s_client(1) - phpMan

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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] [-servername name] [-verify depth]
       [-verify_return_error] [-cert filename] [-certform DER|PEM] [-key filename] [-keyform
       DER|PEM] [-pass arg] [-CApath directory] [-CAfile filename] [-trusted_first]
       [-no_alt_chains] [-reconnect] [-pause] [-showcerts] [-debug] [-msg] [-nbio_test] [-state]
       [-nbio] [-crlf] [-ign_eof] [-no_ign_eof] [-quiet] [-ssl3] [-tls1] [-tls1_1] [-tls1_2]
       [-dtls1] [-no_ssl3] [-no_tls1] [-no_tls1_1] [-no_tls1_2] [-fallback_scsv] [-bugs] [-cipher
       cipherlist] [-krb5svc service] [-serverpref] [-starttls protocol] [-xmpphost hostname]
       [-name hostname] [-engine id] [-tlsextdebug] [-no_ticket] [-sess_out filename] [-sess_in
       filename] [-rand file(s)] [-serverinfo types] [-status] [-alpn protocols] [-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, -trusted_first -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.

       -ssl3, -tls1, -tls1_1, -tls1_2, -dtls1, -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.

       -krb5svc service
           the Kerberos service name to use (default "host"). This means s_server will expect a
           ticket for the principal service/hostname@REALM, and will need keys for that principal
           in its keytab.

       -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", "ftp", "xmpp", "xmpp-server", "irc", "postgres", "lmtp",
           "nntp", "sieve" and "ldap".

       -xmpphost hostname
           This option, when used with "-starttls xmpp" or "-starttls xmpp-server", specifies the
           host for the "to" attribute of the stream element.  If this option is not specified,
           then the host specified with "-connect" will be used.

       -name hostname
           the host name to use with "-starttls smtp".  If this option is not specified, the
           default "openssl.client.net" will be used.

       -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.

       -alpn protocols, -nextprotoneg protocols
           these flags enable the Enable the Application-Layer Protocol Negotiation or Next
           Protocol Negotiation extension, respectively. ALPN is the IETF standard and replaces
           NPN.  The protocols list is a 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, -ssl3, -tls1, -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.

       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.



1.0.2k                                      2017-08-04                                S_CLIENT(1)


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