=pod

=head1 NAME

s_server - SSL/TLS server program

=head1 SYNOPSIS

B<openssl> B<s_server>
[B<-help>]
[B<-port port>]
[B<-accept val>]
[B<-naccept count>]
[B<-unix val>]
[B<-unlink>]
[B<-4>]
[B<-6>]
[B<-context id>]
[B<-verify depth>]
[B<-Verify depth>]
[B<-crl_check>]
[B<-crl_check_all>]
[B<-cert filename>]
[B<-certform DER|PEM>]
[B<-key keyfile>]
[B<-keyform DER|PEM>]
[B<-pass arg>]
[B<-dcert filename>]
[B<-dcertform DER|PEM>]
[B<-dkey keyfile>]
[B<-dkeyform DER|PEM>]
[B<-dpass arg>]
[B<-dhparam filename>]
[B<-nbio>]
[B<-nbio_test>]
[B<-crlf>]
[B<-debug>]
[B<-msg>]
[B<-state>]
[B<-CApath directory>]
[B<-CAfile filename>]
[B<-no-CAfile>]
[B<-no-CApath>]
[B<-attime timestamp>]
[B<-check_ss_sig>]
[B<-explicit_policy>]
[B<-extended_crl>]
[B<-ignore_critical>]
[B<-inhibit_any>]
[B<-inhibit_map>]
[B<-no_check_time>]
[B<-partial_chain>]
[B<-policy arg>]
[B<-policy_check>]
[B<-policy_print>]
[B<-purpose purpose>]
[B<-suiteB_128>]
[B<-suiteB_128_only>]
[B<-suiteB_192>]
[B<-trusted_first>]
[B<-no_alt_chains>]
[B<-use_deltas>]
[B<-auth_level num>]
[B<-nameopt option>]
[B<-verify_depth num>]
[B<-verify_return_error>]
[B<-verify_email email>]
[B<-verify_hostname hostname>]
[B<-verify_ip ip>]
[B<-verify_name name>]
[B<-x509_strict>]
[B<-nocert>]
[B<-client_sigalgs sigalglist>]
[B<-named_curve curve>]
[B<-cipher cipherlist>]
[B<-serverpref>]
[B<-quiet>]
[B<-ssl3>]
[B<-tls1>]
[B<-tls1_1>]
[B<-tls1_2>]
[B<-tls1_3>]
[B<-dtls>]
[B<-dtls1>]
[B<-dtls1_2>]
[B<-sctp>]
[B<-listen>]
[B<-async>]
[B<-split_send_frag>]
[B<-max_pipelines>]
[B<-read_buf>]
[B<-no_ssl3>]
[B<-no_tls1>]
[B<-no_tls1_1>]
[B<-no_tls1_2>]
[B<-no_tls1_3>]
[B<-no_dhe>]
[B<-bugs>]
[B<-comp>]
[B<-no_comp>]
[B<-brief>]
[B<-www>]
[B<-WWW>]
[B<-HTTP>]
[B<-engine id>]
[B<-tlsextdebug>]
[B<-no_ticket>]
[B<-id_prefix arg>]
[B<-rand file(s)>]
[B<-serverinfo file>]
[B<-no_resumption_on_reneg>]
[B<-status>]
[B<-status_verbose>]
[B<-status_timeout nsec>]
[B<-status_url url>]
[B<-status_file file>]
[B<-alpn protocols>]
[B<-nextprotoneg protocols>]
[B<-max_early_data>]
[B<-early_data>]

=head1 DESCRIPTION

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

=head1 OPTIONS

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

=over 4

=item B<-help>

Print out a usage message.

=item B<-port port>

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

=item B<-accept val>

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

=item B<-naccept count>

The server will exit after receiving B<number> connections, default unlimited.

=item B<-unix val>

Unix domain socket to accept on.

=item B<-unlink>

For -unix, unlink existing socket first.

=item B<-4>

Use IPv4 only.

=item B<-6>

Use IPv6 only.

=item B<-context id>

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

=item B<-cert certname>

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.

=item B<-certform format>

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

=item B<-key keyfile>

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

=item B<-keyform format>

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

=item B<-pass arg>

The private key password source. For more information about the format of B<arg>
see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.

=item B<-dcert filename>, B<-dkey keyname>

Specify an additional certificate and private key, these behave in the
same manner as the B<-cert> and B<-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.

=item B<-dcertform format>, B<-dkeyform format>, B<-dpass arg>

Additional certificate and private key format and passphrase respectively.

=item B<-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).

=item B<-dhparam filename>

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 B<s_server>
program will be used.

=item B<-no_dhe>

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

=item B<-crl_check>, B<-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 B<-crl_check_all>
option all CRLs of all CAs in the chain are checked.

=item B<-CApath directory>

The directory to use for client certificate verification. This directory
must be in "hash format", see B<verify> for more information. These are
also used when building the server certificate chain.

=item B<-CAfile file>

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.

=item B<-no-CAfile>

Do not load the trusted CA certificates from the default file location.

=item B<-no-CApath>

Do not load the trusted CA certificates from the default directory location.

