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 B<SUPPORTED COMMAND LINE OPTIONS> section in L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)>.
61 =item B<-connect host:port>
63 This specifies the host and optional port to connect to. If not specified
64 then an attempt is made to connect to the local host on port 4433.
66 =item B<-cert certname>
68 The certificate to use, if one is requested by the server. The default is
69 not to use a certificate.
71 =item B<-certform format>
73 The certificate format to use: DER or PEM. PEM is the default.
77 The private key to use. If not specified then the certificate file will
80 =item B<-keyform format>
82 The private format to use: DER or PEM. PEM is the default.
86 the private key password source. For more information about the format of B<arg>
87 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>.
89 =item B<-verify depth>
91 The verify depth to use. This specifies the maximum length of the
92 server certificate chain and turns on server certificate verification.
93 Currently the verify operation continues after errors so all the problems
94 with a certificate chain can be seen. As a side effect the connection
95 will never fail due to a server certificate verify failure.
97 =item B<-CApath directory>
99 The directory to use for server certificate verification. This directory
100 must be in "hash format", see B<verify> for more information. These are
101 also used when building the client certificate chain.
103 =item B<-CAfile file>
105 A file containing trusted certificates to use during server authentication
106 and to use when attempting to build the client certificate chain.
108 =item B<-purpose, -ignore_critical, -issuer_checks, -crl_check, -crl_check_all, -policy_check, -extended_crl, -x509_strict, -policy -check_ss_sig>
110 Set various certificate chain valiadition option. See the
111 L<B<verify>|verify(1)> manual page for details.
115 reconnects to the same server 5 times using the same session ID, this can
116 be used as a test that session caching is working.
120 pauses 1 second between each read and write call.
124 display the whole server certificate chain: normally only the server
125 certificate itself is displayed.
129 print session information when the program exits. This will always attempt
130 to print out information even if the connection fails. Normally information
131 will only be printed out once if the connection succeeds. This option is useful
132 because the cipher in use may be renegotiated or the connection may fail
133 because a client certificate is required or is requested only after an
134 attempt is made to access a certain URL. Note: the output produced by this
135 option is not always accurate because a connection might never have been
140 prints out the SSL session states.
144 print extensive debugging information including a hex dump of all traffic.
148 show all protocol messages with hex dump.
152 tests non-blocking I/O
156 turns on non-blocking I/O
160 this option translated a line feed from the terminal into CR+LF as required
165 inhibit shutting down the connection when end of file is reached in the
170 inhibit printing of session and certificate information. This implicitly
171 turns on B<-ign_eof> as well.
173 =item B<-psk_identity identity>
175 Use the PSK identity B<identity> when using a PSK cipher suite.
179 Use the PSK key B<key> when using a PSK cipher suite. The key is
180 given as a hexadecimal number without leading 0x, for example -psk
183 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>
185 these options disable the use of certain SSL or TLS protocols. By default
186 the initial handshake uses a method which should be compatible with all
187 servers and permit them to use SSL v3, SSL v2 or TLS as appropriate.
189 Unfortunately there are a lot of ancient and broken servers in use which
190 cannot handle this technique and will fail to connect. Some servers only
191 work if TLS is turned off with the B<-no_tls> option others will only
192 support SSL v2 and may need the B<-ssl2> option.
196 there are several known bug in SSL and TLS implementations. Adding this
197 option enables various workarounds.
201 only provide a brief summary of connection parameters instead of the
202 normal verbose output.
204 =item B<-cipher cipherlist>
206 this allows the cipher list sent by the client to be modified. Although
207 the server determines which cipher suite is used it should take the first
208 supported cipher in the list sent by the client. See the B<ciphers>
209 command for more information.
211 =item B<-starttls protocol>
213 send the protocol-specific message(s) to switch to TLS for communication.
214 B<protocol> is a keyword for the intended protocol. Currently, the only
215 supported keywords are "smtp", "pop3", "imap", and "ftp".
217 =item B<-tlsextdebug>
219 print out a hex dump of any TLS extensions received from the server.
223 disable RFC4507bis session ticket support.
225 =item B<-sess_out filename>
227 output SSL session to B<filename>
229 =item B<-sess_in sess.pem>
231 load SSL session from B<filename>. The client will attempt to resume a
232 connection from this session.
236 specifying an engine (by its unique B<id> string) will cause B<s_client>
237 to attempt to obtain a functional reference to the specified engine,
238 thus initialising it if needed. The engine will then be set as the default
239 for all available algorithms.
241 =item B<-rand file(s)>
243 a file or files containing random data used to seed the random number
244 generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
245 Multiple files can be specified separated by a OS-dependent character.
246 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
251 =head1 CONNECTED COMMANDS
253 If a connection is established with an SSL server then any data received
254 from the server is displayed and any key presses will be sent to the
255 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
256 have been given), the session will be renegotiated if the line begins with an
257 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
258 connection will be closed down.
262 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
265 openssl s_client -connect servername:443
267 would typically be used (https uses port 443). If the connection succeeds
268 then an HTTP command can be given such as "GET /" to retrieve a web page.
270 If the handshake fails then there are several possible causes, if it is
271 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
272 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried
273 in case it is a buggy server. In particular you should play with these
274 options B<before> submitting a bug report to an OpenSSL mailing list.
276 A frequent problem when attempting to get client certificates working
277 is that a web client complains it has no certificates or gives an empty
278 list to choose from. This is normally because the server is not sending
279 the clients certificate authority in its "acceptable CA list" when it
280 requests a certificate. By using B<s_client> the CA list can be viewed
281 and checked. However some servers only request client authentication
282 after a specific URL is requested. To obtain the list in this case it
283 is necessary to use the B<-prexit> option and send an HTTP request
284 for an appropriate page.
286 If a certificate is specified on the command line using the B<-cert>
287 option it will not be used unless the server specifically requests
288 a client certificate. Therefor merely including a client certificate
289 on the command line is no guarantee that the certificate works.
291 If there are problems verifying a server certificate then the
292 B<-showcerts> option can be used to show the whole chain.
294 Since the SSLv23 client hello cannot include compression methods or extensions
295 these will only be supported if its use is disabled, for example by using the
300 Because this program has a lot of options and also because some of
301 the techniques used are rather old, the C source of s_client is rather
302 hard to read and not a model of how things should be done. A typical
303 SSL client program would be much simpler.
305 The B<-verify> option should really exit if the server verification
308 The B<-prexit> option is a bit of a hack. We should really report
309 information whenever a session is renegotiated.
313 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>