6 s_client - SSL/TLS client program
10 B<openssl> B<s_client>
11 [B<-connect> host:port>]
15 [B<-CApath directory>]
34 [B<-cipher cipherlist>]
38 The B<s_client> command implements a generic SSL/TLS client which connects
39 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
46 =item B<-connect host:port>
48 This specifies the host and optional port to connect to. If not specified
49 then an attempt is made to connect to the local host on port 4433.
51 =item B<-cert certname>
53 The certificate to use, if one is requested by the server. The default is
54 not to use a certificate.
58 The private key to use. If not specified then the certificate file will
61 =item B<-verify depth>
63 The verify depth to use. This specifies the maximum length of the
64 server certificate chain and turns on server certificate verification.
65 Currently the verify operation continues after errors so all the problems
66 with a certificate chain can be seen. As a side effect the connection
67 will never fail due to a server certificate verify failure.
69 =item B<-CApath directory>
71 The directory to use for server certificate verification. This directory
72 must be in "hash format", see B<verify> for more information. These are
73 also used when building the client certificate chain.
77 A file containing trusted certificates to use during server authentication
78 and to use when attempting to build the client certificate chain.
82 reconnects to the same server 5 times using the same session ID, this can
83 be used as a test that session caching is working.
87 pauses 1 second between each read and write call.
91 display the whole server certificate chain: normally only the server
92 certificate itself is displayed.
96 print session information when the program exits. This will always attempt
97 to print out information even if the connection fails. Normally information
98 will only be printed out once if the connection succeeds. This option is useful
99 because the cipher in use may be renegotiated or the connection may fail
100 because a client certificate is required or is requested only after an
101 attempt is made to access a certain URL. Note: the output produced by this
102 option is not always accurate because a connection might never have been
107 prints out the SSL session states.
111 print extensive debugging information including a hex dump of all traffic.
115 tests non-blocking I/O
119 turns on non-blocking I/O
123 this option translated a line feed from the terminal into CR+LF as required
128 inhibit shutting down the connection when end of file is reached in the
133 inhibit printing of session and certificate information. This implicitely
134 turns on B<-ign_eof> as well.
136 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>
138 these options disable the use of certain SSL or TLS protocols. By default
139 the initial handshake uses a method which should be compatible with all
140 servers and permit them to use SSL v3, SSL v2 or TLS as appropriate.
142 Unfortunately there are a lot of ancient and broken servers in use which
143 cannot handle this technique and will fail to connect. Some servers only
144 work if TLS is turned off with the B<-no_tls> option others will only
145 support SSL v2 and may need the B<-ssl2> option.
149 there are several known bug in SSL and TLS implementations. Adding this
150 option enables various workarounds.
152 =item B<-cipher cipherlist>
154 this allows the cipher list sent by the client to be modified. Although
155 the server determines which cipher suite is used it should take the first
156 supported cipher in the list sent by the client. See the B<ciphers>
157 command for more information.
161 =head1 CONNECTED COMMANDS
163 If a connection is established with an SSL server then any data received
164 from the server is displayed and any key presses will be sent to the
165 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
166 have been given), the session will be renegociated if the line begins with an
167 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
168 connection will be closed down.
172 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
175 openssl s_client -connect servername:443
177 would typically be used (https uses port 443). If the connection succeeds
178 then an HTTP command can be given such as "GET /" to retrieve a web page.
180 If the handshake fails then there are several possible causes, if it is
181 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
182 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> can be tried
183 in case it is a buggy server. In particular you should play with these
184 options B<before> submitting a bug report to an OpenSSL mailing list.
186 A frequent problem when attempting to get client certificates working
187 is that a web client complains it has no certificates or gives an empty
188 list to choose from. This is normally because the server is not sending
189 the clients certificate authority in its "acceptable CA list" when it
190 requests a certificate. By using B<s_client> the CA list can be viewed
191 and checked. However some servers only request client authentication
192 after a specific URL is requested. To obtain the list in this case it
193 is necessary to use the B<-prexit> command and send an HTTP request
194 for an appropriate page.
196 If a certificate is specified on the command line using the B<-cert>
197 option it will not be used unless the server specifically requests
198 a client certificate. Therefor merely including a client certificate
199 on the command line is no guarantee that the certificate works.
201 If there are problems verifying a server certificate then the
202 B<-showcerts> option can be used to show the whole chain.
206 Because this program has a lot of options and also because some of
207 the techniques used are rather old, the C source of s_client is rather
208 hard to read and not a model of how things should be done. A typical
209 SSL client program would be much simpler.
211 The B<-verify> option should really exit if the server verification
214 The B<-prexit> option is a bit of a hack. We should really report
215 information whenever a session is renegotiated.
219 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>