s_server(1ssl)s_server(1ssl)NAMEs_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]
[-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] [-rand
filename] [-engine id]
OPTIONS
The TCP port to listen on for connections. If not specified 4433 is
used. Sets the SSL context id. It can be given any string value. If
this option is not present a default value will be used. The certifi‐
cate to use. Most server's cipher suites require the use of a certifi‐
cate 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.
The private key to use. If not specified then the certificate file will
be used. Specifies 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). 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. If this option is set then
no certificate is used. This restricts the cipher suites available to
the anonymous ones (currently just anonymous DH). 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. If this option is set then no DH parameters will be loaded
effectively disabling the ephemeral DH cipher suites. Certain export
cipher suites sometimes use a temporary RSA key, this option disables
temporary RSA key generation. 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 cer‐
tificate 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. 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.
A file containing trusted certificates to use during client authentica‐
tion 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. Prints out the SSL session
states. Prints extensive debugging information including a hex dump of
all traffic. Tests non-blocking I/O Turns on non-blocking I/O Trans‐
lates a line feed from the terminal into CR+LF. Inhibits printing of
session and certificate information. Disables 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. There are several known bugs in SSL and
TLS implementations. Adding this option enables various workarounds.
Enables a further workaround for some early Netscape SSL code. 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 is irrelevant. See the
ciphers command for more information. 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. Emu‐
lates a simple web server. Pages will be resolved relative to the cur‐
rent directory. For example, if the URL https://myhost/page.html is
requested, the file will be loaded. 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 an OS-depen‐
dent character. The separator is a semicolon (;) for MS-Windows, a
comma (,) for OpenVMS, and a colon (:) for all others. Specifying an
engine (by its unique id string) will cause s_server to attempt to
obtain a functional reference to the specified engine, thus initializ‐
ing it if needed. The engine will then be set as the default for all
available algorithms.
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: Ends the current SSL connection but still
accept new connections. Ends the current SSL connection and exit.
Renegotiates the SSL session. Renegotiates the SSL session and request
a client certificate. Sends some plain text down the underlying TCP
connection: this should cause the client to disconnect due to a proto‐
col violation. Prints out some session cache status information.
DESCRIPTION
The s_server command implements a generic SSL/TLS server which listens
for connections on a given port using SSL/TLS.
NOTES
The <command role="strong">s_server command can be used to debug SSL
clients. To accept connections from a web browser the following command
can be used: openssl s_server-accept 443 -www
Most web browsers (in particular Netscape and MSIE) only support RSA
cipher suites, so they cannot connect to servers which do not 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 be 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 only 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
Commands: sess_id(1ssl), s_client(1ssl), ciphers(1ssl)s_server(1ssl)
