a secure
396 connection to the malicious server.
397 The malicious server may then be able to violate cross-origin scripting
399 Thus, despite the text of RFC7671, name checks are by default enabled for
400 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
402 In particular, SMTP and XMPP clients should set this option as SRV and MX
403 records already make it possible for a remote domain to redirect client
404 connections to any server of its choice, and in any case SMTP and XMPP clients
405 do not execute scripts downloaded from remote servers.
409 Reconnects to the same server 5 times using the same session ID, this can
410 be used as a test that session caching is working.
414 Displays the server certificate list as sent by the server: it only consists of
415 certificates the server has sent (in the order the server has sent them). It is
416 B<not> a verified chain.
420 Print session information when the program exits. This will always attempt
421 to print out information even if the connection fails. Normally information
422 will only be printed out once if the connection succeeds. This option is useful
423 because the cipher in use may be renegotiated or the connection may fail
424 because a client certificate is required or is requested only after an
425 attempt is made to access a certain URL. Note: the output produced by this
426 option is not always accurate because a connection might never have been
429 =item B<-no-interactive>
431 This flag can be used to run the client in a non-interactive mode.
435 Prints out the SSL session states.
439 Print extensive debugging information including a hex dump of all traffic.
443 Do not use interactive command letters.
445 =item B<-security_debug>
447 Enable security debug messages.
449 =item B<-security_debug_verbose>
451 Output more security debug output.
455 Show protocol messages.
459 Enable send/receive timeout on DTLS connections.
461 =item B<-mtu> I<size>
463 Set MTU of the link layer to the specified size.
467 Disable Encrypt-then-MAC negotiation.
471 Disable Extended master secret negotiation.
473 =item B<-keymatexport> I<label>
475 Export keying material using the specified label.
477 =item B<-keymatexportlen> I<len>
479 Export the specified number of bytes of keying material; default is 20.
481 Show all protocol messages with hex dump.
485 Show verbose trace output of protocol messages.
487 =item B<-msgfile> I<filename>
489 File to send output of B<-msg> or B<-trace> to, default standard output.
493 Tests nonblocking I/O
497 Turns on nonblocking I/O
501 This option translated a line feed from the terminal into CR+LF as required
506 Inhibit shutting down the connection when end of file is reached in the
511 Inhibit printing of session and certificate information. This implicitly
512 turns on B<-ign_eof> as well.
516 Shut down the connection when end of file is reached in the input.
517 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
519 =item B<-psk_identity> I<identity>
521 Use the PSK identity I<identity> when using a PSK cipher suite.
522 The default value is "Client_identity" (without the quotes).
526 Use the PSK key I<key> when using a PSK cipher suite. The key is
527 given as a hexadecimal number without leading 0x, for example -psk
529 This option must be provided in order to use a PSK cipher.
531 =item B<-psk_session> I<file>
533 Use the pem encoded SSL_SESSION data stored in I<file> as the basis of a PSK.
534 Note that this will only work if TLSv1.3 is negotiated.
538 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
539 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
540 available where OpenSSL has support for SCTP enabled.
542 =item B<-sctp_label_bug>
544 Use the incorrect behaviour of older OpenSSL implementations when computing
545 endpoint-pair shared secrets for DTLS/SCTP. This allows communication with
546 older broken implementations but breaks interoperability with correct
547 implementations. Must be used in conjunction with B<-sctp>. This option is only
548 available where OpenSSL has support for SCTP enabled.
550 =item B<-fallback_scsv>
552 Send TLS_FALLBACK_SCSV in the ClientHello.
556 Switch on asynchronous mode. Cryptographic operations will be performed
557 asynchronously. This will only have an effect if an asynchronous capable engine
558 is also used via the B<-engine> option. For test purposes the dummy async engine
559 (dasync) can be used (if available).
