s_client.pod revision 264331
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<-verify_return_error>] 14[B<-cert filename>] 15[B<-certform DER|PEM>] 16[B<-key filename>] 17[B<-keyform DER|PEM>] 18[B<-pass arg>] 19[B<-CApath directory>] 20[B<-CAfile filename>] 21[B<-reconnect>] 22[B<-pause>] 23[B<-showcerts>] 24[B<-debug>] 25[B<-msg>] 26[B<-nbio_test>] 27[B<-state>] 28[B<-nbio>] 29[B<-crlf>] 30[B<-ign_eof>] 31[B<-quiet>] 32[B<-ssl2>] 33[B<-ssl3>] 34[B<-tls1>] 35[B<-no_ssl2>] 36[B<-no_ssl3>] 37[B<-no_tls1>] 38[B<-bugs>] 39[B<-cipher cipherlist>] 40[B<-starttls protocol>] 41[B<-engine id>] 42[B<-tlsextdebug>] 43[B<-no_ticket>] 44[B<-sess_out filename>] 45[B<-sess_in filename>] 46[B<-rand file(s)>] 47 48=head1 DESCRIPTION 49 50The B<s_client> command implements a generic SSL/TLS client which connects 51to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for 52SSL servers. 53 54=head1 OPTIONS 55 56=over 4 57 58=item B<-connect host:port> 59 60This specifies the host and optional port to connect to. If not specified 61then an attempt is made to connect to the local host on port 4433. 62 63=item B<-cert certname> 64 65The certificate to use, if one is requested by the server. The default is 66not to use a certificate. 67 68=item B<-certform format> 69 70The certificate format to use: DER or PEM. PEM is the default. 71 72=item B<-key keyfile> 73 74The private key to use. If not specified then the certificate file will 75be used. 76 77=item B<-keyform format> 78 79The private format to use: DER or PEM. PEM is the default. 80 81=item B<-pass arg> 82 83the private key password source. For more information about the format of B<arg> 84see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>. 85 86=item B<-verify depth> 87 88The verify depth to use. This specifies the maximum length of the 89server certificate chain and turns on server certificate verification. 90Currently the verify operation continues after errors so all the problems 91with a certificate chain can be seen. As a side effect the connection 92will never fail due to a server certificate verify failure. 93 94=item B<-verify_return_error> 95 96Return verification errors instead of continuing. This will typically 97abort the handshake with a fatal error. 98 99=item B<-CApath directory> 100 101The directory to use for server certificate verification. This directory 102must be in "hash format", see B<verify> for more information. These are 103also used when building the client certificate chain. 104 105=item B<-CAfile file> 106 107A file containing trusted certificates to use during server authentication 108and to use when attempting to build the client certificate chain. 109 110=item B<-purpose, -ignore_critical, -issuer_checks, -crl_check, -crl_check_all, -policy_check, -extended_crl, -x509_strict, -policy -check_ss_sig> 111 112Set various certificate chain valiadition option. See the 113L<B<verify>|verify(1)> manual page for details. 114 115=item B<-reconnect> 116 117reconnects to the same server 5 times using the same session ID, this can 118be used as a test that session caching is working. 119 120=item B<-pause> 121 122pauses 1 second between each read and write call. 123 124=item B<-showcerts> 125 126display the whole server certificate chain: normally only the server 127certificate itself is displayed. 128 129=item B<-prexit> 130 131print session information when the program exits. This will always attempt 132to print out information even if the connection fails. Normally information 133will only be printed out once if the connection succeeds. This option is useful 134because the cipher in use may be renegotiated or the connection may fail 135because a client certificate is required or is requested only after an 136attempt is made to access a certain URL. Note: the output produced by this 137option is not always accurate because a connection might never have been 138established. 139 140=item B<-state> 141 142prints out the SSL session states. 143 144=item B<-debug> 145 146print extensive debugging information including a hex dump of all traffic. 147 148=item B<-msg> 149 150show all protocol messages with hex dump. 151 152=item B<-nbio_test> 153 154tests non-blocking I/O 155 156=item B<-nbio> 157 158turns on non-blocking I/O 159 160=item B<-crlf> 161 162this option translated a line feed from the terminal into CR+LF as required 163by some servers. 164 165=item B<-ign_eof> 166 167inhibit shutting down the connection when end of file is reached in the 168input. 169 170=item B<-quiet> 171 172inhibit printing of session and certificate information. This implicitly 173turns on B<-ign_eof> as well. 174 175=item B<-psk_identity identity> 176 177Use the PSK identity B<identity> when using a PSK cipher suite. 178 179=item B<-psk key> 180 181Use the PSK key B<key> when using a PSK cipher suite. The key is 182given as a hexadecimal number without leading 0x, for example -psk 1831a2b3c4d. 184 185=item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> 186 187these options disable the use of certain SSL or TLS protocols. By default 188the initial handshake uses a method which should be compatible with all 189servers and permit them to use SSL v3, SSL v2 or TLS as appropriate. 