s_client.pod revision 337982
1 2=pod 3 4=head1 NAME 5 6openssl-s_client, 7s_client - SSL/TLS client program 8 9=head1 SYNOPSIS 10 11B<openssl> B<s_client> 12[B<-connect host:port>] 13[B<-servername name>] 14[B<-verify depth>] 15[B<-verify_return_error>] 16[B<-cert filename>] 17[B<-certform DER|PEM>] 18[B<-key filename>] 19[B<-keyform DER|PEM>] 20[B<-pass arg>] 21[B<-CApath directory>] 22[B<-CAfile filename>] 23[B<-no_alt_chains>] 24[B<-reconnect>] 25[B<-pause>] 26[B<-showcerts>] 27[B<-debug>] 28[B<-msg>] 29[B<-nbio_test>] 30[B<-state>] 31[B<-nbio>] 32[B<-crlf>] 33[B<-ign_eof>] 34[B<-no_ign_eof>] 35[B<-quiet>] 36[B<-ssl2>] 37[B<-ssl3>] 38[B<-tls1>] 39[B<-no_ssl2>] 40[B<-no_ssl3>] 41[B<-no_tls1>] 42[B<-no_tls1_1>] 43[B<-no_tls1_2>] 44[B<-fallback_scsv>] 45[B<-bugs>] 46[B<-sigalgs sigalglist>] 47[B<-curves curvelist>] 48[B<-cipher cipherlist>] 49[B<-serverpref>] 50[B<-starttls protocol>] 51[B<-engine id>] 52[B<-tlsextdebug>] 53[B<-no_ticket>] 54[B<-sess_out filename>] 55[B<-sess_in filename>] 56[B<-rand file(s)>] 57[B<-serverinfo types>] 58[B<-status>] 59[B<-alpn protocols>] 60[B<-nextprotoneg protocols>] 61 62=head1 DESCRIPTION 63 64The B<s_client> command implements a generic SSL/TLS client which connects 65to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for 66SSL servers. 67 68=head1 OPTIONS 69 70=over 4 71 72=item B<-connect host:port> 73 74This specifies the host and optional port to connect to. If not specified 75then an attempt is made to connect to the local host on port 4433. 76 77=item B<-servername name> 78 79Set the TLS SNI (Server Name Indication) extension in the ClientHello message. 80 81=item B<-cert certname> 82 83The certificate to use, if one is requested by the server. The default is 84not to use a certificate. 85 86=item B<-certform format> 87 88The certificate format to use: DER or PEM. PEM is the default. 89 90=item B<-key keyfile> 91 92The private key to use. If not specified then the certificate file will 93be used. 94 95=item B<-keyform format> 96 97The private format to use: DER or PEM. PEM is the default. 98 99=item B<-pass arg> 100 101the private key password source. For more information about the format of B<arg> 102see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>. 103 104=item B<-verify depth> 105 106The verify depth to use. This specifies the maximum length of the 107server certificate chain and turns on server certificate verification. 108Currently the verify operation continues after errors so all the problems 109with a certificate chain can be seen. As a side effect the connection 110will never fail due to a server certificate verify failure. 111 112=item B<-verify_return_error> 113 114Return verification errors instead of continuing. This will typically 115abort the handshake with a fatal error. 116 117=item B<-CApath directory> 118 119The directory to use for server certificate verification. This directory 120must be in "hash format", see B<verify> for more information. These are 121also used when building the client certificate chain. 122 123=item B<-CAfile file> 124 125A file containing trusted certificates to use during server authentication 126and to use when attempting to build the client certificate chain. 127 128=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> 129 130Set various certificate chain valiadition option. See the 131L<B<verify>|verify(1)> manual page for details. 132 133=item B<-reconnect> 134 135reconnects to the same server 5 times using the same session ID, this can 136be used as a test that session caching is working. 137 138=item B<-pause> 139 140pauses 1 second between each read and write call. 141 142=item B<-showcerts> 143 144Displays the server certificate list as sent by the server: it only consists of 145certificates the server has sent (in the order the server has sent them). It is 146B<not> a verified chain. 147 148=item B<-prexit> 149 150print session information when the program exits. This will always attempt 151to print out information even if the connection fails. Normally information 152will only be printed out once if the connection succeeds. This option is useful 153because the cipher in use may be renegotiated or the connection may fail 154because a client certificate is required or is requested only after an 155attempt is made to access a certain URL. Note: the output produced by this 156option is not always accurate because a connection might never have been 157established. 