1S_CLIENT(1) OpenSSL S_CLIENT(1)
2
6 openssl-s_client, s_client - SSL/TLS client program
7
9 openssl s_client [-help] [-connect host:port] [-bind host:port] [-proxy
10 host:port] [-unix path] [-4] [-6] [-servername name] [-noservername]
11 [-verify depth] [-verify_return_error] [-cert filename] [-certform
12 DER|PEM] [-key filename] [-keyform DER|PEM] [-cert_chain filename]
13 [-build_chain] [-xkey] [-xcert] [-xchain] [-xchain_build] [-xcertform
14 PEM|DER] [-xkeyform PEM|DER] [-pass arg] [-CApath directory] [-CAfile
15 filename] [-chainCApath directory] [-chainCAfile filename] [-no-CAfile]
16 [-no-CApath] [-requestCAfile filename] [-dane_tlsa_domain domain]
17 [-dane_tlsa_rrdata rrdata] [-dane_ee_no_namechecks] [-attime timestamp]
18 [-check_ss_sig] [-crl_check] [-crl_check_all] [-explicit_policy]
19 [-extended_crl] [-ignore_critical] [-inhibit_any] [-inhibit_map]
20 [-no_check_time] [-partial_chain] [-policy arg] [-policy_check]
21 [-policy_print] [-purpose purpose] [-suiteB_128] [-suiteB_128_only]
22 [-suiteB_192] [-trusted_first] [-no_alt_chains] [-use_deltas]
23 [-auth_level num] [-nameopt option] [-verify_depth num] [-verify_email
24 email] [-verify_hostname hostname] [-verify_ip ip] [-verify_name name]
25 [-build_chain] [-x509_strict] [-reconnect] [-showcerts] [-debug] [-msg]
26 [-nbio_test] [-state] [-nbio] [-crlf] [-ign_eof] [-no_ign_eof]
27 [-psk_identity identity] [-psk key] [-psk_session file] [-quiet]
28 [-ssl3] [-tls1] [-tls1_1] [-tls1_2] [-tls1_3] [-no_ssl3] [-no_tls1]
29 [-no_tls1_1] [-no_tls1_2] [-no_tls1_3] [-dtls] [-dtls1] [-dtls1_2]
30 [-sctp] [-fallback_scsv] [-async] [-max_send_frag] [-split_send_frag]
31 [-max_pipelines] [-read_buf] [-bugs] [-comp] [-no_comp]
32 [-allow_no_dhe_kex] [-sigalgs sigalglist] [-curves curvelist] [-cipher
33 cipherlist] [-ciphersuites val] [-serverpref] [-starttls protocol]
34 [-xmpphost hostname] [-name hostname] [-engine id] [-tlsextdebug]
35 [-no_ticket] [-sess_out filename] [-sess_in filename] [-rand file...]
36 [-writerand file] [-serverinfo types] [-status] [-alpn protocols]
37 [-nextprotoneg protocols] [-ct] [-noct] [-ctlogfile] [-keylogfile file]
38 [-early_data file] [-enable_pha] [target]
39
41 The s_client command implements a generic SSL/TLS client which connects
42 to a remote host using SSL/TLS. It is a very useful diagnostic tool for
43 SSL servers.
44
46 In addition to the options below the s_client utility also supports the
47 common and client only options documented in the in the "Supported
48 Command Line Commands" section of the SSL_CONF_cmd(3) manual page.
49 -help
51 Print out a usage message.
52 -connect host:port
54 This specifies the host and optional port to connect to. It is
55 possible to select the host and port using the optional target
56 positional argument instead. If neither this nor the target
57 positional argument are specified then an attempt is made to
58 connect to the local host on port 4433.
59 -bind host:port]
61 This specifies the host address and or port to bind as the source
62 for the connection. For Unix-domain sockets the port is ignored
63 and the host is used as the source socket address.
64 -proxy host:port
66 When used with the -connect flag, the program uses the host and
67 port specified with this flag and issues an HTTP CONNECT command to
68 connect to the desired server.
69 -unix path
71 Connect over the specified Unix-domain socket.
72 -4 Use IPv4 only.
74 -6 Use IPv6 only.
