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>;.
1.1.1k 2021-03-25 S_SERVER(1)
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