6 s_server - SSL/TLS server program
10 B<openssl> B<s_server>
25 [B<-certform PEM|DER>]
30 [B<-dcertform PEM|DER>]
32 [B<-dkeyform PEM|DER>]
46 [B<-no_resume_ephemeral>]
50 [B<-servername_fatal>]
58 [B<-keymatexport val>]
59 [B<-keymatexportlen +int>]
62 [B<-cert_chain infile>]
63 [B<-dcert_chain infile>]
65 [B<-verifyCApath dir>]
69 [B<-verify_return_error>]
72 [B<-chainCAfile infile>]
73 [B<-verifyCAfile infile>]
78 [B<-status_timeout int>]
80 [B<-status_file infile>]
83 [B<-security_debug_verbose>]
88 [B<-max_send_frag +int>]
89 [B<-split_send_frag +int>]
90 [B<-max_pipelines +int>]
103 [B<-legacy_renegotiation>]
104 [B<-no_renegotiation>]
105 [B<-legacy_server_connect>]
106 [B<-no_resumption_on_reneg>]
107 [B<-no_legacy_server_connect>]
108 [B<-allow_no_dhe_kex>]
109 [B<-prioritize_chacha>]
112 [B<-client_sigalgs val>]
115 [B<-named_curve val>]
117 [B<-ciphersuites val>]
119 [B<-record_padding val>]
120 [B<-debug_broken_protocol>]
123 [B<-verify_name val>]
124 [B<-verify_depth int>]
127 [B<-verify_hostname val>]
128 [B<-verify_email val>]
130 [B<-ignore_critical>]
135 [B<-explicit_policy>]
144 [B<-suiteB_128_only>]
150 [B<-allow_proxy_certs>]
155 [B<-xcertform PEM|DER>]
156 [B<-xkeyform PEM|DER>]
158 [B<-psk_identity val>]
161 [B<-psk_session file>]
162 [B<-srpvfile infile>]
163 [B<-srpuserseed val>]
178 [B<-nextprotoneg val>]
182 [B<-keylogfile outfile>]
183 [B<-max_early_data int>]
187 [B<-http_server_binmode>]
191 The B<s_server> command implements a generic SSL/TLS server which listens
192 for connections on a given port using SSL/TLS.
196 In addition to the options below the B<s_server> utility also supports the
197 common and server only options documented in the
198 in the "Supported Command Line Commands" section of the L<SSL_CONF_cmd(3)>
205 Print out a usage message.
209 The TCP port to listen on for connections. If not specified 4433 is used.
213 The optional TCP host and port to listen on for connections. If not specified, *:4433 is used.
217 Unix domain socket to accept on.
229 For -unix, unlink any existing socket first.
231 =item B<-context val>
233 Sets the SSL context id. It can be given any string value. If this option
234 is not present a default value will be used.
236 =item B<-verify int>, B<-Verify int>
238 The verify depth to use. This specifies the maximum length of the
239 client certificate chain and makes the server request a certificate from
240 the client. With the B<-verify> option a certificate is requested but the
241 client does not have to send one, with the B<-Verify> option the client
242 must supply a certificate or an error occurs.
244 If the cipher suite cannot request a client certificate (for example an
245 anonymous cipher suite or PSK) this option has no effect.
247 =item B<-cert infile>
249 The certificate to use, most servers cipher suites require the use of a
250 certificate and some require a certificate with a certain public key type:
251 for example the DSS cipher suites require a certificate containing a DSS
252 (DSA) key. If not specified then the filename "server.pem" will be used.
256 A file containing trusted certificates to use when attempting to build the
257 client/server certificate chain related to the certificate specified via the
260 =item B<-build_chain>
262 Specify whether the application should build the certificate chain to be
263 provided to the client.
265 =item B<-nameopt val>
267 Option which determines how the subject or issuer names are displayed. The
268 B<val> argument can be a single option or multiple options separated by
269 commas. Alternatively the B<-nameopt> switch may be used more than once to
270 set multiple options. See the L<x509(1)> manual page for details.
