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>]
41 [B<-xmpphost hostname>]
45 [B<-sess_out filename>]
46 [B<-sess_in filename>]
48 [B<-serverinfo types>]
50 [B<-auth_require_reneg>]
54 The B<s_client> command implements a generic SSL/TLS client which connects
55 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
60 In addition to the options below the B<s_client> utility also supports the
61 common and client only options documented in the
62 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
67 =item B<-connect host:port>
69 This specifies the host and optional port to connect to. If not specified
70 then an attempt is made to connect to the local host on port 4433.
72 =item B<-cert certname>
74 The certificate to use, if one is requested by the server. The default is
75 not to use a certificate.
77 =item B<-certform format>
79 The certificate format to use: DER or PEM. PEM is the default.
83 The private key to use. If not specified then the certificate file will
86 =item B<-keyform format>
88 The private format to use: DER or PEM. PEM is the default.
92 the private key password source. For more information about the format of B<arg>
93 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>.
95 =item B<-verify depth>
97 The verify depth to use. This specifies the maximum length of the
98 server certificate chain and turns on server certificate verification.
99 Currently the verify operation continues after errors so all the problems
100 with a certificate chain can be seen. As a side effect the connection
101 will never fail due to a server certificate verify failure.
103 =item B<-verify_return_error>
105 Return verification errors instead of continuing. This will typically
106 abort the handshake with a fatal error.
108 =item B<-CApath directory>
110 The directory to use for server certificate verification. This directory
111 must be in "hash format", see B<verify> for more information. These are
112 also used when building the client certificate chain.
114 =item B<-CAfile file>
116 A file containing trusted certificates to use during server authentication
117 and to use when attempting to build the client certificate chain.
119 =item B<-purpose, -ignore_critical, -issuer_checks, -crl_check, -crl_check_all, -policy_check, -extended_crl, -x509_strict, -policy -check_ss_sig>
121 Set various certificate chain valiadition option. See the
122 L<B<verify>|verify(1)> manual page for details.
126 reconnects to the same server 5 times using the same session ID, this can
127 be used as a test that session caching is working.
131 pauses 1 second between each read and write call.
135 display the whole server certificate chain: normally only the server
136 certificate itself is displayed.
140 print session information when the program exits. This will always attempt
141 to print out information even if the connection fails. Normally information
142 will only be printed out once if the connection succeeds. This option is useful
143 because the cipher in use may be renegotiated or the connection may fail
144 because a client certificate is required or is requested only after an
145 attempt is made to access a certain URL. Note: the output produced by this
146 option is not always accurate because a connection might never have been
151 prints out the SSL session states.
155 print extensive debugging information including a hex dump of all traffic.
159 show all protocol messages with hex dump.
163 show verbose trace output of protocol messages. OpenSSL needs to be compiled
164 with B<enable-ssl-trace> for this option to work.
168 file to send output of B<-msg> or B<-trace> to, default standard output.
172 tests non-blocking I/O
176 turns on non-blocking I/O
180 this option translated a line feed from the terminal into CR+LF as required
185 inhibit shutting down the connection when end of file is reached in the
190 inhibit printing of session and certificate information. This implicitly
191 turns on B<-ign_eof> as well.
193 =item B<-psk_identity identity>
195 Use the PSK identity B<identity> when using a PSK cipher suite.
199 Use the PSK key B<key> when using a PSK cipher suite. The key is
200 given as a hexadecimal number without leading 0x, for example -psk
203 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>
205 these options disable the use of certain SSL or TLS protocols. By default
206 the initial handshake uses a method which should be compatible with all
207 servers and permit them to use SSL v3, SSL v2 or TLS as appropriate.
209 Unfortunately there are a lot of ancient and broken servers in use which
210 cannot handle this technique and will fail to connect. Some servers only
211 work if TLS is turned off with the B<-no_tls> option others will only
212 support SSL v2 and may need the B<-ssl2> option.
216 there are several known bug in SSL and TLS implementations. Adding this
217 option enables various workarounds.
221 only provide a brief summary of connection parameters instead of the
222 normal verbose output.
