1S_CLIENT(1) OpenSSL S_CLIENT(1)
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6 s_client - SSL/TLS client program
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9 openssl s_client [-connect host:port] [-verify depth] [-cert filename]
10 [-certform DER⎪PEM] [-key filename] [-keyform DER⎪PEM] [-pass arg]
11 [-CApath directory] [-CAfile filename] [-reconnect] [-pause]
12 [-showcerts] [-debug] [-msg] [-nbio_test] [-state] [-nbio] [-crlf]
13 [-ign_eof] [-quiet] [-ssl2] [-ssl3] [-tls1] [-no_ssl2] [-no_ssl3]
14 [-no_tls1] [-bugs] [-cipher cipherlist] [-starttls protocol] [-engine
15 id] [-rand file(s)]
16
18 The s_client command implements a generic SSL/TLS client which connects
19 to a remote host using SSL/TLS. It is a very useful diagnostic tool for
20 SSL servers.
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23 -connect host:port
24 This specifies the host and optional port to connect to. If not
25 specified then an attempt is made to connect to the local host on
26 port 4433.
27 -cert certname
29 The certificate to use, if one is requested by the server. The
30 default is not to use a certificate.
31 -certform format
33 The certificate format to use: DER or PEM. PEM is the default.
34 -key keyfile
36 The private key to use. If not specified then the certificate file
37 will be used.
38 -keyform format
40 The private format to use: DER or PEM. PEM is the default.
41 -pass arg
43 the private key password source. For more information about the
44 format of arg see the PASS PHRASE ARGUMENTS section in openssl(1).
45 -verify depth
47 The verify depth to use. This specifies the maximum length of the
48 server certificate chain and turns on server certificate verifica‐
49 tion. Currently the verify operation continues after errors so all
50 the problems with a certificate chain can be seen. As a side effect
51 the connection will never fail due to a server certificate verify
52 failure.
53 -CApath directory
55 The directory to use for server certificate verification. This
56 directory must be in "hash format", see verify for more informa‐
57 tion. These are also used when building the client certificate
58 chain.
59 -CAfile file
61 A file containing trusted certificates to use during server authen‐
62 tication and to use when attempting to build the client certificate
63 chain.
64 -reconnect
66 reconnects to the same server 5 times using the same session ID,
67 this can be used as a test that session caching is working.
68 -pause
70 pauses 1 second between each read and write call.
71 -showcerts
73 display the whole server certificate chain: normally only the
74 server certificate itself is displayed.
75 -prexit
77 print session information when the program exits. This will always
78 attempt to print out information even if the connection fails. Nor‐
79 mally information will only be printed out once if the connection
80 succeeds. This option is useful because the cipher in use may be
81 renegotiated or the connection may fail because a client certifi‐
82 cate is required or is requested only after an attempt is made to
83 access a certain URL. Note: the output produced by this option is
84 not always accurate because a connection might never have been
85 established.
86 -state
88 prints out the SSL session states.
89 -debug
91 print extensive debugging information including a hex dump of all
92 traffic.
93 -msg
95 show all protocol messages with hex dump.
96 -nbio_test
98 tests non-blocking I/O
99 -nbio
101 turns on non-blocking I/O
102 -crlf
104 this option translated a line feed from the terminal into CR+LF as
105 required by some servers.
106 -ign_eof
108 inhibit shutting down the connection when end of file is reached in
109 the input.
110 -quiet
112 inhibit printing of session and certificate information. This
113 implicitly turns on -ign_eof as well.
114 -ssl2, -ssl3, -tls1, -no_ssl2, -no_ssl3, -no_tls1
116 these options disable the use of certain SSL or TLS protocols. By
117 default the initial handshake uses a method which should be compat‐
118 ible with all servers and permit them to use SSL v3, SSL v2 or TLS
119 as appropriate.
120 Unfortunately there are a lot of ancient and broken servers in use
122 which cannot handle this technique and will fail to connect. Some
123 servers only work if TLS is turned off with the -no_tls option oth‐
124 ers will only support SSL v2 and may need the -ssl2 option.
125 -bugs
127 there are several known bug in SSL and TLS implementations. Adding
128 this option enables various workarounds.
129 -cipher cipherlist
131 this allows the cipher list sent by the client to be modified.
132 Although the server determines which cipher suite is used it should
133 take the first supported cipher in the list sent by the client. See
134 the ciphers command for more information.
135 -starttls protocol
137 send the protocol-specific message(s) to switch to TLS for communi‐
138 cation. protocol is a keyword for the intended protocol. Cur‐
139 rently, the only supported keywords are "smtp" and "pop3".
140 -engine id
142 specifying an engine (by it's unique id string) will cause s_client
143 to attempt to obtain a functional reference to the specified
144 engine, thus initialising it if needed. The engine will then be set
145 as the default for all available algorithms.
146 -rand file(s)
148 a file or files containing random data used to seed the random num‐
149 ber generator, or an EGD socket (see RAND_egd(3)). Multiple files
150 can be specified separated by a OS-dependent character. The sepa‐
151 rator is ; for MS-Windows, , for OpenVMS, and : for all others.
152
154 If a connection is established with an SSL server then any data
155 received from the server is displayed and any key presses will be sent
156 to the server. When used interactively (which means neither -quiet nor
157 -ign_eof have been given), the session will be renegotiated if the line
158 begins with an R, and if the line begins with a Q or if end of file is
159 reached, the connection will be closed down.
160
162 s_client can be used to debug SSL servers. To connect to an SSL HTTP
163 server the command:
164 openssl s_client -connect servername:443
166 would typically be used (https uses port 443). If the connection suc‐
168 ceeds then an HTTP command can be given such as "GET /" to retrieve a
169 web page.
170 If the handshake fails then there are several possible causes, if it is
172 nothing obvious like no client certificate then the -bugs, -ssl2,
173 -ssl3, -tls1, -no_ssl2, -no_ssl3, -no_tls1 options can be tried in case
174 it is a buggy server. In particular you should play with these options
175 before submitting a bug report to an OpenSSL mailing list.
176 A frequent problem when attempting to get client certificates working
178 is that a web client complains it has no certificates or gives an empty
179 list to choose from. This is normally because the server is not sending
180 the clients certificate authority in its "acceptable CA list" when it
181 requests a certificate. By using s_client the CA list can be viewed and
182 checked. However some servers only request client authentication after
183 a specific URL is requested. To obtain the list in this case it is nec‐
184 essary to use the -prexit option and send an HTTP request for an appro‐
185 priate page.
186 If a certificate is specified on the command line using the -cert
188 option it will not be used unless the server specifically requests a
189 client certificate. Therefor merely including a client certificate on
190 the command line is no guarantee that the certificate works.
191 If there are problems verifying a server certificate then the
193 -showcerts option can be used to show the whole chain.
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196 Because this program has a lot of options and also because some of the
197 techniques used are rather old, the C source of s_client is rather hard
198 to read and not a model of how things should be done. A typical SSL
199 client program would be much simpler.
200 The -verify option should really exit if the server verification fails.
202 The -prexit option is a bit of a hack. We should really report informa‐
204 tion whenever a session is renegotiated.
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207 sess_id(1), s_server(1), ciphers(1)
2080.9.8b 2004-11-16 S_CLIENT(1)