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>]
40 [B<-xmpphost hostname>]
44 [B<-sess_out filename>]
45 [B<-sess_in filename>]
47 [B<-serverinfo types>]
51 The B<s_client> command implements a generic SSL/TLS client which connects
52 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
57 In addition to the options below the B<s_client> utility also supports the
58 common and client only options documented in the
59 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
64 =item B<-connect host:port>
66 This specifies the host and optional port to connect to. If not specified
67 then an attempt is made to connect to the local host on port 4433.
69 =item B<-cert certname>
71 The certificate to use, if one is requested by the server. The default is
72 not to use a certificate.
74 =item B<-certform format>
76 The certificate format to use: DER or PEM. PEM is the default.
80 The private key to use. If not specified then the certificate file will
83 =item B<-keyform format>
85 The private format to use: DER or PEM. PEM is the default.
89 the private key password source. For more information about the format of B<arg>
90 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>.
92 =item B<-verify depth>
94 The verify depth to use. This specifies the maximum length of the
95 server certificate chain and turns on server certificate verification.
96 Currently the verify operation continues after errors so all the problems
97 with a certificate chain can be seen. As a side effect the connection
98 will never fail due to a server certificate verify failure.
100 =item B<-CApath directory>
102 The directory to use for server certificate verification. This directory
103 must be in "hash format", see B<verify> for more information. These are
104 also used when building the client certificate chain.
106 =item B<-CAfile file>
108 A file containing trusted certificates to use during server authentication
109 and to use when attempting to build the client certificate chain.
111 =item B<-purpose, -ignore_critical, -issuer_checks, -crl_check, -crl_check_all, -policy_check, -extended_crl, -x509_strict, -policy -check_ss_sig>
113 Set various certificate chain valiadition option. See the
114 L<B<verify>|verify(1)> manual page for details.
118 reconnects to the same server 5 times using the same session ID, this can
119 be used as a test that session caching is working.
123 pauses 1 second between each read and write call.
127 display the whole server certificate chain: normally only the server
128 certificate itself is displayed.
132 print session information when the program exits. This will always attempt
133 to print out information even if the connection fails. Normally information
134 will only be printed out once if the connection succeeds. This option is useful
135 because the cipher in use may be renegotiated or the connection may fail
136 because a client certificate is required or is requested only after an
137 attempt is made to access a certain URL. Note: the output produced by this
138 option is not always accurate because a connection might never have been
143 prints out the SSL session states.
147 print extensive debugging information including a hex dump of all traffic.
151 show all protocol messages with hex dump.
155 show verbose trace output of protocol messages. OpenSSL needs to be compiled
156 with B<enable-ssl-trace> for this option to work.
160 file to send output of B<-msg> or B<-trace> to, default standard output.
164 tests non-blocking I/O
168 turns on non-blocking I/O
172 this option translated a line feed from the terminal into CR+LF as required
177 inhibit shutting down the connection when end of file is reached in the
182 inhibit printing of session and certificate information. This implicitly
183 turns on B<-ign_eof> as well.
185 =item B<-psk_identity identity>
187 Use the PSK identity B<identity> when using a PSK cipher suite.
191 Use the PSK key B<key> when using a PSK cipher suite. The key is
192 given as a hexadecimal number without leading 0x, for example -psk
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.
213 only provide a brief summary of connection parameters instead of the
214 normal verbose output.
216 =item B<-cipher cipherlist>
218 this allows the cipher list sent by the client to be modified. Although
219 the server determines which cipher suite is used it should take the first
220 supported cipher in the list sent by the client. See the B<ciphers>
221 command for more information.
223 =item B<-starttls protocol>
225 send the protocol-specific message(s) to switch to TLS for communication.
226 B<protocol> is a keyword for the intended protocol. Currently, the only
227 supported keywords are "smtp", "pop3", "imap", "ftp" and "xmpp".
229 =item B<-xmpphost hostname>
231 This option, when used with "-starttls xmpp", specifies the host for the
232 "to" attribute of the stream element.
233 If this option is not specified, then the host specified with "-connect"
236 =item B<-tlsextdebug>
238 print out a hex dump of any TLS extensions received from the server.
242 disable RFC4507bis session ticket support.
244 =item B<-sess_out filename>
246 output SSL session to B<filename>
248 =item B<-sess_in sess.pem>
250 load SSL session from B<filename>. The client will attempt to resume a
251 connection from this session.
255 specifying an engine (by its unique B<id> string) will cause B<s_client>
256 to attempt to obtain a functional reference to the specified engine,
257 thus initialising it if needed. The engine will then be set as the default
258 for all available algorithms.
260 =item B<-rand file(s)>
262 a file or files containing random data used to seed the random number
263 generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
264 Multiple files can be specified separated by a OS-dependent character.
265 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
268 =item B<-serverinfo types>
270 a list of comma-separated TLS Extension Types (numbers between 0 and
271 65535). Each type will be sent as an empty ClientHello TLS Extension.
272 The server's response (if any) will be encoded and displayed as a PEM
277 =head1 CONNECTED COMMANDS
279 If a connection is established with an SSL server then any data received
280 from the server is displayed and any key presses will be sent to the
281 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
282 have been given), the session will be renegotiated if the line begins with an
283 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
284 connection will be closed down.
288 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
291 openssl s_client -connect servername:443
293 would typically be used (https uses port 443). If the connection succeeds
294 then an HTTP command can be given such as "GET /" to retrieve a web page.
296 If the handshake fails then there are several possible causes, if it is
297 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
298 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried
299 in case it is a buggy server. In particular you should play with these
300 options B<before> submitting a bug report to an OpenSSL mailing list.
302 A frequent problem when attempting to get client certificates working
303 is that a web client complains it has no certificates or gives an empty
304 list to choose from. This is normally because the server is not sending
305 the clients certificate authority in its "acceptable CA list" when it
306 requests a certificate. By using B<s_client> the CA list can be viewed
307 and checked. However some servers only request client authentication
308 after a specific URL is requested. To obtain the list in this case it
309 is necessary to use the B<-prexit> option and send an HTTP request
310 for an appropriate page.
312 If a certificate is specified on the command line using the B<-cert>
313 option it will not be used unless the server specifically requests
314 a client certificate. Therefor merely including a client certificate
315 on the command line is no guarantee that the certificate works.
317 If there are problems verifying a server certificate then the
318 B<-showcerts> option can be used to show the whole chain.
320 Since the SSLv23 client hello cannot include compression methods or extensions
321 these will only be supported if its use is disabled, for example by using the
326 Because this program has a lot of options and also because some of
327 the techniques used are rather old, the C source of s_client is rather
328 hard to read and not a model of how things should be done. A typical
329 SSL client program would be much simpler.
331 The B<-verify> option should really exit if the server verification
334 The B<-prexit> option is a bit of a hack. We should really report
335 information whenever a session is renegotiated.
339 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>