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