158 159=item B<-state> 160 161prints out the SSL session states. 162 163=item B<-debug> 164 165print extensive debugging information including a hex dump of all traffic. 166 167=item B<-msg> 168 169show all protocol messages with hex dump. 170 171=item B<-nbio_test> 172 173tests non-blocking I/O 174 175=item B<-nbio> 176 177turns on non-blocking I/O 178 179=item B<-crlf> 180 181this option translated a line feed from the terminal into CR+LF as required 182by some servers. 183 184=item B<-ign_eof> 185 186inhibit shutting down the connection when end of file is reached in the 187input. 188 189=item B<-quiet> 190 191inhibit printing of session and certificate information. This implicitly 192turns on B<-ign_eof> as well. 193 194=item B<-no_ign_eof> 195 196shut down the connection when end of file is reached in the input. 197Can be used to override the implicit B<-ign_eof> after B<-quiet>. 198 199=item B<-psk_identity identity> 200 201Use the PSK identity B<identity> when using a PSK cipher suite. 202The default value is "Client_identity" (without the quotes). 203 204=item B<-psk key> 205 206Use the PSK key B<key> when using a PSK cipher suite. The key is 207given as a hexadecimal number without leading 0x, for example -psk 2081a2b3c4d. 209This option must be provided in order to use a PSK cipher. 210 211=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> 212 213These options require or disable the use of the specified SSL or TLS protocols. 214By default the initial handshake uses a I<version-flexible> method which will 215negotiate the highest mutually supported protocol version. 216 217=item B<-fallback_scsv> 218 219Send TLS_FALLBACK_SCSV in the ClientHello. 220 221=item B<-bugs> 222 223there are several known bug in SSL and TLS implementations. Adding this 224option enables various workarounds. 225 226=item B<-sigalgs sigalglist> 227 228Specifies the list of signature algorithms that are sent by the client. 229The server selects one entry in the list based on its preferences. 230For example strings, see L<SSL_CTX_set1_sigalgs(3)> 231 232=item B<-curves curvelist> 233 234Specifies the list of supported curves to be sent by the client. The curve is 235is ultimately selected by the server. For a list of all curves, use: 236 237 $ openssl ecparam -list_curves 238 239=item B<-cipher cipherlist> 240 241this allows the cipher list sent by the client to be modified. Although 242the server determines which cipher suite is used it should take the first 243supported cipher in the list sent by the client. See the B<ciphers> 244command for more information. 245 246=item B<-serverpref> 247 248use the server's cipher preferences; only used for SSLV2. 249 250=item B<-starttls protocol> 251 252send the protocol-specific message(s) to switch to TLS for communication. 253B<protocol> is a keyword for the intended protocol. Currently, the only 254supported keywords are "smtp", "pop3", "imap", "ftp" and "xmpp". 255 256=item B<-tlsextdebug> 257 258print out a hex dump of any TLS extensions received from the server. 259 260=item B<-no_ticket> 261 262disable RFC4507bis session ticket support. 263 264=item B<-sess_out filename> 265 266output SSL session to B<filename> 267 268=item B<-sess_in sess.pem> 269 270load SSL session from B<filename>. The client will attempt to resume a 271connection from this session. 272 273=item B<-engine id> 274 275specifying an engine (by its unique B<id> string) will cause B<s_client> 276to attempt to obtain a functional reference to the specified engine, 277thus initialising it if needed. The engine will then be set as the default 278for all available algorithms. 279 280=item B<-rand file(s)> 281 282a file or files containing random data used to seed the random number 283generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>). 284Multiple files can be specified separated by a OS-dependent character. 285The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for 286all others. 287 288=item B<-serverinfo types> 289 290a list of comma-separated TLS Extension Types (numbers between 0 and 29165535). Each type will be sent as an empty ClientHello TLS Extension. 