6 s_client - SSL/TLS client program
10 B<openssl> B<s_client>
12 [B<-connect host:port>]
16 [B<-verify_return_error>]
18 [B<-certform DER|PEM>]
22 [B<-CApath directory>]
26 [B<-dane_tlsa_domain domain>]
27 [B<-dane_tlsa_rrdata rrdata>]
28 [B<-attime timestamp>]
48 [B<-verify_depth num>]
49 [B<-verify_email email>]
50 [B<-verify_hostname hostname>]
52 [B<-verify_name name>]
84 [B<-cipher cipherlist>]
86 [B<-starttls protocol>]
87 [B<-xmpphost hostname>]
91 [B<-sess_out filename>]
92 [B<-sess_in filename>]
94 [B<-serverinfo types>]
96 [B<-nextprotoneg protocols>]
97 [B<-noct|requestct|requirect>]
102 The B<s_client> command implements a generic SSL/TLS client which connects
103 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
108 In addition to the options below the B<s_client> utility also supports the
109 common and client only options documented in the
110 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
117 Print out a usage message.
119 =item B<-connect host:port>
121 This specifies the host and optional port to connect to. If not specified
122 then an attempt is made to connect to the local host on port 4433.
124 =item B<-proxy host:port>
126 When used with the B<-connect> flag, the program uses the host and port
127 specified with this flag and issues an HTTP CONNECT command to connect
128 to the desired server.
130 =item B<-servername name>
132 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
134 =item B<-cert certname>
136 The certificate to use, if one is requested by the server. The default is
137 not to use a certificate.
139 =item B<-certform format>
141 The certificate format to use: DER or PEM. PEM is the default.
143 =item B<-key keyfile>
145 The private key to use. If not specified then the certificate file will
148 =item B<-keyform format>
150 The private format to use: DER or PEM. PEM is the default.
154 the private key password source. For more information about the format of B<arg>
155 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
157 =item B<-verify depth>
159 The verify depth to use. This specifies the maximum length of the
160 server certificate chain and turns on server certificate verification.
161 Currently the verify operation continues after errors so all the problems
162 with a certificate chain can be seen. As a side effect the connection
163 will never fail due to a server certificate verify failure.
165 =item B<-verify_return_error>
167 Return verification errors instead of continuing. This will typically
168 abort the handshake with a fatal error.
170 =item B<-CApath directory>
172 The directory to use for server certificate verification. This directory
173 must be in "hash format", see B<verify> for more information. These are
174 also used when building the client certificate chain.
176 =item B<-CAfile file>
178 A file containing trusted certificates to use during server authentication
179 and to use when attempting to build the client certificate chain.
183 Do not load the trusted CA certificates from the default file location
187 Do not load the trusted CA certificates from the default directory location
189 =item B<-dane_tlsa_domain domain>
191 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
192 TLSA base domain which becomes the default SNI hint and the primary
193 reference identifier for hostname checks. This must be used in
194 combination with at least one instance of the B<-dane_tlsa_rrdata>
197 When DANE authentication succeeds, the diagnostic output will include
198 the lowest (closest to 0) depth at which a TLSA record authenticated
199 a chain certificate. When that TLSA record is a "2 1 0" trust
200 anchor public key that signed (rather than matched) the top-most
201 certificate of the chain, the result is reported as "TA public key
202 verified". Otherwise, either the TLSA record "matched TA certificate"
203 at a positive depth or else "matched EE certificate" at depth 0.
205 =item B<-dane_tlsa_rrdata rrdata>
207 Use one or more times to specify the RRDATA fields of the DANE TLSA
208 RRset associated with the target service. The B<rrdata> value is
209 specied in "presentation form", that is four whitespace separated
210 fields that specify the usage, selector, matching type and associated
211 data, with the last of these encoded in hexadecimal. Optional
212 whitespace is ignored in the associated data field. For example:
214 $ openssl s_client -brief -starttls smtp \
215 -connect smtp.example.com:25 \
216 -dane_tlsa_domain smtp.example.com \
217 -dane_tlsa_rrdata "2 1 1
218 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
219 -dane_tlsa_rrdata "2 1 1
220 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
223 Verified peername: smtp.example.com
224 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
227 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
228 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
229 B<-inhibit_map>, B<-no_alt_chains>, B<-partial_chain>, B<-policy>,
230 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
231 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
232 B<-verify_depth>, B<-verify_email>, B<-verify_hostname>, B<-verify_ip>,
233 B<-verify_name>, B<-x509_strict>
235 Set various certificate chain validation options. See the
236 L<verify(1)> manual page for details.
240 reconnects to the same server 5 times using the same session ID, this can
241 be used as a test that session caching is working.
