Provided by: openssl_1.1.1-1ubuntu2_amd64 bug

NAME

       openssl-s_client, s_client - SSL/TLS client program

SYNOPSIS

       openssl s_client [-help] [-connect host:port] [-bind host:port] [-proxy host:port] [-unix
       path] [-4] [-6] [-servername name] [-noservername] [-verify depth] [-verify_return_error]
       [-cert filename] [-certform DER|PEM] [-key filename] [-keyform DER|PEM] [-cert_chain
       filename] [-build_chain] [-xkey] [-xcert] [-xchain] [-xchain_build] [-xcertform PEM|DER]
       [-xkeyform PEM|DER] [-pass arg] [-CApath directory] [-CAfile filename] [-chainCApath
       directory] [-chainCAfile filename] [-no-CAfile] [-no-CApath] [-requestCAfile filename]
       [-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] [-nameopt option] [-verify_depth num] [-verify_email
       email] [-verify_hostname hostname] [-verify_ip ip] [-verify_name name] [-build_chain]
       [-x509_strict] [-reconnect] [-showcerts] [-debug] [-msg] [-nbio_test] [-state] [-nbio]
       [-crlf] [-ign_eof] [-no_ign_eof] [-psk_identity identity] [-psk key] [-psk_session file]
       [-quiet] [-ssl3] [-tls1] [-tls1_1] [-tls1_2] [-tls1_3] [-no_ssl3] [-no_tls1] [-no_tls1_1]
       [-no_tls1_2] [-no_tls1_3] [-dtls] [-dtls1] [-dtls1_2] [-sctp] [-fallback_scsv] [-async]
       [-max_send_frag] [-split_send_frag] [-max_pipelines] [-read_buf] [-bugs] [-comp]
       [-no_comp] [-allow_no_dhe_kex] [-sigalgs sigalglist] [-curves curvelist] [-cipher
       cipherlist] [-ciphersuites val] [-serverpref] [-starttls protocol] [-xmpphost hostname]
       [-name hostname] [-engine id] [-tlsextdebug] [-no_ticket] [-sess_out filename] [-sess_in
       filename] [-rand file...]  [-writerand file] [-serverinfo types] [-status] [-alpn
       protocols] [-nextprotoneg protocols] [-ct] [-noct] [-ctlogfile] [-keylogfile file]
       [-early_data file] [-enable_pha] [target]

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

       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.

       -help
           Print out a usage message.

       -connect host:port
           This specifies the host and optional port to connect to. It is possible to select the
           host and port using the optional target positional argument instead.  If neither this
           nor the target positional argument are specified then an attempt is made to connect to
           the local host on port 4433.

       -bind host:port]
           This specifies the host address and or port to bind as the source for the connection.
           For Unix-domain sockets the port is ignored and the host is used as the source socket
           address.

       -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 to the
           given value. If both this option and the -noservername are not given, the TLS SNI
           extension is still set to the hostname provided to the -connect option, or "localhost"
           if -connect has not been supplied. This is default since OpenSSL 1.1.1.

           Even though SNI name should normally be a DNS name and not an IP address, this option
           will not make the distinction when parsing -connect and will send IP address if one
           passed.

       -noservername
           Suppresses sending of the SNI (Server Name Indication) extension in the ClientHello
           message. Cannot be used in conjunction with the -servername or <-dane_tlsa_domain>
           options.

       -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.

       -cert_chain
           A file containing trusted certificates to use when attempting to build the
           client/server certificate chain related to the certificate specified via the -cert
           option.

       -build_chain
           Specify whether the application should build the certificate chain to be provided to
           the server.

       -xkey infile, -xcert infile, -xchain
           Specify an extra certificate, private key and certificate chain. These behave in the
           same manner as the -cert, -key and -cert_chain options.  When specified, the callback
           returning the first valid chain will be in use by the client.

       -xchain_build
           Specify whether the application should build the certificate chain to be provided to
           the server for the extra certificates provided via -xkey infile, -xcert infile,
           -xchain options.

       -xcertform PEM|DER, -xkeyform PEM|DER
           Extra certificate and private key format respectively.

       -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.

       -nameopt option
           Option which determines how the subject or issuer names are displayed. The option
           argument can be a single option or multiple options separated by commas.
           Alternatively the -nameopt switch may be used more than once to set multiple options.
           See the x509(1) manual page for details.

       -CApath directory
           The directory to use for server certificate verification. This directory must be in
           "hash format", see verify(1) 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.

       -chainCApath directory
           The directory to use for building the chain provided to the server. This directory
           must be in "hash format", see verify(1) for more information.

       -chainCAfile file
           A file containing trusted certificates to use when attempting to build the client
           certificate chain.

       -no-CAfile
           Do not load the trusted CA certificates from the default file location

       -no-CApath
           Do not load the trusted CA certificates from the default directory location

       -requestCAfile file
           A file containing a list of certificates whose subject names will be sent to the
           server in the certificate_authorities extension. Only supported for TLS 1.3

       -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 example:

             $ 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
             ...

