2 {- OpenSSL::safe::output_do_not_edit_headers(); -}
6 openssl-s_server - SSL/TLS server program
10 B<openssl> B<s_server>
23 [B<-certform> B<DER>|B<PEM>|B<P12>]
24 [B<-cert_chain> I<infile>]
26 [B<-serverinfo> I<val>]
27 [B<-key> I<filename>|I<uri>]
28 [B<-key2> I<filename>|I<uri>]
29 [B<-keyform> B<DER>|B<PEM>|B<P12>|B<ENGINE>]
32 [B<-dcertform> B<DER>|B<PEM>|B<P12>]
33 [B<-dcert_chain> I<infile>]
34 [B<-dkey> I<filename>|I<uri>]
35 [B<-dkeyform> B<DER>|B<PEM>|B<P12>|B<ENGINE>]
41 [B<-msgfile> I<outfile>]
45 [B<-no_resume_ephemeral>]
48 [B<-http_server_binmode>]
50 [B<-ignore_unexpected_eof>]
52 [B<-servername_fatal>]
55 [B<-id_prefix> I<val>]
56 [B<-keymatexport> I<val>]
57 [B<-keymatexportlen> I<+int>]
59 [B<-CRLform> B<DER>|B<PEM>]
61 [B<-chainCAfile> I<infile>]
62 [B<-chainCApath> I<dir>]
63 [B<-chainCAstore> I<uri>]
64 [B<-verifyCAfile> I<infile>]
65 [B<-verifyCApath> I<dir>]
66 [B<-verifyCAstore> I<uri>]
69 [B<-verify_return_error>]
77 [B<-status_timeout> I<int>]
78 [B<-proxy> I<[http[s]://][userinfo@]host[:port][/path]>]
79 [B<-no_proxy> I<addresses>]
80 [B<-status_url> I<val>]
81 [B<-status_file> I<infile>]
82 [B<-ssl_config> I<val>]
85 [B<-security_debug_verbose>]
89 [B<-max_send_frag> I<+int>]
90 [B<-split_send_frag> I<+int>]
91 [B<-max_pipelines> I<+int>]
93 [B<-read_buf> I<+int>]
99 [B<-legacy_renegotiation>]
100 [B<-no_renegotiation>]
101 [B<-no_resumption_on_reneg>]
102 [B<-no_legacy_server_connect>]
103 [B<-allow_no_dhe_kex>]
104 [B<-prioritize_chacha>]
107 [B<-client_sigalgs> I<val>]
110 [B<-named_curve> I<val>]
112 [B<-ciphersuites> I<val>]
113 [B<-dhparam> I<infile>]
114 [B<-record_padding> I<val>]
115 [B<-debug_broken_protocol>]
117 [B<-psk_identity> I<val>]
118 [B<-psk_hint> I<val>]
120 [B<-psk_session> I<file>]
121 [B<-srpvfile> I<infile>]
122 [B<-srpuserseed> I<val>]
128 [B<-use_srtp> I<val>]
130 [B<-nextprotoneg> I<val>]
134 [B<-keylogfile> I<outfile>]
135 [B<-recv_max_early_data> I<int>]
136 [B<-max_early_data> I<int>]
143 {- $OpenSSL::safe::opt_name_synopsis -}
144 {- $OpenSSL::safe::opt_version_synopsis -}
145 {- $OpenSSL::safe::opt_v_synopsis -}
146 {- $OpenSSL::safe::opt_s_synopsis -}
147 {- $OpenSSL::safe::opt_x_synopsis -}
148 {- $OpenSSL::safe::opt_trust_synopsis -}
149 {- $OpenSSL::safe::opt_r_synopsis -}
150 {- $OpenSSL::safe::opt_engine_synopsis -}{- $OpenSSL::safe::opt_provider_synopsis -}
154 This command implements a generic SSL/TLS server which
155 listens for connections on a given port using SSL/TLS.
159 In addition to the options below, this command also supports
160 the common and server only options documented
161 L<SSL_CONF_cmd(3)/Supported Command Line Commands>
167 Print out a usage message.
169 =item B<-port> I<+int>
171 The TCP port to listen on for connections. If not specified 4433 is used.
173 =item B<-accept> I<val>
175 The optional TCP host and port to listen on for connections. If not specified, *:4433 is used.
177 =item B<-unix> I<val>
179 Unix domain socket to accept on.
191 For -unix, unlink any existing socket first.
193 =item B<-context> I<val>
195 Sets the SSL context id. It can be given any string value. If this option
196 is not present a default value will be used.
