5 openssl-s_client - SSL/TLS client program
11 [B<-connect> I<host:port>]
12 [B<-bind> I<host:port>]
13 [B<-proxy> I<host:port>]
14 [B<-proxy_user> I<userid>]
15 [B<-proxy_pass> I<arg>]
19 [B<-servername> I<name>]
22 [B<-verify_return_error>]
23 [B<-cert> I<filename>]
24 [B<-certform> B<DER>|B<PEM>]
26 [B<-keyform> B<DER>|B<PEM>]
27 [B<-cert_chain> I<filename>]
33 [B<-xcertform> B<DER>|B<PEM>]
34 [B<-xkeyform> B<DER>|B<PEM>]
36 [B<-CApath> I<directory>]
37 [B<-CAfile> I<filename>]
38 [B<-chainCApath> I<directory>]
39 [B<-chainCAfile> I<filename>]
42 [B<-requestCAfile> I<filename>]
43 [B<-dane_tlsa_domain> I<domain>]
44 [B<-dane_tlsa_rrdata> I<rrdata>]
45 [B<-dane_ee_no_namechecks>]
46 [B<-attime> I<timestamp>]
60 [B<-purpose> I<purpose>]
67 [B<-auth_level> I<num>]
68 [B<-nameopt> I<option>]
69 [B<-verify_depth> I<num>]
70 [B<-verify_email> I<email>]
71 [B<-verify_hostname> I<hostname>]
73 [B<-verify_name> I<name>]
86 [B<-psk_identity> I<identity>]
88 [B<-psk_session> I<file>]
108 [B<-split_send_frag>]
114 [B<-allow_no_dhe_kex>]
115 [B<-sigalgs> I<sigalglist>]
116 [B<-curves> I<curvelist>]
117 [B<-cipher> I<cipherlist>]
118 [B<-ciphersuites> I<val>]
120 [B<-starttls> I<protocol>]
121 [B<-xmpphost> I<hostname>]
122 [B<-name> I<hostname>]
126 [B<-sess_out> I<filename>]
127 [B<-sess_in> I<filename>]
129 [B<-writerand> I<file>]
130 [B<-serverinfo> I<types>]
132 [B<-alpn> I<protocols>]
133 [B<-nextprotoneg> I<protocols>]
137 [B<-keylogfile> I<file>]
138 [B<-early_data> I<file>]
142 =for comment ifdef engine ssl_client_engine ct noct ctlogfile
144 =for comment ifdef ssl3 unix 4 6 use_srtp status trace wdebug nextprotoneg
146 =for comment ifdef ssl3 tls1 tls1_1 tls1_2 tls1_3 dtls mtu dtls1 dtls1_2
148 =for comment ifdef sctp_label_bug sctp
150 =for comment ifdef srpuser srppass srp_lateuser srp_moregroups srp_strength
154 This command implements a generic SSL/TLS client which
155 connects to a remote host using SSL/TLS. It is a I<very> useful diagnostic
156 tool for SSL servers.
160 In addition to the options below, this command also supports the
161 common and client only options documented
162 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
169 Print out a usage message.
171 =item B<-connect> I<host>:I<port>
173 This specifies the host and optional port to connect to. It is possible to
174 select the host and port using the optional target positional argument instead.
175 If neither this nor the target positional argument are specified then an attempt
176 is made to connect to the local host on port 4433.
178 =item B<-bind> I<host:port>]
180 This specifies the host address and or port to bind as the source for the
181 connection. For Unix-domain sockets the port is ignored and the host is
182 used as the source socket address.
184 =item B<-proxy> I<host:port>
186 When used with the B<-connect> flag, the program uses the host and port
187 specified with this flag and issues an HTTP CONNECT command to connect
188 to the desired server.
190 =item B<-proxy_user> I<userid>
192 When used with the B<-proxy> flag, the program will attempt to authenticate
193 with the specified proxy using basic (base64) authentication.
194 NB: Basic authentication is insecure; the credentials are sent to the proxy
195 in easily reversible base64 encoding before any TLS/SSL session is established.
