s_client - SSL/TLS client program



  • S_CLIENT(1SSL)				     OpenSSL				   S_CLIENT(1SSL)
    
    NAME
           s_client - SSL/TLS client program
    
    SYNOPSIS
           openssl s_client [-connect host:port] [-servername name] [-verify depth]
           [-verify_return_error] [-cert filename] [-certform DER|PEM] [-key filename] [-keyform
           DER|PEM] [-pass arg] [-CApath directory] [-CAfile filename] [-no_alt_chains] [-reconnect]
           [-pause] [-showcerts] [-debug] [-msg] [-nbio_test] [-state] [-nbio] [-crlf] [-ign_eof]
           [-no_ign_eof] [-quiet] [-ssl2] [-ssl3] [-tls1] [-no_ssl2] [-no_ssl3] [-no_tls1]
           [-no_tls1_1] [-no_tls1_2] [-fallback_scsv] [-bugs] [-cipher cipherlist] [-serverpref]
           [-starttls protocol] [-engine id] [-tlsextdebug] [-no_ticket] [-sess_out filename]
           [-sess_in filename] [-rand file(s)] [-serverinfo types] [-status] [-nextprotoneg
           protocols]
    
    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.
    
           -servername name
    	   Set the TLS SNI (Server Name Indication) extension in the ClientHello message.
    
           -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.
    
           -verify_return_error
    	   Return verification errors instead of continuing. This will typically abort the
    	   handshake with a fatal error.
    
           -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.
    
           -purpose, -ignore_critical, -issuer_checks, -crl_check, -crl_check_all, -policy_check,
           -extended_crl, -x509_strict, -policy -check_ss_sig -no_alt_chains
    	   Set various certificate chain valiadition option. See the verify manual page for
    	   details.
    
           -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.
    
           -no_ign_eof
    	   shut down the connection when end of file is reached in the input.  Can be used to
    	   override the implicit -ign_eof after -quiet.
    
           -psk_identity identity
    	   Use the PSK identity identity when using a PSK cipher suite.
    
           -psk key
    	   Use the PSK key key when using a PSK cipher suite. The key is given as a hexadecimal
    	   number without leading 0x, for example -psk 1a2b3c4d.
    
           -ssl2, -ssl3, -tls1, -tls1_1, -tls1_2, -no_ssl2, -no_ssl3, -no_tls1, -no_tls1_1,
           -no_tls1_2
    	   These options require or disable the use of the specified SSL or TLS protocols.  By
    	   default the initial handshake uses a version-flexible method which will negotiate the
    	   highest mutually supported protocol version.
    
           -fallback_scsv
    	   Send TLS_FALLBACK_SCSV in the ClientHello.
    
           -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.
    
           -serverpref
    	   use the server's cipher preferences; only used for SSLV2.
    
           -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.
    
           -no_ticket
    	   disable RFC4507bis session ticket support.
    
           -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 its 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.
    
           -serverinfo types
    	   a list of comma-separated TLS Extension Types (numbers between 0 and 65535).  Each
    	   type will be sent as an empty ClientHello TLS Extension.  The server's response (if
    	   any) will be encoded and displayed as a PEM file.
    
           -status
    	   sends a certificate status request to the server (OCSP stapling). The server response
    	   (if any) is printed out.
    
           -nextprotoneg protocols
    	   enable Next Protocol Negotiation TLS extension and provide a list of comma-separated
    	   protocol names that the client should advertise support for. The list should contain
    	   most wanted protocols first.  Protocol names are printable ASCII strings, for example
    	   "http/1.1" or "spdy/3".  Empty list of protocols is treated specially and will cause
    	   the client to advertise support for the TLS extension but disconnect just after
    	   reciving ServerHello with a list of server supported protocols.
    
    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.
    
           The s_client utility is a test tool and is designed to continue the handshake after any
           certificate verification errors. As a result it will accept any certificate chain (trusted
           or not) sent by the peer. None test applications should not do this as it makes them
           vulnerable to a MITM attack. This behaviour can be changed by with the
           -verify_return_error option: any verify errors are then returned aborting the handshake.
    
    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 -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)
    
    HISTORY
           The -no_alt_chains options was first added to OpenSSL 1.0.2b.
    
    1.0.2g					    2016-03-01				   S_CLIENT(1SSL)
    

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