doc/apps/s_client.pod

   1
   2 =pod
   3
   4 =head1 NAME
   5
   6 s_client - SSL/TLS client program
   7
   8 =head1 SYNOPSIS
   9
  10 B<openssl> B<s_client>
  11 [B<-help>]
  12 [B<-connect host:port>]
  13 [B<-proxy host:port>]
  14 [B<-servername name>]
  15 [B<-verify depth>]
  16 [B<-verify_return_error>]
  17 [B<-cert filename>]
  18 [B<-certform DER|PEM>]
  19 [B<-key filename>]
  20 [B<-keyform DER|PEM>]
  21 [B<-pass arg>]
  22 [B<-CApath directory>]
  23 [B<-CAfile filename>]
  24 [B<-no-CAfile>]
  25 [B<-no-CApath>]
  26 [B<-dane_tlsa_domain domain>]
  27 [B<-dane_tlsa_rrdata rrdata>]
  28 [B<-attime timestamp>]
  29 [B<-check_ss_sig>]
  30 [B<-crl_check>]
  31 [B<-crl_check_all>]
  32 [B<-explicit_policy>]
  33 [B<-extended_crl>]
  34 [B<-ignore_critical>]
  35 [B<-inhibit_any>]
  36 [B<-inhibit_map>]
  37 [B<-issuer_checks>]
  38 [B<-partial_chain>]
  39 [B<-policy arg>]
  40 [B<-policy_check>]
  41 [B<-policy_print>]
  42 [B<-purpose purpose>]
  43 [B<-suiteB_128>]
  44 [B<-suiteB_128_only>]
  45 [B<-suiteB_192>]
  46 [B<-trusted_first>]
  47 [B<-no_alt_chains>]
  48 [B<-use_deltas>]
  49 [B<-verify_depth num>]
  50 [B<-verify_email email>]
  51 [B<-verify_hostname hostname>]
  52 [B<-verify_ip ip>]
  53 [B<-verify_name name>]
  54 [B<-x509_strict>]
  55 [B<-reconnect>]
  56 [B<-showcerts>]
  57 [B<-debug>]
  58 [B<-msg>]
  59 [B<-nbio_test>]
  60 [B<-state>]
  61 [B<-nbio>]
  62 [B<-crlf>]
  63 [B<-ign_eof>]
  64 [B<-no_ign_eof>]
  65 [B<-quiet>]
  66 [B<-ssl3>]
  67 [B<-tls1>]
  68 [B<-no_ssl3>]
  69 [B<-no_tls1>]
  70 [B<-no_tls1_1>]
  71 [B<-no_tls1_2>]
  72 [B<-fallback_scsv>]
  73 [B<-async>]
  74 [B<-bugs>]
  75 [B<-comp>]
  76 [B<-no_comp>]
  77 [B<-cipher cipherlist>]
  78 [B<-serverpref>]
  79 [B<-starttls protocol>]
  80 [B<-xmpphost hostname>]
  81 [B<-engine id>]
  82 [B<-tlsextdebug>]
  83 [B<-no_ticket>]
  84 [B<-sess_out filename>]
  85 [B<-sess_in filename>]
  86 [B<-rand file(s)>]
  87 [B<-serverinfo types>]
  88 [B<-status>]
  89 [B<-nextprotoneg protocols>]
  90
  91 =head1 DESCRIPTION
  92
  93 The B<s_client> command implements a generic SSL/TLS client which connects
  94 to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for
  95 SSL servers.
  96
  97 =head1 OPTIONS
  98
  99 In addition to the options below the B<s_client> utility also supports the
 100 common and client only options documented in the
 101 in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>
 102 manual page.
 103
 104 =over 4
 105
 106 =item B<-help>
 107
 108 Print out a usage message.
 109
 110 =item B<-connect host:port>
 111
 112 This specifies the host and optional port to connect to. If not specified
 113 then an attempt is made to connect to the local host on port 4433.
 114
 115 =item B<-proxy host:port>
 116
 117 When used with the B<-connect> flag, the program uses the host and port
 118 specified with this flag and issues an HTTP CONNECT command to connect
 119 to the desired server.
 120
 121 =item B<-servername name>
 122
 123 Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
 124
 125 =item B<-cert certname>
 126
 127 The certificate to use, if one is requested by the server. The default is
 128 not to use a certificate.