=item B<-verify depth>, B<-Verify depth>

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 B<-verify> option a certificate is requested but the
client does not have to send one, with the B<-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.

=item B<-nameopt option>

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

=item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
B<-inhibit_map>, B<-no_alt_chains>, B<-no_check_time>, B<-partial_chain>, B<-policy>,
B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
B<-verify_ip>, B<-verify_name>, B<-x509_strict>

Set different peer certificate verification options.
See the L<verify(1)> manual page for details.

=item B<-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.

=item B<-state>

Prints the SSL session states.

=item B<-debug>

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

=item B<-msg>

Show all protocol messages with hex dump.

=item B<-trace>

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

=item B<-msgfile>

File to send output of B<-msg> or B<-trace> to, default standard output.

=item B<-nbio_test>

Tests non blocking I/O.

=item B<-nbio>

Turns on non blocking I/O.

=item B<-crlf>

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

=item B<-quiet>

Inhibit printing of session and certificate information.

=item B<-psk_hint hint>

Use the PSK identity hint B<hint> when using a PSK cipher suite.

=item B<-psk key>

Use the PSK key B<key> when using a PSK cipher suite. The key is
given as a hexadecimal number without leading 0x, for example -psk
1a2b3c4d.

=item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-tls1_1>, B<-tls1_2>, B<-tls1_3>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>, B<-no_tls1_3>

These options require or disable the use of the specified SSL or TLS protocols.
By default B<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.

=item B<-dtls>, B<-dtls1>, B<-dtls1_2>

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

=item B<-listen>

This option can only be used in conjunction with one of the DTLS options above.
With this option B<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 B<s_server> will connect to
that peer and complete the handshake.

=item B<-sctp>

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

=item B<-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 B<-engine> option. For test purposes the dummy async engine
(dasync) can be used (if available).

=item B<-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
L<SSL_CTX_set_split_send_fragment(3)> for further information.

=item B<-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 L<SSL_CTX_set_max_pipelines(3)> for further information.

=item B<-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 L<SSL_CTX_set_default_read_buffer_len(3)> for
further information).

=item B<-bugs>

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

=item B<-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.

=item B<-no_comp>

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

=item B<-brief>

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

=item B<-client_sigalgs sigalglist>

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

=item B<-named_curve curve>

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

=item B<-cipher cipherlist>

This allows the cipher list used by the server to be modified.  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 irrelevant. See
the B<ciphers> command for more information.

=item B<-serverpref>

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

=item B<-tlsextdebug>

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

=item B<-no_ticket>

Disable RFC4507bis session ticket support.

=item B<-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.

=item B<-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.

=item B<-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).

=item B<-rev>

Simple test server which just reverses the text received from the client
and sends it back to the server. Also sets B<-brief>.

=item B<-engine id>

Specifying an engine (by its unique B<id> string) will cause B<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.

=item B<-id_prefix arg>

Generate SSL/TLS session IDs prefixed by B<arg>. 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).

=item B<-rand file(s)>

A file or files containing random data used to seed the random number
generator, or an EGD socket (see L<RAND_egd(3)>).
Multiple files can be specified separated by an OS-dependent character.
The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
all others.

=item B<-serverinfo file>

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.

=item B<-no_resumption_on_reneg>

Set the B<SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION> option.

=item B<-status>

Enables certificate status request support (aka OCSP stapling).

=item B<-status_verbose>

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

=item B<-status_timeout nsec>

Sets the timeout for OCSP response to B<nsec> seconds.

=item B<-status_url url>

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.

=item B<-status_file file>

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.

=item B<-alpn protocols>, B<-nextprotoneg protocols>

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 B<protocols> 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".

=item B<-keylogfile path>

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

=item B<-max_early_data arg>

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

=item B<-early_data>

Accept early data where possible.

=back

=head1 CONNECTED COMMANDS

If a connection request is established with an SSL client and neither the
B<-www> nor the B<-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 single letter commands are also recognized which perform special
operations: these are listed below.

=over 4

=item B<q>

End the current SSL connection but still accept new connections.

=item B<Q>

End the current SSL connection and exit.

=item B<r>

Renegotiate the SSL session.

=item B<R>

Renegotiate the SSL session and request a client certificate.

=item B<P>

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

=item B<S>

Print out some session cache status information.

=back

=head1 NOTES

B<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.

Most web browsers (in particular Netscape and MSIE) only support RSA cipher
suites, so they cannot connect to servers which don't use a certificate
carrying an RSA key or a version of OpenSSL with RSA disabled.

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 B<sess_id> program.

=head1 BUGS

Because this program has a lot of options and also because some of the
techniques used are rather old, the C source of B<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 B<s_server> program to print out details of any
unknown cipher suites a client says it supports.

=head1 SEE ALSO

L<SSL_CONF_cmd(3)>,
L<sess_id(1)>, L<s_client(1)>, L<ciphers(1)>

=head1 HISTORY

The -no_alt_chains options was first added to OpenSSL 1.1.0.

=head1 COPYRIGHT

Copyright 2000-2017 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
L<https://www.openssl.org/source/license.html>.

=cut