561 =item B<-maxfraglen> I<len>
563 Enable Maximum Fragment Length Negotiation; allowed values are
564 C<512>, C<1024>, C<2048>, and C<4096>.
566 =item B<-max_send_frag> I<int>
568 The maximum size of data fragment to send.
569 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
571 =item B<-split_send_frag> I<int>
573 The size used to split data for encrypt pipelines. If more data is written in
574 one go than this value then it will be split into multiple pipelines, up to the
575 maximum number of pipelines defined by max_pipelines. This only has an effect if
576 a suitable cipher suite has been negotiated, an engine that supports pipelining
577 has been loaded, and max_pipelines is greater than 1. See
578 L<SSL_CTX_set_split_send_fragment(3)> for further information.
580 =item B<-max_pipelines> I<int>
582 The maximum number of encrypt/decrypt pipelines to be used. This will only have
583 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
584 engine) and a suitable cipher suite has been negotiated. The default value is 1.
585 See L<SSL_CTX_set_max_pipelines(3)> for further information.
587 =item B<-read_buf> I<int>
589 The default read buffer size to be used for connections. This will only have an
590 effect if the buffer size is larger than the size that would otherwise be used
591 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
592 further information).
594 =item B<-ignore_unexpected_eof>
596 Some TLS implementations do not send the mandatory close_notify alert on
597 shutdown. If the application tries to wait for the close_notify alert but the
598 peer closes the connection without sending it, an error is generated. When this
599 option is enabled the peer does not need to send the close_notify alert and a
600 closed connection will be treated as if the close_notify alert was received.
601 For more information on shutting down a connection, see L<SSL_shutdown(3)>.
605 There are several known bugs in SSL and TLS implementations. Adding this
606 option enables various workarounds.
608 =item B<-no_tx_cert_comp>
610 Disables support for sending TLSv1.3 compressed certificates.
612 =item B<-no_rx_cert_comp>
614 Disables support for receiving TLSv1.3 compressed certificate.
618 Enables support for SSL/TLS compression.
619 This option was introduced in OpenSSL 1.1.0.
620 TLS compression is not recommended and is off by default as of
625 Disables support for SSL/TLS compression.
626 TLS compression is not recommended and is off by default as of
631 Only provide a brief summary of connection parameters instead of the
632 normal verbose output.
634 =item B<-sigalgs> I<sigalglist>
636 Specifies the list of signature algorithms that are sent by the client.
637 The server selects one entry in the list based on its preferences.
638 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
640 =item B<-curves> I<curvelist>
642 Specifies the list of supported curves to be sent by the client. The curve is
643 ultimately selected by the server. For a list of all curves, use:
645 $ openssl ecparam -list_curves
647 =item B<-cipher> I<cipherlist>
649 This allows the TLSv1.2 and below cipher list sent by the client to be modified.
650 This list will be combined with any TLSv1.3 ciphersuites that have been
651 configured. Although the server determines which ciphersuite is used it should
652 take the first supported cipher in the list sent by the client. See
653 L<openssl-ciphers(1)> for more information.
655 =item B<-ciphersuites> I<val>
657 This allows the TLSv1.3 ciphersuites sent by the client to be modified. This
658 list will be combined with any TLSv1.2 and below ciphersuites that have been
659 configured. Although the server determines which cipher suite is used it should
660 take the first supported cipher in the list sent by the client. See
661 L<openssl-ciphers(1)> for more information. The format for this list is a simple
662 colon (":") separated list of TLSv1.3 ciphersuite names.
664 =item B<-starttls> I<protocol>
666 Send the protocol-specific message(s) to switch to TLS for communication.
667 I<protocol> is a keyword for the intended protocol. Currently, the only
668 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
669 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
671 =item B<-xmpphost> I<hostname>
673 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
674 specifies the host for the "to" attribute of the stream element.
675 If this option is not specified, then the host specified with "-connect"
678 This option is an alias of the B<-name> option for "xmpp" and "xmpp-server".
680 =item B<-name> I<hostname>
682 This option is used to specify hostname information for various protocols
683 used with B<-starttls> option. Currently only "xmpp", "xmpp-server",
684 "smtp" and "lmtp" can utilize this B<-name> option.
686 If this option is used with "-starttls xmpp" or "-starttls xmpp-server",
687 if specifies the host for the "to" attribute of the stream element. If this
688 option is not specified, then the host specified with "-connect" will be used.
690 If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies
691 the name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If
692 this option is not specified, then "mail.example.com" will be used.
694 =item B<-tlsextdebug>
696 Print out a hex dump of any TLS extensions received from the server.
700 Disable RFC4507bis session ticket support.
702 =item B<-sess_out> I<filename>
704 Output SSL session to I<filename>.
706 =item B<-sess_in> I<filename>
708 Load SSL session from I<filename>. The client will attempt to resume a
709 connection from this session.
