s_server

S_SERVER(1)                          OpenSSL                         S_SERVER(1)



NAME
       openssl-s_server, s_server - SSL/TLS server program

SYNOPSIS
       openssl s_server [-help] [-port +int] [-accept val] [-unix val] [-4] [-6]
       [-unlink] [-context val] [-verify int] [-Verify int] [-cert infile]
       [-nameopt val] [-naccept +int] [-serverinfo val] [-certform PEM|DER]
       [-key infile] [-keyform format] [-pass val] [-dcert infile] [-dcertform
       PEM|DER] [-dkey infile] [-dkeyform PEM|DER] [-dpass val] [-nbio_test]
       [-crlf] [-debug] [-msg] [-msgfile outfile] [-state] [-CAfile infile]
       [-CApath dir] [-no-CAfile] [-no-CApath] [-nocert] [-quiet]
       [-no_resume_ephemeral] [-www] [-WWW] [-servername] [-servername_fatal]
       [-cert2 infile] [-key2 infile] [-tlsextdebug] [-HTTP] [-id_prefix val]
       [-rand file...]  [-writerand file] [-keymatexport val] [-keymatexportlen
       +int] [-CRL infile] [-crl_download] [-cert_chain infile] [-dcert_chain
       infile] [-chainCApath dir] [-verifyCApath dir] [-no_cache] [-ext_cache]
       [-CRLform PEM|DER] [-verify_return_error] [-verify_quiet] [-build_chain]
       [-chainCAfile infile] [-verifyCAfile infile] [-ign_eof] [-no_ign_eof]
       [-status] [-status_verbose] [-status_timeout int] [-status_url val]
       [-status_file infile] [-trace] [-security_debug]
       [-security_debug_verbose] [-brief] [-rev] [-async] [-ssl_config val]
       [-max_send_frag +int] [-split_send_frag +int] [-max_pipelines +int]
       [-read_buf +int] [-no_ssl3] [-no_tls1] [-no_tls1_1] [-no_tls1_2]
       [-no_tls1_3] [-bugs] [-no_comp] [-comp] [-no_ticket] [-num_tickets]
       [-serverpref] [-legacy_renegotiation] [-no_renegotiation]
       [-legacy_server_connect] [-no_resumption_on_reneg]
       [-no_legacy_server_connect] [-allow_no_dhe_kex] [-prioritize_chacha]
       [-strict] [-sigalgs val] [-client_sigalgs val] [-groups val] [-curves
       val] [-named_curve val] [-cipher val] [-ciphersuites val] [-dhparam
       infile] [-record_padding val] [-debug_broken_protocol] [-policy val]
       [-purpose val] [-verify_name val] [-verify_depth int] [-auth_level int]
       [-attime intmax] [-verify_hostname val] [-verify_email val] [-verify_ip]
       [-ignore_critical] [-issuer_checks] [-crl_check] [-crl_check_all]
       [-policy_check] [-explicit_policy] [-inhibit_any] [-inhibit_map]
       [-x509_strict] [-extended_crl] [-use_deltas] [-policy_print]
       [-check_ss_sig] [-trusted_first] [-suiteB_128_only] [-suiteB_128]
       [-suiteB_192] [-partial_chain] [-no_alt_chains] [-no_check_time]
       [-allow_proxy_certs] [-xkey] [-xcert] [-xchain] [-xchain_build]
       [-xcertform PEM|DER] [-xkeyform PEM|DER] [-nbio] [-psk_identity val]
       [-psk_hint val] [-psk val] [-psk_session file] [-srpvfile infile]
       [-srpuserseed val] [-ssl3] [-tls1] [-tls1_1] [-tls1_2] [-tls1_3] [-dtls]
       [-timeout] [-mtu +int] [-listen] [-dtls1] [-dtls1_2] [-sctp]
       [-sctp_label_bug] [-no_dhe] [-nextprotoneg val] [-use_srtp val] [-alpn
       val] [-engine val] [-keylogfile outfile] [-max_early_data int]
       [-early_data] [-anti_replay] [-no_anti_replay]

DESCRIPTION
       The s_server command implements a generic SSL/TLS server which listens
       for connections on a given port using SSL/TLS.

OPTIONS
       In addition to the options below the s_server utility also supports the
       common and server only options documented in the "Supported Command Line
       Commands" section of the SSL_CONF_cmd(3) manual page.

       -help
           Print out a usage message.

       -port +int
           The TCP port to listen on for connections. If not specified 4433 is
           used.

       -accept val
           The optional TCP host and port to listen on for connections. If not
           specified, *:4433 is used.

       -unix val
           Unix domain socket to accept on.