198 =item B<-verify> I<int>, B<-Verify> I<int>
200 The verify depth to use. This specifies the maximum length of the
201 client certificate chain and makes the server request a certificate from
202 the client. With the B<-verify> option a certificate is requested but the
203 client does not have to send one, with the B<-Verify> option the client
204 must supply a certificate or an error occurs.
206 If the cipher suite cannot request a client certificate (for example an
207 anonymous cipher suite or PSK) this option has no effect.
209 =item B<-cert> I<infile>
211 The certificate to use, most servers cipher suites require the use of a
212 certificate and some require a certificate with a certain public key type:
213 for example the DSS cipher suites require a certificate containing a DSS
214 (DSA) key. If not specified then the filename F<server.pem> will be used.
216 =item B<-cert2> I<infile>
218 The certificate file to use for servername; default is C<server2.pem>.
220 =item B<-certform> B<DER>|B<PEM>|B<P12>
222 The server certificate file format; unspecified by default.
223 See L<openssl-format-options(1)> for details.
227 A file or URI of untrusted certificates to use when attempting to build the
228 certificate chain related to the certificate specified via the B<-cert> option.
229 The input can be in PEM, DER, or PKCS#12 format.
231 =item B<-build_chain>
233 Specify whether the application should build the server certificate chain to be
234 provided to the client.
236 =item B<-serverinfo> I<val>
238 A file containing one or more blocks of PEM data. Each PEM block
239 must encode a TLS ServerHello extension (2 bytes type, 2 bytes length,
240 followed by "length" bytes of extension data). If the client sends
241 an empty TLS ClientHello extension matching the type, the corresponding
242 ServerHello extension will be returned.
244 =item B<-key> I<filename>|I<uri>
246 The private key to use. If not specified then the certificate file will
249 =item B<-key2> I<filename>|I<uri>
251 The private Key file to use for servername if not given via B<-cert2>.
253 =item B<-keyform> B<DER>|B<PEM>|B<P12>|B<ENGINE>
255 The key format; unspecified by default.
256 See L<openssl-format-options(1)> for details.
258 =item B<-pass> I<val>
260 The private key and certificate file password source.
261 For more information about the format of I<val>,
262 see L<openssl-passphrase-options(1)>.
264 =item B<-dcert> I<infile>, B<-dkey> I<filename>|I<uri>
266 Specify an additional certificate and private key, these behave in the
267 same manner as the B<-cert> and B<-key> options except there is no default
268 if they are not specified (no additional certificate and key is used). As
269 noted above some cipher suites require a certificate containing a key of
270 a certain type. Some cipher suites need a certificate carrying an RSA key
271 and some a DSS (DSA) key. By using RSA and DSS certificates and keys
272 a server can support clients which only support RSA or DSS cipher suites
273 by using an appropriate certificate.
275 =item B<-dcert_chain>
277 A file or URI of untrusted certificates to use when attempting to build the
278 server certificate chain when a certificate specified via the B<-dcert> option
280 The input can be in PEM, DER, or PKCS#12 format.
282 =item B<-dcertform> B<DER>|B<PEM>|B<P12>
284 The format of the additional certificate file; unspecified by default.
285 See L<openssl-format-options(1)> for details.
287 =item B<-dkeyform> B<DER>|B<PEM>|B<P12>|B<ENGINE>
289 The format of the additional private key; unspecified by default.
290 See L<openssl-format-options(1)> for details.
292 =item B<-dpass> I<val>
294 The passphrase for the additional private key and certificate.
295 For more information about the format of I<val>,
296 see L<openssl-passphrase-options(1)>.
300 Tests non blocking I/O.
304 This option translated a line feed from the terminal into CR+LF.
308 Print extensive debugging information including a hex dump of all traffic.
310 =item B<-security_debug>
312 Print output from SSL/TLS security framework.
314 =item B<-security_debug_verbose>
316 Print more output from SSL/TLS security framework
320 Show all protocol messages with hex dump.
322 =item B<-msgfile> I<outfile>
324 File to send output of B<-msg> or B<-trace> to, default standard output.
328 Prints the SSL session states.
330 =item B<-CRL> I<infile>
334 =item B<-CRLform> B<DER>|B<PEM>
336 The CRL file format; unspecified by default.
337 See L<openssl-format-options(1)> for details.
339 =item B<-crl_download>
341 Download CRLs from distribution points given in CDP extensions of certificates
343 =item B<-verifyCAfile> I<filename>
345 A file in PEM format CA containing trusted certificates to use
346 for verifying client certificates.