711 =item B<-serverinfo> I<types>
713 A list of comma-separated TLS Extension Types (numbers between 0 and
714 65535). Each type will be sent as an empty ClientHello TLS Extension.
715 The server's response (if any) will be encoded and displayed as a PEM
720 Sends a certificate status request to the server (OCSP stapling). The server
721 response (if any) is printed out.
723 =item B<-alpn> I<protocols>, B<-nextprotoneg> I<protocols>
725 These flags enable the Enable the Application-Layer Protocol Negotiation
726 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
727 IETF standard and replaces NPN.
728 The I<protocols> list is a comma-separated list of protocol names that
729 the client should advertise support for. The list should contain the most
730 desirable protocols first. Protocol names are printable ASCII strings,
731 for example "http/1.1" or "spdy/3".
732 An empty list of protocols is treated specially and will cause the
733 client to advertise support for the TLS extension but disconnect just
734 after receiving ServerHello with a list of server supported protocols.
735 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
737 =item B<-ct>, B<-noct>
739 Use one of these two options to control whether Certificate Transparency (CT)
740 is enabled (B<-ct>) or disabled (B<-noct>).
741 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
742 the server and reported at handshake completion.
744 Enabling CT also enables OCSP stapling, as this is one possible delivery method
749 A file containing a list of known Certificate Transparency logs. See
750 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
752 =item B<-keylogfile> I<file>
754 Appends TLS secrets to the specified keylog file such that external programs
755 (like Wireshark) can decrypt TLS connections.
757 =item B<-early_data> I<file>
759 Reads the contents of the specified file and attempts to send it as early data
760 to the server. This will only work with resumed sessions that support early
761 data and when the server accepts the early data.
765 For TLSv1.3 only, send the Post-Handshake Authentication extension. This will
766 happen whether or not a certificate has been provided via B<-cert>.
768 =item B<-use_srtp> I<value>
770 Offer SRTP key management, where B<value> is a colon-separated profile list.
772 =item B<-srpuser> I<value>
774 Set the SRP username to the specified value. This option is deprecated.
776 =item B<-srppass> I<value>
778 Set the SRP password to the specified value. This option is deprecated.
780 =item B<-srp_lateuser>
782 SRP username for the second ClientHello message. This option is deprecated.
784 =item B<-srp_moregroups> This option is deprecated.
786 Tolerate other than the known B<g> and B<N> values.
788 =item B<-srp_strength> I<number>
790 Set the minimal acceptable length, in bits, for B<N>. This option is
795 Enable Kernel TLS for sending and receiving.
796 This option was introduced in OpenSSL 3.2.0.
797 Kernel TLS is off by default as of OpenSSL 3.2.0.
801 Enable creation of connections via TCP fast open (RFC7413).
803 {- $OpenSSL::safe::opt_version_item -}
805 {- $OpenSSL::safe::opt_name_item -}
807 {- $OpenSSL::safe::opt_x_item -}
809 {- $OpenSSL::safe::opt_trust_item -}
811 {- $OpenSSL::safe::opt_s_item -}
813 {- $OpenSSL::safe::opt_r_item -}
815 {- $OpenSSL::safe::opt_provider_item -}
817 {- $OpenSSL::safe::opt_engine_item -}
819 {- output_off() if $disabled{"deprecated-3.0"}; "" -}
820 =item B<-ssl_client_engine> I<id>
822 Specify engine to be used for client certificate operations.
823 {- output_on() if $disabled{"deprecated-3.0"}; "" -}
825 {- $OpenSSL::safe::opt_v_item -}
827 Verification errors are displayed, for debugging, but the command will
828 proceed unless the B<-verify_return_error> option is used.
830 =item B<-enable_server_rpk>
832 Enable support for receiving raw public keys (RFC7250) from the server.
833 Use of X.509 certificates by the server becomes optional, and servers that
834 support raw public keys may elect to use them.
835 Servers that don't support raw public keys or prefer to use X.509
836 certificates can still elect to send X.509 certificates as usual.
