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", "pop3", "imap", and "ftp".
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