 129
 130 =item B<-certform format>
 131
 132 The certificate format to use: DER or PEM. PEM is the default.
 133
 134 =item B<-key keyfile>
 135
 136 The private key to use. If not specified then the certificate file will
 137 be used.
 138
 139 =item B<-keyform format>
 140
 141 The private format to use: DER or PEM. PEM is the default.
 142
 143 =item B<-pass arg>
 144
 145 the private key password source. For more information about the format of B<arg>
 146 see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.
 147
 148 =item B<-verify depth>
 149
 150 The verify depth to use. This specifies the maximum length of the
 151 server certificate chain and turns on server certificate verification.
 152 Currently the verify operation continues after errors so all the problems
 153 with a certificate chain can be seen. As a side effect the connection
 154 will never fail due to a server certificate verify failure.
 155
 156 =item B<-verify_return_error>
 157
 158 Return verification errors instead of continuing. This will typically
 159 abort the handshake with a fatal error.
 160
 161 =item B<-CApath directory>
 162
 163 The directory to use for server certificate verification. This directory
 164 must be in "hash format", see B<verify> for more information. These are
 165 also used when building the client certificate chain.
 166
 167 =item B<-CAfile file>
 168
 169 A file containing trusted certificates to use during server authentication
 170 and to use when attempting to build the client certificate chain.
 171
 172 =item B<-no-CAfile>
 173
 174 Do not load the trusted CA certificates from the default file location
 175
 176 =item B<-no-CApath>
 177
 178 Do not load the trusted CA certificates from the default directory location
 179
 180 =item B<-dane_tlsa_domain domain>
 181
 182 Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
 183 TLSA base domain which becomes the default SNI hint and the primary
 184 reference identifier for hostname checks.  This must be used in
 185 combination with at least one instance of the B<-dane_tlsa_rrdata>
 186 option below.
 187
 188 When DANE authentication succeeds, the diagnostic output will include
 189 the lowest (closest to 0) depth at which a TLSA record authenticated
 190 a chain certificate.  When that TLSA record is a "2 1 0" trust
 191 anchor public key that signed (rather than matched) the top-most
 192 certificate of the chain, the result is reported as "TA public key
 193 verified".  Otherwise, either the TLSA record "matched TA certificate"
 194 at a positive depth or else "matched EE certificate" at depth 0.
 195
 196 =item B<-dane_tlsa_rrdata rrdata>
 197
 198 Use one or more times to specify the RRDATA fields of the DANE TLSA
 199 RRset associated with the target service.  The B<rrdata> value is
 200 specied in "presentation form", that is four whitespace separated
 201 fields that specify the usage, selector, matching type and associated
 202 data, with the last of these encoded in hexadecimal.  Optional
 203 whitespace is ignored in the associated data field.  For example:
 204
 205   $ openssl s_client -starttls smtp -connect smtp.example.com:25 \
 206     -dane_tlsa_domain smtp.example.com \
 207     -dane_tlsa_rrdata "2 1 1
 208       B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
 209     -dane_tlsa_rrdata "2 1 1
 210       60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
 211   CONNECTED(00000003)
 212   ...
 213   DANE TLSA 2 1 1 matched TA certificate at depth 1
 214   Verified peername: smtp.example.com
 215   ...
 216       Verify return code: 0 (ok)
 217   ...
 218
 219 =item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,
 220 B<explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,
 221 B<-inhibit_map>, B<-issuer_checks>, B<-partial_chain>, B<-policy>,
 222 B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,
 223 B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-no_alt_chains>,
 224 B<-use_deltas>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,
 225 B<-verify_ip>, B<-verify_name>, B<-x509_strict>
 226
 227 Set various certificate chain validation options. See the
 228 L<verify(1)> manual page for details.
 229
 230 =item B<-reconnect>
 231
 232 reconnects to the same server 5 times using the same session ID, this can
 233 be used as a test that session caching is working.
 234
 235 =item B<-showcerts>
 236
 237 display the whole server certificate chain: normally only the server
 238 certificate itself is displayed.
 239
 240 =item B<-prexit>
 241
 242 print session information when the program exits. This will always attempt
 243 to print out information even if the connection fails. Normally information
 244 will only be printed out once if the connection succeeds. This option is useful
 245 because the cipher in use may be renegotiated or the connection may fail
 246 because a client certificate is required or is requested only after an
 247 attempt is made to access a certain URL. Note: the output produced by this
 248 option is not always accurate because a connection might never have been
 249 established.