838 =item B<-enable_client_rpk>
840 Enable support for sending raw public keys (RFC7250) to the server.
841 A raw public key will be sent by the client, if solicited by the server,
842 provided a suitable key and public certificate pair is configured.
843 Some servers may nevertheless not request any client credentials,
844 or may request a certificate.
846 =item I<host>:I<port>
848 Rather than providing B<-connect>, the target hostname and optional port may
849 be provided as a single positional argument after all options. If neither this
850 nor B<-connect> are provided, falls back to attempting to connect to
851 I<localhost> on port I<4433>.
855 =head1 CONNECTED COMMANDS
857 If a connection is established with an SSL server then any data received
858 from the server is displayed and any key presses will be sent to the
859 server. If end of file is reached then the connection will be closed down. When
860 used interactively (which means neither B<-quiet> nor B<-ign_eof> have been
861 given), then certain commands are also recognized which perform special
862 operations. These commands are a letter which must appear at the start of a
863 line. They are listed below.
869 End the current SSL connection and exit.
873 Renegotiate the SSL session (TLSv1.2 and below only).
877 Send a key update message to the server (TLSv1.3 only)
881 Send a key update message to the server and request one back (TLSv1.3 only)
887 This command can be used to debug SSL servers. To connect to an SSL HTTP
890 openssl s_client -connect servername:443
892 would typically be used (https uses port 443). If the connection succeeds
893 then an HTTP command can be given such as "GET /" to retrieve a web page.
895 If the handshake fails then there are several possible causes, if it is
896 nothing obvious like no client certificate then the B<-bugs>,
897 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
898 in case it is a buggy server. In particular you should play with these
899 options B<before> submitting a bug report to an OpenSSL mailing list.
901 A frequent problem when attempting to get client certificates working
902 is that a web client complains it has no certificates or gives an empty
903 list to choose from. This is normally because the server is not sending
904 the clients certificate authority in its "acceptable CA list" when it
905 requests a certificate. By using this command, the CA list can be viewed
906 and checked. However, some servers only request client authentication
907 after a specific URL is requested. To obtain the list in this case it
908 is necessary to use the B<-prexit> option and send an HTTP request
909 for an appropriate page.
911 If a certificate is specified on the command line using the B<-cert>
912 option it will not be used unless the server specifically requests
913 a client certificate. Therefore, merely including a client certificate
914 on the command line is no guarantee that the certificate works.
916 If there are problems verifying a server certificate then the
917 B<-showcerts> option can be used to show all the certificates sent by the
920 This command is a test tool and is designed to continue the
921 handshake after any certificate verification errors. As a result it will
922 accept any certificate chain (trusted or not) sent by the peer. Non-test
923 applications should B<not> do this as it makes them vulnerable to a MITM
924 attack. This behaviour can be changed by with the B<-verify_return_error>
925 option: any verify errors are then returned aborting the handshake.
927 The B<-bind> option may be useful if the server or a firewall requires
928 connections to come from some particular address and or port.
932 Because this program has a lot of options and also because some of the
933 techniques used are rather old, the C source for this command is rather
934 hard to read and not a model of how things should be done.
935 A typical SSL client program would be much simpler.
937 The B<-prexit> option is a bit of a hack. We should really report
938 information whenever a session is renegotiated.
943 L<openssl-sess_id(1)>,
944 L<openssl-s_server(1)>,
945 L<openssl-ciphers(1)>,
947 L<SSL_CTX_set_max_send_fragment(3)>,
948 L<SSL_CTX_set_split_send_fragment(3)>,
949 L<SSL_CTX_set_max_pipelines(3)>,
950 L<ossl_store-file(7)>
954 The B<-no_alt_chains> option was added in OpenSSL 1.1.0.
955 The B<-name> option was added in OpenSSL 1.1.1.
957 The B<-certform> option has become obsolete in OpenSSL 3.0.0 and has no effect.
959 The B<-engine> option was deprecated in OpenSSL 3.0.
962 B<-enable_client_rpk>,
963 B<-enable_server_rpk>,
967 options were added in OpenSSL 3.2.
971 Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved.
973 Licensed under the Apache License 2.0 (the "License"). You may not use
974 this file except in compliance with the License. You can obtain a copy
975 in the file LICENSE in the source distribution or at
976 L<https://www.openssl.org/source/license.html>.