245 display the whole server certificate chain: normally only the server
246 certificate itself is displayed.
250 print session information when the program exits. This will always attempt
251 to print out information even if the connection fails. Normally information
252 will only be printed out once if the connection succeeds. This option is useful
253 because the cipher in use may be renegotiated or the connection may fail
254 because a client certificate is required or is requested only after an
255 attempt is made to access a certain URL. Note: the output produced by this
256 option is not always accurate because a connection might never have been
261 prints out the SSL session states.
265 print extensive debugging information including a hex dump of all traffic.
269 show all protocol messages with hex dump.
273 show verbose trace output of protocol messages. OpenSSL needs to be compiled
274 with B<enable-ssl-trace> for this option to work.
278 file to send output of B<-msg> or B<-trace> to, default standard output.
282 tests non-blocking I/O
286 turns on non-blocking I/O
290 this option translated a line feed from the terminal into CR+LF as required
295 inhibit shutting down the connection when end of file is reached in the
300 inhibit printing of session and certificate information. This implicitly
301 turns on B<-ign_eof> as well.
305 shut down the connection when end of file is reached in the input.
306 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
308 =item B<-psk_identity identity>
310 Use the PSK identity B<identity> when using a PSK cipher suite.
314 Use the PSK key B<key> when using a PSK cipher suite. The key is
315 given as a hexadecimal number without leading 0x, for example -psk
318 =item B<-ssl3>, B<-tls1>, B<-tls1_1>, B<-tls1_2>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>
320 These options require or disable the use of the specified SSL or TLS protocols.
321 By default B<s_client> will negotiate the highest mutually supported protocol
323 When a specific TLS version is required, only that version will be offered to
324 and accepted from the server.
326 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
328 These options make B<s_client> use DTLS protocols instead of TLS.
329 With B<-dtls>, B<s_client> will negotiate any supported DTLS protcol version,
330 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
333 =item B<-fallback_scsv>
335 Send TLS_FALLBACK_SCSV in the ClientHello.
339 switch on asynchronous mode. Cryptographic operations will be performed
340 asynchronously. This will only have an effect if an asynchronous capable engine
341 is also used via the B<-engine> option. For test purposes the dummy async engine
342 (dasync) can be used (if available).
344 =item B<-split_send_frag int>
346 The size used to split data for encrypt pipelines. If more data is written in
347 one go than this value then it will be split into multiple pipelines, up to the
348 maximum number of pipelines defined by max_pipelines. This only has an effect if
349 a suitable ciphersuite has been negotiated, an engine that supports pipelining
350 has been loaded, and max_pipelines is greater than 1. See
351 L<SSL_CTX_set_split_send_fragment(3)> for further information.
353 =item B<-max_pipelines int>
355 The maximum number of encrypt/decrypt pipelines to be used. This will only have
356 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
357 engine) and a suiteable ciphersuite has been negotiated. The default value is 1.
358 See L<SSL_CTX_set_max_pipelines(3)> for further information.
360 =item B<-read_buf int>
362 The default read buffer size to be used for connections. This will only have an
363 effect if the buffer size is larger than the size that would otherwise be used
364 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
365 further information).
369 there are several known bug in SSL and TLS implementations. Adding this
370 option enables various workarounds.
374 Enables support for SSL/TLS compression.
375 This option was introduced in OpenSSL 1.1.0.
376 TLS compression is not recommended and is off by default as of
381 Disables support for SSL/TLS compression.
382 TLS compression is not recommended and is off by default as of
387 only provide a brief summary of connection parameters instead of the
388 normal verbose output.
390 =item B<-cipher cipherlist>
392 this allows the cipher list sent by the client to be modified. Although
393 the server determines which cipher suite is used it should take the first
394 supported cipher in the list sent by the client. See the B<ciphers>
395 command for more information.
397 =item B<-starttls protocol>
399 send the protocol-specific message(s) to switch to TLS for communication.
400 B<protocol> is a keyword for the intended protocol. Currently, the only
401 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
404 =item B<-xmpphost hostname>
406 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
407 specifies the host for the "to" attribute of the stream element.
408 If this option is not specified, then the host specified with "-connect"
411 =item B<-tlsextdebug>
413 print out a hex dump of any TLS extensions received from the server.
