s_client.pod revision 279265
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<-verify depth>] 13[B<-cert filename>] 14[B<-certform DER|PEM>] 15[B<-key filename>] 16[B<-keyform DER|PEM>] 17[B<-pass arg>] 18[B<-CApath directory>] 19[B<-CAfile filename>] 20[B<-attime timestamp>] 21[B<-check_ss_sig>] 22[B<-crl_check>] 23[B<-crl_check_all>] 24[B<-explicit_policy>] 25[B<-ignore_critical>] 26[B<-inhibit_any>] 27[B<-inhibit_map>] 28[B<-issuer_checks>] 29[B<-policy arg>] 30[B<-policy_check>] 31[B<-policy_print>] 32[B<-purpose purpose>] 33[B<-use_deltas>] 34[B<-verify_depth num>] 35[B<-x509_strict>] 36[B<-reconnect>] 37[B<-pause>] 38[B<-showcerts>] 39[B<-debug>] 40[B<-msg>] 41[B<-nbio_test>] 42[B<-state>] 43[B<-nbio>] 44[B<-crlf>] 45[B<-ign_eof>] 46[B<-quiet>] 47[B<-ssl2>] 48[B<-ssl3>] 49[B<-tls1>] 50[B<-no_ssl2>] 51[B<-no_ssl3>] 52[B<-no_tls1>] 53[B<-fallback_scsv>] 54[B<-bugs>] 55[B<-cipher cipherlist>] 56[B<-starttls protocol>] 57[B<-xmpphost hostname>] 58[B<-engine id>] 59[B<-tlsextdebug>] 60[B<-no_ticket>] 61[B<-sess_out filename>] 62[B<-sess_in filename>] 63[B<-rand file(s)>] 64 65=head1 DESCRIPTION 66 67The B<s_client> command implements a generic SSL/TLS client which connects 68to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for 69SSL servers. 70 71=head1 OPTIONS 72 73In addition to the options below the B<s_client> utility also supports the 74common and client only options documented in the 75in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS> 76manual page. 77 78=over 4 79 80=item B<-connect host:port> 81 82This specifies the host and optional port to connect to. If not specified 83then an attempt is made to connect to the local host on port 4433. 84 85=item B<-cert certname> 86 87The certificate to use, if one is requested by the server. The default is 88not to use a certificate. 89 90=item B<-certform format> 91 92The certificate format to use: DER or PEM. PEM is the default. 93 94=item B<-key keyfile> 95 96The private key to use. If not specified then the certificate file will 97be used. 98 99=item B<-keyform format> 100 101The private format to use: DER or PEM. PEM is the default. 102 103=item B<-pass arg> 104 105the private key password source. For more information about the format of B<arg> 106see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>. 107 108=item B<-verify depth> 109 110The verify depth to use. This specifies the maximum length of the 111server certificate chain and turns on server certificate verification. 112Currently the verify operation continues after errors so all the problems 113with a certificate chain can be seen. As a side effect the connection 114will never fail due to a server certificate verify failure. 115 116=item B<-CApath directory> 117 118The directory to use for server certificate verification. This directory 119must be in "hash format", see B<verify> for more information. These are 120also used when building the client certificate chain. 121 122=item B<-CAfile file> 123 124A file containing trusted certificates to use during server authentication 125and to use when attempting to build the client certificate chain. 126 127=item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>, 128B<explicit_policy>, B<-ignore_critical>, B<-inhibit_any>, 129B<-inhibit_map>, B<-issuer_checks>, B<-policy>, 130B<-policy_check>, B<-policy_print>, B<-purpose>, 131B<-use_deltas>, B<-verify_depth>, B<-x509_strict> 132 133Set various certificate chain valiadition options. See the 134L<B<verify>|verify(1)> manual page for details. 135 136=item B<-reconnect> 137 138reconnects to the same server 5 times using the same session ID, this can 139be used as a test that session caching is working. 140 141=item B<-pause> 142 143pauses 1 second between each read and write call. 144 145=item B<-showcerts> 146 147display the whole server certificate chain: normally only the server 148certificate itself is displayed. 149 150=item B<-prexit> 151 152print session information when the program exits. This will always attempt 153to print out information even if the connection fails. Normally information 154will only be printed out once if the connection succeeds. This option is useful 155because the cipher in use may be renegotiated or the connection may fail 156because a client certificate is required or is requested only after an 157attempt is made to access a certain URL. Note: the output produced by this 158option is not always accurate because a connection might never have been 159established. 160 161=item B<-state> 162 163prints out the SSL session states. 164 165=item B<-debug> 166 167print extensive debugging information including a hex dump of all traffic. 168 169=item B<-msg> 170 171show all protocol messages with hex dump. 172 173=item B<-nbio_test> 174 175tests non-blocking I/O 176 177=item B<-nbio> 178 179turns on non-blocking I/O 180 181=item B<-crlf> 182 183this option translated a line feed from the terminal into CR+LF as required 184by some servers. 185 186=item B<-ign_eof> 187 188inhibit shutting down the connection when end of file is reached in the 189input. 190 191=item B<-quiet> 192 193inhibit printing of session and certificate information. This implicitly 194turns on B<-ign_eof> as well. 195 196=item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> 197 198these options disable the use of certain SSL or TLS protocols. By default 199the initial handshake uses a method which should be compatible with all 200servers and permit them to use SSL v3, SSL v2 or TLS as appropriate. 