76 -servername name
78 Set the TLS SNI (Server Name Indication) extension in the
79 ClientHello message to the given value. If both this option and the
80 -noservername are not given, the TLS SNI extension is still set to
81 the hostname provided to the -connect option, or "localhost" if
82 -connect has not been supplied. This is default since OpenSSL
83 1.1.1.
84 Even though SNI name should normally be a DNS name and not an IP
86 address, this option will not make the distinction when parsing
87 -connect and will send IP address if one passed.
88 -noservername
90 Suppresses sending of the SNI (Server Name Indication) extension in
91 the ClientHello message. Cannot be used in conjunction with the
92 -servername or <-dane_tlsa_domain> options.
93 -cert certname
95 The certificate to use, if one is requested by the server. The
96 default is not to use a certificate.
97 -certform format
99 The certificate format to use: DER or PEM. PEM is the default.
100 -key keyfile
102 The private key to use. If not specified then the certificate file
103 will be used.
104 -keyform format
106 The private format to use: DER or PEM. PEM is the default.
107 -cert_chain
109 A file containing trusted certificates to use when attempting to
110 build the client/server certificate chain related to the
111 certificate specified via the -cert option.
112 -build_chain
114 Specify whether the application should build the certificate chain
115 to be provided to the server.
116 -xkey infile, -xcert infile, -xchain
118 Specify an extra certificate, private key and certificate chain.
119 These behave in the same manner as the -cert, -key and -cert_chain
120 options. When specified, the callback returning the first valid
121 chain will be in use by the client.
122 -xchain_build
124 Specify whether the application should build the certificate chain
125 to be provided to the server for the extra certificates provided
126 via -xkey infile, -xcert infile, -xchain options.
127 -xcertform PEM|DER, -xkeyform PEM|DER
129 Extra certificate and private key format respectively.
130 -pass arg
132 the private key password source. For more information about the
133 format of arg see the PASS PHRASE ARGUMENTS section in openssl(1).
134 -verify depth
136 The verify depth to use. This specifies the maximum length of the
137 server certificate chain and turns on server certificate
138 verification. Currently the verify operation continues after
139 errors so all the problems with a certificate chain can be seen. As
140 a side effect the connection will never fail due to a server
141 certificate verify failure.
142 -verify_return_error
144 Return verification errors instead of continuing. This will
145 typically abort the handshake with a fatal error.
146 -nameopt option
148 Option which determines how the subject or issuer names are
149 displayed. The option argument can be a single option or multiple
150 options separated by commas. Alternatively the -nameopt switch may
151 be used more than once to set multiple options. See the x509(1)
152 manual page for details.
153 -CApath directory
155 The directory to use for server certificate verification. This
156 directory must be in "hash format", see verify(1) for more
157 information. These are also used when building the client
158 certificate chain.
159 -CAfile file
161 A file containing trusted certificates to use during server
162 authentication and to use when attempting to build the client
163 certificate chain.
164 -chainCApath directory
166 The directory to use for building the chain provided to the server.
167 This directory must be in "hash format", see verify(1) for more
168 information.
169 -chainCAfile file
171 A file containing trusted certificates to use when attempting to
172 build the client certificate chain.
173 -no-CAfile
175 Do not load the trusted CA certificates from the default file
176 location
177 -no-CApath
179 Do not load the trusted CA certificates from the default directory
180 location
181 -requestCAfile file
183 A file containing a list of certificates whose subject names will
184 be sent to the server in the certificate_authorities extension.
185 Only supported for TLS 1.3
186 -dane_tlsa_domain domain
188 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
189 TLSA base domain which becomes the default SNI hint and the primary
190 reference identifier for hostname checks. This must be used in
191 combination with at least one instance of the -dane_tlsa_rrdata
192 option below.
193 When DANE authentication succeeds, the diagnostic output will
195 include the lowest (closest to 0) depth at which a TLSA record
196 authenticated a chain certificate. When that TLSA record is a "2 1
197 0" trust anchor public key that signed (rather than matched) the
198 top-most certificate of the chain, the result is reported as "TA
199 public key verified". Otherwise, either the TLSA record "matched
200 TA certificate" at a positive depth or else "matched EE
201 certificate" at depth 0.
