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>]
49 [B<-verify_depth num>]
50 [B<-verify_email email>]
51 [B<-verify_hostname hostname>]
53 [B<-verify_name name>]
85 [B<-cipher cipherlist>]
87 [B<-starttls protocol>]
88 [B<-xmpphost hostname>]
92 [B<-sess_out filename>]
93 [B<-sess_in filename>]
95 [B<-serverinfo types>]
97 [B<-nextprotoneg protocols>]
98 [B<-noct|requestct|requirect>]
103 The B<s_client> command implements a generic SSL/TLS client which connects
104 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
109 In addition to the options below the B<s_client> utility also supports the
110 common and client only options documented in the
111 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
118 Print out a usage message.
120 =item B<-connect host:port>
122 This specifies the host and optional port to connect to. If not specified
123 then an attempt is made to connect to the local host on port 4433.
125 =item B<-proxy host:port>
127 When used with the B<-connect> flag, the program uses the host and port
128 specified with this flag and issues an HTTP CONNECT command to connect
129 to the desired server.
131 =item B<-servername name>
133 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
135 =item B<-cert certname>
137 The certificate to use, if one is requested by the server. The default is
138 not to use a certificate.
140 =item B<-certform format>
142 The certificate format to use: DER or PEM. PEM is the default.
144 =item B<-key keyfile>
146 The private key to use. If not specified then the certificate file will
149 =item B<-keyform format>
151 The private format to use: DER or PEM. PEM is the default.
155 the private key password source. For more information about the format of B<arg>
156 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
158 =item B<-verify depth>
160 The verify depth to use. This specifies the maximum length of the
161 server certificate chain and turns on server certificate verification.
162 Currently the verify operation continues after errors so all the problems
163 with a certificate chain can be seen. As a side effect the connection
164 will never fail due to a server certificate verify failure.
166 =item B<-verify_return_error>
168 Return verification errors instead of continuing. This will typically
169 abort the handshake with a fatal error.
171 =item B<-CApath directory>
173 The directory to use for server certificate verification. This directory
174 must be in "hash format", see B<verify> for more information. These are
175 also used when building the client certificate chain.
177 =item B<-CAfile file>
179 A file containing trusted certificates to use during server authentication
180 and to use when attempting to build the client certificate chain.
184 Do not load the trusted CA certificates from the default file location
188 Do not load the trusted CA certificates from the default directory location
190 =item B<-dane_tlsa_domain domain>
192 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
193 TLSA base domain which becomes the default SNI hint and the primary
194 reference identifier for hostname checks. This must be used in
195 combination with at least one instance of the B<-dane_tlsa_rrdata>
198 When DANE authentication succeeds, the diagnostic output will include
199 the lowest (closest to 0) depth at which a TLSA record authenticated
200 a chain certificate. When that TLSA record is a "2 1 0" trust
201 anchor public key that signed (rather than matched) the top-most
202 certificate of the chain, the result is reported as "TA public key
203 verified". Otherwise, either the TLSA record "matched TA certificate"
204 at a positive depth or else "matched EE certificate" at depth 0.
206 =item B<-dane_tlsa_rrdata rrdata>
208 Use one or more times to specify the RRDATA fields of the DANE TLSA
209 RRset associated with the target service. The B<rrdata> value is
210 specied in "presentation form", that is four whitespace separated
211 fields that specify the usage, selector, matching type and associated
212 data, with the last of these encoded in hexadecimal. Optional
213 whitespace is ignored in the associated data field. For example:
215 $ openssl s_client -brief -starttls smtp \
216 -connect smtp.example.com:25 \
217 -dane_tlsa_domain smtp.example.com \
218 -dane_tlsa_rrdata "2 1 1
219 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
220 -dane_tlsa_rrdata "2 1 1
221 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
224 Verified peername: smtp.example.com
225 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
228 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
229 B<-explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
230 B<-inhibit_map>, B<-no_alt_chains>, B<-partial_chain>, B<-policy>,
231 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
232 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-use_deltas>,
233 B<-auth_level>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
234 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
236 Set various certificate chain validation options. See the
237 L<verify(1)> manual page for details.
241 reconnects to the same server 5 times using the same session ID, this can
242 be used as a test that session caching is working.
246 display the whole server certificate chain: normally only the server
247 certificate itself is displayed.
