S_CLIENT(1SSL)                      OpenSSL                     S_CLIENT(1SSL)

       openssl-s_client, s_client - SSL/TLS client program

       openssl s_client [-help] [-connect host:port] [-proxy host:port] [-unix
       path] [-4] [-6] [-servername name] [-verify depth]
       [-verify_return_error] [-cert filename] [-certform DER|PEM] [-key
       filename] [-keyform DER|PEM] [-pass arg] [-CApath directory] [-CAfile
       filename] [-no-CAfile] [-no-CApath] [-dane_tlsa_domain domain]
       [-dane_tlsa_rrdata rrdata] [-dane_ee_no_namechecks] [-attime timestamp]
       [-check_ss_sig] [-crl_check] [-crl_check_all] [-explicit_policy]
       [-extended_crl] [-ignore_critical] [-inhibit_any] [-inhibit_map]
       [-no_check_time] [-partial_chain] [-policy arg] [-policy_check]
       [-policy_print] [-purpose purpose] [-suiteB_128] [-suiteB_128_only]
       [-suiteB_192] [-trusted_first] [-no_alt_chains] [-use_deltas]
       [-auth_level num] [-verify_depth num] [-verify_email email]
       [-verify_hostname hostname] [-verify_ip ip] [-verify_name name]
       [-x509_strict] [-reconnect] [-showcerts] [-debug] [-msg] [-nbio_test]
       [-state] [-nbio] [-crlf] [-ign_eof] [-no_ign_eof] [-quiet] [-ssl3]
       [-tls1] [-tls1_1] [-tls1_2] [-no_ssl3] [-no_tls1] [-no_tls1_1]
       [-no_tls1_2] [-dtls] [-dtls1] [-dtls1_2] [-fallback_scsv] [-async]
       [-split_send_frag] [-max_pipelines] [-read_buf] [-bugs] [-comp]
       [-no_comp] [-sigalgs sigalglist] [-curves curvelist] [-cipher
       cipherlist] [-serverpref] [-starttls protocol] [-xmpphost hostname]
       [-engine id] [-tlsextdebug] [-no_ticket] [-sess_out filename] [-sess_in
       filename] [-rand file(s)] [-serverinfo types] [-status] [-alpn
       protocols] [-nextprotoneg protocols] [-ct|noct] [-ctlogfile]

       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.

       In addition to the options below the s_client utility also supports the
       common and client only options documented in the in the "Supported
       Command Line Commands" section of the SSL_CONF_cmd(3) manual page.

           Print out a usage message.

       -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.

       -proxy host:port
           When used with the -connect flag, the program uses the host and
           port specified with this flag and issues an HTTP CONNECT command to
           connect to the desired server.

       -unix path
           Connect over the specified Unix-domain socket.

       -4  Use IPv4 only.

       -6  Use IPv6 only.

       -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.

           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.

           Do not load the trusted CA certificates from the default file

           Do not load the trusted CA certificates from the default directory

       -dane_tlsa_domain domain
           Enable RFC6698/RFC7671 DANE TLSA authentication and specify the
           TLSA base domain which becomes the default SNI hint and the primary
           reference identifier for hostname checks.  This must be used in
           combination with at least one instance of the -dane_tlsa_rrdata
           option below.

           When DANE authentication succeeds, the diagnostic output will
           include the lowest (closest to 0) depth at which a TLSA record
           authenticated a chain certificate.  When that TLSA record is a "2 1
           0" trust anchor public key that signed (rather than matched) the
           top-most certificate of the chain, the result is reported as "TA
           public key verified".  Otherwise, either the TLSA record "matched
           TA certificate" at a positive depth or else "matched EE
           certificate" at depth 0.

       -dane_tlsa_rrdata rrdata
           Use one or more times to specify the RRDATA fields of the DANE TLSA
           RRset associated with the target service.  The rrdata value is
           specied in "presentation form", that is four whitespace separated
           fields that specify the usage, selector, matching type and
           associated data, with the last of these encoded in hexadecimal.
           Optional whitespace is ignored in the associated data field.  For

             $ openssl s_client -brief -starttls smtp \
               -connect smtp.example.com:25 \
               -dane_tlsa_domain smtp.example.com \
               -dane_tlsa_rrdata "2 1 1
                 B111DD8A1C2091A89BD4FD60C57F0716CCE50FEEFF8137CDBEE0326E 02CF362B" \
               -dane_tlsa_rrdata "2 1 1
                 60B87575447DCBA2A36B7D11AC09FB24A9DB406FEE12D2CC90180517 616E8A18"
             Verification: OK
             Verified peername: smtp.example.com
             DANE TLSA 2 1 1 ...ee12d2cc90180517616e8a18 matched TA certificate at depth 1

