Provided by: openssl_1.1.1-1ubuntu2_amd64 bug

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]
       [-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] [-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 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 the
           PASS PHRASE ARGUMENTS section 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.

       -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.

       -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).

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

       -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 bug 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.

       -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.

       -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.

       -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 first added to OpenSSL 1.1.0.

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

COPYRIGHT

       Copyright 2000-2018 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>.