       -4  Use IPv4 only.

       -6  Use IPv6 only.

       -unlink
           For -unix, unlink any existing socket first.

       -context val
           Sets the SSL context id. It can be given any string value. If this
           option is not present a default value will be used.

       -verify int, -Verify int
           The verify depth to use. This specifies the maximum length of the
           client certificate chain and makes the server request a certificate
           from the client. With the -verify option a certificate is requested
           but the client does not have to send one, with the -Verify option the
           client must supply a certificate or an error occurs.

           If the cipher suite cannot request a client certificate (for example
           an anonymous cipher suite or PSK) this option has no effect.

       -cert infile
           The certificate to use, most servers cipher suites require the use of
           a certificate and some require a certificate with a certain public
           key type: for example the DSS cipher suites require a certificate
           containing a DSS (DSA) key. If not specified then the filename
           "server.pem" will be used.

       -cert_chain
           A file containing trusted certificates to use when attempting to
           build the client/server certificate chain related to the certificate
           specified via the -cert option.

       -build_chain
           Specify whether the application should build the certificate chain to
           be provided to the client.

       -nameopt val
           Option which determines how the subject or issuer names are
           displayed. The val argument can be a single option or multiple
           options separated by commas.  Alternatively the -nameopt switch may
           be used more than once to set multiple options. See the x509(1)
           manual page for details.

       -naccept +int
           The server will exit after receiving the specified number of
           connections, default unlimited.

       -serverinfo val
           A file containing one or more blocks of PEM data.  Each PEM block
           must encode a TLS ServerHello extension (2 bytes type, 2 bytes
           length, followed by "length" bytes of extension data).  If the client
           sends an empty TLS ClientHello extension matching the type, the
           corresponding ServerHello extension will be returned.

       -certform PEM|DER
           The certificate format to use: DER or PEM. PEM is the default.

       -key infile
           The private key to use. If not specified then the certificate file
           will be used.

       -keyform format
           The private format to use: DER or PEM. PEM is the default.

       -pass val
           The private key password source. For more information about the
           format of val see "Pass Phrase Options" in openssl(1).

       -dcert infile, -dkey infile
           Specify an additional certificate and private key, these behave in
           the same manner as the -cert and -key options except there is no
           default if they are not specified (no additional certificate and key
           is used). As noted above some cipher suites require a certificate
           containing a key of a certain type. Some cipher suites need a
           certificate carrying an RSA key and some a DSS (DSA) key. By using
           RSA and DSS certificates and keys a server can support clients which
           only support RSA or DSS cipher suites by using an appropriate
           certificate.

       -dcert_chain
           A file containing trusted certificates to use when attempting to
           build the server certificate chain when a certificate specified via
           the -dcert option is in use.

       -dcertform PEM|DER, -dkeyform PEM|DER, -dpass val
           Additional certificate and private key format and passphrase
           respectively.

       -xkey infile, -xcert infile, -xchain
           Specify an extra certificate, private key and certificate chain.
           These behave in the same manner as the -cert, -key and -cert_chain
           options.  When specified, the callback returning the first valid
           chain will be in use by the server.

       -xchain_build
           Specify whether the application should build the certificate chain to
           be provided to the client for the extra certificates provided via
           -xkey infile, -xcert infile, -xchain options.

       -xcertform PEM|DER, -xkeyform PEM|DER
           Extra certificate and private key format respectively.

       -nbio_test
           Tests non blocking I/O.

       -crlf
           This option translated a line feed from the terminal into CR+LF.

       -debug
           Print extensive debugging information including a hex dump of all
           traffic.

       -msg
           Show all protocol messages with hex dump.

       -msgfile outfile
           File to send output of -msg or -trace to, default standard output.

       -state
           Prints the SSL session states.

       -CAfile infile
           A file containing trusted certificates to use during client
           authentication and to use when attempting to build the server
           certificate chain. The list is also used in the list of acceptable
           client CAs passed to the client when a certificate is requested.

       -CApath dir
           The directory to use for client certificate verification. This
           directory must be in "hash format", see verify(1) for more
           information. These are also used when building the server certificate
           chain.

       -chainCApath dir
           The directory to use for building the chain provided to the client.
           This directory must be in "hash format", see verify(1) for more
           information.

       -chainCAfile file
           A file containing trusted certificates to use when attempting to
           build the server certificate chain.

       -no-CAfile
           Do not load the trusted CA certificates from the default file
           location.

       -no-CApath
           Do not load the trusted CA certificates from the default directory
           location.

       -nocert
           If this option is set then no certificate is used. This restricts the
           cipher suites available to the anonymous ones (currently just
           anonymous DH).

