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<-reconnect>] 21[B<-pause>] 22[B<-showcerts>] 23[B<-debug>] 24[B<-msg>] 25[B<-nbio_test>] 26[B<-state>] 27[B<-nbio>] 28[B<-crlf>] 29[B<-ign_eof>] 30[B<-quiet>] 31[B<-ssl2>] 32[B<-ssl3>] 33[B<-tls1>] 34[B<-no_ssl2>] 35[B<-no_ssl3>] 36[B<-no_tls1>] 37[B<-bugs>] 38[B<-cipher cipherlist>] 39[B<-starttls protocol>] 40[B<-engine id>] 41[B<-tlsextdebug>] 42[B<-no_ticket>] 43[B<-sess_out filename>] 44[B<-sess_in filename>] 45[B<-rand file(s)>] 46 47=head1 DESCRIPTION 48 49The B<s_client> command implements a generic SSL/TLS client which connects 50to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for 51SSL servers. 52 53=head1 OPTIONS 54 55=over 4 56 57=item B<-connect host:port> 58 59This specifies the host and optional port to connect to. If not specified 60then an attempt is made to connect to the local host on port 4433. 61 62=item B<-cert certname> 63 64The certificate to use, if one is requested by the server. The default is 65not to use a certificate. 66 67=item B<-certform format> 68 69The certificate format to use: DER or PEM. PEM is the default. 70 71=item B<-key keyfile> 72 73The private key to use. If not specified then the certificate file will 74be used. 75 76=item B<-keyform format> 77 78The private format to use: DER or PEM. PEM is the default. 79 80=item B<-pass arg> 81 82the private key password source. For more information about the format of B<arg> 83see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)|openssl(1)>. 84 85=item B<-verify depth> 86 87The verify depth to use. This specifies the maximum length of the 88server certificate chain and turns on server certificate verification. 89Currently the verify operation continues after errors so all the problems 90with a certificate chain can be seen. As a side effect the connection 91will never fail due to a server certificate verify failure. 92 93=item B<-CApath directory> 94 95The directory to use for server certificate verification. This directory 96must be in "hash format", see B<verify> for more information. These are 97also used when building the client certificate chain. 98 99=item B<-CAfile file> 100 101A file containing trusted certificates to use during server authentication 102and to use when attempting to build the client certificate chain. 103 104=item B<-reconnect> 105 106reconnects to the same server 5 times using the same session ID, this can 107be used as a test that session caching is working. 108 109=item B<-pause> 110 111pauses 1 second between each read and write call. 112 113=item B<-showcerts> 114 115display the whole server certificate chain: normally only the server 116certificate itself is displayed. 117 118=item B<-prexit> 119 120print session information when the program exits. This will always attempt 121to print out information even if the connection fails. Normally information 122will only be printed out once if the connection succeeds. This option is useful 123because the cipher in use may be renegotiated or the connection may fail 124because a client certificate is required or is requested only after an 125attempt is made to access a certain URL. Note: the output produced by this 126option is not always accurate because a connection might never have been 127established. 128 129=item B<-state> 130 131prints out the SSL session states. 132 133=item B<-debug> 134 135print extensive debugging information including a hex dump of all traffic. 136 137=item B<-msg> 138 139show all protocol messages with hex dump. 140 141=item B<-nbio_test> 142 143tests non-blocking I/O 144 145=item B<-nbio> 146 147turns on non-blocking I/O 148 149=item B<-crlf> 150 151this option translated a line feed from the terminal into CR+LF as required 152by some servers. 153 154=item B<-ign_eof> 155 156inhibit shutting down the connection when end of file is reached in the 157input. 158 159=item B<-quiet> 160 161inhibit printing of session and certificate information. This implicitly 162turns on B<-ign_eof> as well. 163 164=item B<-ssl2>, B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> 165 166these options disable the use of certain SSL or TLS protocols. By default 167the initial handshake uses a method which should be compatible with all 168servers and permit them to use SSL v3, SSL v2 or TLS as appropriate. 169 170Unfortunately there are a lot of ancient and broken servers in use which 171cannot handle this technique and will fail to connect. Some servers only 172work if TLS is turned off with the B<-no_tls> option others will only 173support SSL v2 and may need the B<-ssl2> option. 174 175=item B<-bugs> 176 177there are several known bug in SSL and TLS implementations. Adding this 178option enables various workarounds. 