202 -dane_tlsa_rrdata rrdata
204 Use one or more times to specify the RRDATA fields of the DANE TLSA
205 RRset associated with the target service. The rrdata value is
206 specied in "presentation form", that is four whitespace separated
207 fields that specify the usage, selector, matching type and
208 associated data, with the last of these encoded in hexadecimal.
209 Optional whitespace is ignored in the associated data field. For
210 example:
211 $ openssl s_client -brief -starttls smtp \
213 -connect smtp.example.com:25 \
214 -dane_tlsa_domain smtp.example.com \
215 -dane_tlsa_rrdata "2 1 1
216 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
217 -dane_tlsa_rrdata "2 1 1
218 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
219 ...
220 Verification: OK
221 Verified peername: smtp.example.com
222 DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1
223 ...
224 -dane_ee_no_namechecks
226 This disables server name checks when authenticating via DANE-EE(3)
227 TLSA records. For some applications, primarily web browsers, it is
228 not safe to disable name checks due to "unknown key share" attacks,
229 in which a malicious server can convince a client that a connection
230 to a victim server is instead a secure connection to the malicious
231 server. The malicious server may then be able to violate cross-
232 origin scripting restrictions. Thus, despite the text of RFC7671,
233 name checks are by default enabled for DANE-EE(3) TLSA records, and
234 can be disabled in applications where it is safe to do so. In
235 particular, SMTP and XMPP clients should set this option as SRV and
236 MX records already make it possible for a remote domain to redirect
237 client connections to any server of its choice, and in any case
238 SMTP and XMPP clients do not execute scripts downloaded from remote
239 servers.
240 -attime, -check_ss_sig, -crl_check, -crl_check_all, -explicit_policy,
242 -extended_crl, -ignore_critical, -inhibit_any, -inhibit_map,
243 -no_alt_chains, -no_check_time, -partial_chain, -policy, -policy_check,
244 -policy_print, -purpose, -suiteB_128, -suiteB_128_only, -suiteB_192,
245 -trusted_first, -use_deltas, -auth_level, -verify_depth, -verify_email,
246 -verify_hostname, -verify_ip, -verify_name, -x509_strict
247 Set various certificate chain validation options. See the verify(1)
248 manual page for details.
249 -reconnect
251 Reconnects to the same server 5 times using the same session ID,
252 this can be used as a test that session caching is working.
253 -showcerts
255 Displays the server certificate list as sent by the server: it only
256 consists of certificates the server has sent (in the order the
257 server has sent them). It is not a verified chain.
258 -prexit
260 Print session information when the program exits. This will always
261 attempt to print out information even if the connection fails.
262 Normally information will only be printed out once if the
263 connection succeeds. This option is useful because the cipher in
264 use may be renegotiated or the connection may fail because a client
265 certificate is required or is requested only after an attempt is
266 made to access a certain URL. Note: the output produced by this
267 option is not always accurate because a connection might never have
268 been established.
269 -state
271 Prints out the SSL session states.
272 -debug
274 Print extensive debugging information including a hex dump of all
275 traffic.
276 -msg
278 Show all protocol messages with hex dump.
279 -trace
281 Show verbose trace output of protocol messages. OpenSSL needs to be
282 compiled with enable-ssl-trace for this option to work.
283 -msgfile
285 File to send output of -msg or -trace to, default standard output.
286 -nbio_test
288 Tests non-blocking I/O
289 -nbio
291 Turns on non-blocking I/O
292 -crlf
294 This option translated a line feed from the terminal into CR+LF as
295 required by some servers.
296 -ign_eof
298 Inhibit shutting down the connection when end of file is reached in
299 the input.
300 -quiet
302 Inhibit printing of session and certificate information. This
303 implicitly turns on -ign_eof as well.
304 -no_ign_eof
306 Shut down the connection when end of file is reached in the input.
307 Can be used to override the implicit -ign_eof after -quiet.
308 -psk_identity identity
310 Use the PSK identity identity when using a PSK cipher suite. The
311 default value is "Client_identity" (without the quotes).
312 -psk key
314 Use the PSK key key when using a PSK cipher suite. The key is given
315 as a hexadecimal number without leading 0x, for example -psk
316 1a2b3c4d. This option must be provided in order to use a PSK
317 cipher.