       -quiet
           Inhibit printing of session and certificate information.

       -www
           Sends a status message back to the client when it connects. This
           includes information about the ciphers used and various session
           parameters.  The output is in HTML format so this option will
           normally be used with a web browser. Cannot be used in conjunction
           with -early_data.

       -WWW
           Emulates a simple web server. Pages will be resolved relative to the
           current directory, for example if the URL https://myhost/page.html is
           requested the file ./page.html will be loaded. Cannot be used in
           conjunction with -early_data.

       -tlsextdebug
           Print a hex dump of any TLS extensions received from the server.

       -HTTP
           Emulates a simple web server. Pages will be resolved relative to the
           current directory, for example if the URL https://myhost/page.html is
           requested the file ./page.html will be loaded. The files loaded are
           assumed to contain a complete and correct HTTP response (lines that
           are part of the HTTP response line and headers must end with CRLF).
           Cannot be used in conjunction with -early_data.

       -id_prefix val
           Generate SSL/TLS session IDs prefixed by val. This is mostly useful
           for testing any SSL/TLS code (e.g. proxies) that wish to deal with
           multiple servers, when each of which might be generating a unique
           range of session IDs (e.g. with a certain prefix).

       -rand file...
           A file or files containing random data used to seed the random number
           generator.  Multiple files can be specified separated by an OS-
           dependent character.  The separator is ; for MS-Windows, , for
           OpenVMS, and : for all others.

       [-writerand file]
           Writes random data to the specified file upon exit.  This can be used
           with a subsequent -rand flag.

       -verify_return_error
           Verification errors normally just print a message but allow the
           connection to continue, for debugging purposes.  If this option is
           used, then verification errors close the connection.

       -status
           Enables certificate status request support (aka OCSP stapling).

       -status_verbose
           Enables certificate status request support (aka OCSP stapling) and
           gives a verbose printout of the OCSP response.

       -status_timeout int
           Sets the timeout for OCSP response to int seconds.

       -status_url val
           Sets a fallback responder URL to use if no responder URL is present
           in the server certificate. Without this option an error is returned
           if the server certificate does not contain a responder address.

       -status_file infile
           Overrides any OCSP responder URLs from the certificate and always
           provides the OCSP Response stored in the file. The file must be in
           DER format.

       -trace
           Show verbose trace output of protocol messages. OpenSSL needs to be
           compiled with enable-ssl-trace for this option to work.

       -brief
           Provide a brief summary of connection parameters instead of the
           normal verbose output.

       -rev
           Simple test server which just reverses the text received from the
           client and sends it back to the server. Also sets -brief. Cannot be
           used in conjunction with -early_data.

       -async
           Switch on asynchronous mode. Cryptographic operations will be
           performed asynchronously. This will only have an effect if an
           asynchronous capable engine is also used via the -engine option. For
           test purposes the dummy async engine (dasync) can be used (if
           available).

       -max_send_frag +int
           The maximum size of data fragment to send.  See
           SSL_CTX_set_max_send_fragment(3) for further information.

       -split_send_frag +int
           The size used to split data for encrypt pipelines. If more data is
           written in one go than this value then it will be split into multiple
           pipelines, up to the maximum number of pipelines defined by
           max_pipelines. This only has an effect if a suitable cipher suite has
           been negotiated, an engine that supports pipelining has been loaded,
           and max_pipelines is greater than 1. See
           SSL_CTX_set_split_send_fragment(3) for further information.

       -max_pipelines +int
           The maximum number of encrypt/decrypt pipelines to be used. This will
           only have an effect if an engine has been loaded that supports
           pipelining (e.g. the dasync engine) and a suitable cipher suite has
           been negotiated. The default value is 1.  See
           SSL_CTX_set_max_pipelines(3) for further information.

       -read_buf +int
           The default read buffer size to be used for connections. This will
           only have an effect if the buffer size is larger than the size that
           would otherwise be used and pipelining is in use (see
           SSL_CTX_set_default_read_buffer_len(3) for further information).

       -ssl2, -ssl3, -tls1, -tls1_1, -tls1_2, -tls1_3, -no_ssl2, -no_ssl3,
       -no_tls1, -no_tls1_1, -no_tls1_2, -no_tls1_3
           These options require or disable the use of the specified SSL or TLS
           protocols.  By default s_server will negotiate the highest mutually
           supported protocol version.  When a specific TLS version is required,
           only that version will be accepted from the client.  Note that not
           all protocols and flags may be available, depending on how OpenSSL
           was built.

       -bugs
           There are several known bugs in SSL and TLS implementations. Adding
           this option enables various workarounds.