190 191Unfortunately there are a lot of ancient and broken servers in use which 192cannot handle this technique and will fail to connect. Some servers only 193work if TLS is turned off with the B<-no_tls> option others will only 194support SSL v2 and may need the B<-ssl2> option. 195 196=item B<-bugs> 197 198there are several known bug in SSL and TLS implementations. Adding this 199option enables various workarounds. 200 201=item B<-cipher cipherlist> 202 203this allows the cipher list sent by the client to be modified. Although 204the server determines which cipher suite is used it should take the first 205supported cipher in the list sent by the client. See the B<ciphers> 206command for more information. 207 208=item B<-starttls protocol> 209 210send the protocol-specific message(s) to switch to TLS for communication. 211B<protocol> is a keyword for the intended protocol. Currently, the only 212supported keywords are "smtp", "pop3", "imap", and "ftp". 213 214=item B<-tlsextdebug> 215 216print out a hex dump of any TLS extensions received from the server. 217 218=item B<-no_ticket> 219 220disable RFC4507bis session ticket support. 221 222=item B<-sess_out filename> 223 224output SSL session to B<filename> 225 226=item B<-sess_in sess.pem> 227 228load SSL session from B<filename>. The client will attempt to resume a 229connection from this session. 230 231=item B<-engine id> 232 233specifying an engine (by its unique B<id> string) will cause B<s_client> 234to attempt to obtain a functional reference to the specified engine, 235thus initialising it if needed. The engine will then be set as the default 236for all available algorithms. 237 238=item B<-rand file(s)> 239 240a file or files containing random data used to seed the random number 241generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>). 242Multiple files can be specified separated by a OS-dependent character. 243The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for 244all others. 245 246=back 247 248=head1 CONNECTED COMMANDS 249 250If a connection is established with an SSL server then any data received 251from the server is displayed and any key presses will be sent to the 252server. When used interactively (which means neither B<-quiet> nor B<-ign_eof> 253have been given), the session will be renegotiated if the line begins with an 254B<R>, and if the line begins with a B<Q> or if end of file is reached, the 255connection will be closed down. 256 257=head1 NOTES 258 259B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP 260server the command: 261 262 openssl s_client -connect servername:443 263 264would typically be used (https uses port 443). If the connection succeeds 265then an HTTP command can be given such as "GET /" to retrieve a web page. 266 267If the handshake fails then there are several possible causes, if it is 268nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>, 269B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried 270in case it is a buggy server. In particular you should play with these 271options B<before> submitting a bug report to an OpenSSL mailing list. 272 273A frequent problem when attempting to get client certificates working 274is that a web client complains it has no certificates or gives an empty 275list to choose from. This is normally because the server is not sending 276the clients certificate authority in its "acceptable CA list" when it 277requests a certificate. By using B<s_client> the CA list can be viewed 278and checked. However some servers only request client authentication 279after a specific URL is requested. To obtain the list in this case it 280is necessary to use the B<-prexit> option and send an HTTP request 281for an appropriate page. 282 283If a certificate is specified on the command line using the B<-cert> 284option it will not be used unless the server specifically requests 285a client certificate. Therefor merely including a client certificate 286on the command line is no guarantee that the certificate works. 287 288If there are problems verifying a server certificate then the 289B<-showcerts> option can be used to show the whole chain. 290 291Since the SSLv23 client hello cannot include compression methods or extensions 292these will only be supported if its use is disabled, for example by using the 293B<-no_sslv2> option. 294 295The B<s_client> utility is a test tool and is designed to continue the 296handshake after any certificate verification errors. As a result it will 297accept any certificate chain (trusted or not) sent by the peer. None test 298applications should B<not> do this as it makes them vulnerable to a MITM 299attack. This behaviour can be changed by with the B<-verify_return_error> 300option: any verify errors are then returned aborting the handshake. 301 302=head1 BUGS 303 304Because this program has a lot of options and also because some of 305the techniques used are rather old, the C source of s_client is rather 306hard to read and not a model of how things should be done. A typical 307SSL client program would be much simpler. 308 309The B<-prexit> option is a bit of a hack. We should really report 310information whenever a session is renegotiated. 311 312=head1 SEE ALSO 313 314L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)> 315 316=cut 317