s_client.pod revision 306195
1 2=pod 3 4=head1 NAME 5 6s_client - SSL/TLS client program 7 8=head1 SYNOPSIS 9 10B<openssl> B<s_client> 11[B<-connect host:port>] 12[B<-servername name>] 13[B<-verify depth>] 14[B<-verify_return_error>] 15[B<-cert filename>] 16[B<-certform DER|PEM>] 17[B<-key filename>] 18[B<-keyform DER|PEM>] 19[B<-pass arg>] 20[B<-CApath directory>] 21[B<-CAfile filename>] 22[B<-no_alt_chains>] 23[B<-reconnect>] 24[B<-pause>] 25[B<-showcerts>] 26[B<-debug>] 27[B<-msg>] 28[B<-nbio_test>] 29[B<-state>] 30[B<-nbio>] 31[B<-crlf>] 32[B<-ign_eof>] 33[B<-no_ign_eof>] 34[B<-quiet>] 35[B<-ssl2>] 36[B<-ssl3>] 37[B<-tls1>] 38[B<-no_ssl2>] 39[B<-no_ssl3>] 40[B<-no_tls1>] 41[B<-no_tls1_1>] 42[B<-no_tls1_2>] 43[B<-fallback_scsv>] 44[B<-bugs>] 45[B<-cipher cipherlist>] 46[B<-serverpref>] 47[B<-starttls protocol>] 48[B<-engine id>] 49[B<-tlsextdebug>] 50[B<-no_ticket>] 51[B<-sess_out filename>] 52[B<-sess_in filename>] 53[B<-rand file(s)>] 54[B<-serverinfo types>] 55[B<-status>] 56[B<-alpn protocols>] 57[B<-nextprotoneg protocols>] 58 59=head1 DESCRIPTION 60 61The B<s_client> command implements a generic SSL/TLS client which connects 62to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for 63SSL servers. 64 65=head1 OPTIONS 66 67=over 4 68 69=item B<-connect host:port> 70 71This specifies the host and optional port to connect to. If not specified 72then an attempt is made to connect to the local host on port 4433. 73 74=item B<-servername name> 75 76Set the TLS SNI (Server Name Indication) extension in the ClientHello message. 77 78=item B<-cert certname> 79 80The certificate to use, if one is requested by the server. The default is 81not to use a certificate. 82 83=item B<-certform format> 84 85The certificate format to use: DER or PEM. PEM is the default. 86 87=item B<-key keyfile> 88 89The private key to use. If not specified then the certificate file will 90be used. 91 92=item B<-keyform format> 93 94The private format to use: DER or PEM. PEM is the default. 95 96=item B<-pass arg> 97 98the private key password source. For more information about the format of B<arg> 99see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>. 100 101=item B<-verify depth> 102 103The verify depth to use. This specifies the maximum length of the 104server certificate chain and turns on server certificate verification. 105Currently the verify operation continues after errors so all the problems 106with a certificate chain can be seen. As a side effect the connection 107will never fail due to a server certificate verify failure. 108 109=item B<-verify_return_error> 110 111Return verification errors instead of continuing. This will typically 112abort the handshake with a fatal error. 113 114=item B<-CApath directory> 115 116The directory to use for server certificate verification. This directory 117must be in "hash format", see B<verify> for more information. These are 118also used when building the client certificate chain. 119 120=item B<-CAfile file> 121 122A file containing trusted certificates to use during server authentication 123and to use when attempting to build the client certificate chain. 124 125=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> 126 127Set various certificate chain valiadition option. See the 128L<B<verify>|verify(1)> manual page for details. 129 130=item B<-reconnect> 131 132reconnects to the same server 5 times using the same session ID, this can 133be used as a test that session caching is working. 134 135=item B<-pause> 136 137pauses 1 second between each read and write call. 138 139=item B<-showcerts> 140 141display the whole server certificate chain: normally only the server 142certificate itself is displayed. 143 144=item B<-prexit> 145 146print session information when the program exits. This will always attempt 147to print out information even if the connection fails. Normally information 148will only be printed out once if the connection succeeds. This option is useful 149because the cipher in use may be renegotiated or the connection may fail 150because a client certificate is required or is requested only after an 151attempt is made to access a certain URL. Note: the output produced by this 152option is not always accurate because a connection might never have been 153established. 154 155=item B<-state> 156 157prints out the SSL session states. 158 159=item B<-debug> 160 161print extensive debugging information including a hex dump of all traffic. 162 163=item B<-msg> 164 165show all protocol messages with hex dump. 166 167=item B<-nbio_test> 168 169tests non-blocking I/O 170 171=item B<-nbio> 172 173turns on non-blocking I/O 174 175=item B<-crlf> 176 177this option translated a line feed from the terminal into CR+LF as required 178by some servers. 179 180=item B<-ign_eof> 181 182inhibit shutting down the connection when end of file is reached in the 183input. 184 185=item B<-quiet> 186 187inhibit printing of session and certificate information. This implicitly 188turns on B<-ign_eof> as well. 189 190=item B<-no_ign_eof> 191 192shut down the connection when end of file is reached in the input. 193Can be used to override the implicit B<-ign_eof> after B<-quiet>. 194 195=item B<-psk_identity identity> 196 197Use the PSK identity B<identity> when using a PSK cipher suite. 198 199=item B<-psk key> 200 201Use the PSK key B<key> when using a PSK cipher suite. The key is 202given as a hexadecimal number without leading 0x, for example -psk 2031a2b3c4d. 204 205=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> 206 207These options require or disable the use of the specified SSL or TLS protocols. 208By default the initial handshake uses a I<version-flexible> method which will 209negotiate the highest mutually supported protocol version. 210 211=item B<-fallback_scsv> 212 213Send TLS_FALLBACK_SCSV in the ClientHello. 214 215=item B<-bugs> 216 217there are several known bug in SSL and TLS implementations. Adding this 218option enables various workarounds. 