       -no_comp
           Disable negotiation of TLS compression.  TLS compression is not
           recommended and is off by default as of OpenSSL 1.1.0.

       -comp
           Enable negotiation of TLS compression.  This option was introduced in
           OpenSSL 1.1.0.  TLS compression is not recommended and is off by
           default as of OpenSSL 1.1.0.

       -no_ticket
           Disable RFC4507bis session ticket support. This option has no effect
           if TLSv1.3 is negotiated. See -num_tickets.

       -num_tickets
           Control the number of tickets that will be sent to the client after a
           full handshake in TLSv1.3. The default number of tickets is 2. This
           option does not affect the number of tickets sent after a resumption
           handshake.

       -serverpref
           Use the server's cipher preferences, rather than the client's
           preferences.

       -prioritize_chacha
           Prioritize ChaCha ciphers when preferred by clients. Requires
           -serverpref.

       -no_resumption_on_reneg
           Set the SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION option.

       -client_sigalgs val
           Signature algorithms to support for client certificate authentication
           (colon-separated list).

       -named_curve val
           Specifies the elliptic curve to use. NOTE: this is single curve, not
           a list.  For a list of all possible curves, use:

               $ openssl ecparam -list_curves

       -cipher val
           This allows the list of TLSv1.2 and below ciphersuites used by the
           server to be modified. This list is combined with any TLSv1.3
           ciphersuites that have been configured. When the client sends a list
           of supported ciphers the first client cipher also included in the
           server list is used. Because the client specifies the preference
           order, the order of the server cipherlist is irrelevant. See the
           ciphers command for more information.

       -ciphersuites val
           This allows the list of TLSv1.3 ciphersuites used by the server to be
           modified.  This list is combined with any TLSv1.2 and below
           ciphersuites that have been configured. When the client sends a list
           of supported ciphers the first client cipher also included in the
           server list is used. Because the client specifies the preference
           order, the order of the server cipherlist is irrelevant. See the
           ciphers command for more information. The format for this list is a
           simple colon (":") separated list of TLSv1.3 ciphersuite names.

       -dhparam infile
           The DH parameter file to use. The ephemeral DH cipher suites generate
           keys using a set of DH parameters. If not specified then an attempt
           is made to load the parameters from the server certificate file.  If
           this fails then a static set of parameters hard coded into the
           s_server program will be used.

       -attime, -check_ss_sig, -crl_check, -crl_check_all, -explicit_policy,
       -extended_crl, -ignore_critical, -inhibit_any, -inhibit_map,
       -no_alt_chains, -no_check_time, -partial_chain, -policy, -policy_check,
       -policy_print, -purpose, -suiteB_128, -suiteB_128_only, -suiteB_192,
       -trusted_first, -use_deltas, -auth_level, -verify_depth, -verify_email,
       -verify_hostname, -verify_ip, -verify_name, -x509_strict
           Set different peer certificate verification options.  See the
           verify(1) manual page for details.

       -crl_check, -crl_check_all
           Check the peer certificate has not been revoked by its CA.  The
           CRL(s) are appended to the certificate file. With the -crl_check_all
           option all CRLs of all CAs in the chain are checked.

       -nbio
           Turns on non blocking I/O.

       -psk_identity val
           Expect the client to send PSK identity val when using a PSK cipher
           suite, and warn if they do not.  By default, the expected PSK
           identity is the string "Client_identity".

       -psk_hint val
           Use the PSK identity hint val when using a PSK cipher suite.

       -psk val
           Use the PSK key val when using a PSK cipher suite. The key is given
           as a hexadecimal number without leading 0x, for example -psk
           1a2b3c4d.  This option must be provided in order to use a PSK cipher.

       -psk_session file
           Use the pem encoded SSL_SESSION data stored in file as the basis of a
           PSK.  Note that this will only work if TLSv1.3 is negotiated.

       -listen
           This option can only be used in conjunction with one of the DTLS
           options above.  With this option s_server will listen on a UDP port
           for incoming connections.  Any ClientHellos that arrive will be
           checked to see if they have a cookie in them or not.  Any without a
           cookie will be responded to with a HelloVerifyRequest.  If a
           ClientHello with a cookie is received then s_server will connect to
           that peer and complete the handshake.

       -dtls, -dtls1, -dtls1_2
           These options make s_server use DTLS protocols instead of TLS.  With
           -dtls, s_server will negotiate any supported DTLS protocol version,
           whilst -dtls1 and -dtls1_2 will only support DTLSv1.0 and DTLSv1.2
           respectively.

