openssl-s_server, s_server - SSL/TLS server program
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]
The s_server command implements a generic SSL/TLS server which listens
  for connections on a given port using SSL/TLS.
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 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. 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.
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)
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.
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.
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)
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 2000-2020 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>.