 250
 251 =item B<-state>
 252
 253 prints out the SSL session states.
 254
 255 =item B<-debug>
 256
 257 print extensive debugging information including a hex dump of all traffic.
 258
 259 =item B<-msg>
 260
 261 show all protocol messages with hex dump.
 262
 263 =item B<-trace>
 264
 265 show verbose trace output of protocol messages. OpenSSL needs to be compiled
 266 with B<enable-ssl-trace> for this option to work.
 267
 268 =item B<-msgfile>
 269
 270 file to send output of B<-msg> or B<-trace> to, default standard output.
 271
 272 =item B<-nbio_test>
 273
 274 tests non-blocking I/O
 275
 276 =item B<-nbio>
 277
 278 turns on non-blocking I/O
 279
 280 =item B<-crlf>
 281
 282 this option translated a line feed from the terminal into CR+LF as required
 283 by some servers.
 284
 285 =item B<-ign_eof>
 286
 287 inhibit shutting down the connection when end of file is reached in the
 288 input.
 289
 290 =item B<-quiet>
 291
 292 inhibit printing of session and certificate information.  This implicitly
 293 turns on B<-ign_eof> as well.
 294
 295 =item B<-no_ign_eof>
 296
 297 shut down the connection when end of file is reached in the input.
 298 Can be used to override the implicit B<-ign_eof> after B<-quiet>.
 299
 300 =item B<-psk_identity identity>
 301
 302 Use the PSK identity B<identity> when using a PSK cipher suite.
 303
 304 =item B<-psk key>
 305
 306 Use the PSK key B<key> when using a PSK cipher suite. The key is
 307 given as a hexadecimal number without leading 0x, for example -psk
 308 1a2b3c4d.
 309
 310 =item B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>
 311
 312 these options disable the use of certain SSL or TLS protocols. By default
 313 the initial handshake uses a method which should be compatible with all
 314 servers and permit them to use SSL v3 or TLS as appropriate.
 315
 316 Unfortunately there are still ancient and broken servers in use which
 317 cannot handle this technique and will fail to connect. Some servers only
 318 work if TLS is turned off.
 319
 320 =item B<-fallback_scsv>
 321
 322 Send TLS_FALLBACK_SCSV in the ClientHello.
 323
 324 =item B<-async>
 325
 326 switch on asynchronous mode. Cryptographic operations will be performed
 327 asynchronously. This will only have an effect if an asynchronous capable engine
 328 is also used via the B<-engine> option. For test purposes the dummy async engine
 329 (dasync) can be used (if available).
 330
 331 =item B<-bugs>
 332
 333 there are several known bug in SSL and TLS implementations. Adding this
 334 option enables various workarounds.
 335
 336 =item B<-comp>
 337
 338 Enables support for SSL/TLS compression.
 339 This option was introduced in OpenSSL 1.1.0.
 340 TLS compression is not recommended and is off by default as of
 341 OpenSSL 1.1.0.
 342
 343 =item B<-no_comp>
 344
 345 Disables support for SSL/TLS compression.
 346 TLS compression is not recommended and is off by default as of
 347 OpenSSL 1.1.0.
 348
 349 =item B<-brief>
 350
 351 only provide a brief summary of connection parameters instead of the
 352 normal verbose output.
 353
 354 =item B<-cipher cipherlist>
 355
 356 this allows the cipher list sent by the client to be modified. Although
 357 the server determines which cipher suite is used it should take the first
 358 supported cipher in the list sent by the client. See the B<ciphers>
 359 command for more information.
 360
 361 =item B<-starttls protocol>
 362
 363 send the protocol-specific message(s) to switch to TLS for communication.
 364 B<protocol> is a keyword for the intended protocol.  Currently, the only
 365 supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",
 366 and "irc."
 367
 368 =item B<-xmpphost hostname>
 369
 370 This option, when used with "-starttls xmpp" or "-starttls xmpp-server",
 371 specifies the host for the "to" attribute of the stream element.
 372 If this option is not specified, then the host specified with "-connect"
 373 will be used.
 374
 375 =item B<-tlsextdebug>
 376
 377 print out a hex dump of any TLS extensions received from the server.
 378
 379 =item B<-no_ticket>
 380
 381 disable RFC4507bis session ticket support.
 382
 383 =item B<-sess_out filename>
 384
 385 output SSL session to B<filename>
 386
 387 =item B<-sess_in sess.pem>
 388
 389 load SSL session from B<filename>. The client will attempt to resume a
 390 connection from this session.
