s_server
S_SERVER(1) OpenSSL S_SERVER(1)
NAME
s_server - SSL/TLS server program
SYNOPSIS
openssl s_server [-accept port] [-context id] [-verify depth] [-Verify
depth] [-cert filename] [-key keyfile] [-dcert filename] [-dkey key-
file] [-dhparam filename] [-nbio] [-nbio_test] [-crlf] [-debug] [-msg]
[-state] [-CApath directory] [-CAfile filename] [-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] [-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 cer-
tificate containing a DSS (DSA) key. If not specified then the
filename "server.pem" will be used.
-key keyfile
The private key to use. If not specified then the certificate file
will be used.
-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 certifi-
cate 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 appropri-
ate certificate.
-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 gen-
erate 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 effec-
tively 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 certifi-
cate from the client. With the -verify option a certificate is
requested but the client does not have to send one, with the -Ver-
ify option the client must supply a certificate or an error
occurs.
-CApath directory
The directory to use for client certificate verification. This
directory must be in "hash format", see verify for more informa-
tion. 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 cer-
tificate chain. The list is also used in the list of acceptable
client CAs passed to the client when a certificate is requested.
-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.
-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 com-
patible 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 informa-
tion.
-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 it’s unique id string) will cause
s_server to attempt to obtain a functional reference to the speci-
fied engine, thus initialising it if needed. The engine will then
be set as the default for all available algorithms.
-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 oth-
ers.
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 spe-
cial 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 dis-
abled.
Although specifying an empty list of CAs when requesting a client cer-
tificate is strictly speaking a protocol violation, some SSL clients
interpret this to mean any CA is acceptable. This is useful for debug-
ging 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)
0.9.7a 2001-11-09 S_SERVER(1)