196 Therefore these credentials are easily recovered by anyone able to sniff/trace
197 the network. Use with caution.
199 =item B<-proxy_pass> I<arg>
201 The proxy password source, used with the B<-proxy_user> flag.
202 For more information about the format of B<arg>
203 see L<openssl(1)/Pass phrase options>.
205 =item B<-unix> I<path>
207 Connect over the specified Unix-domain socket.
217 =item B<-servername> I<name>
219 Set the TLS SNI (Server Name Indication) extension in the ClientHello message to
221 If B<-servername> is not provided, the TLS SNI extension will be populated with
222 the name given to B<-connect> if it follows a DNS name format. If B<-connect> is
223 not provided either, the SNI is set to "localhost".
224 This is the default since OpenSSL 1.1.1.
226 Even though SNI should normally be a DNS name and not an IP address, if
227 B<-servername> is provided then that name will be sent, regardless of whether
228 it is a DNS name or not.
230 This option cannot be used in conjunction with B<-noservername>.
232 =item B<-noservername>
234 Suppresses sending of the SNI (Server Name Indication) extension in the
235 ClientHello message. Cannot be used in conjunction with the B<-servername> or
236 <-dane_tlsa_domain> options.
238 =item B<-cert> I<certname>
240 The certificate to use, if one is requested by the server. The default is
241 not to use a certificate.
243 =item B<-certform> I<format>
245 The certificate format to use: DER or PEM. PEM is the default.
247 =item B<-key> I<keyfile>
249 The private key to use. If not specified then the certificate file will
252 =item B<-keyform> I<format>
254 The private format to use: DER or PEM. PEM is the default.
258 A file containing trusted certificates to use when attempting to build the
259 client/server certificate chain related to the certificate specified via the
262 =item B<-build_chain>
264 Specify whether the application should build the certificate chain to be
265 provided to the server.
267 =item B<-xkey> I<infile>, B<-xcert> I<infile>, B<-xchain>
269 Specify an extra certificate, private key and certificate chain. These behave
270 in the same manner as the B<-cert>, B<-key> and B<-cert_chain> options. When
271 specified, the callback returning the first valid chain will be in use by the
274 =item B<-xchain_build>
276 Specify whether the application should build the certificate chain to be
277 provided to the server for the extra certificates provided via B<-xkey> I<infile>,
278 B<-xcert> I<infile>, B<-xchain> options.
280 =item B<-xcertform> B<DER>|B<PEM>, B<-xkeyform> B<DER>|B<PEM>
282 Extra certificate and private key format respectively.
284 =item B<-pass> I<arg>
286 the private key password source. For more information about the format of I<arg>
287 see L<openssl(1)/Pass phrase options>.
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<-nameopt> I<option>
304 Option which determines how the subject or issuer names are displayed. The
305 I<option> argument can be a single option or multiple options separated by
306 commas. Alternatively the B<-nameopt> switch may be used more than once to
307 set multiple options. See the L<openssl-x509(1)> manual page for details.
309 =item B<-CApath> I<directory>
311 The directory to use for server certificate verification. This directory
312 must be in "hash format", see L<openssl-verify(1)> for more information.
313 These are also used when building the client certificate chain.
315 =item B<-CAfile> I<file>
317 A file containing trusted certificates to use during server authentication
318 and to use when attempting to build the client certificate chain.
320 =item B<-chainCApath> I<directory>
322 The directory to use for building the chain provided to the server. This
323 directory must be in "hash format", see L<openssl-verify(1)> for more
326 =item B<-chainCAfile> I<file>
328 A file containing trusted certificates to use when attempting to build the
329 client certificate chain.