318 -psk_session file
320 Use the pem encoded SSL_SESSION data stored in file as the basis of
321 a PSK. Note that this will only work if TLSv1.3 is negotiated.
322 -ssl3, -tls1, -tls1_1, -tls1_2, -tls1_3, -no_ssl3, -no_tls1,
324 -no_tls1_1, -no_tls1_2, -no_tls1_3
325 These options require or disable the use of the specified SSL or
326 TLS protocols. By default s_client will negotiate the highest
327 mutually supported protocol version. When a specific TLS version
328 is required, only that version will be offered to and accepted from
329 the server. Note that not all protocols and flags may be
330 available, depending on how OpenSSL was built.
331 -dtls, -dtls1, -dtls1_2
333 These options make s_client use DTLS protocols instead of TLS.
334 With -dtls, s_client will negotiate any supported DTLS protocol
335 version, whilst -dtls1 and -dtls1_2 will only support DTLS1.0 and
336 DTLS1.2 respectively.
337 -sctp
339 Use SCTP for the transport protocol instead of UDP in DTLS. Must be
340 used in conjunction with -dtls, -dtls1 or -dtls1_2. This option is
341 only available where OpenSSL has support for SCTP enabled.
342 -fallback_scsv
344 Send TLS_FALLBACK_SCSV in the ClientHello.
345 -async
347 Switch on asynchronous mode. Cryptographic operations will be
348 performed asynchronously. This will only have an effect if an
349 asynchronous capable engine is also used via the -engine option.
350 For test purposes the dummy async engine (dasync) can be used (if
351 available).
352 -max_send_frag int
354 The maximum size of data fragment to send. See
355 SSL_CTX_set_max_send_fragment(3) for further information.
356 -split_send_frag int
358 The size used to split data for encrypt pipelines. If more data is
359 written in one go than this value then it will be split into
360 multiple pipelines, up to the maximum number of pipelines defined
361 by max_pipelines. This only has an effect if a suitable cipher
362 suite has been negotiated, an engine that supports pipelining has
363 been loaded, and max_pipelines is greater than 1. See
364 SSL_CTX_set_split_send_fragment(3) for further information.
365 -max_pipelines int
367 The maximum number of encrypt/decrypt pipelines to be used. This
368 will only have an effect if an engine has been loaded that supports
369 pipelining (e.g. the dasync engine) and a suitable cipher suite has
370 been negotiated. The default value is 1. See
371 SSL_CTX_set_max_pipelines(3) for further information.
372 -read_buf int
374 The default read buffer size to be used for connections. This will
375 only have an effect if the buffer size is larger than the size that
376 would otherwise be used and pipelining is in use (see
377 SSL_CTX_set_default_read_buffer_len(3) for further information).
378 -bugs
380 There are several known bug in SSL and TLS implementations. Adding
381 this option enables various workarounds.
382 -comp
384 Enables support for SSL/TLS compression. This option was
385 introduced in OpenSSL 1.1.0. TLS compression is not recommended
386 and is off by default as of OpenSSL 1.1.0.
387 -no_comp
389 Disables support for SSL/TLS compression. TLS compression is not
390 recommended and is off by default as of OpenSSL 1.1.0.
391 -brief
393 Only provide a brief summary of connection parameters instead of
394 the normal verbose output.
395 -sigalgs sigalglist
397 Specifies the list of signature algorithms that are sent by the
398 client. The server selects one entry in the list based on its
399 preferences. For example strings, see SSL_CTX_set1_sigalgs(3)
400 -curves curvelist
402 Specifies the list of supported curves to be sent by the client.
403 The curve is ultimately selected by the server. For a list of all
404 curves, use:
405 $ openssl ecparam -list_curves
407 -cipher cipherlist
409 This allows the TLSv1.2 and below cipher list sent by the client to
410 be modified. This list will be combined with any TLSv1.3
411 ciphersuites that have been configured. Although the server
412 determines which ciphersuite is used it should take the first
413 supported cipher in the list sent by the client. See the ciphers
414 command for more information.
