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>]
38 [B<-cipher cipherlist>]
39 [B<-starttls protocol>]
43 [B<-sess_out filename>]
44 [B<-sess_in filename>]
49 The B<s_client> command implements a generic SSL/TLS client which connects
50 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
57 =item B<-connect host:port>
59 This specifies the host and optional port to connect to. If not specified
60 then an attempt is made to connect to the local host on port 4433.
62 =item B<-cert certname>
64 The certificate to use, if one is requested by the server. The default is
65 not to use a certificate.
67 =item B<-certform format>
69 The certificate format to use: DER or PEM. PEM is the default.
73 The private key to use. If not specified then the certificate file will
76 =item B<-keyform format>
78 The private format to use: DER or PEM. PEM is the default.
82 the private key password source. For more information about the format of B<arg>
83 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>.
85 =item B<-verify depth>
87 The verify depth to use. This specifies the maximum length of the
88 server certificate chain and turns on server certificate verification.
89 Currently the verify operation continues after errors so all the problems
90 with a certificate chain can be seen. As a side effect the connection
91 will never fail due to a server certificate verify failure.
93 =item B<-CApath directory>
95 The directory to use for server certificate verification. This directory
96 must be in "hash format", see B<verify> for more information. These are
97 also used when building the client certificate chain.
101 A file containing trusted certificates to use during server authentication
102 and to use when attempting to build the client certificate chain.
106 reconnects to the same server 5 times using the same session ID, this can
107 be used as a test that session caching is working.
111 pauses 1 second between each read and write call.
115 display the whole server certificate chain: normally only the server
116 certificate itself is displayed.
120 print session information when the program exits. This will always attempt
121 to print out information even if the connection fails. Normally information
122 will only be printed out once if the connection succeeds. This option is useful
123 because the cipher in use may be renegotiated or the connection may fail
124 because a client certificate is required or is requested only after an
125 attempt is made to access a certain URL. Note: the output produced by this
126 option is not always accurate because a connection might never have been
131 prints out the SSL session states.
135 print extensive debugging information including a hex dump of all traffic.
139 show all protocol messages with hex dump.
143 tests non-blocking I/O
147 turns on non-blocking I/O
151 this option translated a line feed from the terminal into CR+LF as required
156 inhibit shutting down the connection when end of file is reached in the
161 inhibit printing of session and certificate information. This implicitly
162 turns on B<-ign_eof> as well.
164 =item B<-psk_identity identity>
166 Use the PSK identity B<identity> when using a PSK cipher suite.
170 Use the PSK key B<key> when using a PSK cipher suite. The key is
171 given as a hexadecimal number without leading 0x, for example -psk
174 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>
176 these options disable the use of certain SSL or TLS protocols. By default
177 the initial handshake uses a method which should be compatible with all
178 servers and permit them to use SSL v3, SSL v2 or TLS as appropriate.
180 Unfortunately there are a lot of ancient and broken servers in use which
181 cannot handle this technique and will fail to connect. Some servers only
182 work if TLS is turned off with the B<-no_tls> option others will only
183 support SSL v2 and may need the B<-ssl2> option.
187 there are several known bug in SSL and TLS implementations. Adding this
188 option enables various workarounds.
190 =item B<-cipher cipherlist>
192 this allows the cipher list sent by the client to be modified. Although
193 the server determines which cipher suite is used it should take the first
194 supported cipher in the list sent by the client. See the B<ciphers>
195 command for more information.
197 =item B<-starttls protocol>
199 send the protocol-specific message(s) to switch to TLS for communication.
200 B<protocol> is a keyword for the intended protocol. Currently, the only
201 supported keywords are "smtp", "pop3", "imap", and "ftp".
203 =item B<-tlsextdebug>
205 print out a hex dump of any TLS extensions received from the server.
209 disable RFC4507bis session ticket support.
211 =item B<-sess_out filename>
213 output SSL session to B<filename>
215 =item B<-sess_in sess.pem>
217 load SSL session from B<filename>. The client will attempt to resume a
218 connection from this session.
222 specifying an engine (by it's unique B<id> string) will cause B<s_client>
223 to attempt to obtain a functional reference to the specified engine,
224 thus initialising it if needed. The engine will then be set as the default
225 for all available algorithms.
227 =item B<-rand file(s)>
229 a file or files containing random data used to seed the random number
230 generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
231 Multiple files can be specified separated by a OS-dependent character.
232 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
237 =head1 CONNECTED COMMANDS
239 If a connection is established with an SSL server then any data received
240 from the server is displayed and any key presses will be sent to the
241 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
242 have been given), the session will be renegotiated if the line begins with an
243 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
244 connection will be closed down.
248 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
251 openssl s_client -connect servername:443
253 would typically be used (https uses port 443). If the connection succeeds
254 then an HTTP command can be given such as "GET /" to retrieve a web page.
256 If the handshake fails then there are several possible causes, if it is
257 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
258 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried
259 in case it is a buggy server. In particular you should play with these
260 options B<before> submitting a bug report to an OpenSSL mailing list.
262 A frequent problem when attempting to get client certificates working
263 is that a web client complains it has no certificates or gives an empty
264 list to choose from. This is normally because the server is not sending
265 the clients certificate authority in its "acceptable CA list" when it
266 requests a certificate. By using B<s_client> the CA list can be viewed
267 and checked. However some servers only request client authentication
268 after a specific URL is requested. To obtain the list in this case it
269 is necessary to use the B<-prexit> option and send an HTTP request
270 for an appropriate page.
272 If a certificate is specified on the command line using the B<-cert>
273 option it will not be used unless the server specifically requests
274 a client certificate. Therefor merely including a client certificate
275 on the command line is no guarantee that the certificate works.
277 If there are problems verifying a server certificate then the
278 B<-showcerts> option can be used to show the whole chain.
280 Since the SSLv23 client hello cannot include compression methods or extensions
281 these will only be supported if its use is disabled, for example by using the
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)>