348 =item B<-verifyCApath> I<dir>
350 A directory containing trusted certificates to use
351 for verifying client certificates.
352 This directory must be in "hash format",
353 see L<openssl-verify(1)> for more information.
355 =item B<-verifyCAstore> I<uri>
357 The URI of a store containing trusted certificates to use
358 for verifying client certificates.
360 =item B<-chainCAfile> I<file>
362 A file in PEM format containing trusted certificates to use
363 when attempting to build the server certificate chain.
365 =item B<-chainCApath> I<dir>
367 A directory containing trusted certificates to use
368 for building the server certificate chain provided to the client.
369 This directory must be in "hash format",
370 see L<openssl-verify(1)> for more information.
372 =item B<-chainCAstore> I<uri>
374 The URI of a store containing trusted certificates to use
375 for building the server certificate chain provided to the client.
376 The URI may indicate a single certificate, as well as a collection of them.
377 With URIs in the C<file:> scheme, this acts as B<-chainCAfile> or
378 B<-chainCApath>, depending on if the URI indicates a directory or a
380 See L<ossl_store-file(7)> for more information on the C<file:> scheme.
384 If this option is set then no certificate is used. This restricts the
385 cipher suites available to the anonymous ones (currently just anonymous
390 Inhibit printing of session and certificate information.
392 =item B<-no_resume_ephemeral>
394 Disable caching and tickets if ephemeral (EC)DH is used.
396 =item B<-tlsextdebug>
398 Print a hex dump of any TLS extensions received from the server.
402 Sends a status message back to the client when it connects. This includes
403 information about the ciphers used and various session parameters.
404 The output is in HTML format so this option can be used with a web browser.
405 The special URL C</renegcert> turns on client cert validation, and C</reneg>
406 tells the server to request renegotiation.
407 The B<-early_data> option cannot be used with this option.
409 =item B<-WWW>, B<-HTTP>
411 Emulates a simple web server. Pages will be resolved relative to the
412 current directory, for example if the URL C<https://myhost/page.html> is
413 requested the file F<./page.html> will be sent.
414 If the B<-HTTP> flag is used, the files are sent directly, and should contain
415 any HTTP response headers (including status response line).
416 If the B<-WWW> option is used,
417 the response headers are generated by the server, and the file extension is
418 examined to determine the B<Content-Type> header.
419 Extensions of C<html>, C<htm>, and C<php> are C<text/html> and all others are
421 In addition, the special URL C</stats> will return status
422 information like the B<-www> option.
423 Neither of these options can be used in conjunction with B<-early_data>.
425 =item B<-http_server_binmode>
427 When acting as web-server (using option B<-WWW> or B<-HTTP>) open files requested
428 by the client in binary mode.
430 =item B<-no_ca_names>
432 Disable TLS Extension CA Names. You may want to disable it for security reasons
433 or for compatibility with some Windows TLS implementations crashing when this
434 extension is larger than 1024 bytes.
436 =item B<-ignore_unexpected_eof>
438 Some TLS implementations do not send the mandatory close_notify alert on
439 shutdown. If the application tries to wait for the close_notify alert but the
440 peer closes the connection without sending it, an error is generated. When this
441 option is enabled the peer does not need to send the close_notify alert and a
442 closed connection will be treated as if the close_notify alert was received.
443 For more information on shutting down a connection, see L<SSL_shutdown(3)>.
447 Servername for HostName TLS extension.
449 =item B<-servername_fatal>
451 On servername mismatch send fatal alert (default: warning alert).
453 =item B<-id_prefix> I<val>
455 Generate SSL/TLS session IDs prefixed by I<val>. This is mostly useful
456 for testing any SSL/TLS code (e.g. proxies) that wish to deal with multiple
457 servers, when each of which might be generating a unique range of session
458 IDs (e.g. with a certain prefix).
460 =item B<-keymatexport>
462 Export keying material using label.
464 =item B<-keymatexportlen>
466 Export the given number of bytes of keying material; default 20.
470 Disable session cache.
474 Disable internal cache, set up and use external cache.
476 =item B<-verify_return_error>
478 Verification errors normally just print a message but allow the
479 connection to continue, for debugging purposes.