201 202Unfortunately there are still ancient and broken servers in use which 203cannot handle this technique and will fail to connect. Some servers only 204work if TLS is turned off. 205 206=item B<-fallback_scsv> 207 208Send TLS_FALLBACK_SCSV in the ClientHello. 209 210=item B<-bugs> 211 212there are several known bug in SSL and TLS implementations. Adding this 213option enables various workarounds. 214 215=item B<-cipher cipherlist> 216 217this allows the cipher list sent by the client to be modified. Although 218the server determines which cipher suite is used it should take the first 219supported cipher in the list sent by the client. See the B<ciphers> 220command for more information. 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", "ftp" and "xmpp". 227 228=item B<-xmpphost hostname> 229 230This option, when used with "-starttls xmpp", specifies the host for the 231"to" attribute of the stream element. 232If this option is not specified, then the host specified with "-connect" 233will be used. 234 235=item B<-tlsextdebug> 236 237print out a hex dump of any TLS extensions received from the server. 238 239=item B<-no_ticket> 240 241disable RFC4507bis session ticket support. 242 243=item B<-sess_out filename> 244 245output SSL session to B<filename> 246 247=item B<-sess_in sess.pem> 248 249load SSL session from B<filename>. The client will attempt to resume a 250connection from this session. 251 252=item B<-engine id> 253 254specifying an engine (by its unique B<id> string) will cause B<s_client> 255to attempt to obtain a functional reference to the specified engine, 256thus initialising it if needed. The engine will then be set as the default 257for all available algorithms. 258 259=item B<-rand file(s)> 260 261a file or files containing random data used to seed the random number 262generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>). 263Multiple files can be specified separated by a OS-dependent character. 264The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for 265all others. 266 267=back 268 269=head1 CONNECTED COMMANDS 270 271If a connection is established with an SSL server then any data received 272from the server is displayed and any key presses will be sent to the 273server. When used interactively (which means neither B<-quiet> nor B<-ign_eof> 274have been given), the session will be renegotiated if the line begins with an 275B<R>, and if the line begins with a B<Q> or if end of file is reached, the 276connection will be closed down. 277 278=head1 NOTES 279 280B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP 281server the command: 282 283 openssl s_client -connect servername:443 284 285would typically be used (https uses port 443). If the connection succeeds 286then an HTTP command can be given such as "GET /" to retrieve a web page. 287 288If the handshake fails then there are several possible causes, if it is 289nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>, 290B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried 291in case it is a buggy server. In particular you should play with these 292options B<before> submitting a bug report to an OpenSSL mailing list. 293 294A frequent problem when attempting to get client certificates working 295is that a web client complains it has no certificates or gives an empty 296list to choose from. This is normally because the server is not sending 297the clients certificate authority in its "acceptable CA list" when it 298requests a certificate. By using B<s_client> the CA list can be viewed 299and checked. However some servers only request client authentication 300after a specific URL is requested. To obtain the list in this case it 301is necessary to use the B<-prexit> option and send an HTTP request 302for an appropriate page. 303 304If a certificate is specified on the command line using the B<-cert> 305option it will not be used unless the server specifically requests 306a client certificate. Therefor merely including a client certificate 307on the command line is no guarantee that the certificate works. 308 309If there are problems verifying a server certificate then the 310B<-showcerts> option can be used to show the whole chain. 311 312Since the SSLv23 client hello cannot include compression methods or extensions 313these will only be supported if its use is disabled, for example by using the 314B<-no_sslv2> option. 315 316The B<s_client> utility is a test tool and is designed to continue the 317handshake after any certificate verification errors. As a result it will 318accept any certificate chain (trusted or not) sent by the peer. None test 319applications should B<not> do this as it makes them vulnerable to a MITM 320attack. 321 322=head1 BUGS 323 324Because this program has a lot of options and also because some of 325the techniques used are rather old, the C source of s_client is rather 326hard to read and not a model of how things should be done. A typical 327SSL client program would be much simpler. 328 329The B<-prexit> option is a bit of a hack. We should really report 330information whenever a session is renegotiated. 331 332=head1 SEE ALSO 333 334L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)> 335 336=cut 337