272 =item B<-naccept +int>
274 The server will exit after receiving the specified number of connections,
277 =item B<-serverinfo val>
279 A file containing one or more blocks of PEM data. Each PEM block
280 must encode a TLS ServerHello extension (2 bytes type, 2 bytes length,
281 followed by "length" bytes of extension data). If the client sends
282 an empty TLS ClientHello extension matching the type, the corresponding
283 ServerHello extension will be returned.
285 =item B<-certform PEM|DER>
287 The certificate format to use: DER or PEM. PEM is the default.
291 The private key to use. If not specified then the certificate file will
294 =item B<-keyform format>
296 The private format to use: DER or PEM. PEM is the default.
300 The private key password source. For more information about the format of B<val>
301 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
303 =item B<-dcert infile>, B<-dkey infile>
305 Specify an additional certificate and private key, these behave in the
306 same manner as the B<-cert> and B<-key> options except there is no default
307 if they are not specified (no additional certificate and key is used). As
308 noted above some cipher suites require a certificate containing a key of
309 a certain type. Some cipher suites need a certificate carrying an RSA key
310 and some a DSS (DSA) key. By using RSA and DSS certificates and keys
311 a server can support clients which only support RSA or DSS cipher suites
312 by using an appropriate certificate.
314 =item B<-dcert_chain>
316 A file containing trusted certificates to use when attempting to build the
317 server certificate chain when a certificate specified via the B<-dcert> option
320 =item B<-dcertform PEM|DER>, B<-dkeyform PEM|DER>, B<-dpass val>
322 Additional certificate and private key format and passphrase respectively.
324 =item B<-xkey infile>, B<-xcert infile>, B<-xchain>
326 Specify an extra certificate, private key and certificate chain. These behave
327 in the same manner as the B<-cert>, B<-key> and B<-cert_chain> options. When
328 specified, the callback returning the first valid chain will be in use by
331 =item B<-xchain_build>
333 Specify whether the application should build the certificate chain to be
334 provided to the client for the extra certificates provided via B<-xkey infile>,
335 B<-xcert infile>, B<-xchain> options.
337 =item B<-xcertform PEM|DER>, B<-xkeyform PEM|DER>
339 Extra certificate and private key format respectively.
343 Tests non blocking I/O.
347 This option translated a line feed from the terminal into CR+LF.
351 Print extensive debugging information including a hex dump of all traffic.
355 Show all protocol messages with hex dump.
357 =item B<-msgfile outfile>
359 File to send output of B<-msg> or B<-trace> to, default standard output.
363 Prints the SSL session states.
365 =item B<-CAfile infile>
367 A file containing trusted certificates to use during client authentication
368 and to use when attempting to build the server certificate chain. The list
369 is also used in the list of acceptable client CAs passed to the client when
370 a certificate is requested.
374 The directory to use for client certificate verification. This directory
375 must be in "hash format", see L<verify(1)> for more information. These are
376 also used when building the server certificate chain.
378 =item B<-chainCApath dir>
380 The directory to use for building the chain provided to the client. This
381 directory must be in "hash format", see L<verify(1)> for more information.
383 =item B<-chainCAfile file>
385 A file containing trusted certificates to use when attempting to build the
386 server certificate chain.
390 Do not load the trusted CA certificates from the default file location.
394 Do not load the trusted CA certificates from the default directory location.
398 If this option is set then no certificate is used. This restricts the
399 cipher suites available to the anonymous ones (currently just anonymous
404 Inhibit printing of session and certificate information.
408 Sends a status message back to the client when it connects. This includes
409 information about the ciphers used and various session parameters.
410 The output is in HTML format so this option will normally be used with a
411 web browser. Cannot be used in conjunction with B<-early_data>.
415 Emulates a simple web server. Pages will be resolved relative to the
416 current directory, for example if the URL https://myhost/page.html is
417 requested the file ./page.html will be loaded. Cannot be used in conjunction
420 =item B<-tlsextdebug>
422 Print a hex dump of any TLS extensions received from the server.
426 Emulates a simple web server. Pages will be resolved relative to the
427 current directory, for example if the URL https://myhost/page.html is
428 requested the file ./page.html will be loaded. The files loaded are
429 assumed to contain a complete and correct HTTP response (lines that
430 are part of the HTTP response line and headers must end with CRLF). Cannot be
431 used in conjunction with B<-early_data>.
