s_client.pod revision 296317
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<-bugs>] 42[B<-cipher cipherlist>] 43[B<-serverpref>] 44[B<-starttls protocol>] 45[B<-engine id>] 46[B<-tlsextdebug>] 47[B<-no_ticket>] 48[B<-sess_out filename>] 49[B<-sess_in filename>] 50[B<-rand file(s)>] 51[B<-status>] 52[B<-nextprotoneg protocols>] 53 54=head1 DESCRIPTION 55 56The B<s_client> command implements a generic SSL/TLS client which connects 57to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for 58SSL servers. 59 60=head1 OPTIONS 61 62=over 4 63 64=item B<-connect host:port> 65 66This specifies the host and optional port to connect to. If not specified 67then an attempt is made to connect to the local host on port 4433. 68 69=item B<-servername name> 70 71Set the TLS SNI (Server Name Indication) extension in the ClientHello message. 72 73=item B<-cert certname> 74 75The certificate to use, if one is requested by the server. The default is 76not to use a certificate. 77 78=item B<-certform format> 79 80The certificate format to use: DER or PEM. PEM is the default. 81 82=item B<-key keyfile> 83 84The private key to use. If not specified then the certificate file will 85be used. 86 87=item B<-keyform format> 88 89The private format to use: DER or PEM. PEM is the default. 90 91=item B<-pass arg> 92 93the private key password source. For more information about the format of B<arg> 94see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>. 95 96=item B<-verify depth> 97 98The verify depth to use. This specifies the maximum length of the 99server certificate chain and turns on server certificate verification. 100Currently the verify operation continues after errors so all the problems 101with a certificate chain can be seen. As a side effect the connection 102will never fail due to a server certificate verify failure. 103 104=item B<-verify_return_error> 105 106Return verification errors instead of continuing. This will typically 107abort the handshake with a fatal error. 108 109=item B<-CApath directory> 110 111The directory to use for server certificate verification. This directory 112must be in "hash format", see B<verify> for more information. These are 113also used when building the client certificate chain. 114 115=item B<-CAfile file> 116 117A file containing trusted certificates to use during server authentication 118and to use when attempting to build the client certificate chain. 119 120=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> 121 122Set various certificate chain valiadition option. See the 123L<B<verify>|verify(1)> manual page for details. 124 125=item B<-reconnect> 126 127reconnects to the same server 5 times using the same session ID, this can 128be used as a test that session caching is working. 129 130=item B<-pause> 131 132pauses 1 second between each read and write call. 133 134=item B<-showcerts> 135 136display the whole server certificate chain: normally only the server 137certificate itself is displayed. 138 139=item B<-prexit> 140 141print session information when the program exits. This will always attempt 142to print out information even if the connection fails. Normally information 143will only be printed out once if the connection succeeds. This option is useful 144because the cipher in use may be renegotiated or the connection may fail 145because a client certificate is required or is requested only after an 146attempt is made to access a certain URL. Note: the output produced by this 147option is not always accurate because a connection might never have been 148established. 149 150=item B<-state> 151 152prints out the SSL session states. 153 154=item B<-debug> 155 156print extensive debugging information including a hex dump of all traffic. 157 158=item B<-msg> 159 160show all protocol messages with hex dump. 161 162=item B<-nbio_test> 163 164tests non-blocking I/O 165 166=item B<-nbio> 167 168turns on non-blocking I/O 169 170=item B<-crlf> 171 172this option translated a line feed from the terminal into CR+LF as required 173by some servers. 174 175=item B<-ign_eof> 176 177inhibit shutting down the connection when end of file is reached in the 178input. 179 180=item B<-quiet> 181 182inhibit printing of session and certificate information. This implicitly 183turns on B<-ign_eof> as well. 184 185=item B<-no_ign_eof> 186 187shut down the connection when end of file is reached in the input. 188Can be used to override the implicit B<-ign_eof> after B<-quiet>. 189 190=item B<-psk_identity identity> 191 192Use the PSK identity B<identity> when using a PSK cipher suite. 193 194=item B<-psk key> 195 196Use the PSK key B<key> when using a PSK cipher suite. The key is 197given as a hexadecimal number without leading 0x, for example -psk 1981a2b3c4d. 199 200=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> 201 202These options require or disable the use of the specified SSL or TLS protocols. 203By default the initial handshake uses a I<version-flexible> method which will 204negotiate the highest mutually supported protocol version. 205 206=item B<-bugs> 207 208there are several known bug in SSL and TLS implementations. Adding this 209option enables various workarounds. 210 211=item B<-cipher cipherlist> 212 213this allows the cipher list sent by the client to be modified. Although 214the server determines which cipher suite is used it should take the first 215supported cipher in the list sent by the client. See the B<ciphers> 216command for more information. 