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>]
46 [B<-serverinfo types>]
50 The B<s_client> command implements a generic SSL/TLS client which connects
51 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
56 In addition to the options below the B<s_client> utility also supports the
57 common and client only options documented in the
58 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
63 =item B<-connect host:port>
65 This specifies the host and optional port to connect to. If not specified
66 then an attempt is made to connect to the local host on port 4433.
68 =item B<-cert certname>
70 The certificate to use, if one is requested by the server. The default is
71 not to use a certificate.
73 =item B<-certform format>
75 The certificate format to use: DER or PEM. PEM is the default.
79 The private key to use. If not specified then the certificate file will
82 =item B<-keyform format>
84 The private format to use: DER or PEM. PEM is the default.
88 the private key password source. For more information about the format of B<arg>
89 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>.
91 =item B<-verify depth>
93 The verify depth to use. This specifies the maximum length of the
94 server certificate chain and turns on server certificate verification.
95 Currently the verify operation continues after errors so all the problems
96 with a certificate chain can be seen. As a side effect the connection
97 will never fail due to a server certificate verify failure.
99 =item B<-CApath directory>
101 The directory to use for server certificate verification. This directory
102 must be in "hash format", see B<verify> for more information. These are
103 also used when building the client certificate chain.
105 =item B<-CAfile file>
107 A file containing trusted certificates to use during server authentication
108 and to use when attempting to build the client certificate chain.
110 =item B<-purpose, -ignore_critical, -issuer_checks, -crl_check, -crl_check_all, -policy_check, -extended_crl, -x509_strict, -policy -check_ss_sig>
112 Set various certificate chain valiadition option. See the
113 L<B<verify>|verify(1)> manual page for details.
117 reconnects to the same server 5 times using the same session ID, this can
118 be used as a test that session caching is working.
122 pauses 1 second between each read and write call.
126 display the whole server certificate chain: normally only the server
127 certificate itself is displayed.
131 print session information when the program exits. This will always attempt
132 to print out information even if the connection fails. Normally information
133 will only be printed out once if the connection succeeds. This option is useful
134 because the cipher in use may be renegotiated or the connection may fail
135 because a client certificate is required or is requested only after an
136 attempt is made to access a certain URL. Note: the output produced by this
137 option is not always accurate because a connection might never have been
142 prints out the SSL session states.
146 print extensive debugging information including a hex dump of all traffic.
150 show all protocol messages with hex dump.
154 show verbose trace output of protocol messages. OpenSSL needs to be compiled
155 with B<enable-ssl-trace> for this option to work.
159 file to send output of B<-msg> or B<-trace> to, default standard output.
163 tests non-blocking I/O
167 turns on non-blocking I/O
171 this option translated a line feed from the terminal into CR+LF as required
176 inhibit shutting down the connection when end of file is reached in the
181 inhibit printing of session and certificate information. This implicitly
182 turns on B<-ign_eof> as well.
184 =item B<-psk_identity identity>
186 Use the PSK identity B<identity> when using a PSK cipher suite.
190 Use the PSK key B<key> when using a PSK cipher suite. The key is
191 given as a hexadecimal number without leading 0x, for example -psk
194 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>
196 these options disable the use of certain SSL or TLS protocols. By default
197 the initial handshake uses a method which should be compatible with all
198 servers and permit them to use SSL v3, SSL v2 or TLS as appropriate.
200 Unfortunately there are a lot of ancient and broken servers in use which
201 cannot handle this technique and will fail to connect. Some servers only
202 work if TLS is turned off with the B<-no_tls> option others will only
203 support SSL v2 and may need the B<-ssl2> option.
207 there are several known bug in SSL and TLS implementations. Adding this
208 option enables various workarounds.
212 only provide a brief summary of connection parameters instead of the
213 normal verbose output.
215 =item B<-cipher cipherlist>
217 this allows the cipher list sent by the client to be modified. Although
218 the server determines which cipher suite is used it should take the first
219 supported cipher in the list sent by the client. See the B<ciphers>
220 command for more information.
222 =item B<-starttls protocol>
224 send the protocol-specific message(s) to switch to TLS for communication.
225 B<protocol> is a keyword for the intended protocol. Currently, the only
226 supported keywords are "smtp", "pop3", "imap", and "ftp".
228 =item B<-tlsextdebug>
230 print out a hex dump of any TLS extensions received from the server.
234 disable RFC4507bis session ticket support.
236 =item B<-sess_out filename>
238 output SSL session to B<filename>
240 =item B<-sess_in sess.pem>
242 load SSL session from B<filename>. The client will attempt to resume a
243 connection from this session.
247 specifying an engine (by its unique B<id> string) will cause B<s_client>
248 to attempt to obtain a functional reference to the specified engine,
249 thus initialising it if needed. The engine will then be set as the default
250 for all available algorithms.
252 =item B<-rand file(s)>
254 a file or files containing random data used to seed the random number
255 generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
256 Multiple files can be specified separated by a OS-dependent character.
257 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
260 =item B<-serverinfo types>
262 a list of comma-separated TLS Extension Types (numbers between 0 and
263 65535). Each type will be sent as an empty ClientHello TLS Extension.
264 The server's response (if any) will be encoded and displayed as a PEM
269 =head1 CONNECTED COMMANDS
271 If a connection is established with an SSL server then any data received
272 from the server is displayed and any key presses will be sent to the
273 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
274 have been given), the session will be renegotiated if the line begins with an
275 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
276 connection will be closed down.
280 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
283 openssl s_client -connect servername:443
285 would typically be used (https uses port 443). If the connection succeeds
286 then an HTTP command can be given such as "GET /" to retrieve a web page.
288 If the handshake fails then there are several possible causes, if it is
289 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
290 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried
291 in case it is a buggy server. In particular you should play with these
292 options B<before> submitting a bug report to an OpenSSL mailing list.
294 A frequent problem when attempting to get client certificates working
295 is that a web client complains it has no certificates or gives an empty
296 list to choose from. This is normally because the server is not sending
297 the clients certificate authority in its "acceptable CA list" when it
298 requests a certificate. By using B<s_client> the CA list can be viewed
299 and checked. However some servers only request client authentication
300 after a specific URL is requested. To obtain the list in this case it
301 is necessary to use the B<-prexit> option and send an HTTP request
302 for an appropriate page.
304 If a certificate is specified on the command line using the B<-cert>
305 option it will not be used unless the server specifically requests
306 a client certificate. Therefor merely including a client certificate
307 on the command line is no guarantee that the certificate works.
309 If there are problems verifying a server certificate then the
310 B<-showcerts> option can be used to show the whole chain.
312 Since the SSLv23 client hello cannot include compression methods or extensions
313 these will only be supported if its use is disabled, for example by using the
318 Because this program has a lot of options and also because some of
319 the techniques used are rather old, the C source of s_client is rather
320 hard to read and not a model of how things should be done. A typical
321 SSL client program would be much simpler.
323 The B<-verify> option should really exit if the server verification
326 The B<-prexit> option is a bit of a hack. We should really report
327 information whenever a session is renegotiated.
331 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>