RT4292: Remove ===== line

=pod

=head1 NAME

s_client - SSL/TLS client program

=head1 SYNOPSIS

B<openssl> B<s_client>

[B<-connect host:port>]

[B<-proxy host:port>]

[B<-servername name>]

[B<-verify depth>]

[B<-verify_return_error>]

[B<-cert filename>]

[B<-certform DER|PEM>]

[B<-key filename>]

[B<-keyform DER|PEM>]

[B<-pass arg>]

[B<-CApath directory>]

[B<-CAfile filename>]

[B<-no-CAfile>]

[B<-no-CApath>]

[B<-dane_tlsa_domain domain>]

[B<-dane_tlsa_rrdata rrdata>]

[B<-attime timestamp>]

[B<-check_ss_sig>]

[B<-crl_check>]

[B<-crl_check_all>]

[B<-explicit_policy>]

[B<-extended_crl>]

[B<-ignore_critical>]

[B<-inhibit_any>]

[B<-inhibit_map>]

[B<-issuer_checks>]

[B<-partial_chain>]

[B<-policy arg>]

[B<-policy_check>]

[B<-policy_print>]

[B<-purpose purpose>]

[B<-suiteB_128>]

[B<-suiteB_128_only>]

[B<-suiteB_192>]

[B<-trusted_first>]

[B<-no_alt_chains>]

[B<-use_deltas>]

[B<-verify_depth num>]

[B<-verify_email email>]

[B<-verify_hostname hostname>]

[B<-verify_ip ip>]

[B<-verify_name name>]

[B<-x509_strict>]

[B<-reconnect>]

[B<-showcerts>]

[B<-debug>]

[B<-msg>]

[B<-nbio_test>]

[B<-state>]

[B<-nbio>]

[B<-crlf>]

[B<-ign_eof>]

[B<-no_ign_eof>]

[B<-quiet>]

[B<-ssl3>]

[B<-tls1>]

[B<-no_ssl3>]

[B<-no_tls1>]

[B<-no_tls1_1>]

[B<-no_tls1_2>]

[B<-fallback_scsv>]

[B<-async>]

[B<-bugs>]

[B<-comp>]

[B<-no_comp>]

[B<-cipher cipherlist>]

[B<-serverpref>]

[B<-starttls protocol>]

[B<-xmpphost hostname>]

[B<-engine id>]

[B<-tlsextdebug>]

[B<-no_ticket>]

[B<-sess_out filename>]

[B<-sess_in filename>]

[B<-rand file(s)>]

[B<-serverinfo types>]

[B<-status>]

[B<-nextprotoneg protocols>]

=head1 DESCRIPTION

The B<s_client> command implements a generic SSL/TLS client which connects

to a remote host using SSL/TLS. It is a I<very> useful diagnostic tool for

SSL servers.

=head1 OPTIONS

In addition to the options below the B<s_client> utility also supports the

common and client only options documented in the

in the L<SSL_CONF_cmd(3)|SSL_CONF_cmd(3)/SUPPORTED COMMAND LINE COMMANDS>

manual page.

=over 4

=item B<-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.

=item B<-proxy host:port>

When used with the B<-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.

=item B<-servername name>

Set the TLS SNI (Server Name Indication) extension in the ClientHello message.

=item B<-cert certname>

The certificate to use, if one is requested by the server. The default is

not to use a certificate.

=item B<-certform format>

The certificate format to use: DER or PEM. PEM is the default.

=item B<-key keyfile>

The private key to use. If not specified then the certificate file will

be used.

=item B<-keyform format>

The private format to use: DER or PEM. PEM is the default.

=item B<-pass arg>

the private key password source. For more information about the format of B<arg>

see the B<PASS PHRASE ARGUMENTS> section in L<openssl(1)>.

=item B<-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.

=item B<-verify_return_error>

Return verification errors instead of continuing. This will typically

abort the handshake with a fatal error.

=item B<-CApath directory>

The directory to use for server certificate verification. This directory

must be in "hash format", see B<verify> for more information. These are

also used when building the client certificate chain.

=item B<-CAfile file>

A file containing trusted certificates to use during server authentication

and to use when attempting to build the client certificate chain.

=item B<-no-CAfile>

Do not load the trusted CA certificates from the default file location

=item B<-no-CApath>

Do not load the trusted CA certificates from the default directory location

=item B<-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 B<-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.

=item B<-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 B<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 -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"

  CONNECTED(00000003)

  ...

  DANE TLSA 2 1 1 matched TA certificate at depth 1

  Verified peername: smtp.example.com

  ...

      Verify return code: 0 (ok)

  ...

=item B<-attime>, B<-check_ss_sig>, B<-crl_check>, B<-crl_check_all>,

B<explicit_policy>, B<-extended_crl>, B<-ignore_critical>, B<-inhibit_any>,

B<-inhibit_map>, B<-issuer_checks>, B<-partial_chain>, B<-policy>,

B<-policy_check>, B<-policy_print>, B<-purpose>, B<-suiteB_128>,

B<-suiteB_128_only>, B<-suiteB_192>, B<-trusted_first>, B<-no_alt_chains>,

B<-use_deltas>, B<-verify_depth>, B<-verify_email>, B<-verify_hostname>,

B<-verify_ip>, B<-verify_name>, B<-x509_strict>

Set various certificate chain validation options. See the

L<verify(1)> manual page for details.