           This disables server name checks when authenticating via DANE-EE(3)
           TLSA records.  For some applications, primarily web browsers, it is
           not safe to disable name checks due to "unknown key share" attacks,
           in which a malicious server can convince a client that a connection
           to a victim server is instead a secure connection to the malicious
           server.  The malicious server may then be able to violate cross-
           origin scripting restrictions.  Thus, despite the text of RFC7671,
           name checks are by default enabled for DANE-EE(3) TLSA records, and
           can be disabled in applications where it is safe to do so.  In
           particular, SMTP and XMPP clients should set this option as SRV and
           MX records already make it possible for a remote domain to redirect
           client connections to any server of its choice, and in any case
           SMTP and XMPP clients do not execute scripts downloaded from remote

       -attime, -check_ss_sig, -crl_check, -crl_check_all, -explicit_policy,
       -extended_crl, -ignore_critical, -inhibit_any, -inhibit_map,
       -no_alt_chains, -no_check_time, -partial_chain, -policy, -policy_check,
       -policy_print, -purpose, -suiteB_128, -suiteB_128_only, -suiteB_192,
       -trusted_first, -use_deltas, -auth_level, -verify_depth, -verify_email,
       -verify_hostname, -verify_ip, -verify_name, -x509_strict
           Set various certificate chain validation options. See the verify(1)
           manual page for details.

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

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

           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.

           prints out the SSL session states.

           print extensive debugging information including a hex dump of all

           show all protocol messages with hex dump.

           show verbose trace output of protocol messages. OpenSSL needs to be
           compiled with enable-ssl-trace for this option to work.

           file to send output of -msg or -trace to, default standard output.

           tests non-blocking I/O

           turns on non-blocking I/O

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

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

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

           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

       -ssl3, -tls1, -tls1_1, -tls1_2, -no_ssl3, -no_tls1, -no_tls1_1,
           These options require or disable the use of the specified SSL or
           TLS protocols.  By default s_client will negotiate the highest
           mutually supported protocol version.  When a specific TLS version
           is required, only that version will be offered to and accepted from
           the server.

       -dtls, -dtls1, -dtls1_2
           These options make s_client use DTLS protocols instead of TLS.
           With -dtls, s_client will negotiate any supported DTLS protocol
           version, whilst -dtls1 and -dtls1_2 will only support DTLS1.0 and
           DTLS1.2 respectively.

           Send TLS_FALLBACK_SCSV in the ClientHello.

           switch on asynchronous mode. Cryptographic operations will be
           performed asynchronously. This will only have an effect if an
           asynchronous capable engine is also used via the -engine option.
           For test purposes the dummy async engine (dasync) can be used (if

       -split_send_frag int
           The size used to split data for encrypt pipelines. If more data is
           written in one go than this value then it will be split into
           multiple pipelines, up to the maximum number of pipelines defined
           by max_pipelines. This only has an effect if a suitable ciphersuite
           has been negotiated, an engine that supports pipelining has been
           loaded, and max_pipelines is greater than 1. See
           SSL_CTX_set_split_send_fragment(3) for further information.

       -max_pipelines int
           The maximum number of encrypt/decrypt pipelines to be used. This
           will only have an effect if an engine has been loaded that supports
           pipelining (e.g. the dasync engine) and a suitable ciphersuite has
           been negotiated. The default value is 1.  See
           SSL_CTX_set_max_pipelines(3) for further information.

       -read_buf int
           The default read buffer size to be used for connections. This will
           only have an effect if the buffer size is larger than the size that
           would otherwise be used and pipelining is in use (see
           SSL_CTX_set_default_read_buffer_len(3) for further information).

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

           Enables support for SSL/TLS compression.  This option was
           introduced in OpenSSL 1.1.0.  TLS compression is not recommended
           and is off by default as of OpenSSL 1.1.0.

           Disables support for SSL/TLS compression.  TLS compression is not
           recommended and is off by default as of OpenSSL 1.1.0.

           only provide a brief summary of connection parameters instead of
           the normal verbose output.

       -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.

       -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", and "irc."

       -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.

           print out a hex dump of any TLS extensions received from the

           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 an 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.

           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 receiving ServerHello with a list of server
           supported protocols.

           Use one of these two options to control whether Certificate
           Transparency (CT) is enabled (-ct) or disabled (-noct).  If CT is
           enabled, signed certificate timestamps (SCTs) will be requested
           from the server and reported at handshake completion.

           Enabling CT also enables OCSP stapling, as this is one possible
           delivery method for SCTs.

           A file containing a list of known Certificate Transparency logs.
           See SSL_CTX_set_ctlog_list_file(3) for the expected file format.

       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.

       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.

       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.

       SSL_CONF_cmd(3), sess_id(1), s_server(1), ciphers(1)

       The -no_alt_chains options was first added to OpenSSL 1.1.0.

       Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (the "License").  You may not use
       this file except in compliance with the License.  You can obtain a copy
       in the file LICENSE in the source distribution or at

1.1.0h                            2018-05-12                    S_CLIENT(1SSL)
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