415 -ciphersuites val
417 This allows the TLSv1.3 ciphersuites sent by the client to be
418 modified. This list will be combined with any TLSv1.2 and below
419 ciphersuites that have been configured. Although the server
420 determines which cipher suite is used it should take the first
421 supported cipher in the list sent by the client. See the ciphers
422 command for more information. The format for this list is a simple
423 colon (":") separated list of TLSv1.3 ciphersuite names.
424 -starttls protocol
426 Send the protocol-specific message(s) to switch to TLS for
427 communication. protocol is a keyword for the intended protocol.
428 Currently, the only supported keywords are "smtp", "pop3", "imap",
429 "ftp", "xmpp", "xmpp-server", "irc", "postgres", "mysql", "lmtp",
430 "nntp", "sieve" and "ldap".
431 -xmpphost hostname
433 This option, when used with "-starttls xmpp" or "-starttls xmpp-
434 server", specifies the host for the "to" attribute of the stream
435 element. If this option is not specified, then the host specified
436 with "-connect" will be used.
437 This option is an alias of the -name option for "xmpp" and "xmpp-
439 server".
440 -name hostname
442 This option is used to specify hostname information for various
443 protocols used with -starttls option. Currently only "xmpp", "xmpp-
444 server", "smtp" and "lmtp" can utilize this -name option.
445 If this option is used with "-starttls xmpp" or "-starttls xmpp-
447 server", if specifies the host for the "to" attribute of the stream
448 element. If this option is not specified, then the host specified
449 with "-connect" will be used.
450 If this option is used with "-starttls lmtp" or "-starttls smtp",
452 it specifies the name to use in the "LMTP LHLO" or "SMTP EHLO"
453 message, respectively. If this option is not specified, then
454 "mail.example.com" will be used.
455 -tlsextdebug
457 Print out a hex dump of any TLS extensions received from the
458 server.
459 -no_ticket
461 Disable RFC4507bis session ticket support.
462 -sess_out filename
464 Output SSL session to filename.
465 -sess_in sess.pem
467 Load SSL session from filename. The client will attempt to resume a
468 connection from this session.
469 -engine id
471 Specifying an engine (by its unique id string) will cause s_client
472 to attempt to obtain a functional reference to the specified
473 engine, thus initialising it if needed. The engine will then be set
474 as the default for all available algorithms.
475 -rand file...
477 A file or files containing random data used to seed the random
478 number generator. Multiple files can be specified separated by an
479 OS-dependent character. The separator is ; for MS-Windows, , for
480 OpenVMS, and : for all others.
481 [-writerand file]
483 Writes random data to the specified file upon exit. This can be
484 used with a subsequent -rand flag.
485 -serverinfo types
487 A list of comma-separated TLS Extension Types (numbers between 0
488 and 65535). Each type will be sent as an empty ClientHello TLS
489 Extension. The server's response (if any) will be encoded and
490 displayed as a PEM file.
491 -status
493 Sends a certificate status request to the server (OCSP stapling).
494 The server response (if any) is printed out.
495 -alpn protocols, -nextprotoneg protocols
497 These flags enable the Enable the Application-Layer Protocol
498 Negotiation or Next Protocol Negotiation (NPN) extension,
499 respectively. ALPN is the IETF standard and replaces NPN. The
500 protocols list is a comma-separated list of protocol names that the
501 client should advertise support for. The list should contain the
502 most desirable protocols first. Protocol names are printable ASCII
503 strings, for example "http/1.1" or "spdy/3". An empty list of
504 protocols is treated specially and will cause the client to
505 advertise support for the TLS extension but disconnect just after
506 receiving ServerHello with a list of server supported protocols.
507 The flag -nextprotoneg cannot be specified if -tls1_3 is used.
508 -ct, -noct
510 Use one of these two options to control whether Certificate
511 Transparency (CT) is enabled (-ct) or disabled (-noct). If CT is
512 enabled, signed certificate timestamps (SCTs) will be requested
513 from the server and reported at handshake completion.
514 Enabling CT also enables OCSP stapling, as this is one possible
516 delivery method for SCTs.
517 -ctlogfile
519 A file containing a list of known Certificate Transparency logs.
520 See SSL_CTX_set_ctlog_list_file(3) for the expected file format.
521 -keylogfile file
523 Appends TLS secrets to the specified keylog file such that external
524 programs (like Wireshark) can decrypt TLS connections.
