6 s_client - SSL/TLS client program
10 B<openssl> B<s_client>
11 [B<-connect host:port>]
13 [B<-verify_return_error>]
15 [B<-certform DER|PEM>]
19 [B<-CApath directory>]
39 [B<-cipher cipherlist>]
40 [B<-starttls protocol>]
44 [B<-sess_out filename>]
45 [B<-sess_in filename>]
47 [B<-serverinfo types>]
49 [B<-auth_require_reneg>]
53 The B<s_client> command implements a generic SSL/TLS client which connects
54 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
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<-verify_return_error>
99 Return verification errors instead of continuing. This will typically
100 abort the handshake with a fatal error.
102 =item B<-CApath directory>
104 The directory to use for server certificate verification. This directory
105 must be in "hash format", see B<verify> for more information. These are
106 also used when building the client certificate chain.
108 =item B<-CAfile file>
110 A file containing trusted certificates to use during server authentication
111 and to use when attempting to build the client certificate chain.
113 =item B<-purpose, -ignore_critical, -issuer_checks, -crl_check, -crl_check_all, -policy_check, -extended_crl, -x509_strict, -policy -check_ss_sig>
115 Set various certificate chain valiadition option. See the
116 L<B<verify>|verify(1)> manual page for details.
120 reconnects to the same server 5 times using the same session ID, this can
121 be used as a test that session caching is working.
125 pauses 1 second between each read and write call.
129 display the whole server certificate chain: normally only the server
130 certificate itself is displayed.
134 print session information when the program exits. This will always attempt
135 to print out information even if the connection fails. Normally information
136 will only be printed out once if the connection succeeds. This option is useful
137 because the cipher in use may be renegotiated or the connection may fail
138 because a client certificate is required or is requested only after an
139 attempt is made to access a certain URL. Note: the output produced by this
140 option is not always accurate because a connection might never have been
145 prints out the SSL session states.
149 print extensive debugging information including a hex dump of all traffic.
153 show all protocol messages with hex dump.
157 tests non-blocking I/O
161 turns on non-blocking I/O
165 this option translated a line feed from the terminal into CR+LF as required
170 inhibit shutting down the connection when end of file is reached in the
175 inhibit printing of session and certificate information. This implicitly
176 turns on B<-ign_eof> as well.
178 =item B<-psk_identity identity>
180 Use the PSK identity B<identity> when using a PSK cipher suite.
184 Use the PSK key B<key> when using a PSK cipher suite. The key is
185 given as a hexadecimal number without leading 0x, for example -psk
188 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>
190 these options disable the use of certain SSL or TLS protocols. By default
191 the initial handshake uses a method which should be compatible with all
192 servers and permit them to use SSL v3, SSL v2 or TLS as appropriate.
194 Unfortunately there are a lot of ancient and broken servers in use which
195 cannot handle this technique and will fail to connect. Some servers only
196 work if TLS is turned off with the B<-no_tls> option others will only
197 support SSL v2 and may need the B<-ssl2> option.
201 there are several known bug in SSL and TLS implementations. Adding this
202 option enables various workarounds.
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
249 =item B<-serverinfo types>
251 a list of comma-separated TLS Extension Types (numbers between 0 and
252 65535). Each type will be sent as an empty ClientHello TLS Extension.
253 The server's response (if any) will be encoded and displayed as a PEM
258 send RFC 5878 client and server authorization extensions in the Client Hello as well as
259 supplemental data if the server also sent the authorization extensions in the Server Hello.
261 =item B<-auth_require_reneg>
263 only send RFC 5878 client and server authorization extensions during renegotiation.
267 =head1 CONNECTED COMMANDS
269 If a connection is established with an SSL server then any data received
270 from the server is displayed and any key presses will be sent to the
271 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
272 have been given), the session will be renegotiated if the line begins with an
273 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
274 connection will be closed down.
278 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
281 openssl s_client -connect servername:443
283 would typically be used (https uses port 443). If the connection succeeds
284 then an HTTP command can be given such as "GET /" to retrieve a web page.
286 If the handshake fails then there are several possible causes, if it is
287 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
288 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried
289 in case it is a buggy server. In particular you should play with these
290 options B<before> submitting a bug report to an OpenSSL mailing list.
292 A frequent problem when attempting to get client certificates working
293 is that a web client complains it has no certificates or gives an empty
294 list to choose from. This is normally because the server is not sending
295 the clients certificate authority in its "acceptable CA list" when it
296 requests a certificate. By using B<s_client> the CA list can be viewed
297 and checked. However some servers only request client authentication
298 after a specific URL is requested. To obtain the list in this case it
299 is necessary to use the B<-prexit> option and send an HTTP request
300 for an appropriate page.
302 If a certificate is specified on the command line using the B<-cert>
303 option it will not be used unless the server specifically requests
304 a client certificate. Therefor merely including a client certificate
305 on the command line is no guarantee that the certificate works.
307 If there are problems verifying a server certificate then the
308 B<-showcerts> option can be used to show the whole chain.
310 Since the SSLv23 client hello cannot include compression methods or extensions
311 these will only be supported if its use is disabled, for example by using the
314 The B<s_client> utility is a test tool and is designed to continue the
315 handshake after any certificate verification errors. As a result it will
316 accept any certificate chain (trusted or not) sent by the peer. None test
317 applications should B<not> do this as it makes them vulnerable to a MITM
318 attack. This behaviour can be changed by with the B<-verify_return_error>
319 option: any verify errors are then returned aborting the handshake.
323 Because this program has a lot of options and also because some of
324 the techniques used are rather old, the C source of s_client is rather
325 hard to read and not a model of how things should be done. A typical
326 SSL client program would be much simpler.
328 The B<-prexit> option is a bit of a hack. We should really report
329 information whenever a session is renegotiated.
333 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>