DOC HOME SITE MAP MAN PAGES GNU INFO SEARCH PRINT BOOK
 

/usr/man/cat.1/openssl-s_client.1(/usr/man/cat.1/openssl-s_client.1)




S_CLIENT(1)                  OpenSSL                  S_CLIENT(1)


NAME

     openssl-s_client, 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] [-sigalgs sigalglist] [-curves
     curvelist] [-cipher cipherlist] [-serverpref] [-starttls
     protocol] [-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

1.0.2t               Last change: 2019-09-10                    1

S_CLIENT(1)                  OpenSSL                  S_CLIENT(1)

         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.


-crl_check_all, -policy_check, -extended_crl, -x509_strict,


-policy -check_ss_sig -no_alt_chains

     -purpose, -ignore_critical, -issuer_checks, -crl_check,
         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
         Displays the server certificate list as sent by the
         server: it only consists of certificates the server has
         sent (in the order the server has sent them). It is not
         a verified chain.

     -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

1.0.2t               Last change: 2019-09-10                    2

S_CLIENT(1)                  OpenSSL                  S_CLIENT(1)

         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.  The default value is "Client_identity" (without
         the quotes).

     -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.  This option must be provided
         in order to use a PSK cipher.


-no_tls1, -no_tls1_1, -no_tls1_2


1.0.2t               Last change: 2019-09-10                    3

S_CLIENT(1)                  OpenSSL                  S_CLIENT(1)

     -ssl2, -ssl3, -tls1, -tls1_1, -tls1_2, -no_ssl2, -no_ssl3,
         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.

     -sigalgs sigalglist
         Specifies the list of signature algorithms that are sent
         by the client.  The server selects one entry in the list
         based on its preferences.  For example strings, see
         SSL_CTX_set1_sigalgs(3)

     -curves curvelist
         Specifies the list of supported curves to be sent by the
         client. The curve is is ultimately selected by the
         server. For a list of all curves, use:

             $ openssl ecparam -list_curves

     -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", "ftp" and "xmpp".

     -tlsextdebug
         print out a hex dump of any TLS extensions received from
         the server.

     -no_ticket
         disable RFC4507bis session ticket support.

1.0.2t               Last change: 2019-09-10                    4

S_CLIENT(1)                  OpenSSL                  S_CLIENT(1)

     -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

1.0.2t               Last change: 2019-09-10                    5

S_CLIENT(1)                  OpenSSL                  S_CLIENT(1)

     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 all the
     certificates sent by the server.

     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.

1.0.2t               Last change: 2019-09-10                    6

S_CLIENT(1)                  OpenSSL                  S_CLIENT(1)


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.

1.0.2t               Last change: 2019-09-10                    7

See also s_client(1)

Man(1) output converted with man2html