       -sctp
           Use SCTP for the transport protocol instead of UDP in DTLS. Must be
           used in conjunction with -dtls, -dtls1 or -dtls1_2. This option is
           only available where OpenSSL has support for SCTP enabled.

       -sctp_label_bug
           Use the incorrect behaviour of older OpenSSL implementations when
           computing endpoint-pair shared secrets for DTLS/SCTP. This allows
           communication with older broken implementations but breaks
           interoperability with correct implementations. Must be used in
           conjunction with -sctp. This option is only available where OpenSSL
           has support for SCTP enabled.

       -no_dhe
           If this option is set then no DH parameters will be loaded
           effectively disabling the ephemeral DH cipher suites.

       -alpn val, -nextprotoneg val
           These flags enable the Enable the Application-Layer Protocol
           Negotiation or Next Protocol Negotiation (NPN) extension,
           respectively. ALPN is the IETF standard and replaces NPN.  The val
           list is a comma-separated list of supported protocol names.  The list
           should contain the most desirable protocols first.  Protocol names
           are printable ASCII strings, for example "http/1.1" or "spdy/3".  The
           flag -nextprotoneg cannot be specified if -tls1_3 is used.

       -engine val
           Specifying an engine (by its unique id string in val) will cause
           s_server to attempt to obtain a functional reference to the specified
           engine, thus initialising it if needed. The engine will then be set
           as the default for all available algorithms.

       -keylogfile outfile
           Appends TLS secrets to the specified keylog file such that external
           programs (like Wireshark) can decrypt TLS connections.

       -max_early_data int
           Change the default maximum early data bytes that are specified for
           new sessions and any incoming early data (when used in conjunction
           with the -early_data flag). The default value is approximately 16k.
           The argument must be an integer greater than or equal to 0.

       -early_data
           Accept early data where possible. Cannot be used in conjunction with
           -www, -WWW, -HTTP or -rev.

       -anti_replay, -no_anti_replay
           Switches replay protection on or off, respectively. Replay protection
           is on by default unless overridden by a configuration file. When it
           is on, OpenSSL will automatically detect if a session ticket has been
           used more than once, TLSv1.3 has been negotiated, and early data is
           enabled on the server. A full handshake is forced if a session ticket
           is used a second or subsequent time. Any early data that was sent
           will be rejected.

CONNECTED COMMANDS
       If a connection request is established with an SSL client and neither the
       -www nor the -WWW option has been used then normally any data received
       from the client is displayed and any key presses will be sent to the
       client.

       Certain commands are also recognized which perform special operations.
       These commands are a letter which must appear at the start of a line.
       They are listed below.

       q   End the current SSL connection but still accept new connections.

       Q   End the current SSL connection and exit.

       r   Renegotiate the SSL session (TLSv1.2 and below only).

       R   Renegotiate the SSL session and request a client certificate (TLSv1.2
           and below only).

       P   Send some plain text down the underlying TCP connection: this should
           cause the client to disconnect due to a protocol violation.

       S   Print out some session cache status information.

       B   Send a heartbeat message to the client (DTLS only)

       k   Send a key update message to the client (TLSv1.3 only)

       K   Send a key update message to the client and request one back (TLSv1.3
           only)

       c   Send a certificate request to the client (TLSv1.3 only)

NOTES
       s_server can be used to debug SSL clients. To accept connections from a
       web browser the command:

        openssl s_server -accept 443 -www

       can be used for example.

       Although specifying an empty list of CAs when requesting a client
       certificate is strictly speaking a protocol violation, some SSL clients
       interpret this to mean any CA is acceptable. This is useful for debugging
       purposes.

       The session parameters can printed out using the sess_id program.

BUGS
       Because this program has a lot of options and also because some of the
       techniques used are rather old, the C source of s_server is rather hard
       to read and not a model of how things should be done.  A typical SSL
       server program would be much simpler.

       The output of common ciphers is wrong: it just gives the list of ciphers
       that OpenSSL recognizes and the client supports.

       There should be a way for the s_server program to print out details of
       any unknown cipher suites a client says it supports.

SEE ALSO
       SSL_CONF_cmd(3), sess_id(1), s_client(1), ciphers(1)
       SSL_CTX_set_max_send_fragment(3), SSL_CTX_set_split_send_fragment(3),
       SSL_CTX_set_max_pipelines(3)

HISTORY
       The -no_alt_chains option was added in OpenSSL 1.1.0.

       The -allow-no-dhe-kex and -prioritize_chacha options were added in
       OpenSSL 1.1.1.

COPYRIGHT
       Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (the "License").  You may not use this
       file except in compliance with the License.  You can obtain a copy in the
       file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.



1.1.1j                             2021-02-16                        S_SERVER(1)