480 If this option is used, then verification errors close the connection.
482 =item B<-verify_quiet>
484 No verify output except verify errors.
488 Ignore input EOF (default: when B<-quiet>).
492 Do not ignore input EOF.
496 Disable Encrypt-then-MAC negotiation.
500 Disable Extended master secret negotiation.
504 Enables certificate status request support (aka OCSP stapling).
506 =item B<-status_verbose>
508 Enables certificate status request support (aka OCSP stapling) and gives
509 a verbose printout of the OCSP response.
511 =item B<-status_timeout> I<int>
513 Sets the timeout for OCSP response to I<int> seconds.
515 =item B<-proxy> I<[http[s]://][userinfo@]host[:port][/path]>
517 The HTTP(S) proxy server to use for reaching the OCSP server unless B<-no_proxy>
519 The proxy port defaults to 80 or 443 if the scheme is C<https>; apart from that
520 the optional C<http://> or C<https://> prefix is ignored,
521 as well as any userinfo and path components.
522 Defaults to the environment variable C<http_proxy> if set, else C<HTTP_PROXY>
523 in case no TLS is used, otherwise C<https_proxy> if set, else C<HTTPS_PROXY>.
525 =item B<-no_proxy> I<addresses>
527 List of IP addresses and/or DNS names of servers
528 not to use an HTTP(S) proxy for, separated by commas and/or whitespace
529 (where in the latter case the whole argument must be enclosed in "...").
530 Default is from the environment variable C<no_proxy> if set, else C<NO_PROXY>.
532 =item B<-status_url> I<val>
534 Sets a fallback responder URL to use if no responder URL is present in the
535 server certificate. Without this option an error is returned if the server
536 certificate does not contain a responder address.
537 The optional userinfo and fragment URL components are ignored.
538 Any given query component is handled as part of the path component.
540 =item B<-status_file> I<infile>
542 Overrides any OCSP responder URLs from the certificate and always provides the
543 OCSP Response stored in the file. The file must be in DER format.
545 =item B<-ssl_config> I<val>
547 Configure SSL_CTX using the given configuration value.
551 Show verbose trace output of protocol messages.
555 Provide a brief summary of connection parameters instead of the normal verbose
560 Simple echo server that sends back received text reversed. Also sets B<-brief>.
561 Cannot be used in conjunction with B<-early_data>.
565 Switch on asynchronous mode. Cryptographic operations will be performed
566 asynchronously. This will only have an effect if an asynchronous capable engine
567 is also used via the B<-engine> option. For test purposes the dummy async engine
568 (dasync) can be used (if available).
570 =item B<-max_send_frag> I<+int>
572 The maximum size of data fragment to send.
573 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
575 =item B<-split_send_frag> I<+int>
577 The size used to split data for encrypt pipelines. If more data is written in
578 one go than this value then it will be split into multiple pipelines, up to the
579 maximum number of pipelines defined by max_pipelines. This only has an effect if
580 a suitable cipher suite has been negotiated, an engine that supports pipelining
581 has been loaded, and max_pipelines is greater than 1. See
582 L<SSL_CTX_set_split_send_fragment(3)> for further information.
584 =item B<-max_pipelines> I<+int>
586 The maximum number of encrypt/decrypt pipelines to be used. This will only have
587 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
588 engine) and a suitable cipher suite has been negotiated. The default value is 1.
589 See L<SSL_CTX_set_max_pipelines(3)> for further information.
591 =item B<-naccept> I<+int>
593 The server will exit after receiving the specified number of connections,
596 =item B<-read_buf> I<+int>
598 The default read buffer size to be used for connections. This will only have an
599 effect if the buffer size is larger than the size that would otherwise be used
600 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
601 further information).
605 There are several known bugs in SSL and TLS implementations. Adding this
606 option enables various workarounds.
610 Disable negotiation of TLS compression.
611 TLS compression is not recommended and is off by default as of
616 Enable negotiation of TLS compression.
617 This option was introduced in OpenSSL 1.1.0.
618 TLS compression is not recommended and is off by default as of
623 Disable RFC4507bis session ticket support. This option has no effect if TLSv1.3
624 is negotiated. See B<-num_tickets>.
626 =item B<-num_tickets>
628 Control the number of tickets that will be sent to the client after a full
629 handshake in TLSv1.3. The default number of tickets is 2. This option does not
630 affect the number of tickets sent after a resumption handshake.
634 Use the server's cipher preferences, rather than the client's preferences.
636 =item B<-prioritize_chacha>
638 Prioritize ChaCha ciphers when preferred by clients. Requires B<-serverpref>.
640 =item B<-no_resumption_on_reneg>
642 Set the B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> option.
644 =item B<-client_sigalgs> I<val>
646 Signature algorithms to support for client certificate authentication
647 (colon-separated list).
