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>]
39 The B<s_client> command implements a generic SSL/TLS client which connects
40 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
47 =item B<-connect host:port>
49 This specifies the host and optional port to connect to. If not specified
50 then an attempt is made to connect to the local host on port 4433.
52 =item B<-cert certname>
54 The certificate to use, if one is requested by the server. The default is
55 not to use a certificate.
59 The private key to use. If not specified then the certificate file will
62 =item B<-verify depth>
64 The verify depth to use. This specifies the maximum length of the
65 server certificate chain and turns on server certificate verification.
66 Currently the verify operation continues after errors so all the problems
67 with a certificate chain can be seen. As a side effect the connection
68 will never fail due to a server certificate verify failure.
70 =item B<-CApath directory>
72 The directory to use for server certificate verification. This directory
73 must be in "hash format", see B<verify> for more information. These are
74 also used when building the client certificate chain.
78 A file containing trusted certificates to use during server authentication
79 and to use when attempting to build the client certificate chain.
83 reconnects to the same server 5 times using the same session ID, this can
84 be used as a test that session caching is working.
88 pauses 1 second between each read and write call.
92 display the whole server certificate chain: normally only the server
93 certificate itself is displayed.
97 print session information when the program exits. This will always attempt
98 to print out information even if the connection fails. Normally information
99 will only be printed out once if the connection succeeds. This option is useful
100 because the cipher in use may be renegotiated or the connection may fail
101 because a client certificate is required or is requested only after an
102 attempt is made to access a certain URL. Note: the output produced by this
103 option is not always accurate because a connection might never have been
108 prints out the SSL session states.
112 print extensive debugging information including a hex dump of all traffic.
116 tests non-blocking I/O
120 turns on non-blocking I/O
124 this option translated a line feed from the terminal into CR+LF as required
129 inhibit shutting down the connection when end of file is reached in the
134 inhibit printing of session and certificate information. This implicitely
135 turns on B<-ign_eof> as well.
137 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>
139 these options disable the use of certain SSL or TLS protocols. By default
140 the initial handshake uses a method which should be compatible with all
141 servers and permit them to use SSL v3, SSL v2 or TLS as appropriate.
143 Unfortunately there are a lot of ancient and broken servers in use which
144 cannot handle this technique and will fail to connect. Some servers only
145 work if TLS is turned off with the B<-no_tls> option others will only
146 support SSL v2 and may need the B<-ssl2> option.
150 there are several known bug in SSL and TLS implementations. Adding this
151 option enables various workarounds.
153 =item B<-cipher cipherlist>
155 this allows the cipher list sent by the client to be modified. Although
156 the server determines which cipher suite is used it should take the first
157 supported cipher in the list sent by the client. See the B<ciphers>
158 command for more information.
162 specifying an engine (by it's unique B<id> string) will cause B<s_client>
163 to attempt to obtain a functional reference to the specified engine,
164 thus initialising it if needed. The engine will then be set as the default
165 for all available algorithms.
169 =head1 CONNECTED COMMANDS
171 If a connection is established with an SSL server then any data received
172 from the server is displayed and any key presses will be sent to the
173 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
174 have been given), the session will be renegociated if the line begins with an
175 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
176 connection will be closed down.
180 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
183 openssl s_client -connect servername:443
185 would typically be used (https uses port 443). If the connection succeeds
186 then an HTTP command can be given such as "GET /" to retrieve a web page.
188 If the handshake fails then there are several possible causes, if it is
189 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
190 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> can be tried
191 in case it is a buggy server. In particular you should play with these
192 options B<before> submitting a bug report to an OpenSSL mailing list.
194 A frequent problem when attempting to get client certificates working
195 is that a web client complains it has no certificates or gives an empty
196 list to choose from. This is normally because the server is not sending
197 the clients certificate authority in its "acceptable CA list" when it
198 requests a certificate. By using B<s_client> the CA list can be viewed
199 and checked. However some servers only request client authentication
200 after a specific URL is requested. To obtain the list in this case it
201 is necessary to use the B<-prexit> command and send an HTTP request
202 for an appropriate page.
204 If a certificate is specified on the command line using the B<-cert>
205 option it will not be used unless the server specifically requests
206 a client certificate. Therefor merely including a client certificate
207 on the command line is no guarantee that the certificate works.
209 If there are problems verifying a server certificate then the
210 B<-showcerts> option can be used to show the whole chain.
214 Because this program has a lot of options and also because some of
215 the techniques used are rather old, the C source of s_client is rather
216 hard to read and not a model of how things should be done. A typical
217 SSL client program would be much simpler.
219 The B<-verify> option should really exit if the server verification
222 The B<-prexit> option is a bit of a hack. We should really report
223 information whenever a session is renegotiated.
227 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>