179 180=item B<-cipher cipherlist> 181 182this allows the cipher list sent by the client to be modified. Although 183the server determines which cipher suite is used it should take the first 184supported cipher in the list sent by the client. See the B<ciphers> 185command for more information. 186 187=item B<-starttls protocol> 188 189send the protocol-specific message(s) to switch to TLS for communication. 190B<protocol> is a keyword for the intended protocol. Currently, the only 191supported keywords are "smtp", "pop3", "imap", and "ftp". 192 193=item B<-tlsextdebug> 194 195print out a hex dump of any TLS extensions received from the server. Note: this 196option is only available if extension support is explicitly enabled at compile 197time 198 199=item B<-no_ticket> 200 201disable RFC4507bis session ticket support. Note: this option is only available 202if extension support is explicitly enabled at compile time 203 204=item B<-sess_out filename> 205 206output SSL session to B<filename> 207 208=item B<-sess_in sess.pem> 209 210load SSL session from B<filename>. The client will attempt to resume a 211connection from this session. 212 213=item B<-engine id> 214 215specifying an engine (by it's unique B<id> string) will cause B<s_client> 216to attempt to obtain a functional reference to the specified engine, 217thus initialising it if needed. The engine will then be set as the default 218for all available algorithms. 219 220=item B<-rand file(s)> 221 222a file or files containing random data used to seed the random number 223generator, or an EGD socket (see L<RAND_egd(3)|RAND_egd(3)>). 224Multiple files can be specified separated by a OS-dependent character. 225The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for 226all others. 227 228=back 229 230=head1 CONNECTED COMMANDS 231 232If a connection is established with an SSL server then any data received 233from the server is displayed and any key presses will be sent to the 234server. When used interactively (which means neither B<-quiet> nor B<-ign_eof> 235have been given), the session will be renegotiated if the line begins with an 236B<R>, and if the line begins with a B<Q> or if end of file is reached, the 237connection will be closed down. 238 239=head1 NOTES 240 241B<s_client> can be used to debug SSL servers. To connect to an SSL HTTP 242server the command: 243 244 openssl s_client -connect servername:443 245 246would typically be used (https uses port 443). If the connection succeeds 247then an HTTP command can be given such as "GET /" to retrieve a web page. 248 249If the handshake fails then there are several possible causes, if it is 250nothing obvious like no client certificate then the B<-bugs>, B<-ssl2>, 251B<-ssl3>, B<-tls1>, B<-no_ssl2>, B<-no_ssl3>, B<-no_tls1> options can be tried 252in case it is a buggy server. In particular you should play with these 253options B<before> submitting a bug report to an OpenSSL mailing list. 254 255A frequent problem when attempting to get client certificates working 256is that a web client complains it has no certificates or gives an empty 257list to choose from. This is normally because the server is not sending 258the clients certificate authority in its "acceptable CA list" when it 259requests a certificate. By using B<s_client> the CA list can be viewed 260and checked. However some servers only request client authentication 261after a specific URL is requested. To obtain the list in this case it 262is necessary to use the B<-prexit> option and send an HTTP request 263for an appropriate page. 264 265If a certificate is specified on the command line using the B<-cert> 266option it will not be used unless the server specifically requests 267a client certificate. Therefor merely including a client certificate 268on the command line is no guarantee that the certificate works. 269 270If there are problems verifying a server certificate then the 271B<-showcerts> option can be used to show the whole chain. 272 273Since the SSLv23 client hello cannot include compression methods or extensions 274these will only be supported if its use is disabled, for example by using the 275B<-no_sslv2> option. 276 277TLS extensions are only supported in OpenSSL 0.9.8 if they are explictly 278enabled at compile time using for example the B<enable-tlsext> switch. 279 280=head1 BUGS 281 282Because this program has a lot of options and also because some of 283the techniques used are rather old, the C source of s_client is rather 284hard to read and not a model of how things should be done. A typical 285SSL client program would be much simpler. 286 287The B<-verify> option should really exit if the server verification 288fails. 289 290The B<-prexit> option is a bit of a hack. We should really report 291information whenever a session is renegotiated. 292 293=head1 SEE ALSO 294 295L<sess_id(1)|sess_id(1)>, L<s_server(1)|s_server(1)>, L<ciphers(1)|ciphers(1)> 296 297=cut 298