649 =item B<-named_curve> I<val>
651 Specifies the elliptic curve to use. NOTE: this is single curve, not a list.
652 For a list of all possible curves, use:
654 $ openssl ecparam -list_curves
656 =item B<-cipher> I<val>
658 This allows the list of TLSv1.2 and below ciphersuites used by the server to be
659 modified. This list is combined with any TLSv1.3 ciphersuites that have been
660 configured. When the client sends a list of supported ciphers the first client
661 cipher also included in the server list is used. Because the client specifies
662 the preference order, the order of the server cipherlist is irrelevant. See
663 L<openssl-ciphers(1)> for more information.
665 =item B<-ciphersuites> I<val>
667 This allows the list of TLSv1.3 ciphersuites used by the server to be modified.
668 This list is combined with any TLSv1.2 and below ciphersuites that have been
669 configured. When the client sends a list of supported ciphers the first client
670 cipher also included in the server list is used. Because the client specifies
671 the preference order, the order of the server cipherlist is irrelevant. See
672 L<openssl-ciphers(1)> command for more information. The format for this list is
673 a simple colon (":") separated list of TLSv1.3 ciphersuite names.
675 =item B<-dhparam> I<infile>
677 The DH parameter file to use. The ephemeral DH cipher suites generate keys
678 using a set of DH parameters. If not specified then an attempt is made to
679 load the parameters from the server certificate file.
680 If this fails then a static set of parameters hard coded into this command
685 Turns on non blocking I/O.
695 =item B<-psk_identity> I<val>
697 Expect the client to send PSK identity I<val> when using a PSK
698 cipher suite, and warn if they do not. By default, the expected PSK
699 identity is the string "Client_identity".
701 =item B<-psk_hint> I<val>
703 Use the PSK identity hint I<val> when using a PSK cipher suite.
707 Use the PSK key I<val> when using a PSK cipher suite. The key is
708 given as a hexadecimal number without leading 0x, for example -psk
710 This option must be provided in order to use a PSK cipher.
712 =item B<-psk_session> I<file>
714 Use the pem encoded SSL_SESSION data stored in I<file> as the basis of a PSK.
715 Note that this will only work if TLSv1.3 is negotiated.
719 The verifier file for SRP.
720 This option is deprecated.
722 =item B<-srpuserseed>
724 A seed string for a default user salt.
725 This option is deprecated.
729 This option can only be used in conjunction with one of the DTLS options above.
730 With this option, this command will listen on a UDP port for incoming
732 Any ClientHellos that arrive will be checked to see if they have a cookie in
734 Any without a cookie will be responded to with a HelloVerifyRequest.
735 If a ClientHello with a cookie is received then this command will
736 connect to that peer and complete the handshake.
740 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
741 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
742 available where OpenSSL has support for SCTP enabled.
744 =item B<-sctp_label_bug>
746 Use the incorrect behaviour of older OpenSSL implementations when computing
747 endpoint-pair shared secrets for DTLS/SCTP. This allows communication with
748 older broken implementations but breaks interoperability with correct
749 implementations. Must be used in conjunction with B<-sctp>. This option is only
750 available where OpenSSL has support for SCTP enabled.
754 Offer SRTP key management with a colon-separated profile list.
758 If this option is set then no DH parameters will be loaded effectively
759 disabling the ephemeral DH cipher suites.
761 =item B<-alpn> I<val>, B<-nextprotoneg> I<val>
763 These flags enable the Application-Layer Protocol Negotiation
764 or Next Protocol Negotiation (NPN) extension, respectively. ALPN is the
765 IETF standard and replaces NPN.
766 The I<val> list is a comma-separated list of supported protocol
767 names. The list should contain the most desirable protocols first.
768 Protocol names are printable ASCII strings, for example "http/1.1" or
770 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
774 Enable Kernel TLS for sending and receiving.
775 This option was introduced in OpenSSL 3.1.0.
776 Kernel TLS is off by default as of OpenSSL 3.1.0.
780 If this option is set and KTLS is enabled, SSL_sendfile() will be used
781 instead of BIO_write() to send the HTTP response requested by a client.
782 This option is only valid when B<-ktls> along with B<-WWW> or B<-HTTP>
785 =item B<-keylogfile> I<outfile>
787 Appends TLS secrets to the specified keylog file such that external programs
788 (like Wireshark) can decrypt TLS connections.