219 220=item B<-cipher cipherlist> 221 222this allows the cipher list sent by the client to be modified. Although 223the server determines which cipher suite is used it should take the first 224supported cipher in the list sent by the client. See the B<ciphers> 225command for more information. 226 227=item B<-serverpref> 228 229use the server's cipher preferences; only used for SSLV2. 230 231=item B<-starttls protocol> 232 233send the protocol-specific message(s) to switch to TLS for communication. 234B<protocol> is a keyword for the intended protocol. Currently, the only 235supported keywords are "smtp", "pop3", "imap", and "ftp". 236 237=item B<-tlsextdebug> 238 239print out a hex dump of any TLS extensions received from the server. 240 241=item B<-no_ticket> 242 243disable RFC4507bis session ticket support. 244 245=item B<-sess_out filename> 246 247output SSL session to B<filename> 248 249=item B<-sess_in sess.pem> 250 251load SSL session from B<filename>. The client will attempt to resume a 252connection from this session. 253 254=item B<-engine id> 255 256specifying an engine (by its unique B<id> string) will cause B<s_client> 257to attempt to obtain a functional reference to the specified engine, 258thus initialising it if needed. The engine will then be set as the default 259for all available algorithms. 260 261=item B<-rand file(s)> 262 263a file or files containing random data used to seed the random number 264generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>). 265Multiple files can be specified separated by a OS-dependent character. 266The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for 267all others. 268 269=item B<-serverinfo types> 270 271a list of comma-separated TLS Extension Types (numbers between 0 and 27265535). Each type will be sent as an empty ClientHello TLS Extension. 273The server's response (if any) will be encoded and displayed as a PEM 274file. 275 276=item B<-status> 277 278sends a certificate status request to the server (OCSP stapling). The server 279response (if any) is printed out. 280 281=item B<-alpn protocols>, B<-nextprotoneg protocols> 282 283these flags enable the 284Enable the Application-Layer Protocol Negotiation or Next Protocol 285Negotiation extension, respectively. ALPN is the IETF standard and 286replaces NPN. 287The B<protocols> list is a 288comma-separated protocol names that the client should advertise 289support for. The list should contain most wanted protocols first. 290Protocol names are printable ASCII strings, for example "http/1.1" or 291"spdy/3". 292Empty list of protocols is treated specially and will cause the client to 293advertise support for the TLS extension but disconnect just after 294reciving ServerHello with a list of server supported protocols. 295 296=back 297 298=head1 CONNECTED COMMANDS 299 300If a connection is established with an SSL server then any data received 301from the server is displayed and any key presses will be sent to the 302server. When used interactively (which means neither B<-quiet> nor B<-ign_eof> 303have been given), the session will be renegotiated if the line begins with an 304B<R>, and if the line begins with a B<Q> or if end of file is reached, the 305connection will be closed down. 306 307=head1 NOTES 308 309B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP 310server the command: 311 312 openssl s_client -connect servername:443 313 314would typically be used (https uses port 443). If the connection succeeds 315then an HTTP command can be given such as "GET /" to retrieve a web page. 316 317If the handshake fails then there are several possible causes, if it is 318nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>, 319B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried 320in case it is a buggy server. In particular you should play with these 321options B<before> submitting a bug report to an OpenSSL mailing list. 322 323A frequent problem when attempting to get client certificates working 324is that a web client complains it has no certificates or gives an empty 325list to choose from. This is normally because the server is not sending 326the clients certificate authority in its "acceptable CA list" when it 327requests a certificate. By using B<s_client> the CA list can be viewed 328and checked. However some servers only request client authentication 329after a specific URL is requested. To obtain the list in this case it 330is necessary to use the B<-prexit> option and send an HTTP request 331for an appropriate page. 332 333If a certificate is specified on the command line using the B<-cert> 334option it will not be used unless the server specifically requests 335a client certificate. Therefor merely including a client certificate 336on the command line is no guarantee that the certificate works. 337 338If there are problems verifying a server certificate then the 339B<-showcerts> option can be used to show the whole chain. 340 341Since the SSLv23 client hello cannot include compression methods or extensions 342these will only be supported if its use is disabled, for example by using the 343B<-no_sslv2> option. 344 345The B<s_client> utility is a test tool and is designed to continue the 346handshake after any certificate verification errors. As a result it will 347accept any certificate chain (trusted or not) sent by the peer. None test 348applications should B<not> do this as it makes them vulnerable to a MITM 349attack. This behaviour can be changed by with the B<-verify_return_error> 350option: any verify errors are then returned aborting the handshake. 351 352=head1 BUGS 353 354Because this program has a lot of options and also because some of 355the techniques used are rather old, the C source of s_client is rather 356hard to read and not a model of how things should be done. A typical 357SSL client program would be much simpler. 358 359The B<-prexit> option is a bit of a hack. We should really report 360information whenever a session is renegotiated. 361 362=head1 SEE ALSO 363 364L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)> 365 366=head1 HISTORY 367 368The -no_alt_chains options was first added to OpenSSL 1.0.2b. 369 370=cut 371