333 Do not load the trusted CA certificates from the default file location
337 Do not load the trusted CA certificates from the default directory location
339 =item B<-requestCAfile> I<file>
341 A file containing a list of certificates whose subject names will be sent
342 to the server in the B<certificate_authorities> extension. Only supported
345 =item B<-dane_tlsa_domain> I<domain>
347 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
348 TLSA base domain which becomes the default SNI hint and the primary
349 reference identifier for hostname checks. This must be used in
350 combination with at least one instance of the B<-dane_tlsa_rrdata>
353 When DANE authentication succeeds, the diagnostic output will include
354 the lowest (closest to 0) depth at which a TLSA record authenticated
355 a chain certificate. When that TLSA record is a "2 1 0" trust
356 anchor public key that signed (rather than matched) the top-most
357 certificate of the chain, the result is reported as "TA public key
358 verified". Otherwise, either the TLSA record "matched TA certificate"
359 at a positive depth or else "matched EE certificate" at depth 0.
361 =item B<-dane_tlsa_rrdata> I<rrdata>
363 Use one or more times to specify the RRDATA fields of the DANE TLSA
364 RRset associated with the target service. The I<rrdata> value is
365 specied in "presentation form", that is four whitespace separated
366 fields that specify the usage, selector, matching type and associated
367 data, with the last of these encoded in hexadecimal. Optional
368 whitespace is ignored in the associated data field. For example:
370 $ openssl s_client -brief -starttls smtp \
371 -connect smtp.example.com:25 \
372 -dane_tlsa_domain smtp.example.com \
373 -dane_tlsa_rrdata "2 1 1
374 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
375 -dane_tlsa_rrdata "2 1 1
376 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
379 Verified peername: smtp.example.com
380 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
383 =item B<-dane_ee_no_namechecks>
385 This disables server name checks when authenticating via DANE-EE(3) TLSA
387 For some applications, primarily web browsers, it is not safe to disable name
388 checks due to "unknown key share" attacks, in which a malicious server can
389 convince a client that a connection to a victim server is instead a secure
390 connection to the malicious server.
391 The malicious server may then be able to violate cross-origin scripting
393 Thus, despite the text of RFC7671, name checks are by default enabled for
394 DANE-EE(3) TLSA records, and can be disabled in applications where it is safe
396 In particular, SMTP and XMPP clients should set this option as SRV and MX
397 records already make it possible for a remote domain to redirect client
398 connections to any server of its choice, and in any case SMTP and XMPP clients
399 do not execute scripts downloaded from remote servers.
401 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
402 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
403 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
404 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
405 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
406 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
407 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
409 Set various certificate chain validation options. See the
410 L<openssl-verify(1)> manual page for details.
414 Reconnects to the same server 5 times using the same session ID, this can
415 be used as a test that session caching is working.
419 Displays the server certificate list as sent by the server: it only consists of
420 certificates the server has sent (in the order the server has sent them). It is
421 B<not> a verified chain.
425 Print session information when the program exits. This will always attempt
426 to print out information even if the connection fails. Normally information
427 will only be printed out once if the connection succeeds. This option is useful
428 because the cipher in use may be renegotiated or the connection may fail
429 because a client certificate is required or is requested only after an
430 attempt is made to access a certain URL. Note: the output produced by this
431 option is not always accurate because a connection might never have been
436 Prints out the SSL session states.
440 Print extensive debugging information including a hex dump of all traffic.
444 Show all protocol messages with hex dump.
448 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
449 with B<enable-ssl-trace> for this option to work.
453 File to send output of B<-msg> or B<-trace> to, default standard output.
457 Tests non-blocking I/O
461 Turns on non-blocking I/O
465 This option translated a line feed from the terminal into CR+LF as required
470 Inhibit shutting down the connection when end of file is reached in the
475 Inhibit printing of session and certificate information. This implicitly
476 turns on B<-ign_eof> as well.
