Provided by: openssl_1.1.1f-1ubuntu2.23_amd64 
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 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 (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. 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 2000-2019 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>.