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S_CLIENT(1)                                        OpenSSL                                       S_CLIENT(1)



NAME
       s_client - SSL/TLS client program

SYNOPSIS
       openssl s_client [-connect host:port] [-verify depth] [-cert filename] [-certform DER|PEM] [-key
       filename] [-keyform DER|PEM] [-pass arg] [-CApath directory] [-CAfile filename] [-reconnect] [-pause]
       [-showcerts] [-debug] [-msg] [-nbio_test] [-state] [-nbio] [-crlf] [-ign_eof] [-quiet] [-ssl2]
       [-ssl3] [-tls1] [-no_ssl2] [-no_ssl3] [-no_tls1] [-bugs] [-cipher cipherlist] [-starttls protocol]
       [-engine id] [-tlsextdebug] [-no_ticket] [-sess_out filename] [-sess_in filename] [-rand file(s)]

DESCRIPTION
       The s_client command implements a generic SSL/TLS client which connects to a remote host using
       SSL/TLS. It is a very useful diagnostic tool for SSL servers.

OPTIONS
       -connect host:port
           This specifies the host and optional port to connect to. If not specified then an attempt is made
           to connect to the local host on port 4433.

       -cert certname
           The certificate to use, if one is requested by the server. The default is not to use a
           certificate.

       -certform format
           The certificate format to use: DER or PEM. PEM is the default.

       -key keyfile
           The private key to use. If not specified then the certificate file will be used.

       -keyform format
           The private format to use: DER or PEM. PEM is the default.

       -pass arg
           the private key password source. For more information about the format of arg see the PASS PHRASE
           ARGUMENTS section in openssl(1).

       -verify depth
           The verify depth to use. This specifies the maximum length of the server certificate chain and
           turns on server certificate verification.  Currently the verify operation continues after errors
           so all the problems with a certificate chain can be seen. As a side effect the connection will
           never fail due to a server certificate verify failure.

       -CApath directory
           The directory to use for server certificate verification. This directory must be in "hash
           format", see verify for more information. These are also used when building the client
           certificate chain.

       -CAfile file
           A file containing trusted certificates to use during server authentication and to use when
           attempting to build the client certificate chain.

       -reconnect
           reconnects to the same server 5 times using the same session ID, this can be used as a test that
           session caching is working.

       -pause
           pauses 1 second between each read and write call.

       -showcerts
           display the whole server certificate chain: normally only the server certificate itself is
           displayed.

       -prexit
           print session information when the program exits. This will always attempt to print out
           information even if the connection fails. Normally information will only be printed out once if
           the connection succeeds. This option is useful because the cipher in use may be renegotiated or
           the connection may fail because a client certificate is required or is requested only after an
           attempt is made to access a certain URL. Note: the output produced by this option is not always
           accurate because a connection might never have been established.

       -state
           prints out the SSL session states.

       -debug
           print extensive debugging information including a hex dump of all traffic.

       -msg
           show all protocol messages with hex dump.

       -nbio_test
           tests non-blocking I/O

       -nbio
           turns on non-blocking I/O

       -crlf
           this option translated a line feed from the terminal into CR+LF as required by some servers.

       -ign_eof
           inhibit shutting down the connection when end of file is reached in the input.

       -quiet
           inhibit printing of session and certificate information.  This implicitly turns on -ign_eof as
           well.

       -ssl2, -ssl3, -tls1, -no_ssl2, -no_ssl3, -no_tls1
           these options disable the use of certain SSL or TLS protocols. By default the initial handshake
           uses a method which should be compatible with all servers and permit them to use SSL v3, SSL v2
           or TLS as appropriate.

           Unfortunately there are a lot of ancient and broken servers in use which cannot handle this
           technique and will fail to connect. Some servers only work if TLS is turned off with the -no_tls
           option others will only support SSL v2 and may need the -ssl2 option.

       -bugs
           there are several known bug in SSL and TLS implementations. Adding this option enables various
           workarounds.

       -cipher cipherlist
           this allows the cipher list sent by the client to be modified. Although the server determines
           which cipher suite is used it should take the first supported cipher in the list sent by the
           client. See the ciphers command for more information.

       -starttls protocol
           send the protocol-specific message(s) to switch to TLS for communication.  protocol is a keyword
           for the intended protocol.  Currently, the only supported keywords are "smtp", "pop3", "imap",
           and "ftp".

       -tlsextdebug
           print out a hex dump of any TLS extensions received from the server. Note: this option is only
           available if extension support is explicitly enabled at compile time

       -no_ticket
           disable RFC4507bis session ticket support. Note: this option is only available if extension
           support is explicitly enabled at compile time

       -sess_out filename
           output SSL session to filename

       -sess_in sess.pem
           load SSL session from filename. The client will attempt to resume a connection from this session.

       -engine id
           specifying an engine (by it's unique id string) will cause s_client to attempt to obtain a
           functional reference to the specified engine, thus initialising it if needed. The engine will
           then be set as the default for all available algorithms.

       -rand file(s)
           a file or files containing random data used to seed the random number generator, or an EGD socket
           (see RAND_egd(3)).  Multiple files can be specified separated by a OS-dependent character.  The
           separator is ; for MS-Windows, , for OpenVMS, and : for all others.

CONNECTED COMMANDS
       If a connection is established with an SSL server then any data received from the server is displayed
       and any key presses will be sent to the server. When used interactively (which means neither -quiet
       nor -ign_eof have been given), the session will be renegotiated if the line begins with an R, and if
       the line begins with a Q or if end of file is reached, the connection will be closed down.

NOTES
       s_client can be used to debug SSL servers. To connect to an SSL HTTP server the command:

        openssl s_client -connect servername:443

       would typically be used (https uses port 443). If the connection succeeds then an HTTP command can be
       given such as "GET /" to retrieve a web page.

       If the handshake fails then there are several possible causes, if it is nothing obvious like no
       client certificate then the -bugs, -ssl2, -ssl3, -tls1, -no_ssl2, -no_ssl3, -no_tls1 options can be
       tried in case it is a buggy server. In particular you should play with these options before
       submitting a bug report to an OpenSSL mailing list.

       A frequent problem when attempting to get client certificates working is that a web client complains
       it has no certificates or gives an empty list to choose from. This is normally because the server is
       not sending the clients certificate authority in its "acceptable CA list" when it requests a
       certificate. By using s_client the CA list can be viewed and checked. However some servers only
       request client authentication after a specific URL is requested. To obtain the list in this case it
       is necessary to use the -prexit option and send an HTTP request for an appropriate page.

       If a certificate is specified on the command line using the -cert option it will not be used unless
       the server specifically requests a client certificate. Therefor merely including a client certificate
       on the command line is no guarantee that the certificate works.

       If there are problems verifying a server certificate then the -showcerts option can be used to show
       the whole chain.

       Since the SSLv23 client hello cannot include compression methods or extensions these will only be
       supported if its use is disabled, for example by using the -no_sslv2 option.

       TLS extensions are only supported in OpenSSL 0.9.8 if they are explictly enabled at compile time
       using for example the enable-tlsext switch.

BUGS
       Because this program has a lot of options and also because some of the techniques used are rather
       old, the C source of s_client is rather hard to read and not a model of how things should be done. A
       typical SSL client program would be much simpler.

       The -verify option should really exit if the server verification fails.

       The -prexit option is a bit of a hack. We should really report information whenever a session is
       renegotiated.

SEE ALSO
       sess_id(1), s_server(1), ciphers(1)



50                                               2013-03-05                                      S_CLIENT(1)

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