doc/apps/s_client.pod - third_party/openssl - Git at Google


 =pod

 =head1 NAME

 s_client - SSL/TLS client program

 =head1 SYNOPSIS

 B<openssl> B<s_client>
 [B<-connect> host:port>]
 [B<-verify depth>]
 [B<-cert filename>]
 [B<-key filename>]
 [B<-CApath directory>]
 [B<-CAfile filename>]
 [B<-reconnect>]
 [B<-pause>]
 [B<-showcerts>]
 [B<-debug>]
 [B<-nbio_test>]
 [B<-state>]
 [B<-nbio>]
 [B<-crlf>]
 [B<-ign_eof>]
 [B<-quiet>]
 [B<-ssl2>]
 [B<-ssl3>]
 [B<-tls1>]
 [B<-no_ssl2>]
 [B<-no_ssl3>]
 [B<-no_tls1>]
 [B<-bugs>]
 [B<-cipher cipherlist>]

 =head1 DESCRIPTION

 The B<s_client> command implements a generic SSL/TLS client which connects
 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
 SSL servers.

 =head1 OPTIONS

 =over 4

 =item B<-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.

 =item B<-cert certname>

 The certificate to use, if one is requested by the server. The default is
 not to use a certificate.

 =item B<-key keyfile>

 The private key to use. If not specified then the certificate file will
 be used.

 =item B<-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.

 =item B<-CApath directory>

 The directory to use for server certificate verification. This directory
 must be in "hash format", see B<verify> for more information. These are
 also used when building the client certificate chain.

 =item B<-CAfile file>

 A file containing trusted certificates to use during server authentication
 and to use when attempting to build the client certificate chain.

 =item B<-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.

 =item B<-pause>

 pauses 1 second between each read and write call.

 =item B<-showcerts>

 display the whole server certificate chain: normally only the server
 certificate itself is displayed.

 =item B<-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.

 =item B<-state>

 prints out the SSL session states.

 =item B<-debug>

 print extensive debugging information including a hex dump of all traffic.

 =item B<-nbio_test>

 tests non-blocking I/O

 =item B<-nbio>

 turns on non-blocking I/O

 =item B<-crlf>

 this option translated a line feed from the terminal into CR+LF as required
 by some servers.

 =item B<-ign_eof>

 inhibit shutting down the connection when end of file is reached in the
 input.

 =item B<-quiet>

 inhibit printing of session and certificate information.  This implicitely
 turns on B<-ign_eof> as well.

 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-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 B<-no_tls> option others will only
 support SSL v2 and may need the B<-ssl2> option.

 =item B<-bugs>

 there are several known bug in SSL and TLS implementations. Adding this
 option enables various workarounds.

 =item B<-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 B<ciphers>
 command for more information.

 =back

 =head1 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 B<-quiet> nor B<-ign_eof>
 have been given), the session will be renegociated if the line begins with an
 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
 connection will be closed down.

 =head1 NOTES

 B<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 B<-bugs>, B<-ssl2>,
 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> can be tried
 in case it is a buggy server. In particular you should play with these
 options B<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 B<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 B<-prexit> command and send an HTTP request
 for an appropriate page.

 If a certificate is specified on the command line using the B<-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
 B<-showcerts> option can be used to show the whole chain.

 =head1 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 B<-verify> option should really exit if the server verification
 fails.

 The B<-prexit> option is a bit of a hack. We should really report
 information whenever a session is renegotiated.

 =head1 SEE ALSO

 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>

 =cut

	=pod

	=head1 NAME

	s_client - SSL/TLS client program

	=head1 SYNOPSIS

	B<openssl> B<s_client>
	[B<-connect> host:port>]
	[B<-verify depth>]
	[B<-cert filename>]
	[B<-key filename>]
	[B<-CApath directory>]
	[B<-CAfile filename>]
	[B<-reconnect>]
	[B<-pause>]
	[B<-showcerts>]
	[B<-debug>]
	[B<-nbio_test>]
	[B<-state>]
	[B<-nbio>]
	[B<-crlf>]
	[B<-ign_eof>]
	[B<-quiet>]
	[B<-ssl2>]
	[B<-ssl3>]
	[B<-tls1>]
	[B<-no_ssl2>]
	[B<-no_ssl3>]
	[B<-no_tls1>]
	[B<-bugs>]
	[B<-cipher cipherlist>]

	=head1 DESCRIPTION

	The B<s_client> command implements a generic SSL/TLS client which connects
	to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
	SSL servers.

	=head1 OPTIONS

	=over 4

	=item B<-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.

	=item B<-cert certname>

	The certificate to use, if one is requested by the server. The default is
	not to use a certificate.

	=item B<-key keyfile>

	The private key to use. If not specified then the certificate file will
	be used.

	=item B<-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.

	=item B<-CApath directory>

	The directory to use for server certificate verification. This directory
	must be in "hash format", see B<verify> for more information. These are
	also used when building the client certificate chain.

	=item B<-CAfile file>

	A file containing trusted certificates to use during server authentication
	and to use when attempting to build the client certificate chain.

	=item B<-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.

	=item B<-pause>

	pauses 1 second between each read and write call.

	=item B<-showcerts>

	display the whole server certificate chain: normally only the server
	certificate itself is displayed.

	=item B<-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.

	=item B<-state>

	prints out the SSL session states.

	=item B<-debug>

	print extensive debugging information including a hex dump of all traffic.

	=item B<-nbio_test>

	tests non-blocking I/O

	=item B<-nbio>

	turns on non-blocking I/O

	=item B<-crlf>

	this option translated a line feed from the terminal into CR+LF as required
	by some servers.

	=item B<-ign_eof>

	inhibit shutting down the connection when end of file is reached in the
	input.

	=item B<-quiet>

	inhibit printing of session and certificate information. This implicitely
	turns on B<-ign_eof> as well.

	=item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-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 B<-no_tls> option others will only
	support SSL v2 and may need the B<-ssl2> option.

	=item B<-bugs>

	there are several known bug in SSL and TLS implementations. Adding this
	option enables various workarounds.

	=item B<-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 B<ciphers>
	command for more information.

	=back

	=head1 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 B<-quiet> nor B<-ign_eof>
	have been given), the session will be renegociated if the line begins with an
	B<R>, and if the line begins with a B<Q> or if end of file is reached, the
	connection will be closed down.

	=head1 NOTES

	B<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 B<-bugs>, B<-ssl2>,
	B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> can be tried
	in case it is a buggy server. In particular you should play with these
	options B<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 B<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 B<-prexit> command and send an HTTP request
	for an appropriate page.

	If a certificate is specified on the command line using the B<-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
	B<-showcerts> option can be used to show the whole chain.

	=head1 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 B<-verify> option should really exit if the server verification
	fails.

	The B<-prexit> option is a bit of a hack. We should really report
	information whenever a session is renegotiated.

	=head1 SEE ALSO

	L<sess_id(1)\|sess_id(1)>, L<s_server(1)\|s_server(1)>, L<ciphers(1)\|ciphers(1)>

	=cut