480 Shut down the connection when end of file is reached in the input.
481 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
483 =item B<-psk_identity> I<identity>
485 Use the PSK identity I<identity> when using a PSK cipher suite.
486 The default value is "Client_identity" (without the quotes).
490 Use the PSK key I<key> when using a PSK cipher suite. The key is
491 given as a hexadecimal number without leading 0x, for example -psk
493 This option must be provided in order to use a PSK cipher.
495 =item B<-psk_session> I<file>
497 Use the pem encoded SSL_SESSION data stored in I<file> as the basis of a PSK.
498 Note that this will only work if TLSv1.3 is negotiated.
500 =item B<-ssl3>, B<-tls1>, B<-tls1_1>, B<-tls1_2>, B<-tls1_3>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>, B<-no_tls1_3>
502 These options require or disable the use of the specified SSL or TLS protocols.
503 By default, this command will negotiate the highest mutually supported protocol
505 When a specific TLS version is required, only that version will be offered to
506 and accepted from the server.
507 Note that not all protocols and flags may be available, depending on how
510 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
512 These options make this command use DTLS protocols instead of TLS.
513 With B<-dtls>, it will negotiate any supported DTLS protocol version,
514 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
519 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
520 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
521 available where OpenSSL has support for SCTP enabled.
523 =item B<-sctp_label_bug>
525 Use the incorrect behaviour of older OpenSSL implementations when computing
526 endpoint-pair shared secrets for DTLS/SCTP. This allows communication with
527 older broken implementations but breaks interoperability with correct
528 implementations. Must be used in conjunction with B<-sctp>. This option is only
529 available where OpenSSL has support for SCTP enabled.
531 =item B<-fallback_scsv>
533 Send TLS_FALLBACK_SCSV in the ClientHello.
537 Switch on asynchronous mode. Cryptographic operations will be performed
538 asynchronously. This will only have an effect if an asynchronous capable engine
539 is also used via the B<-engine> option. For test purposes the dummy async engine
540 (dasync) can be used (if available).
542 =item B<-max_send_frag> I<int>
544 The maximum size of data fragment to send.
545 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
547 =item B<-split_send_frag> I<int>
549 The size used to split data for encrypt pipelines. If more data is written in
550 one go than this value then it will be split into multiple pipelines, up to the
551 maximum number of pipelines defined by max_pipelines. This only has an effect if
552 a suitable cipher suite has been negotiated, an engine that supports pipelining
553 has been loaded, and max_pipelines is greater than 1. See
554 L<SSL_CTX_set_split_send_fragment(3)> for further information.
556 =item B<-max_pipelines> I<int>
558 The maximum number of encrypt/decrypt pipelines to be used. This will only have
559 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
560 engine) and a suitable cipher suite has been negotiated. The default value is 1.
561 See L<SSL_CTX_set_max_pipelines(3)> for further information.
563 =item B<-read_buf> I<int>
565 The default read buffer size to be used for connections. This will only have an
566 effect if the buffer size is larger than the size that would otherwise be used
567 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
568 further information).
572 There are several known bugs in SSL and TLS implementations. Adding this
573 option enables various workarounds.
577 Enables support for SSL/TLS compression.
578 This option was introduced in OpenSSL 1.1.0.
579 TLS compression is not recommended and is off by default as of
584 Disables support for SSL/TLS compression.
585 TLS compression is not recommended and is off by default as of
590 Only provide a brief summary of connection parameters instead of the
591 normal verbose output.
593 =item B<-sigalgs> I<sigalglist>
595 Specifies the list of signature algorithms that are sent by the client.
596 The server selects one entry in the list based on its preferences.
597 For example strings, see L<SSL_CTX_set1_sigalgs(3)>
599 =item B<-curves> I<curvelist>
601 Specifies the list of supported curves to be sent by the client. The curve is
602 ultimately selected by the server. For a list of all curves, use:
604 $ openssl ecparam -list_curves
606 =item B<-cipher> I<cipherlist>
608 This allows the TLSv1.2 and below cipher list sent by the client to be modified.
609 This list will be combined with any TLSv1.3 ciphersuites that have been
610 configured. Although the server determines which ciphersuite is used it should
611 take the first supported cipher in the list sent by the client. See
612 L<openssl-ciphers(1)> for more information.
614 =item B<-ciphersuites> I<val>
616 This allows the TLSv1.3 ciphersuites sent by the client to be modified. This
617 list will be combined with any TLSv1.2 and below ciphersuites that have been
618 configured. Although the server determines which cipher suite is used it should
619 take the first supported cipher in the list sent by the client. See
620 L<openssl-ciphers(1)> for more information. The format for this list is a simple
621 colon (":") separated list of TLSv1.3 ciphersuite names.