251 print session information when the program exits. This will always attempt
252 to print out information even if the connection fails. Normally information
253 will only be printed out once if the connection succeeds. This option is useful
254 because the cipher in use may be renegotiated or the connection may fail
255 because a client certificate is required or is requested only after an
256 attempt is made to access a certain URL. Note: the output produced by this
257 option is not always accurate because a connection might never have been
262 prints out the SSL session states.
266 print extensive debugging information including a hex dump of all traffic.
270 show all protocol messages with hex dump.
274 show verbose trace output of protocol messages. OpenSSL needs to be compiled
275 with B<enable-ssl-trace> for this option to work.
279 file to send output of B<-msg> or B<-trace> to, default standard output.
283 tests non-blocking I/O
287 turns on non-blocking I/O
291 this option translated a line feed from the terminal into CR+LF as required
296 inhibit shutting down the connection when end of file is reached in the
301 inhibit printing of session and certificate information. This implicitly
302 turns on B<-ign_eof> as well.
306 shut down the connection when end of file is reached in the input.
307 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
309 =item B<-psk_identity identity>
311 Use the PSK identity B<identity> when using a PSK cipher suite.
315 Use the PSK key B<key> when using a PSK cipher suite. The key is
316 given as a hexadecimal number without leading 0x, for example -psk
319 =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>
321 These options require or disable the use of the specified SSL or TLS protocols.
322 By default B<s_client> will negotiate the highest mutually supported protocol
324 When a specific TLS version is required, only that version will be offered to
325 and accepted from the server.
327 =item B<-dtls>, B<-dtls1>, B<-dtls1_2>
329 These options make B<s_client> use DTLS protocols instead of TLS.
330 With B<-dtls>, B<s_client> will negotiate any supported DTLS protcol version,
331 whilst B<-dtls1> and B<-dtls1_2> will only support DTLS1.0 and DTLS1.2
334 =item B<-fallback_scsv>
336 Send TLS_FALLBACK_SCSV in the ClientHello.
340 switch on asynchronous mode. Cryptographic operations will be performed
341 asynchronously. This will only have an effect if an asynchronous capable engine
342 is also used via the B<-engine> option. For test purposes the dummy async engine
343 (dasync) can be used (if available).
345 =item B<-split_send_frag int>
347 The size used to split data for encrypt pipelines. If more data is written in
348 one go than this value then it will be split into multiple pipelines, up to the
349 maximum number of pipelines defined by max_pipelines. This only has an effect if
350 a suitable ciphersuite has been negotiated, an engine that supports pipelining
351 has been loaded, and max_pipelines is greater than 1. See
352 L<SSL_CTX_set_split_send_fragment(3)> for further information.
354 =item B<-max_pipelines int>
356 The maximum number of encrypt/decrypt pipelines to be used. This will only have
357 an effect if an engine has been loaded that supports pipelining (e.g. the dasync
358 engine) and a suiteable ciphersuite has been negotiated. The default value is 1.
359 See L<SSL_CTX_set_max_pipelines(3)> for further information.
361 =item B<-read_buf int>
363 The default read buffer size to be used for connections. This will only have an
364 effect if the buffer size is larger than the size that would otherwise be used
365 and pipelining is in use (see L<SSL_CTX_set_default_read_buffer_len(3)> for
366 further information).
370 there are several known bug in SSL and TLS implementations. Adding this
371 option enables various workarounds.
375 Enables support for SSL/TLS compression.
376 This option was introduced in OpenSSL 1.1.0.
377 TLS compression is not recommended and is off by default as of
382 Disables support for SSL/TLS compression.
383 TLS compression is not recommended and is off by default as of
388 only provide a brief summary of connection parameters instead of the
389 normal verbose output.
391 =item B<-cipher cipherlist>
393 this allows the cipher list sent by the client to be modified. Although
394 the server determines which cipher suite is used it should take the first
395 supported cipher in the list sent by the client. See the B<ciphers>
396 command for more information.
398 =item B<-starttls protocol>
400 send the protocol-specific message(s) to switch to TLS for communication.
401 B<protocol> is a keyword for the intended protocol. Currently, the only
402 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
405 =item B<-xmpphost hostname>
407 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
408 specifies the host for the "to" attribute of the stream element.
409 If this option is not specified, then the host specified with "-connect"
412 =item B<-tlsextdebug>
414 print out a hex dump of any TLS extensions received from the server.
418 disable RFC4507bis session ticket support.
