6 s_client - SSL/TLS client program
10 B<openssl> B<s_client>
11 [B<-connect host:port>]
14 [B<-certform DER|PEM>]
18 [B<-CApath directory>]
39 [B<-cipher cipherlist>]
40 [B<-starttls protocol>]
44 [B<-sess_out filename>]
45 [B<-sess_in filename>]
50 The B<s_client> command implements a generic SSL/TLS client which connects
51 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
58 =item B<-connect host:port>
60 This specifies the host and optional port to connect to. If not specified
61 then an attempt is made to connect to the local host on port 4433.
63 =item B<-cert certname>
65 The certificate to use, if one is requested by the server. The default is
66 not to use a certificate.
68 =item B<-certform format>
70 The certificate format to use: DER or PEM. PEM is the default.
74 The private key to use. If not specified then the certificate file will
77 =item B<-keyform format>
79 The private format to use: DER or PEM. PEM is the default.
83 the private key password source. For more information about the format of B<arg>
84 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>.
86 =item B<-verify depth>
88 The verify depth to use. This specifies the maximum length of the
89 server certificate chain and turns on server certificate verification.
90 Currently the verify operation continues after errors so all the problems
91 with a certificate chain can be seen. As a side effect the connection
92 will never fail due to a server certificate verify failure.
94 =item B<-CApath directory>
96 The directory to use for server certificate verification. This directory
97 must be in "hash format", see B<verify> for more information. These are
98 also used when building the client certificate chain.
100 =item B<-CAfile file>
102 A file containing trusted certificates to use during server authentication
103 and to use when attempting to build the client certificate chain.
107 reconnects to the same server 5 times using the same session ID, this can
108 be used as a test that session caching is working.
112 pauses 1 second between each read and write call.
116 display the whole server certificate chain: normally only the server
117 certificate itself is displayed.
121 print session information when the program exits. This will always attempt
122 to print out information even if the connection fails. Normally information
123 will only be printed out once if the connection succeeds. This option is useful
124 because the cipher in use may be renegotiated or the connection may fail
125 because a client certificate is required or is requested only after an
126 attempt is made to access a certain URL. Note: the output produced by this
127 option is not always accurate because a connection might never have been
132 prints out the SSL session states.
136 print extensive debugging information including a hex dump of all traffic.
140 show all protocol messages with hex dump.
144 tests non-blocking I/O
148 turns on non-blocking I/O
152 this option translated a line feed from the terminal into CR+LF as required
157 inhibit shutting down the connection when end of file is reached in the
162 inhibit printing of session and certificate information. This implicitly
163 turns on B<-ign_eof> as well.
165 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>
167 these options disable the use of certain SSL or TLS protocols. By default
168 the initial handshake uses a method which should be compatible with all
169 servers and permit them to use SSL v3, SSL v2 or TLS as appropriate.
171 Unfortunately there are still ancient and broken servers in use which
172 cannot handle this technique and will fail to connect. Some servers only
173 work if TLS is turned off.
175 =item B<-fallback_scsv>
177 Send TLS_FALLBACK_SCSV in the ClientHello.
181 there are several known bug in SSL and TLS implementations. Adding this
182 option enables various workarounds.
184 =item B<-cipher cipherlist>
186 this allows the cipher list sent by the client to be modified. Although
187 the server determines which cipher suite is used it should take the first
188 supported cipher in the list sent by the client. See the B<ciphers>
189 command for more information.
191 =item B<-starttls protocol>
193 send the protocol-specific message(s) to switch to TLS for communication.
194 B<protocol> is a keyword for the intended protocol. Currently, the only
195 supported keywords are "smtp", "pop3", "imap", and "ftp".
197 =item B<-tlsextdebug>
199 print out a hex dump of any TLS extensions received from the server. Note: this
200 option is only available if extension support is explicitly enabled at compile
205 disable RFC4507bis session ticket support. Note: this option is only available
206 if extension support is explicitly enabled at compile time
208 =item B<-sess_out filename>
210 output SSL session to B<filename>
212 =item B<-sess_in sess.pem>
214 load SSL session from B<filename>. The client will attempt to resume a
215 connection from this session.
219 specifying an engine (by it's unique B<id> string) will cause B<s_client>
220 to attempt to obtain a functional reference to the specified engine,
221 thus initialising it if needed. The engine will then be set as the default
222 for all available algorithms.
224 =item B<-rand file(s)>
226 a file or files containing random data used to seed the random number
227 generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
228 Multiple files can be specified separated by a OS-dependent character.
229 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
234 =head1 CONNECTED COMMANDS
236 If a connection is established with an SSL server then any data received
237 from the server is displayed and any key presses will be sent to the
238 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
239 have been given), the session will be renegotiated if the line begins with an
240 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
241 connection will be closed down.
245 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
248 openssl s_client -connect servername:443
250 would typically be used (https uses port 443). If the connection succeeds
251 then an HTTP command can be given such as "GET /" to retrieve a web page.
253 If the handshake fails then there are several possible causes, if it is
254 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
255 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried
256 in case it is a buggy server. In particular you should play with these
257 options B<before> submitting a bug report to an OpenSSL mailing list.
259 A frequent problem when attempting to get client certificates working
260 is that a web client complains it has no certificates or gives an empty
261 list to choose from. This is normally because the server is not sending
262 the clients certificate authority in its "acceptable CA list" when it
263 requests a certificate. By using B<s_client> the CA list can be viewed
264 and checked. However some servers only request client authentication
265 after a specific URL is requested. To obtain the list in this case it
266 is necessary to use the B<-prexit> option and send an HTTP request
267 for an appropriate page.
269 If a certificate is specified on the command line using the B<-cert>
270 option it will not be used unless the server specifically requests
271 a client certificate. Therefor merely including a client certificate
272 on the command line is no guarantee that the certificate works.
274 If there are problems verifying a server certificate then the
275 B<-showcerts> option can be used to show the whole chain.
277 Since the SSLv23 client hello cannot include compression methods or extensions
278 these will only be supported if its use is disabled, for example by using the
281 TLS extensions are only supported in OpenSSL 0.9.8 if they are explictly
282 enabled at compile time using for example the B<enable-tlsext> switch.
286 Because this program has a lot of options and also because some of
287 the techniques used are rather old, the C source of s_client is rather
288 hard to read and not a model of how things should be done. A typical
289 SSL client program would be much simpler.
291 The B<-verify> option should really exit if the server verification
294 The B<-prexit> option is a bit of a hack. We should really report
295 information whenever a session is renegotiated.
299 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>