417 disable RFC4507bis session ticket support.
419 =item B<-sess_out filename>
421 output SSL session to B<filename>
423 =item B<-sess_in sess.pem>
425 load SSL session from B<filename>. The client will attempt to resume a
426 connection from this session.
430 specifying an engine (by its unique B<id> string) will cause B<s_client>
431 to attempt to obtain a functional reference to the specified engine,
432 thus initialising it if needed. The engine will then be set as the default
433 for all available algorithms.
435 =item B<-rand file(s)>
437 a file or files containing random data used to seed the random number
438 generator, or an EGD socket (see L<RAND_egd(3)>).
439 Multiple files can be specified separated by a OS-dependent character.
440 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
443 =item B<-serverinfo types>
445 a list of comma-separated TLS Extension Types (numbers between 0 and
446 65535). Each type will be sent as an empty ClientHello TLS Extension.
447 The server's response (if any) will be encoded and displayed as a PEM
452 sends a certificate status request to the server (OCSP stapling). The server
453 response (if any) is printed out.
455 =item B<-nextprotoneg protocols>
457 enable Next Protocol Negotiation TLS extension and provide a list of
458 comma-separated protocol names that the client should advertise
459 support for. The list should contain most wanted protocols first.
460 Protocol names are printable ASCII strings, for example "http/1.1" or
462 Empty list of protocols is treated specially and will cause the client to
463 advertise support for the TLS extension but disconnect just after
464 receiving ServerHello with a list of server supported protocols.
466 =item B<-noct|requestct|requirect>
468 Use one of these three options to control whether Certificate Transparency (CT)
469 is disabled (-noct), enabled but not enforced (-requestct), or enabled and
470 enforced (-requirect). If CT is enabled, signed certificate timestamps (SCTs)
471 will be requested from the server and invalid SCTs will cause the connection to
472 be aborted. If CT is enforced, at least one valid SCT from a recognised CT log
473 (see B<-ctlogfile>) will be required or the connection will be aborted.
475 Enabling CT also enables OCSP stapling, as this is one possible delivery method
480 A file containing a list of known Certificate Transparency logs. See
481 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
485 =head1 CONNECTED COMMANDS
487 If a connection is established with an SSL server then any data received
488 from the server is displayed and any key presses will be sent to the
489 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
490 have been given), the session will be renegotiated if the line begins with an
491 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
492 connection will be closed down.
496 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
499 openssl s_client -connect servername:443
501 would typically be used (https uses port 443). If the connection succeeds
502 then an HTTP command can be given such as "GET /" to retrieve a web page.
504 If the handshake fails then there are several possible causes, if it is
505 nothing obvious like no client certificate then the B<-bugs>,
506 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
507 in case it is a buggy server. In particular you should play with these
508 options B<before> submitting a bug report to an OpenSSL mailing list.
510 A frequent problem when attempting to get client certificates working
511 is that a web client complains it has no certificates or gives an empty
512 list to choose from. This is normally because the server is not sending
513 the clients certificate authority in its "acceptable CA list" when it
514 requests a certificate. By using B<s_client> the CA list can be viewed
515 and checked. However some servers only request client authentication
516 after a specific URL is requested. To obtain the list in this case it
517 is necessary to use the B<-prexit> option and send an HTTP request
518 for an appropriate page.
520 If a certificate is specified on the command line using the B<-cert>
521 option it will not be used unless the server specifically requests
522 a client certificate. Therefor merely including a client certificate
523 on the command line is no guarantee that the certificate works.
525 If there are problems verifying a server certificate then the
526 B<-showcerts> option can be used to show the whole chain.
528 The B<s_client> utility is a test tool and is designed to continue the
529 handshake after any certificate verification errors. As a result it will
530 accept any certificate chain (trusted or not) sent by the peer. None test
531 applications should B<not> do this as it makes them vulnerable to a MITM
532 attack. This behaviour can be changed by with the B<-verify_return_error>
533 option: any verify errors are then returned aborting the handshake.
537 Because this program has a lot of options and also because some of the
538 techniques used are rather old, the C source of B<s_client> is rather hard to
539 read and not a model of how things should be done.
540 A typical SSL client program would be much simpler.
542 The B<-prexit> option is a bit of a hack. We should really report
543 information whenever a session is renegotiated.
547 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
551 The -no_alt_chains options was first added to OpenSSL 1.1.0.