224 =item B<-cipher cipherlist>
226 this allows the cipher list sent by the client to be modified. Although
227 the server determines which cipher suite is used it should take the first
228 supported cipher in the list sent by the client. See the B<ciphers>
229 command for more information.
231 =item B<-starttls protocol>
233 send the protocol-specific message(s) to switch to TLS for communication.
234 B<protocol> is a keyword for the intended protocol. Currently, the only
235 supported keywords are "smtp", "pop3", "imap", "ftp" and "xmpp".
237 =item B<-xmpphost hostname>
239 This option, when used with "-starttls xmpp", specifies the host for the
240 "to" attribute of the stream element.
241 If this option is not specified, then the host specified with "-connect"
244 =item B<-tlsextdebug>
246 print out a hex dump of any TLS extensions received from the server.
250 disable RFC4507bis session ticket support.
252 =item B<-sess_out filename>
254 output SSL session to B<filename>
256 =item B<-sess_in sess.pem>
258 load SSL session from B<filename>. The client will attempt to resume a
259 connection from this session.
263 specifying an engine (by its unique B<id> string) will cause B<s_client>
264 to attempt to obtain a functional reference to the specified engine,
265 thus initialising it if needed. The engine will then be set as the default
266 for all available algorithms.
268 =item B<-rand file(s)>
270 a file or files containing random data used to seed the random number
271 generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>).
272 Multiple files can be specified separated by a OS-dependent character.
273 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
276 =item B<-serverinfo types>
278 a list of comma-separated TLS Extension Types (numbers between 0 and
279 65535). Each type will be sent as an empty ClientHello TLS Extension.
280 The server's response (if any) will be encoded and displayed as a PEM
285 send RFC 5878 client and server authorization extensions in the Client Hello as well as
286 supplemental data if the server also sent the authorization extensions in the Server Hello.
288 =item B<-auth_require_reneg>
290 only send RFC 5878 client and server authorization extensions during renegotiation.
294 =head1 CONNECTED COMMANDS
296 If a connection is established with an SSL server then any data received
297 from the server is displayed and any key presses will be sent to the
298 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
299 have been given), the session will be renegotiated if the line begins with an
300 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
301 connection will be closed down.
305 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
308 openssl s_client -connect servername:443
310 would typically be used (https uses port 443). If the connection succeeds
311 then an HTTP command can be given such as "GET /" to retrieve a web page.
313 If the handshake fails then there are several possible causes, if it is
314 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
315 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried
316 in case it is a buggy server. In particular you should play with these
317 options B<before> submitting a bug report to an OpenSSL mailing list.
319 A frequent problem when attempting to get client certificates working
320 is that a web client complains it has no certificates or gives an empty
321 list to choose from. This is normally because the server is not sending
322 the clients certificate authority in its "acceptable CA list" when it
323 requests a certificate. By using B<s_client> the CA list can be viewed
324 and checked. However some servers only request client authentication
325 after a specific URL is requested. To obtain the list in this case it
326 is necessary to use the B<-prexit> option and send an HTTP request
327 for an appropriate page.
329 If a certificate is specified on the command line using the B<-cert>
330 option it will not be used unless the server specifically requests
331 a client certificate. Therefor merely including a client certificate
332 on the command line is no guarantee that the certificate works.
334 If there are problems verifying a server certificate then the
335 B<-showcerts> option can be used to show the whole chain.
337 Since the SSLv23 client hello cannot include compression methods or extensions
338 these will only be supported if its use is disabled, for example by using the
341 The B<s_client> utility is a test tool and is designed to continue the
342 handshake after any certificate verification errors. As a result it will
343 accept any certificate chain (trusted or not) sent by the peer. None test
344 applications should B<not> do this as it makes them vulnerable to a MITM
345 attack. This behaviour can be changed by with the B<-verify_return_error>
346 option: any verify errors are then returned aborting the handshake.
350 Because this program has a lot of options and also because some of
351 the techniques used are rather old, the C source of s_client is rather
352 hard to read and not a model of how things should be done. A typical
353 SSL client program would be much simpler.
355 The B<-prexit> option is a bit of a hack. We should really report
356 information whenever a session is renegotiated.
360 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>