433 =item B<-id_prefix val>
435 Generate SSL/TLS session IDs prefixed by B<val>. This is mostly useful
436 for testing any SSL/TLS code (eg. proxies) that wish to deal with multiple
437 servers, when each of which might be generating a unique range of session
438 IDs (eg. with a certain prefix).
440 =item B<-rand file...>
442 A file or files containing random data used to seed the random number
444 Multiple files can be specified separated by an OS-dependent character.
445 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
448 =item [B<-writerand file>]
450 Writes random data to the specified I<file> upon exit.
451 This can be used with a subsequent B<-rand> flag.
453 =item B<-verify_return_error>
455 Verification errors normally just print a message but allow the
456 connection to continue, for debugging purposes.
457 If this option is used, then verification errors close the connection.
461 Enables certificate status request support (aka OCSP stapling).
463 =item B<-status_verbose>
465 Enables certificate status request support (aka OCSP stapling) and gives
466 a verbose printout of the OCSP response.
468 =item B<-status_timeout int>
470 Sets the timeout for OCSP response to B<int> seconds.
472 =item B<-status_url val>
474 Sets a fallback responder URL to use if no responder URL is present in the
475 server certificate. Without this option an error is returned if the server
476 certificate does not contain a responder address.
478 =item B<-status_file infile>
480 Overrides any OCSP responder URLs from the certificate and always provides the
481 OCSP Response stored in the file. The file must be in DER format.
485 Show verbose trace output of protocol messages. OpenSSL needs to be compiled
486 with B<enable-ssl-trace> for this option to work.
490 Provide a brief summary of connection parameters instead of the normal verbose
495 Simple test server which just reverses the text received from the client
496 and sends it back to the server. Also sets B<-brief>. Cannot be used in
497 conjunction with B<-early_data>.
501 Switch on asynchronous mode. Cryptographic operations will be performed
502 asynchronously. This will only have an effect if an asynchronous capable engine
503 is also used via the B<-engine> option. For test purposes the dummy async engine
504 (dasync) can be used (if available).
506 =item B<-max_send_frag +int>
508 The maximum size of data fragment to send.
509 See L<SSL_CTX_set_max_send_fragment(3)> for further information.
511 =item B<-split_send_frag +int>
513 The size used to split data for encrypt pipelines. If more data is written in
514 one go than this value then it will be split into multiple pipelines, up to the
515 maximum number of pipelines defined by max_pipelines. This only has an effect if
516 a suitable cipher suite has been negotiated, an engine that supports pipelining
517 has been loaded, and max_pipelines is greater than 1. See
518 L<SSL_CTX_set_split_send_fragment(3)> for further information.
520 =item B<-max_pipelines +int>
522 The maximum number of encrypt/decrypt pipelines to be used. This will only have
523 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
524 engine) and a suitable cipher suite has been negotiated. The default value is 1.
525 See L<SSL_CTX_set_max_pipelines(3)> for further information.
527 =item B<-read_buf +int>
529 The default read buffer size to be used for connections. This will only have an
530 effect if the buffer size is larger than the size that would otherwise be used
531 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
532 further information).
534 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-tls1_1>, B<-tls1_2>, B<-tls1_3>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>, B<-no_tls1_3>
536 These options require or disable the use of the specified SSL or TLS protocols.
537 By default B<s_server> will negotiate the highest mutually supported protocol
539 When a specific TLS version is required, only that version will be accepted
541 Note that not all protocols and flags may be available, depending on how
546 There are several known bugs in SSL and TLS implementations. Adding this
547 option enables various workarounds.
551 Disable negotiation of TLS compression.
552 TLS compression is not recommended and is off by default as of
557 Enable negotiation of TLS compression.
558 This option was introduced in OpenSSL 1.1.0.
559 TLS compression is not recommended and is off by default as of
564 Disable RFC4507bis session ticket support. This option has no effect if TLSv1.3
565 is negotiated. See B<-num_tickets>.
567 =item B<-num_tickets>
569 Control the number of tickets that will be sent to the client after a full
570 handshake in TLSv1.3. The default number of tickets is 2. This option does not
571 affect the number of tickets sent after a resumption handshake.