525 -early_data file
527 Reads the contents of the specified file and attempts to send it as
528 early data to the server. This will only work with resumed sessions
529 that support early data and when the server accepts the early data.
530 -enable_pha
532 For TLSv1.3 only, send the Post-Handshake Authentication extension.
533 This will happen whether or not a certificate has been provided via
534 -cert.
535 [target]
537 Rather than providing -connect, the target hostname and optional
538 port may be provided as a single positional argument after all
539 options. If neither this nor -connect are provided, falls back to
540 attempting to connect to localhost on port 4433.
541
543 If a connection is established with an SSL server then any data
544 received from the server is displayed and any key presses will be sent
545 to the server. If end of file is reached then the connection will be
546 closed down. When used interactively (which means neither -quiet nor
547 -ign_eof have been given), then certain commands are also recognized
548 which perform special operations. These commands are a letter which
549 must appear at the start of a line. They are listed below.
550 Q End the current SSL connection and exit.
552 R Renegotiate the SSL session (TLSv1.2 and below only).
554 B Send a heartbeat message to the server (DTLS only)
556 k Send a key update message to the server (TLSv1.3 only)
558 K Send a key update message to the server and request one back
560 (TLSv1.3 only)
561
563 s_client can be used to debug SSL servers. To connect to an SSL HTTP
564 server the command:
565 openssl s_client -connect servername:443
567 would typically be used (https uses port 443). If the connection
569 succeeds then an HTTP command can be given such as "GET /" to retrieve
570 a web page.
571 If the handshake fails then there are several possible causes, if it is
573 nothing obvious like no client certificate then the -bugs, -ssl3,
574 -tls1, -no_ssl3, -no_tls1 options can be tried in case it is a buggy
575 server. In particular you should play with these options before
576 submitting a bug report to an OpenSSL mailing list.
577 A frequent problem when attempting to get client certificates working
579 is that a web client complains it has no certificates or gives an empty
580 list to choose from. This is normally because the server is not sending
581 the clients certificate authority in its "acceptable CA list" when it
582 requests a certificate. By using s_client the CA list can be viewed and
583 checked. However some servers only request client authentication after
584 a specific URL is requested. To obtain the list in this case it is
585 necessary to use the -prexit option and send an HTTP request for an
586 appropriate page.
587 If a certificate is specified on the command line using the -cert
589 option it will not be used unless the server specifically requests a
590 client certificate. Therefor merely including a client certificate on
591 the command line is no guarantee that the certificate works.
592 If there are problems verifying a server certificate then the
594 -showcerts option can be used to show all the certificates sent by the
595 server.
596 The s_client utility is a test tool and is designed to continue the
598 handshake after any certificate verification errors. As a result it
599 will accept any certificate chain (trusted or not) sent by the peer.
600 None test applications should not do this as it makes them vulnerable
601 to a MITM attack. This behaviour can be changed by with the
602 -verify_return_error option: any verify errors are then returned
603 aborting the handshake.
604 The -bind option may be useful if the server or a firewall requires
606 connections to come from some particular address and or port.
607
609 Because this program has a lot of options and also because some of the
610 techniques used are rather old, the C source of s_client is rather hard
611 to read and not a model of how things should be done. A typical SSL
612 client program would be much simpler.
613 The -prexit option is a bit of a hack. We should really report
615 information whenever a session is renegotiated.
616
618 SSL_CONF_cmd(3), sess_id(1), s_server(1), ciphers(1),
619 SSL_CTX_set_max_send_fragment(3), SSL_CTX_set_split_send_fragment(3),
620 SSL_CTX_set_max_pipelines(3)
621
623 The -no_alt_chains option was first added to OpenSSL 1.1.0. The -name
624 option was added in OpenSSL 1.1.1.
625
627 Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
628 Licensed under the OpenSSL license (the "License"). You may not use
630 this file except in compliance with the License. You can obtain a copy
631 in the file LICENSE in the source distribution or at
632 <https://www.openssl.org/source/license.html>.
6331.1.1 2018-09-11 S_CLIENT(1)