623 =item B<-starttls> I<protocol>
625 Send the protocol-specific message(s) to switch to TLS for communication.
626 I<protocol> is a keyword for the intended protocol. Currently, the only
627 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
628 "irc", "postgres", "mysql", "lmtp", "nntp", "sieve" and "ldap".
630 =item B<-xmpphost> I<hostname>
632 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
633 specifies the host for the "to" attribute of the stream element.
634 If this option is not specified, then the host specified with "-connect"
637 This option is an alias of the B<-name> option for "xmpp" and "xmpp-server".
639 =item B<-name> I<hostname>
641 This option is used to specify hostname information for various protocols
642 used with B<-starttls> option. Currently only "xmpp", "xmpp-server",
643 "smtp" and "lmtp" can utilize this B<-name> option.
645 If this option is used with "-starttls xmpp" or "-starttls xmpp-server",
646 if specifies the host for the "to" attribute of the stream element. If this
647 option is not specified, then the host specified with "-connect" will be used.
649 If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies
650 the name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If
651 this option is not specified, then "mail.example.com" will be used.
653 =item B<-tlsextdebug>
655 Print out a hex dump of any TLS extensions received from the server.
659 Disable RFC4507bis session ticket support.
661 =item B<-sess_out> I<filename>
663 Output SSL session to I<filename>.
665 =item B<-sess_in> I<filename>
667 Load SSL session from I<filename>. The client will attempt to resume a
668 connection from this session.
670 =item B<-engine> I<id>
672 Specifying an engine (by its unique I<id> string) will cause this command
673 to attempt to obtain a functional reference to the specified engine,
674 thus initialising it if needed. The engine will then be set as the default
675 for all available algorithms.
677 =item B<-rand> I<files>
679 The files containing random data used to seed the random number generator.
680 Multiple files can be specified separated by an OS-dependent character.
681 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
684 =item B<-writerand> I<file>
686 Writes random data to the specified I<file> upon exit.
687 This can be used with a subsequent B<-rand> flag.
689 =item B<-serverinfo> I<types>
691 A list of comma-separated TLS Extension Types (numbers between 0 and
692 65535). Each type will be sent as an empty ClientHello TLS Extension.
693 The server's response (if any) will be encoded and displayed as a PEM
698 Sends a certificate status request to the server (OCSP stapling). The server
699 response (if any) is printed out.
701 =item B<-alpn> I<protocols>, B<-nextprotoneg> I<protocols>
703 These flags enable the Enable the Application-Layer Protocol Negotiation
704 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
705 IETF standard and replaces NPN.
706 The I<protocols> list is a comma-separated list of protocol names that
707 the client should advertise support for. The list should contain the most
708 desirable protocols first. Protocol names are printable ASCII strings,
709 for example "http/1.1" or "spdy/3".
710 An empty list of protocols is treated specially and will cause the
711 client to advertise support for the TLS extension but disconnect just
712 after receiving ServerHello with a list of server supported protocols.
713 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
715 =item B<-ct>, B<-noct>
717 Use one of these two options to control whether Certificate Transparency (CT)
718 is enabled (B<-ct>) or disabled (B<-noct>).
719 If CT is enabled, signed certificate timestamps (SCTs) will be requested from
720 the server and reported at handshake completion.
722 Enabling CT also enables OCSP stapling, as this is one possible delivery method
727 A file containing a list of known Certificate Transparency logs. See
728 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
730 =item B<-keylogfile> I<file>
732 Appends TLS secrets to the specified keylog file such that external programs
733 (like Wireshark) can decrypt TLS connections.