575 Use the server's cipher preferences, rather than the client's preferences.
577 =item B<-prioritize_chacha>
579 Prioritize ChaCha ciphers when preferred by clients. Requires B<-serverpref>.
581 =item B<-no_resumption_on_reneg>
583 Set the B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> option.
585 =item B<-client_sigalgs val>
587 Signature algorithms to support for client certificate authentication
588 (colon-separated list).
590 =item B<-named_curve val>
592 Specifies the elliptic curve to use. NOTE: this is single curve, not a list.
593 For a list of all possible curves, use:
595 $ openssl ecparam -list_curves
599 This allows the list of TLSv1.2 and below ciphersuites used by the server to be
600 modified. This list is combined with any TLSv1.3 ciphersuites that have been
601 configured. When the client sends a list of supported ciphers the first client
602 cipher also included in the server list is used. Because the client specifies
603 the preference order, the order of the server cipherlist is irrelevant. See
604 the B<ciphers> command for more information.
606 =item B<-ciphersuites val>
608 This allows the list of TLSv1.3 ciphersuites used by the server to be modified.
609 This list is combined with any TLSv1.2 and below ciphersuites that have been
610 configured. When the client sends a list of supported ciphers the first client
611 cipher also included in the server list is used. Because the client specifies
612 the preference order, the order of the server cipherlist is irrelevant. See
613 the B<ciphers> command for more information. The format for this list is a
614 simple colon (":") separated list of TLSv1.3 ciphersuite names.
616 =item B<-dhparam infile>
618 The DH parameter file to use. The ephemeral DH cipher suites generate keys
619 using a set of DH parameters. If not specified then an attempt is made to
620 load the parameters from the server certificate file.
621 If this fails then a static set of parameters hard coded into the B<s_server>
622 program will be used.
624 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
625 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
626 B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
627 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
628 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
629 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
630 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
632 Set different peer certificate verification options.
633 See the L<verify(1)> manual page for details.
635 =item B<-crl_check>, B<-crl_check_all>
637 Check the peer certificate has not been revoked by its CA.
638 The CRL(s) are appended to the certificate file. With the B<-crl_check_all>
639 option all CRLs of all CAs in the chain are checked.
643 Turns on non blocking I/O.
645 =item B<-psk_identity val>
647 Expect the client to send PSK identity B<val> when using a PSK
648 cipher suite, and warn if they do not. By default, the expected PSK
649 identity is the string "Client_identity".
651 =item B<-psk_hint val>
653 Use the PSK identity hint B<val> when using a PSK cipher suite.
657 Use the PSK key B<val> when using a PSK cipher suite. The key is
658 given as a hexadecimal number without leading 0x, for example -psk
660 This option must be provided in order to use a PSK cipher.
662 =item B<-psk_session file>
664 Use the pem encoded SSL_SESSION data stored in B<file> as the basis of a PSK.
665 Note that this will only work if TLSv1.3 is negotiated.
669 This option can only be used in conjunction with one of the DTLS options above.
670 With this option B<s_server> will listen on a UDP port for incoming connections.
671 Any ClientHellos that arrive will be checked to see if they have a cookie in
673 Any without a cookie will be responded to with a HelloVerifyRequest.
674 If a ClientHello with a cookie is received then B<s_server> will connect to
675 that peer and complete the handshake.
677 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
679 These options make B<s_server> use DTLS protocols instead of TLS.
680 With B<-dtls>, B<s_server> will negotiate any supported DTLS protocol version,
681 whilst B<-dtls1> and B<-dtls1_2> will only support DTLSv1.0 and DTLSv1.2
686 Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
687 conjunction with B<-dtls>, B<-dtls1> or B<-dtls1_2>. This option is only
688 available where OpenSSL has support for SCTP enabled.
690 =item B<-sctp_label_bug>
692 Use the incorrect behaviour of older OpenSSL implementations when computing
693 endpoint-pair shared secrets for DTLS/SCTP. This allows communication with
694 older broken implementations but breaks interoperability with correct
695 implementations. Must be used in conjunction with B<-sctp>. This option is only
696 available where OpenSSL has support for SCTP enabled.
700 If this option is set then no DH parameters will be loaded effectively
701 disabling the ephemeral DH cipher suites.
