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 keyfile] [-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] [-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.
-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 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.
-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.
-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.
-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 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.
-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 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.
Restrictions
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)