/xlv3/openssl/0.9.7e-sgipl1/work/0.9.7e-sgipl1/openssl-
0.9.7e/doc/apps
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S_CLIENT(1) 4/Jan/2004 (0.9.7e) S_CLIENT(1)
NAME
s_client - SSL/TLS client program
SYNOPSIS
openssl s_client [-connect host:port] [-verify depth] [-cert
filename] [-key filename] [-CApath directory] [-CAfile
filename] [-reconnect] [-pause] [-showcerts] [-debug] [-msg]
[-nbio_test] [-state] [-nbio] [-crlf] [-ign_eof] [-quiet]
[-ssl2] [-ssl3] [-tls1] [-no_ssl2] [-no_ssl3] [-no_tls1]
[-bugs] [-cipher cipherlist] [-starttls protocol] [-engine
id] [-randfile(s)]
DESCRIPTION
The s_client command implements a generic SSL/TLS client
which connects to a remote host using SSL/TLS. It is a very
useful diagnostic tool for SSL servers.
OPTIONS
-connect host:port
This specifies the host and optional port to connect to.
If not specified then an attempt is made to connect to
the local host on port 4433.
-cert certname
The certificate to use, if one is requested by the
server. The default is not to use a certificate.
-key keyfile
The private key to use. If not specified then the
certificate file will be used.
-verify depth
The verify depth to use. This specifies the maximum
length of the server certificate chain and turns on
server certificate verification. Currently the verify
operation continues after errors so all the problems
with a certificate chain can be seen. As a side effect
the connection will never fail due to a server
certificate verify failure.
-CApath directory
The directory to use for server certificate
verification. This directory must be in "hash format",
see verify for more information. These are also used
when building the client certificate chain.
-CAfile file
A file containing trusted certificates to use during
server authentication and to use when attempting to
build the client certificate chain.
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S_CLIENT(1) 4/Jan/2004 (0.9.7e) S_CLIENT(1)-reconnect
reconnects to the same server 5 times using the same
session ID, this can be used as a test that session
caching is working.
-pause
pauses 1 second between each read and write call.
-showcerts
display the whole server certificate chain: normally
only the server certificate itself is displayed.
-prexit
print session information when the program exits. This
will always attempt to print out information even if the
connection fails. Normally information will only be
printed out once if the connection succeeds. This option
is useful because the cipher in use may be renegotiated
or the connection may fail because a client certificate
is required or is requested only after an attempt is
made to access a certain URL. Note: the output produced
by this option is not always accurate because a
connection might never have been established.
-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 as required by some servers.
-ign_eof
inhibit shutting down the connection when end of file is
reached in the input.
-quiet
inhibit printing of session and certificate information.
This implicitly turns on -ign_eof as well.
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S_CLIENT(1) 4/Jan/2004 (0.9.7e) S_CLIENT(1)-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.
Unfortunately there are a lot of ancient and broken
servers in use which cannot handle this technique and
will fail to connect. Some servers only work if TLS is
turned off with the -no_tls option others will only
support SSL v2 and may need the -ssl2 option.
-bugs
there are several known bug in SSL and TLS
implementations. Adding this option enables various
workarounds.
-cipher cipherlist
this allows the cipher list sent by the client to be
modified. Although the server determines which cipher
suite is used it should take the first supported cipher
in the list sent by the client. See the ciphers command
for more information.
-starttls protocol
send the protocol-specific message(s) to switch to TLS
for communication. protocol is a keyword for the
intended protocol. Currently, the only supported
keywords are "smtp" and "pop3".
-engine id
specifying an engine (by it's unique id string) will
cause s_client 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.
-randfile(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 is established with an SSL server then any
data received from the server is displayed and any key
presses will be sent to the server. When used interactively
(which means neither -quiet nor -ign_eof have been given),
the session will be renegotiated if the line begins with an
R, and if the line begins with a Q or if end of file is
reached, the connection will be closed down.
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S_CLIENT(1) 4/Jan/2004 (0.9.7e) S_CLIENT(1)
NOTES
s_client can be used to debug SSL servers. To connect to an
SSL HTTP server the command:
openssl s_client-connect servername:443
would typically be used (https uses port 443). If the
connection succeeds then an HTTP command can be given such
as "GET /" to retrieve a web page.
If the handshake fails then there are several possible
causes, if it is nothing obvious like no client certificate
then the -bugs, -ssl2, -ssl3, -tls1, -no_ssl2, -no_ssl3,
-no_tls1 options can be tried in case it is a buggy server.
In particular you should play with these options before
submitting a bug report to an OpenSSL mailing list.
A frequent problem when attempting to get client
certificates working is that a web client complains it has
no certificates or gives an empty list to choose from. This
is normally because the server is not sending the clients
certificate authority in its "acceptable CA list" when it
requests a certificate. By using s_client the CA list can be
viewed and checked. However some servers only request client
authentication after a specific URL is requested. To obtain
the list in this case it is necessary to use the -prexit
option and send an HTTP request for an appropriate page.
If a certificate is specified on the command line using the
-cert option it will not be used unless the server
specifically requests a client certificate. Therefor merely
including a client certificate on the command line is no
guarantee that the certificate works.
If there are problems verifying a server certificate then
the -showcerts option can be used to show the whole chain.
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_client is rather hard to read and not a model of how
things should be done. A typical SSL client program would be
much simpler.
The -verify option should really exit if the server
verification fails.
The -prexit option is a bit of a hack. We should really
report information whenever a session is renegotiated.
SEE ALSO
sess_id(1), s_server(1), ciphers(1)
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