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
55 In addition to the options below the B<s_client> utility also supports the
56 common and client only options documented in the
57 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
62 =item B<-connect host:port>
64 This specifies the host and optional port to connect to. If not specified
65 then an attempt is made to connect to the local host on port 4433.
67 =item B<-cert certname>
69 The certificate to use, if one is requested by the server. The default is
70 not to use a certificate.
72 =item B<-certform format>
74 The certificate format to use: DER or PEM. PEM is the default.
78 The private key to use. If not specified then the certificate file will
81 =item B<-keyform format>
83 The private format to use: DER or PEM. PEM is the default.
87 the private key password source. For more information about the format of B<arg>
88 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>.
90 =item B<-verify depth>
92 The verify depth to use. This specifies the maximum length of the
93 server certificate chain and turns on server certificate verification.
94 Currently the verify operation continues after errors so all the problems
95 with a certificate chain can be seen. As a side effect the connection
96 will never fail due to a server certificate verify failure.
98 =item B<-CApath directory>
100 The directory to use for server certificate verification. This directory
101 must be in "hash format", see B<verify> for more information. These are
102 also used when building the client certificate chain.
104 =item B<-CAfile file>
106 A file containing trusted certificates to use during server authentication
107 and to use when attempting to build the client certificate chain.
109 =item B<-purpose, -ignore_critical, -issuer_checks, -crl_check, -crl_check_all, -policy_check, -extended_crl, -x509_strict, -policy -check_ss_sig>
111 Set various certificate chain valiadition option. See the
112 L<B<verify>|verify(1)> manual page for details.
116 reconnects to the same server 5 times using the same session ID, this can
117 be used as a test that session caching is working.
121 pauses 1 second between each read and write call.
125 display the whole server certificate chain: normally only the server
126 certificate itself is displayed.
130 print session information when the program exits. This will always attempt
131 to print out information even if the connection fails. Normally information
132 will only be printed out once if the connection succeeds. This option is useful
133 because the cipher in use may be renegotiated or the connection may fail
134 because a client certificate is required or is requested only after an
135 attempt is made to access a certain URL. Note: the output produced by this
136 option is not always accurate because a connection might never have been
141 prints out the SSL session states.
145 print extensive debugging information including a hex dump of all traffic.
149 show all protocol messages with hex dump.
153 show verbose trace output of protocol messages. OpenSSL needs to be compiled
154 with B<enable-ssl-trace> for this option to work.
158 file to send output of B<-msg> or B<-trace> to, default standard output.
162 tests non-blocking I/O
166 turns on non-blocking I/O
170 this option translated a line feed from the terminal into CR+LF as required
175 inhibit shutting down the connection when end of file is reached in the
180 inhibit printing of session and certificate information. This implicitly
181 turns on B<-ign_eof> as well.
183 =item B<-psk_identity identity>
185 Use the PSK identity B<identity> when using a PSK cipher suite.
189 Use the PSK key B<key> when using a PSK cipher suite. The key is
190 given as a hexadecimal number without leading 0x, for example -psk
193 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>
195 these options disable the use of certain SSL or TLS protocols. By default
196 the initial handshake uses a method which should be compatible with all
197 servers and permit them to use SSL v3, SSL v2 or TLS as appropriate.
199 Unfortunately there are a lot of ancient and broken servers in use which
200 cannot handle this technique and will fail to connect. Some servers only
201 work if TLS is turned off with the B<-no_tls> option others will only
202 support SSL v2 and may need the B<-ssl2> option.
206 there are several known bug in SSL and TLS implementations. Adding this
207 option enables various workarounds.
211 only provide a brief summary of connection parameters instead of the
212 normal verbose output.
214 =item B<-cipher cipherlist>
216 this allows the cipher list sent by the client to be modified. Although
217 the server determines which cipher suite is used it should take the first
218 supported cipher in the list sent by the client. See the B<ciphers>
219 command for more information.
221 =item B<-starttls protocol>
223 send the protocol-specific message(s) to switch to TLS for communication.
224 B<protocol> is a keyword for the intended protocol. Currently, the only
225 supported keywords are "smtp", "pop3", "imap", and "ftp".
227 =item B<-tlsextdebug>
229 print out a hex dump of any TLS extensions received from the server.
233 disable RFC4507bis session ticket support.
235 =item B<-sess_out filename>
237 output SSL session to B<filename>
239 =item B<-sess_in sess.pem>
241 load SSL session from B<filename>. The client will attempt to resume a
242 connection from this session.
246 specifying an engine (by its unique B<id> string) will cause B<s_client>
247 to attempt to obtain a functional reference to the specified engine,
248 thus initialising it if needed. The engine will then be set as the default
249 for all available algorithms.
251 =item B<-rand file(s)>
253 a file or files containing random data used to seed the random number
254 generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
255 Multiple files can be specified separated by a OS-dependent character.
256 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
261 =head1 CONNECTED COMMANDS
263 If a connection is established with an SSL server then any data received
264 from the server is displayed and any key presses will be sent to the
265 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
266 have been given), the session will be renegotiated if the line begins with an
267 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
268 connection will be closed down.
272 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
275 openssl s_client -connect servername:443
277 would typically be used (https uses port 443). If the connection succeeds
278 then an HTTP command can be given such as "GET /" to retrieve a web page.
280 If the handshake fails then there are several possible causes, if it is
281 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
282 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried
283 in case it is a buggy server. In particular you should play with these
284 options B<before> submitting a bug report to an OpenSSL mailing list.
286 A frequent problem when attempting to get client certificates working
287 is that a web client complains it has no certificates or gives an empty
288 list to choose from. This is normally because the server is not sending
289 the clients certificate authority in its "acceptable CA list" when it
290 requests a certificate. By using B<s_client> the CA list can be viewed
291 and checked. However some servers only request client authentication
292 after a specific URL is requested. To obtain the list in this case it
293 is necessary to use the B<-prexit> option and send an HTTP request
294 for an appropriate page.
296 If a certificate is specified on the command line using the B<-cert>
297 option it will not be used unless the server specifically requests
298 a client certificate. Therefor merely including a client certificate
299 on the command line is no guarantee that the certificate works.
301 If there are problems verifying a server certificate then the
302 B<-showcerts> option can be used to show the whole chain.
304 Since the SSLv23 client hello cannot include compression methods or extensions
305 these will only be supported if its use is disabled, for example by using the
310 Because this program has a lot of options and also because some of
311 the techniques used are rather old, the C source of s_client is rather
312 hard to read and not a model of how things should be done. A typical
313 SSL client program would be much simpler.
315 The B<-verify> option should really exit if the server verification
318 The B<-prexit> option is a bit of a hack. We should really report
319 information whenever a session is renegotiated.
323 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>