6 s_client - SSL/TLS client program
10 B<openssl> B<s_client>
11 [B<-connect> host:port>]
15 [B<-CApath directory>]
33 [B<-cipher cipherlist>]
37 The B<s_client> command implements a generic SSL/TLS client which connects
38 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
45 =item B<-connect host:port>
47 This specifies the host and optional port to connect to. If not specified
48 then an attempt is made to connect to the local host on port 4433.
50 =item B<-cert certname>
52 The certificate to use, if one is requested by the server. The default is
53 not to use a certificate.
57 The private key to use. If not specified then the certificate file will
60 =item B<-verify depth>
62 The verify depth to use. This specifies the maximum length of the
63 server certificate chain and turns on server certificate verification.
64 Currently the verify operation continues after errors so all the problems
65 with a certificate chain can be seen. As a side effect the connection
66 will never fail due to a server certificate verify failure.
68 =item B<-CApath directory>
70 The directory to use for server certificate verification. This directory
71 must be in "hash format", see B<verify> for more information. These are
72 also used when building the client certificate chain.
76 A file containing trusted certificates to use during server authentication
77 and to use when attempting to build the client certificate chain.
81 reconnects to the same server 5 times using the same session ID, this can
82 be used as a test that session caching is working.
86 pauses 1 second between each read and write call.
90 display the whole server certificate chain: normally only the server
91 certificate itself is displayed.
95 print session information when the program exits. This will always attempt
96 to print out information even if the connection fails. Normally information
97 will only be printed out once if the connection succeeds. This option is useful
98 because the cipher in use may be renegotiated or the connection may fail
99 because a client certificate is required or is requested only after an
100 attempt is made to access a certain URL. Note: the output produced by this
101 option is not always accurate because a connection might never have been
106 prints out the SSL session states.
110 print extensive debugging information including a hex dump of all traffic.
114 tests non blocking I/O
118 turns on non blocking I/O
122 this option translated a line feed from the terminal into CR+LF as required
127 inhibit printing of session and certificate information.
129 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>
131 these options disable the use of certain SSL or TLS protocols. By default
132 the initial handshake uses a method which should be compatible with all
133 servers and permit them to use SSL v3, SSL v2 or TLS as appropriate.
135 Unfortunately there are a lot of ancient and broken servers in use which
136 cannot handle this technique and will fail to connect. Some servers only
137 work if TLS is turned off with the B<-no_tls> option others will only
138 support SSL v2 and may need the B<-ssl2> option.
142 there are several known bug in SSL and TLS implementations. Adding this
143 option enables various workarounds.
145 =item B<-cipher cipherlist>
147 this allows the cipher list sent by the client to be modified. Although
148 the server determines which cipher suite is used it should take the first
149 supported cipher in the list sent by the client. See the B<ciphers>
150 command for more information.
154 =head1 CONNECTED COMMANDS
156 If a connection is established with an SSL server then any data received
157 from the server is displayed and any key presses will be sent to the
158 server. If the line begins with an B<R> then the session will be
159 renegotiated. If the line begins with a B<Q> the connection will be closed
164 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
167 openssl s_client -connect servername:443
169 would typically be used (https uses port 443). If the connection succeeds
170 then an HTTP command can be given such as "GET /" to retrieve a web page.
172 If the handshake fails then there are several possible causes, if it is
173 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
174 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> can be tried
175 in case it is a buggy server. In particular you should play with these
176 options B<before> submitting a bug report to an OpenSSL mailing list.
178 A frequent problem when attempting to get client certificates working
179 is that a web client complains it has no certificates or gives an empty
180 list to choose from. This is normally because the server is not sending
181 the clients certificate authority in its "acceptable CA list" when it
182 requests a certificate. By using B<s_client> the CA list can be viewed
183 and checked. However some servers only request client authentication
184 after a specific URL is requested. To obtain the list in this case it
185 is necessary to use the B<-prexit> command and send an HTTP request
186 for an appropriate page.
188 If a certificate is specified on the command line using the B<-cert>
189 option it will not be used unless the server specifically requests
190 a client certificate. Therefor merely including a client certificate
191 on the command line is no guarantee that the certificate works.
193 If there are problems verifying a server certificate then the
194 B<-showcerts> option can be used to show the whole chain.
198 Because this program has a lot of options and also because some of
199 the techniques used are rather old, the C source of s_client is rather
200 hard to read and not a model of how things should be done. A typical
201 SSL client program would be much simpler.
203 The B<-verify> option should really exit if the server verification
206 The B<-prexit> option is a bit of a hack. We should really report
207 information whenever a session is renegotiated.
211 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>