217 218=item B<-serverpref> 219 220use the server's cipher preferences; only used for SSLV2. 221 222=item B<-starttls protocol> 223 224send the protocol-specific message(s) to switch to TLS for communication. 225B<protocol> is a keyword for the intended protocol. Currently, the only 226supported keywords are "smtp", "pop3", "imap", and "ftp". 227 228=item B<-tlsextdebug> 229 230print out a hex dump of any TLS extensions received from the server. 231 232=item B<-no_ticket> 233 234disable RFC4507bis session ticket support. 235 236=item B<-sess_out filename> 237 238output SSL session to B<filename> 239 240=item B<-sess_in sess.pem> 241 242load SSL session from B<filename>. The client will attempt to resume a 243connection from this session. 244 245=item B<-engine id> 246 247specifying an engine (by its unique B<id> string) will cause B<s_client> 248to attempt to obtain a functional reference to the specified engine, 249thus initialising it if needed. The engine will then be set as the default 250for all available algorithms. 251 252=item B<-rand file(s)> 253 254a file or files containing random data used to seed the random number 255generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>). 256Multiple files can be specified separated by a OS-dependent character. 257The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for 258all others. 259 260=item B<-status> 261 262sends a certificate status request to the server (OCSP stapling). The server 263response (if any) is printed out. 264 265=item B<-nextprotoneg protocols> 266 267enable Next Protocol Negotiation TLS extension and provide a list of 268comma-separated protocol names that the client should advertise 269support for. The list should contain most wanted protocols first. 270Protocol names are printable ASCII strings, for example "http/1.1" or 271"spdy/3". 272Empty list of protocols is treated specially and will cause the client to 273advertise support for the TLS extension but disconnect just after 274reciving ServerHello with a list of server supported protocols. 275 276=back 277 278=head1 CONNECTED COMMANDS 279 280If a connection is established with an SSL server then any data received 281from the server is displayed and any key presses will be sent to the 282server. When used interactively (which means neither B<-quiet> nor B<-ign_eof> 283have been given), the session will be renegotiated if the line begins with an 284B<R>, and if the line begins with a B<Q> or if end of file is reached, the 285connection will be closed down. 286 287=head1 NOTES 288 289B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP 290server the command: 291 292 openssl s_client -connect servername:443 293 294would typically be used (https uses port 443). If the connection succeeds 295then an HTTP command can be given such as "GET /" to retrieve a web page. 296 297If the handshake fails then there are several possible causes, if it is 298nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>, 299B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried 300in case it is a buggy server. In particular you should play with these 301options B<before> submitting a bug report to an OpenSSL mailing list. 302 303A frequent problem when attempting to get client certificates working 304is that a web client complains it has no certificates or gives an empty 305list to choose from. This is normally because the server is not sending 306the clients certificate authority in its "acceptable CA list" when it 307requests a certificate. By using B<s_client> the CA list can be viewed 308and checked. However some servers only request client authentication 309after a specific URL is requested. To obtain the list in this case it 310is necessary to use the B<-prexit> option and send an HTTP request 311for an appropriate page. 312 313If a certificate is specified on the command line using the B<-cert> 314option it will not be used unless the server specifically requests 315a client certificate. Therefor merely including a client certificate 316on the command line is no guarantee that the certificate works. 317 318If there are problems verifying a server certificate then the 319B<-showcerts> option can be used to show the whole chain. 320 321Since the SSLv23 client hello cannot include compression methods or extensions 322these will only be supported if its use is disabled, for example by using the 323B<-no_sslv2> option. 324 325The B<s_client> utility is a test tool and is designed to continue the 326handshake after any certificate verification errors. As a result it will 327accept any certificate chain (trusted or not) sent by the peer. None test 328applications should B<not> do this as it makes them vulnerable to a MITM 329attack. This behaviour can be changed by with the B<-verify_return_error> 330option: any verify errors are then returned aborting the handshake. 331 332=head1 BUGS 333 334Because this program has a lot of options and also because some of 335the techniques used are rather old, the C source of s_client is rather 336hard to read and not a model of how things should be done. A typical 337SSL client program would be much simpler. 338 339The B<-prexit> option is a bit of a hack. We should really report 340information whenever a session is renegotiated. 341 342=head1 SEE ALSO 343 344L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)> 345 346=head1 HISTORY 347 348The -no_alt_chains options was first added to OpenSSL 1.0.1n and 1.0.2b. 349 350=cut 351