openssl_s_server(1)
- NetBSD Manual Pages
S_SERVER(1) OpenSSL S_SERVER(1)
NAME
s_server - SSL/TLS server program
LIBRARY
libcrypto, -lcrypto
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] [-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 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 exam-
ple the DSS cipher suites require a certificate con-
taining 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 cer-
tificate 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 appropriate
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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 gener-
ation.
-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 verifica-
tion. 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.
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-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 informa-
tion.
-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 appropri-
ate.
-bugs
there are several known bug in SSL and TLS implementa-
tions. 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 con-
nects. This includes lots of information about the
ciphers used and various session parameters. The out-
put 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.
-rand file(s)
a file or files containing random data used to seed
the random number generator, or an EGD socket (see
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RAND_egd(3)). Multiple files can be specified sepa-
rated 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 dis-
played 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 cer-
tificate.
P send some plain text down the underlying TCP connec-
tion: 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 con-
nections 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 viola-
tion, 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
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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
openssl_sess_id(1), openssl_s_client(1),
openssl_ciphers(1)
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