735 =item B<-early_data> I<file>
737 Reads the contents of the specified file and attempts to send it as early data
738 to the server. This will only work with resumed sessions that support early
739 data and when the server accepts the early data.
743 For TLSv1.3 only, send the Post-Handshake Authentication extension. This will
744 happen whether or not a certificate has been provided via B<-cert>.
746 =item I<host>:I<port>
748 Rather than providing B<-connect>, the target hostname and optional port may
749 be provided as a single positional argument after all options. If neither this
750 nor B<-connect> are provided, falls back to attempting to connect to
751 I<localhost> on port I<4433>.
755 =head1 CONNECTED COMMANDS
757 If a connection is established with an SSL server then any data received
758 from the server is displayed and any key presses will be sent to the
759 server. If end of file is reached then the connection will be closed down. When
760 used interactively (which means neither B<-quiet> nor B<-ign_eof> have been
761 given), then certain commands are also recognized which perform special
762 operations. These commands are a letter which must appear at the start of a
763 line. They are listed below.
769 End the current SSL connection and exit.
773 Renegotiate the SSL session (TLSv1.2 and below only).
777 Send a key update message to the server (TLSv1.3 only)
781 Send a key update message to the server and request one back (TLSv1.3 only)
787 This command can be used to debug SSL servers. To connect to an SSL HTTP
790 openssl s_client -connect servername:443
792 would typically be used (https uses port 443). If the connection succeeds
793 then an HTTP command can be given such as "GET /" to retrieve a web page.
795 If the handshake fails then there are several possible causes, if it is
796 nothing obvious like no client certificate then the B<-bugs>,
797 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
798 in case it is a buggy server. In particular you should play with these
799 options B<before> submitting a bug report to an OpenSSL mailing list.
801 A frequent problem when attempting to get client certificates working
802 is that a web client complains it has no certificates or gives an empty
803 list to choose from. This is normally because the server is not sending
804 the clients certificate authority in its "acceptable CA list" when it
805 requests a certificate. By using this command, the CA list can be viewed
806 and checked. However some servers only request client authentication
807 after a specific URL is requested. To obtain the list in this case it
808 is necessary to use the B<-prexit> option and send an HTTP request
809 for an appropriate page.
811 If a certificate is specified on the command line using the B<-cert>
812 option it will not be used unless the server specifically requests
813 a client certificate. Therefor merely including a client certificate
814 on the command line is no guarantee that the certificate works.
816 If there are problems verifying a server certificate then the
817 B<-showcerts> option can be used to show all the certificates sent by the
820 This command is a test tool and is designed to continue the
821 handshake after any certificate verification errors. As a result it will
822 accept any certificate chain (trusted or not) sent by the peer. None test
823 applications should B<not> do this as it makes them vulnerable to a MITM
824 attack. This behaviour can be changed by with the B<-verify_return_error>
825 option: any verify errors are then returned aborting the handshake.
827 The B<-bind> option may be useful if the server or a firewall requires
828 connections to come from some particular address and or port.
832 Because this program has a lot of options and also because some of the
833 techniques used are rather old, the C source for this command is rather
834 hard to read and not a model of how things should be done.
835 A typical SSL client program would be much simpler.
837 The B<-prexit> option is a bit of a hack. We should really report
838 information whenever a session is renegotiated.
843 L<openssl-sess_id(1)>,
844 L<openssl-s_server(1)>,
845 L<openssl-ciphers(1)>,
847 L<SSL_CTX_set_max_send_fragment(3)>,
848 L<SSL_CTX_set_split_send_fragment(3)>,
849 L<SSL_CTX_set_max_pipelines(3)>
853 The B<-no_alt_chains> option was added in OpenSSL 1.1.0.
854 The B<-name> option was added in OpenSSL 1.1.1.
858 Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.
860 Licensed under the Apache License 2.0 (the "License"). You may not use
861 this file except in compliance with the License. You can obtain a copy
862 in the file LICENSE in the source distribution or at
863 L<https://www.openssl.org/source/license.html>.