703 =item B<-alpn val>, B<-nextprotoneg val>
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 B<val> list is a comma-separated list of supported protocol
709 names. The list should contain the most desirable protocols first.
710 Protocol names are printable ASCII strings, for example "http/1.1" or
712 The flag B<-nextprotoneg> cannot be specified if B<-tls1_3> is used.
716 Specifying an engine (by its unique id string in B<val>) will cause B<s_server>
717 to attempt to obtain a functional reference to the specified engine,
718 thus initialising it if needed. The engine will then be set as the default
719 for all available algorithms.
721 =item B<-keylogfile outfile>
723 Appends TLS secrets to the specified keylog file such that external programs
724 (like Wireshark) can decrypt TLS connections.
726 =item B<-max_early_data int>
728 Change the default maximum early data bytes that are specified for new sessions
729 and any incoming early data (when used in conjunction with the B<-early_data>
730 flag). The default value is approximately 16k. The argument must be an integer
731 greater than or equal to 0.
735 Accept early data where possible. Cannot be used in conjunction with B<-www>,
736 B<-WWW>, B<-HTTP> or B<-rev>.
738 =item B<-anti_replay>, B<-no_anti_replay>
740 Switches replay protection on or off, respectively. Replay protection is on by
741 default unless overridden by a configuration file. When it is on, OpenSSL will
742 automatically detect if a session ticket has been used more than once, TLSv1.3
743 has been negotiated, and early data is enabled on the server. A full handshake
744 is forced if a session ticket is used a second or subsequent time. Any early
745 data that was sent will be rejected.
747 =item B<-http_server_binmode>
749 When acting as web-server (using option B<-WWW> or B<-HTTP>) open files requested
750 by the client in binary mode.
754 =head1 CONNECTED COMMANDS
756 If a connection request is established with an SSL client and neither the
757 B<-www> nor the B<-WWW> option has been used then normally any data received
758 from the client is displayed and any key presses will be sent to the client.
760 Certain commands are also recognized which perform special operations. These
761 commands are a letter which must appear at the start of a line. They are listed
768 End the current SSL connection but still accept new connections.
772 End the current SSL connection and exit.
776 Renegotiate the SSL session (TLSv1.2 and below only).
780 Renegotiate the SSL session and request a client certificate (TLSv1.2 and below
785 Send some plain text down the underlying TCP connection: this should
786 cause the client to disconnect due to a protocol violation.
790 Print out some session cache status information.
794 Send a key update message to the client (TLSv1.3 only)
798 Send a key update message to the client and request one back (TLSv1.3 only)
802 Send a certificate request to the client (TLSv1.3 only)
808 B<s_server> can be used to debug SSL clients. To accept connections from
809 a web browser the command:
811 openssl s_server -accept 443 -www
813 can be used for example.
815 Although specifying an empty list of CAs when requesting a client certificate
816 is strictly speaking a protocol violation, some SSL clients interpret this to
817 mean any CA is acceptable. This is useful for debugging purposes.
819 The session parameters can printed out using the B<sess_id> program.
823 Because this program has a lot of options and also because some of the
824 techniques used are rather old, the C source of B<s_server> is rather hard to
825 read and not a model of how things should be done.
826 A typical SSL server program would be much simpler.
828 The output of common ciphers is wrong: it just gives the list of ciphers that
829 OpenSSL recognizes and the client supports.
831 There should be a way for the B<s_server> program to print out details of any
832 unknown cipher suites a client says it supports.
836 L<SSL_CONF_cmd(3)>, L<sess_id(1)>, L<s_client(1)>, L<ciphers(1)>
837 L<SSL_CTX_set_max_send_fragment(3)>,
838 L<SSL_CTX_set_split_send_fragment(3)>,
839 L<SSL_CTX_set_max_pipelines(3)>
843 The -no_alt_chains option was added in OpenSSL 1.1.0.
846 -allow-no-dhe-kex and -prioritize_chacha options were added in OpenSSL 1.1.1.
850 Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
852 Licensed under the Apache License 2.0 (the "License"). You may not use
853 this file except in compliance with the License. You can obtain a copy
854 in the file LICENSE in the source distribution or at
855 L<https://www.openssl.org/source/license.html>.