790 =item B<-max_early_data> I<int>
792 Change the default maximum early data bytes that are specified for new sessions
793 and any incoming early data (when used in conjunction with the B<-early_data>
794 flag). The default value is approximately 16k. The argument must be an integer
795 greater than or equal to 0.
797 =item B<-recv_max_early_data> I<int>
799 Specify the hard limit on the maximum number of early data bytes that will
804 Accept early data where possible. Cannot be used in conjunction with B<-www>,
805 B<-WWW>, B<-HTTP> or B<-rev>.
809 Require TLSv1.3 cookies.
811 =item B<-anti_replay>, B<-no_anti_replay>
813 Switches replay protection on or off, respectively. Replay protection is on by
814 default unless overridden by a configuration file. When it is on, OpenSSL will
815 automatically detect if a session ticket has been used more than once, TLSv1.3
816 has been negotiated, and early data is enabled on the server. A full handshake
817 is forced if a session ticket is used a second or subsequent time. Any early
818 data that was sent will be rejected.
822 Enable acceptance of TCP Fast Open (RFC7413) connections.
825 {- $OpenSSL::safe::opt_name_item -}
827 {- $OpenSSL::safe::opt_version_item -}
829 {- $OpenSSL::safe::opt_s_item -}
831 {- $OpenSSL::safe::opt_x_item -}
833 {- $OpenSSL::safe::opt_trust_item -}
835 {- $OpenSSL::safe::opt_r_item -}
837 {- $OpenSSL::safe::opt_engine_item -}
839 {- $OpenSSL::safe::opt_provider_item -}
841 {- $OpenSSL::safe::opt_v_item -}
843 If the server requests a client certificate, then
844 verification errors are displayed, for debugging, but the command will
845 proceed unless the B<-verify_return_error> option is used.
849 =head1 CONNECTED COMMANDS
851 If a connection request is established with an SSL client and neither the
852 B<-www> nor the B<-WWW> option has been used then normally any data received
853 from the client is displayed and any key presses will be sent to the client.
855 Certain commands are also recognized which perform special operations. These
856 commands are a letter which must appear at the start of a line. They are listed
863 End the current SSL connection but still accept new connections.
867 End the current SSL connection and exit.
871 Renegotiate the SSL session (TLSv1.2 and below only).
875 Renegotiate the SSL session and request a client certificate (TLSv1.2 and below
880 Send some plain text down the underlying TCP connection: this should
881 cause the client to disconnect due to a protocol violation.
885 Print out some session cache status information.
889 Send a key update message to the client (TLSv1.3 only)
893 Send a key update message to the client and request one back (TLSv1.3 only)
897 Send a certificate request to the client (TLSv1.3 only)
903 This command can be used to debug SSL clients. To accept connections
904 from a web browser the command:
906 openssl s_server -accept 443 -www
908 can be used for example.
910 Although specifying an empty list of CAs when requesting a client certificate
911 is strictly speaking a protocol violation, some SSL clients interpret this to
912 mean any CA is acceptable. This is useful for debugging purposes.
914 The session parameters can printed out using the L<openssl-sess_id(1)> command.
918 Because this program has a lot of options and also because some of the
919 techniques used are rather old, the C source for this command is rather
920 hard to read and not a model of how things should be done.
921 A typical SSL server program would be much simpler.
923 The output of common ciphers is wrong: it just gives the list of ciphers that
924 OpenSSL recognizes and the client supports.
926 There should be a way for this command to print out details
927 of any unknown cipher suites a client says it supports.
932 L<openssl-sess_id(1)>,
933 L<openssl-s_client(1)>,
934 L<openssl-ciphers(1)>,
936 L<SSL_CTX_set_max_send_fragment(3)>,
937 L<SSL_CTX_set_split_send_fragment(3)>,
938 L<SSL_CTX_set_max_pipelines(3)>,
939 L<ossl_store-file(7)>
943 The -no_alt_chains option was added in OpenSSL 1.1.0.
946 -allow-no-dhe-kex and -prioritize_chacha options were added in OpenSSL 1.1.1.
948 The B<-srpvfile>, B<-srpuserseed>, and B<-engine>
949 option were deprecated in OpenSSL 3.0.
951 The -tfo option was added in OpenSSL 3.1.
955 Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
957 Licensed under the Apache License 2.0 (the "License"). You may not use
958 this file except in compliance with the License. You can obtain a copy
959 in the file LICENSE in the source distribution or at
960 L<https://www.openssl.org/source/license.html>.