=item B<-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.

=item B<-showcerts>

display the whole server certificate chain: normally only the server

certificate itself is displayed.

=item B<-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.

=item B<-state>

prints out the SSL session states.

=item B<-debug>

print extensive debugging information including a hex dump of all traffic.

=item B<-msg>

show all protocol messages with hex dump.

=item B<-trace>

show verbose trace output of protocol messages. OpenSSL needs to be compiled

with B<enable-ssl-trace> for this option to work.

=item B<-msgfile>

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

=item B<-nbio_test>

tests non-blocking I/O

=item B<-nbio>

turns on non-blocking I/O

=item B<-crlf>

this option translated a line feed from the terminal into CR+LF as required

by some servers.

=item B<-ign_eof>

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

input.

=item B<-quiet>

inhibit printing of session and certificate information.  This implicitly

turns on B<-ign_eof> as well.

=item B<-no_ign_eof>

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

Can be used to override the implicit B<-ign_eof> after B<-quiet>.

=item B<-psk_identity identity>

Use the PSK identity B<identity> when using a PSK cipher suite.

=item B<-psk key>

Use the PSK key B<key> when using a PSK cipher suite. The key is

given as a hexadecimal number without leading 0x, for example -psk

1a2b3c4d.

=item B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1>, B<-no_tls1_1>, B<-no_tls1_2>

these options disable the use of certain SSL or TLS protocols. By default

the initial handshake uses a method which should be compatible with all

servers and permit them to use SSL v3 or TLS as appropriate.

Unfortunately there are still ancient and broken servers in use which

cannot handle this technique and will fail to connect. Some servers only

work if TLS is turned off.

=item B<-fallback_scsv>

Send TLS_FALLBACK_SCSV in the ClientHello.

=item B<-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 B<-engine> option. For test purposes the dummy async engine

(dasync) can be used (if available).

=item B<-bugs>

there are several known bug in SSL and TLS implementations. Adding this

option enables various workarounds.

=item B<-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.

=item B<-no_comp>

Disables support for SSL/TLS compression.

TLS compression is not recommended and is off by default as of

OpenSSL 1.1.0.

=item B<-brief>

only provide a brief summary of connection parameters instead of the

normal verbose output.

=item B<-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 B<ciphers>

command for more information.

=item B<-starttls protocol>

send the protocol-specific message(s) to switch to TLS for communication.

B<protocol> is a keyword for the intended protocol.  Currently, the only

supported keywords are "smtp", "pop3", "imap", "ftp", "xmpp", "xmpp-server",

and "irc."

=item B<-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.

=item B<-tlsextdebug>

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

=item B<-no_ticket>

disable RFC4507bis session ticket support. 

=item B<-sess_out filename>

output SSL session to B<filename>

=item B<-sess_in sess.pem>

load SSL session from B<filename>. The client will attempt to resume a

connection from this session.

=item B<-engine id>

specifying an engine (by its unique B<id> string) will cause B<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.

=item B<-rand file(s)>

a file or files containing random data used to seed the random number

generator, or an EGD socket (see L<RAND_egd(3)>).

Multiple files can be specified separated by a OS-dependent character.

The separator is B<;> for MS-Windows, B<,> for OpenVMS, and B<:> for

all others.

=item B<-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.

=item B<-status>

sends a certificate status request to the server (OCSP stapling). The server

response (if any) is printed out.

=item B<-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

receiving ServerHello with a list of server supported protocols.

=back

=head1 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 B<-quiet> nor B<-ign_eof>

have been given), the session will be renegotiated if the line begins with an

B<R>, and if the line begins with a B<Q> or if end of file is reached, the

connection will be closed down.

=head1 NOTES

B<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 B<-bugs>,

B<-ssl3>, B<-tls1>, B<-no_ssl3>, B<-no_tls1> options can be tried

in case it is a buggy server. In particular you should play with these

options B<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 B<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 B<-prexit> option and send an HTTP request

for an appropriate page.

If a certificate is specified on the command line using the B<-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

B<-showcerts> option can be used to show the whole chain.

The B<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 B<not> do this as it makes them vulnerable to a MITM

attack. This behaviour can be changed by with the B<-verify_return_error>

option: any verify errors are then returned aborting the handshake.

=head1 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 B<-prexit> option is a bit of a hack. We should really report

information whenever a session is renegotiated.

=head1 SEE ALSO

L<sess_id(1)>, L<s_server(1)>, L<ciphers(1)>

=head1 HISTORY

The -no_alt_chains options was first added to OpenSSL 1.1.0.

=cut

L<ssl(3)>, L<SSL_read(3)>, L<SSL_write(3)>, L<SSL_get_error(3)>

=======

=head1 HISTORY

SSL_MODE_ASYNC was first added to OpenSSL 1.1.0.