 391
 392 =item B<-engine id>
 393
 394 specifying an engine (by its unique B<id> string) will cause B<s_client>
 395 to attempt to obtain a functional reference to the specified engine,
 396 thus initialising it if needed. The engine will then be set as the default
 397 for all available algorithms.
 398
 399 =item B<-rand file(s)>
 400
 401 a file or files containing random data used to seed the random number
 402 generator, or an EGD socket (see L<RAND_egd(3)>).
 403 Multiple files can be specified separated by a OS-dependent character.
 404 The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for
 405 all others.
 406
 407 =item B<-serverinfo types>
 408
 409 a list of comma-separated TLS Extension Types (numbers between 0 and
 410 65535).  Each type will be sent as an empty ClientHello TLS Extension.
 411 The server's response (if any) will be encoded and displayed as a PEM
 412 file.
 413
 414 =item B<-status>
 415
 416 sends a certificate status request to the server (OCSP stapling). The server
 417 response (if any) is printed out.
 418
 419 =item B<-nextprotoneg protocols>
 420
 421 enable Next Protocol Negotiation TLS extension and provide a list of
 422 comma-separated protocol names that the client should advertise
 423 support for. The list should contain most wanted protocols first.
 424 Protocol names are printable ASCII strings, for example "http/1.1" or
 425 "spdy/3".
 426 Empty list of protocols is treated specially and will cause the client to
 427 advertise support for the TLS extension but disconnect just after
 428 receiving ServerHello with a list of server supported protocols.
 429
 430 =back
 431
 432 =head1 CONNECTED COMMANDS
 433
 434 If a connection is established with an SSL server then any data received
 435 from the server is displayed and any key presses will be sent to the
 436 server. When used interactively (which means neither B<-quiet> nor B<-ign_eof>
 437 have been given), the session will be renegotiated if the line begins with an
 438 B<R>, and if the line begins with a B<Q> or if end of file is reached, the
 439 connection will be closed down.
 440
 441 =head1 NOTES
 442
 443 B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP
 444 server the command:
 445
 446  openssl s_client -connect servername:443
 447
 448 would typically be used (https uses port 443). If the connection succeeds
 449 then an HTTP command can be given such as "GET /" to retrieve a web page.
 450
 451 If the handshake fails then there are several possible causes, if it is
 452 nothing obvious like no client certificate then the B<-bugs>,
 453 B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried
 454 in case it is a buggy server. In particular you should play with these
 455 options B<before> submitting a bug report to an OpenSSL mailing list.
 456
 457 A frequent problem when attempting to get client certificates working
 458 is that a web client complains it has no certificates or gives an empty
 459 list to choose from. This is normally because the server is not sending
 460 the clients certificate authority in its "acceptable CA list" when it
 461 requests a certificate. By using B<s_client> the CA list can be viewed
 462 and checked. However some servers only request client authentication
 463 after a specific URL is requested. To obtain the list in this case it
 464 is necessary to use the B<-prexit> option and send an HTTP request
 465 for an appropriate page.
 466
 467 If a certificate is specified on the command line using the B<-cert>
 468 option it will not be used unless the server specifically requests
 469 a client certificate. Therefor merely including a client certificate
 470 on the command line is no guarantee that the certificate works.
 471
 472 If there are problems verifying a server certificate then the
 473 B<-showcerts> option can be used to show the whole chain.
 474
 475 The B<s_client> utility is a test tool and is designed to continue the
 476 handshake after any certificate verification errors. As a result it will
 477 accept any certificate chain (trusted or not) sent by the peer. None test
 478 applications should B<not> do this as it makes them vulnerable to a MITM
 479 attack. This behaviour can be changed by with the B<-verify_return_error>
 480 option: any verify errors are then returned aborting the handshake.
 481
 482 =head1 BUGS
 483
 484 Because this program has a lot of options and also because some of
 485 the techniques used are rather old, the C source of s_client is rather
 486 hard to read and not a model of how things should be done. A typical
 487 SSL client program would be much simpler.
 488
 489 The B<-prexit> option is a bit of a hack. We should really report
 490 information whenever a session is renegotiated.
 491
 492 =head1 SEE ALSO
 493
 494 L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>
 495
 496 =head1 HISTORY
 497
 498 The -no_alt_chains options was first added to OpenSSL 1.1.0.
 499
 500 =cut