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>]
20 [B<-attime timestamp>]
34 [B<-verify_depth num>]
54 [B<-cipher cipherlist>]
55 [B<-starttls protocol>]
56 [B<-xmpphost hostname>]
60 [B<-sess_out filename>]
61 [B<-sess_in filename>]
66 The B<s_client> command implements a generic SSL/TLS client which connects
67 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
72 In addition to the options below the B<s_client> utility also supports the
73 common and client only options documented in the
74 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
79 =item B<-connect host:port>
81 This specifies the host and optional port to connect to. If not specified
82 then an attempt is made to connect to the local host on port 4433.
84 =item B<-cert certname>
86 The certificate to use, if one is requested by the server. The default is
87 not to use a certificate.
89 =item B<-certform format>
91 The certificate format to use: DER or PEM. PEM is the default.
95 The private key to use. If not specified then the certificate file will
98 =item B<-keyform format>
100 The private format to use: DER or PEM. PEM is the default.
104 the private key password source. For more information about the format of B<arg>
105 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>.
107 =item B<-verify depth>
109 The verify depth to use. This specifies the maximum length of the
110 server certificate chain and turns on server certificate verification.
111 Currently the verify operation continues after errors so all the problems
112 with a certificate chain can be seen. As a side effect the connection
113 will never fail due to a server certificate verify failure.
115 =item B<-CApath directory>
117 The directory to use for server certificate verification. This directory
118 must be in "hash format", see B<verify> for more information. These are
119 also used when building the client certificate chain.
121 =item B<-CAfile file>
123 A file containing trusted certificates to use during server authentication
124 and to use when attempting to build the client certificate chain.
126 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
127 B<explicit_policy>, B<-ignore_critical>, B<-inhibit_any>,
128 B<-inhibit_map>, B<-issuer_checks>, B<-policy>,
129 B<-policy_check>, B<-policy_print>, B<-purpose>,
130 B<-use_deltas>, B<-verify_depth>, B<-x509_strict>
132 Set various certificate chain valiadition options. See the
133 L<B<verify>|verify(1)> manual page for details.
137 reconnects to the same server 5 times using the same session ID, this can
138 be used as a test that session caching is working.
142 pauses 1 second between each read and write call.
146 display the whole server certificate chain: normally only the server
147 certificate itself is displayed.
151 print session information when the program exits. This will always attempt
152 to print out information even if the connection fails. Normally information
153 will only be printed out once if the connection succeeds. This option is useful
154 because the cipher in use may be renegotiated or the connection may fail
155 because a client certificate is required or is requested only after an
156 attempt is made to access a certain URL. Note: the output produced by this
157 option is not always accurate because a connection might never have been
162 prints out the SSL session states.
166 print extensive debugging information including a hex dump of all traffic.
170 show all protocol messages with hex dump.
174 tests non-blocking I/O
178 turns on non-blocking I/O
182 this option translated a line feed from the terminal into CR+LF as required
187 inhibit shutting down the connection when end of file is reached in the
192 inhibit printing of session and certificate information. This implicitly
193 turns on B<-ign_eof> as well.
195 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>
197 these options disable the use of certain SSL or TLS protocols. By default
198 the initial handshake uses a method which should be compatible with all
199 servers and permit them to use SSL v3, SSL v2 or TLS as appropriate.
201 Unfortunately there are a lot of ancient and broken servers in use which
202 cannot handle this technique and will fail to connect. Some servers only
203 work if TLS is turned off with the B<-no_tls> option others will only
204 support SSL v2 and may need the B<-ssl2> option.
208 there are several known bug in SSL and TLS implementations. Adding this
209 option enables various workarounds.
211 =item B<-cipher cipherlist>
213 this allows the cipher list sent by the client to be modified. Although
214 the server determines which cipher suite is used it should take the first
215 supported cipher in the list sent by the client. See the B<ciphers>
216 command for more information.
218 =item B<-starttls protocol>
220 send the protocol-specific message(s) to switch to TLS for communication.
221 B<protocol> is a keyword for the intended protocol. Currently, the only
222 supported keywords are "smtp", "pop3", "imap", "ftp" and "xmpp".
224 =item B<-xmpphost hostname>
226 This option, when used with "-starttls xmpp", specifies the host for the
227 "to" attribute of the stream element.
228 If this option is not specified, then the host specified with "-connect"
231 =item B<-tlsextdebug>
233 print out a hex dump of any TLS extensions received from the server.
237 disable RFC4507bis session ticket support.
239 =item B<-sess_out filename>
241 output SSL session to B<filename>
243 =item B<-sess_in sess.pem>
245 load SSL session from B<filename>. The client will attempt to resume a
246 connection from this session.
250 specifying an engine (by its unique B<id> string) will cause B<s_client>
251 to attempt to obtain a functional reference to the specified engine,
252 thus initialising it if needed. The engine will then be set as the default
253 for all available algorithms.
255 =item B<-rand file(s)>
257 a file or files containing random data used to seed the random number
258 generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
259 Multiple files can be specified separated by a OS-dependent character.
260 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
265 =head1 CONNECTED COMMANDS
267 If a connection is established with an SSL server then any data received
268 from the server is displayed and any key presses will be sent to the
269 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
270 have been given), the session will be renegotiated if the line begins with an
271 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
272 connection will be closed down.
276 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
279 openssl s_client -connect servername:443
281 would typically be used (https uses port 443). If the connection succeeds
282 then an HTTP command can be given such as "GET /" to retrieve a web page.
284 If the handshake fails then there are several possible causes, if it is
285 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
286 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried
287 in case it is a buggy server. In particular you should play with these
288 options B<before> submitting a bug report to an OpenSSL mailing list.
290 A frequent problem when attempting to get client certificates working
291 is that a web client complains it has no certificates or gives an empty
292 list to choose from. This is normally because the server is not sending
293 the clients certificate authority in its "acceptable CA list" when it
294 requests a certificate. By using B<s_client> the CA list can be viewed
295 and checked. However some servers only request client authentication
296 after a specific URL is requested. To obtain the list in this case it
297 is necessary to use the B<-prexit> option and send an HTTP request
298 for an appropriate page.
300 If a certificate is specified on the command line using the B<-cert>
301 option it will not be used unless the server specifically requests
302 a client certificate. Therefor merely including a client certificate
303 on the command line is no guarantee that the certificate works.
305 If there are problems verifying a server certificate then the
306 B<-showcerts> option can be used to show the whole chain.
308 Since the SSLv23 client hello cannot include compression methods or extensions
309 these will only be supported if its use is disabled, for example by using the
312 The B<s_client> utility is a test tool and is designed to continue the
313 handshake after any certificate verification errors. As a result it will
314 accept any certificate chain (trusted or not) sent by the peer. None test
315 applications should B<not> do this as it makes them vulnerable to a MITM
320 Because this program has a lot of options and also because some of
321 the techniques used are rather old, the C source of s_client is rather
322 hard to read and not a model of how things should be done. A typical
323 SSL client program would be much simpler.
325 The B<-prexit> option is a bit of a hack. We should really report
326 information whenever a session is renegotiated.
330 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>