Provided by: openssl_1.0.1f-1ubuntu2.27_amd64 
NAME
s_server - SSL/TLS server program
SYNOPSIS
openssl s_server [-accept port] [-context id] [-verify depth] [-Verify depth] [-crl_check]
[-crl_check_all] [-cert filename] [-certform DER|PEM] [-key keyfile] [-keyform DER|PEM] [-pass arg]
[-dcert filename] [-dcertform DER|PEM] [-dkey keyfile] [-dkeyform DER|PEM] [-dpass arg] [-dhparam
filename] [-nbio] [-nbio_test] [-crlf] [-debug] [-msg] [-state] [-CApath directory] [-CAfile filename]
[-no_alt_chains] [-nocert] [-cipher cipherlist] [-quiet] [-no_tmp_rsa] [-ssl2] [-ssl3] [-tls1] [-no_ssl2]
[-no_ssl3] [-no_tls1] [-no_dhe] [-bugs] [-hack] [-www] [-WWW] [-HTTP] [-engine id] [-tlsextdebug]
[-no_ticket] [-id_prefix arg] [-rand file(s)]
DESCRIPTION
The s_server command implements a generic SSL/TLS server which listens for connections on a given port
using SSL/TLS.
OPTIONS
-accept port
the TCP port to listen on for connections. If not specified 4433 is used.
-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.
-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.
-certform format
The certificate format to use: DER or PEM. PEM is the default.
-key keyfile
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 arg
the private key password source. For more information about the format of arg see the PASS PHRASE
ARGUMENTS section in openssl(1).
-dcert filename, -dkey keyname
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.
-dcertform format, -dkeyform format, -dpass arg
additional certificate and private key format and passphrase respectively.
-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).
-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 s_server program
will be used.
-no_dhe
if this option is set then no DH parameters will be loaded effectively disabling the ephemeral DH
cipher suites.
-no_tmp_rsa
certain export cipher suites sometimes use a temporary RSA key, this option disables temporary RSA
key generation.
-verify depth, -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 -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.
-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.
-CApath directory
The directory to use for client certificate verification. This directory must be in "hash format",
see verify for more information. These are also used when building the server certificate chain.
-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.
-no_alt_chains
See the verify manual page for details.
-state
prints out the SSL session states.
-debug
print extensive debugging information including a hex dump of all traffic.
-msg
show all protocol messages with hex dump.
-nbio_test
tests non blocking I/O
-nbio
turns on non blocking I/O
-crlf
this option translated a line feed from the terminal into CR+LF.
-quiet
inhibit printing of session and certificate information.
-psk_hint hint
Use the PSK identity hint hint when using a PSK cipher suite.
-psk key
Use the PSK key key when using a PSK cipher suite. The key is given as a hexadecimal number without
leading 0x, for example -psk 1a2b3c4d.
-ssl2, -ssl3, -tls1, -no_ssl2, -no_ssl3, -no_tls1
these options disable the use of certain SSL or TLS protocols. By default the initial handshake uses
a method which should be compatible with all servers and permit them to use SSL v3, SSL v2 or TLS as
appropriate.
-bugs
there are several known bug in SSL and TLS implementations. Adding this option enables various
workarounds.
-hack
this option enables a further workaround for some some early Netscape SSL code (?).
-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 ciphers
command for more information.
-tlsextdebug
print out a hex dump of any TLS extensions received from the server.
-no_ticket
disable RFC4507bis session ticket support.
-www
sends a status message back to the client when it connects. This includes lots of 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.
-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).
-engine id
specifying an engine (by its unique id string) 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.
-id_prefix arg
generate SSL/TLS session IDs prefixed by 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).
-rand file(s)
a file or files containing random data used to seed the random number generator, or an EGD socket
(see RAND_egd(3)). Multiple files can be specified separated by a OS-dependent character. The
separator is ; for MS-Windows, , for OpenVMS, and : for all others.
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 single letter commands are also recognized which perform special operations: these 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.
R renegotiate the SSL session and request a client certificate.
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.
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.
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 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
sess_id(1), s_client(1), ciphers(1)
HISTORY
The -no_alt_chains options was first added to OpenSSL 1.0.1n and 1.0.2b.
1.0.1f 2018-12-04 S_SERVER(1SSL)