292The server's response (if any) will be encoded and displayed as a PEM 293file. 294 295=item B<-status> 296 297sends a certificate status request to the server (OCSP stapling). The server 298response (if any) is printed out. 299 300=item B<-alpn protocols>, B<-nextprotoneg protocols> 301 302these flags enable the 303Enable the Application-Layer Protocol Negotiation or Next Protocol 304Negotiation extension, respectively. ALPN is the IETF standard and 305replaces NPN. 306The B<protocols> list is a 307comma-separated protocol names that the client should advertise 308support for. The list should contain most wanted protocols first. 309Protocol names are printable ASCII strings, for example "http/1.1" or 310"spdy/3". 311Empty list of protocols is treated specially and will cause the client to 312advertise support for the TLS extension but disconnect just after 313reciving ServerHello with a list of server supported protocols. 314 315=back 316 317=head1 CONNECTED COMMANDS 318 319If a connection is established with an SSL server then any data received 320from the server is displayed and any key presses will be sent to the 321server. When used interactively (which means neither B<-quiet> nor B<-ign_eof> 322have been given), the session will be renegotiated if the line begins with an 323B<R>, and if the line begins with a B<Q> or if end of file is reached, the 324connection will be closed down. 325 326=head1 NOTES 327 328B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP 329server the command: 330 331 openssl s_client -connect servername:443 332 333would typically be used (https uses port 443). If the connection succeeds 334then an HTTP command can be given such as "GET /" to retrieve a web page. 335 336If the handshake fails then there are several possible causes, if it is 337nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>, 338B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried 339in case it is a buggy server. In particular you should play with these 340options B<before> submitting a bug report to an OpenSSL mailing list. 341 342A frequent problem when attempting to get client certificates working 343is that a web client complains it has no certificates or gives an empty 344list to choose from. This is normally because the server is not sending 345the clients certificate authority in its "acceptable CA list" when it 346requests a certificate. By using B<s_client> the CA list can be viewed 347and checked. However some servers only request client authentication 348after a specific URL is requested. To obtain the list in this case it 349is necessary to use the B<-prexit> option and send an HTTP request 350for an appropriate page. 351 352If a certificate is specified on the command line using the B<-cert> 353option it will not be used unless the server specifically requests 354a client certificate. Therefor merely including a client certificate 355on the command line is no guarantee that the certificate works. 356 357If there are problems verifying a server certificate then the 358B<-showcerts> option can be used to show all the certificates sent by the 359server. 360 361Since the SSLv23 client hello cannot include compression methods or extensions 362these will only be supported if its use is disabled, for example by using the 363B<-no_sslv2> option. 364 365The B<s_client> utility is a test tool and is designed to continue the 366handshake after any certificate verification errors. As a result it will 367accept any certificate chain (trusted or not) sent by the peer. None test 368applications should B<not> do this as it makes them vulnerable to a MITM 369attack. This behaviour can be changed by with the B<-verify_return_error> 370option: any verify errors are then returned aborting the handshake. 371 372=head1 BUGS 373 374Because this program has a lot of options and also because some of 375the techniques used are rather old, the C source of s_client is rather 376hard to read and not a model of how things should be done. A typical 377SSL client program would be much simpler. 378 379The B<-prexit> option is a bit of a hack. We should really report 380information whenever a session is renegotiated. 381 382=head1 SEE ALSO 383 384L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)> 385 386=head1 HISTORY 387 388The -no_alt_chains options was first added to OpenSSL 1.0.2b. 389 390=cut 391