       -dane_ee_no_namechecks
           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 servers.

       -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.

       -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.

       -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 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.

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

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

       -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.

       -psk_session file
           Use the pem encoded SSL_SESSION data stored in file as the basis of a PSK.  Note that
           this will only work if TLSv1.3 is negotiated.

       -ssl3, -tls1, -tls1_1, -tls1_2, -tls1_3, -no_ssl3, -no_tls1, -no_tls1_1, -no_tls1_2,
       -no_tls1_3
           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.  Note that not all protocols and flags may be available, depending on
           how OpenSSL was built.

       -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.

       -sctp
           Use SCTP for the transport protocol instead of UDP in DTLS. Must be used in
           conjunction with -dtls, -dtls1 or -dtls1_2. This option is only available where
           OpenSSL has support for SCTP enabled.

       -fallback_scsv
           Send TLS_FALLBACK_SCSV in the ClientHello.

       -async
           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 available).

       -max_send_frag int
           The maximum size of data fragment to send.  See SSL_CTX_set_max_send_fragment(3) for
           further information.

       -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
           cipher suite 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 cipher suite 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).

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

       -comp
           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.

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

       -brief
           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
           ultimately selected by the server. For a list of all curves, use:

               $ openssl ecparam -list_curves

       -cipher cipherlist
           This allows the TLSv1.2 and below cipher list sent by the client to be modified.  This
           list will be combined with any TLSv1.3 ciphersuites that have been configured.
           Although the server determines which ciphersuite is used it should take the first
           supported cipher in the list sent by the client. See the ciphers command for more
           information.

       -ciphersuites val
           This allows the TLSv1.3 ciphersuites sent by the client to be modified. This list will
           be combined with any TLSv1.2 and below ciphersuites that have been configured.
           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. The format for this list is a simple colon (":") separated list of
           TLSv1.3 ciphersuite names.

       -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", "mysql",
           "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.

           This option is an alias of the -name option for "xmpp" and "xmpp-server".

       -name hostname
           This option is used to specify hostname information for various protocols used with
           -starttls option. Currently only "xmpp", "xmpp-server", "smtp" and "lmtp" can utilize
           this -name option.

           If this option is used with "-starttls xmpp" or "-starttls xmpp-server", if 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.

           If this option is used with "-starttls lmtp" or "-starttls smtp", it specifies the
           name to use in the "LMTP LHLO" or "SMTP EHLO" message, respectively. If this option is
           not specified, then "mail.example.com" 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...
           A file or files containing random data used to seed the random number generator.
           Multiple files can be specified separated by an OS-dependent character.  The separator
           is ; for MS-Windows, , for OpenVMS, and : for all others.

       [-writerand file]
           Writes random data to the specified file upon exit.  This can be used with a
           subsequent -rand flag.

       -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 (NPN) extension, respectively. ALPN is the IETF standard and
           replaces NPN.  The protocols list is a comma-separated list of protocol names that the
           client should advertise support for. The list should contain the most desirable
           protocols first.  Protocol names are printable ASCII strings, for example "http/1.1"
           or "spdy/3".  An 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.  The flag -nextprotoneg cannot
           be specified if -tls1_3 is used.

       -ct, -noct
           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.

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

       -keylogfile file
           Appends TLS secrets to the specified keylog file such that external programs (like
           Wireshark) can decrypt TLS connections.

       -early_data file
           Reads the contents of the specified file and attempts to send it as early data to the
           server. This will only work with resumed sessions that support early data and when the
           server accepts the early data.

       -enable_pha
           For TLSv1.3 only, send the Post-Handshake Authentication extension. This will happen
           whether or not a certificate has been provided via -cert.

       [target]
           Rather than providing -connect, the target hostname and optional port may be provided
           as a single positional argument after all options. If neither this nor -connect are
           provided, falls back to attempting to connect to localhost on port 4433.

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. If end of file is reached
       then the connection will be closed down. When used interactively (which means neither
       -quiet nor -ign_eof have been given), then certain commands are also recognized which
       perform special operations. These commands are a letter which must appear at the start of
       a line. They are listed below.

       Q   End the current SSL connection and exit.

       R   Renegotiate the SSL session (TLSv1.2 and below only).

       B   Send a heartbeat message to the server (DTLS only)

       k   Send a key update message to the server (TLSv1.3 only)

       K   Send a key update message to the server and request one back (TLSv1.3 only)

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 all the certificates sent by the server.

       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.

       The -bind option may be useful if the server or a firewall requires connections to come
       from some particular address and or port.

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

       SSL_CONF_cmd(3), sess_id(1), s_server(1), ciphers(1), SSL_CTX_set_max_send_fragment(3),
       SSL_CTX_set_split_send_fragment(3), SSL_CTX_set_max_pipelines(3)

HISTORY

       The -no_alt_chains option was first added to OpenSSL 1.1.0.  The -name option was added in
       OpenSSL 1.1.1.

COPYRIGHT

       Copyright 2000-2018 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 <https://www.openssl.org/source/license.html>.