6 s_client - SSL/TLS client program
10 B<openssl> B<s_client>
11 [B<-connect host:port>]
14 [B<-verify_return_error>]
16 [B<-certform DER|PEM>]
20 [B<-CApath directory>]
42 [B<-cipher cipherlist>]
44 [B<-starttls protocol>]
48 [B<-sess_out filename>]
49 [B<-sess_in filename>]
52 [B<-nextprotoneg protocols>]
56 The B<s_client> command implements a generic SSL/TLS client which connects
57 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
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<-servername name>
71 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
73 =item B<-cert certname>
75 The certificate to use, if one is requested by the server. The default is
76 not to use a certificate.
78 =item B<-certform format>
80 The certificate format to use: DER or PEM. PEM is the default.
84 The private key to use. If not specified then the certificate file will
87 =item B<-keyform format>
89 The private format to use: DER or PEM. PEM is the default.
93 the private key password source. For more information about the format of B<arg>
94 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>.
96 =item B<-verify depth>
98 The verify depth to use. This specifies the maximum length of the
99 server certificate chain and turns on server certificate verification.
100 Currently the verify operation continues after errors so all the problems
101 with a certificate chain can be seen. As a side effect the connection
102 will never fail due to a server certificate verify failure.
104 =item B<-verify_return_error>
106 Return verification errors instead of continuing. This will typically
107 abort the handshake with a fatal error.
109 =item B<-CApath directory>
111 The directory to use for server certificate verification. This directory
112 must be in "hash format", see B<verify> for more information. These are
113 also used when building the client certificate chain.
115 =item B<-CAfile file>
117 A file containing trusted certificates to use during server authentication
118 and to use when attempting to build the client certificate chain.
120 =item B<-purpose, -ignore_critical, -issuer_checks, -crl_check, -crl_check_all, -policy_check, -extended_crl, -x509_strict, -policy -check_ss_sig -no_alt_chains>
122 Set various certificate chain valiadition option. See the
123 L<B<verify>|verify(1)> manual page for details.
127 reconnects to the same server 5 times using the same session ID, this can
128 be used as a test that session caching is working.
132 pauses 1 second between each read and write call.
136 display the whole server certificate chain: normally only the server
137 certificate itself is displayed.
141 print session information when the program exits. This will always attempt
142 to print out information even if the connection fails. Normally information
143 will only be printed out once if the connection succeeds. This option is useful
144 because the cipher in use may be renegotiated or the connection may fail
145 because a client certificate is required or is requested only after an
146 attempt is made to access a certain URL. Note: the output produced by this
147 option is not always accurate because a connection might never have been
152 prints out the SSL session states.
156 print extensive debugging information including a hex dump of all traffic.
160 show all protocol messages with hex dump.
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.
187 shut down the connection when end of file is reached in the input.
188 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
190 =item B<-psk_identity identity>
192 Use the PSK identity B<identity> when using a PSK cipher suite.
196 Use the PSK key B<key> when using a PSK cipher suite. The key is
197 given as a hexadecimal number without leading 0x, for example -psk
200 =item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-tls1_1>, B<-tls1_2>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>
202 These options require or disable the use of the specified SSL or TLS protocols.
203 By default the initial handshake uses a I<version-flexible> method which will
204 negotiate the highest mutually supported protocol version.
208 there are several known bug in SSL and TLS implementations. Adding this
209 option enables various workarounds.
211 =item B<-cipher cipherlist>
213 this allows the cipher list sent by the client to be modified. Although
214 the server determines which cipher suite is used it should take the first
215 supported cipher in the list sent by the client. See the B<ciphers>
216 command for more information.
220 use the server's cipher preferences; only used for SSLV2.
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
262 sends a certificate status request to the server (OCSP stapling). The server
263 response (if any) is printed out.
265 =item B<-nextprotoneg protocols>
267 enable Next Protocol Negotiation TLS extension and provide a list of
268 comma-separated protocol names that the client should advertise
269 support for. The list should contain most wanted protocols first.
270 Protocol names are printable ASCII strings, for example "http/1.1" or
272 Empty list of protocols is treated specially and will cause the client to
273 advertise support for the TLS extension but disconnect just after
274 reciving ServerHello with a list of server supported protocols.
278 =head1 CONNECTED COMMANDS
280 If a connection is established with an SSL server then any data received
281 from the server is displayed and any key presses will be sent to the
282 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
283 have been given), the session will be renegotiated if the line begins with an
284 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
285 connection will be closed down.
289 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
292 openssl s_client -connect servername:443
294 would typically be used (https uses port 443). If the connection succeeds
295 then an HTTP command can be given such as "GET /" to retrieve a web page.
297 If the handshake fails then there are several possible causes, if it is
298 nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>,
299 B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried
300 in case it is a buggy server. In particular you should play with these
301 options B<before> submitting a bug report to an OpenSSL mailing list.
303 A frequent problem when attempting to get client certificates working
304 is that a web client complains it has no certificates or gives an empty
305 list to choose from. This is normally because the server is not sending
306 the clients certificate authority in its "acceptable CA list" when it
307 requests a certificate. By using B<s_client> the CA list can be viewed
308 and checked. However some servers only request client authentication
309 after a specific URL is requested. To obtain the list in this case it
310 is necessary to use the B<-prexit> option and send an HTTP request
311 for an appropriate page.
313 If a certificate is specified on the command line using the B<-cert>
314 option it will not be used unless the server specifically requests
315 a client certificate. Therefor merely including a client certificate
316 on the command line is no guarantee that the certificate works.
318 If there are problems verifying a server certificate then the
319 B<-showcerts> option can be used to show the whole chain.
321 Since the SSLv23 client hello cannot include compression methods or extensions
322 these will only be supported if its use is disabled, for example by using the
325 The B<s_client> utility is a test tool and is designed to continue the
326 handshake after any certificate verification errors. As a result it will
327 accept any certificate chain (trusted or not) sent by the peer. None test
328 applications should B<not> do this as it makes them vulnerable to a MITM
329 attack. This behaviour can be changed by with the B<-verify_return_error>
330 option: any verify errors are then returned aborting the handshake.
334 Because this program has a lot of options and also because some of
335 the techniques used are rather old, the C source of s_client is rather
336 hard to read and not a model of how things should be done. A typical
337 SSL client program would be much simpler.
339 The B<-prexit> option is a bit of a hack. We should really report
340 information whenever a session is renegotiated.
344 L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)>
348 The -no_alt_chains options was first added to OpenSSL 1.0.1n and 1.0.2b.