420 =item B<-sess_out filename>
422 output SSL session to B<filename>
424 =item B<-sess_in sess.pem>
426 load SSL session from B<filename>. The client will attempt to resume a
427 connection from this session.
431 specifying an engine (by its unique B<id> string) will cause B<s_client>
432 to attempt to obtain a functional reference to the specified engine,
433 thus initialising it if needed. The engine will then be set as the default
434 for all available algorithms.
436 =item B<-rand file(s)>
438 a file or files containing random data used to seed the random number
439 generator, or an EGD socket (see L<RAND_egd(3)>).
440 Multiple files can be specified separated by an OS-dependent character.
441 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
444 =item B<-serverinfo types>
446 a list of comma-separated TLS Extension Types (numbers between 0 and
447 65535). Each type will be sent as an empty ClientHello TLS Extension.
448 The server's response (if any) will be encoded and displayed as a PEM
453 sends a certificate status request to the server (OCSP stapling). The server
454 response (if any) is printed out.
456 =item B<-nextprotoneg protocols>
458 enable Next Protocol Negotiation TLS extension and provide a list of
459 comma-separated protocol names that the client should advertise
460 support for. The list should contain most wanted protocols first.
461 Protocol names are printable ASCII strings, for example "http/1.1" or
463 Empty list of protocols is treated specially and will cause the client to
464 advertise support for the TLS extension but disconnect just after
465 receiving ServerHello with a list of server supported protocols.
467 =item B<-noct|requestct|requirect>
469 Use one of these three options to control whether Certificate Transparency (CT)
470 is disabled (-noct), enabled but not enforced (-requestct), or enabled and
471 enforced (-requirect). If CT is enabled, signed certificate timestamps (SCTs)
472 will be requested from the server and invalid SCTs will cause the connection to
473 be aborted. If CT is enforced, at least one valid SCT from a recognised CT log
474 (see B<-ctlogfile>) will be required or the connection will be aborted.
476 Enabling CT also enables OCSP stapling, as this is one possible delivery method
481 A file containing a list of known Certificate Transparency logs. See
482 L<SSL_CTX_set_ctlog_list_file(3)> for the expected file format.
486 =head1 CONNECTED COMMANDS
488 If a connection is established with an SSL server then any data received
489 from the server is displayed and any key presses will be sent to the
490 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
491 have been given), the session will be renegotiated if the line begins with an
492 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
493 connection will be closed down.
497 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
500 openssl s_client -connect servername:443
502 would typically be used (https uses port 443). If the connection succeeds
503 then an HTTP command can be given such as "GET /" to retrieve a web page.
505 If the handshake fails then there are several possible causes, if it is
506 nothing obvious like no client certificate then the B<-bugs>,
507 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
508 in case it is a buggy server. In particular you should play with these
509 options B<before> submitting a bug report to an OpenSSL mailing list.
511 A frequent problem when attempting to get client certificates working
512 is that a web client complains it has no certificates or gives an empty
513 list to choose from. This is normally because the server is not sending
514 the clients certificate authority in its "acceptable CA list" when it
515 requests a certificate. By using B<s_client> the CA list can be viewed
516 and checked. However some servers only request client authentication
517 after a specific URL is requested. To obtain the list in this case it
518 is necessary to use the B<-prexit> option and send an HTTP request
519 for an appropriate page.
521 If a certificate is specified on the command line using the B<-cert>
522 option it will not be used unless the server specifically requests
523 a client certificate. Therefor merely including a client certificate
524 on the command line is no guarantee that the certificate works.
526 If there are problems verifying a server certificate then the
527 B<-showcerts> option can be used to show the whole chain.
529 The B<s_client> utility is a test tool and is designed to continue the
530 handshake after any certificate verification errors. As a result it will
531 accept any certificate chain (trusted or not) sent by the peer. None test
532 applications should B<not> do this as it makes them vulnerable to a MITM
533 attack. This behaviour can be changed by with the B<-verify_return_error>
534 option: any verify errors are then returned aborting the handshake.
538 Because this program has a lot of options and also because some of the
539 techniques used are rather old, the C source of B<s_client> is rather hard to
540 read and not a model of how things should be done.
541 A typical SSL client program would be much simpler.
543 The B<-prexit> option is a bit of a hack. We should really report
544 information whenever a session is renegotiated.
548 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
552 The -no_alt_chains options was first added to OpenSSL 1.1.0.