<dd><b>tls::unimport</b> <em>channel</em></dd>
	<dt>&nbsp;</dt>
	<dd><b>tls::ciphers</b> <em>?protocol? ?verbose? ?supported?</em></dd>
	<dd><b>tls::protocols</b></dd>
	<dd><b>tls::version</b></dd>
    </dl></dd>
    <dd><a href="#COMMANDS">COMMANDS</a></dd>
    <dd><a href="#CERTIFICATE VALIDATION">CERTIFICATE VALIDATION</a></dd>
    <dd><a href="#CALLBACK OPTIONS">CALLBACK OPTIONS</a></dd>
    <dd><a href="#DEBUG">DEBUG</a></dd>
    <dd><a href="#HTTPS EXAMPLE">HTTPS EXAMPLE</a></dd>
    <dd><a href="#SPECIAL CONSIDERATIONS">SPECIAL CONSIDERATIONS</a></dd>
    <dd><a href="#SEE ALSO">SEE ALSO</a></dd>
</dl>
<br>

<hr>

<h3><a name="NAME">NAME</a></h3>

<p><strong>tls</strong> - binding to <strong>OpenSSL</strong> library
for encrypted socket and I/O channel communications.</p>
<br>

<hr>

<h3><a name="SYNOPSIS">SYNOPSIS</a></h3>

<p><b>package require Tcl</b> <em>?<b>8.5-</b>?</em><br>
<b>package require tls</b> <em>?<b>1.8-</b>?</em><br>

<a href="#tls::import"><b>tls::import</b> <i>channel ?options?</i></a><br>
<a href="#tls::unimport"><b>tls::unimport</b> <i>channel</i></a><br>
<br>
<a href="#tls::ciphers"><b>tls::ciphers</b> <i>?protocol? ?verbose? ?supported?</i></a><br>
<a href="#tls::protocols"><b>tls::protocols</b></a><br>
<a href="#tls::version"><b>tls::version</b></a><br>
</p>
<br>

<hr>

<h3><a name="DESCRIPTION">DESCRIPTION</a></h3>

<p>This extension provides TCL script access to secure socket communications
using the Transport Layer Security (TLS) protocol. It provides a generic
binding to <a href="https://www.openssl.org/">OpenSSL</a>, utilizing the
<strong>Tcl_StackChannel</strong> API in TCL 8.4 and higher.
These sockets behave exactly the same as channels created using the built-in
<strong>socket</strong> command, along with additional options for controlling
the SSL/TLS session.
</p>
<br>

<hr>

<h3><a name="COMMANDS">COMMANDS</a></h3>

<p>Typically one would use the <strong>tls::socket </strong>command
which provides compatibility with the native TCL <strong>socket</strong>

	<dt><strong>-alpn</strong> <em>list</em></dt>
	<dd>List of protocols to offer during Application-Layer
	    Protocol Negotiation (ALPN). For example: <em>h2</em> and
	    <em>http/1.1</em>, but not <em>h3</em> or <em>quic</em>.</dd>
	<dt><strong>-cadir</strong> <em>dir</em></dt>
	<dd>Specifies the directory where the Certificate Authority (CA)
	    certificates are stored. The default is platform specific and can be
	    set at compile time. The default location can be overridden via the
	    <b>SSL_CERT_DIR</b> environment variable.
	    See <a href="#CERTIFICATE VALIDATION">CERTIFICATE VALIDATION</a>.</dd>
	<dt><strong>-cafile </strong><em>filename</em></dt>
	<dd>Specifies the file with the Certificate Authority (CA) certificates
	    to use. The default is <b>cert.pem</b>, in the OpenSSL directory.
	    The default file can be overridden via the <b>SSL_CERT_FILE</b>
	    environment variable.
	    See <a href="#CERTIFICATE VALIDATION">CERTIFICATE VALIDATION</a>.</dd>
	<dt><strong>-castore</strong> <em>URI</em></dt>
	<dd>URI for a Certificate Authority (CA) store, which may be a single
	    container or a catalog of containers. Starting with OpenSSL 3.2 on
	    Windows, set to "org.openssl.winstore://" to use the built-in
	    Windows Cert Store. The Windows cert store only supports root
	    certificate stores.
	    See <a href="#CERTIFICATE VALIDATION">CERTIFICATE VALIDATION</a>.</dd>
	<dt><strong>-certfile</strong> <em>filename</em></dt>
	<dd>Specifies the file with the certificate to use in PEM format.
	    This also contains the public key.</dd>
	<dt><strong>-cert</strong> <em>binary_string</em></dt>
	<dd>Specifies the certificate to use as a DER encoded string (X.509 DER).</dd>
	<dt><strong>-cipher</strong> <em>string</em></dt>
	<dd>Specifies the list of ciphers to use for TLS 1.2 and earlier. String is a

	    obtain a password. This is typically used to unlock the private key of
	    a certificate. The callback should return a password string.
	    See <a href="#CALLBACK OPTIONS">CALLBACK OPTIONS</a> for more info.</dd>
	<dt><strong>-post_handshake</strong> <em>bool</em></dt>
	<dd>Allow post-handshake session ticket updates.</dd>
	<dt><strong>-request </strong><em>bool</em></dt>
	<dd>Request a certificate from peer during the SSL handshake. This is
	    needed to do certificate validation. (default is <em>true</em>).
	    See <a href="#CERTIFICATE VALIDATION">CERTIFICATE VALIDATION</a>.</dd>
	<dt><strong>-require</strong> <em>bool</em></dt>
	<dd>Require a valid certificate from peer during SSL handshake. If this
	    is set to true, then <strong>-request</strong> must also be set to
	    true and a either a -cadir, -cafile, -castore, or platform default
	    must be provided in order to validate against. (default is <em>false</em>).
	    See <a href="#CERTIFICATE VALIDATION">CERTIFICATE VALIDATION</a>.</dd>
	<dt><strong>-security_level</strong> <em>integer</em></dt>
	<dd>Specifies the security level (value from 0 to 5). The security level
	    affects the cipher suite encryption algorithms, supported ECC curves,
	    supported signature algorithms, DH parameter sizes, certificate key
	    sizes and signature algorithms. The default is 1 prior to OpenSSL 3.2
	    and 2 thereafter. Level 3 and higher disable support for session
	    tickets and only accept cipher suites that provide forward secrecy.</dd>

	<b>ssl2</b>, <b>ssl3</b>, <b>tls1</b>, <b>tls1.1</b>, <b>tls1.2</b>,
	and <b>tls1.3</b>. Exact list depends on OpenSSL version and
	compile time flags.</dd>
    <dt>&nbsp;</dt>
    <dt><a name="tls::version"><strong>tls::version</strong></a></dt>
    <dd>Returns the OpenSSL version string.</dd>
</dl>
<br>

<hr>

<h3><a name="CERTIFICATE VALIDATION">CERTIFICATE VALIDATION</a></h3>

<p>
By default, a client TLS connection is set to NOT request nor validate the
server certificates. This limitation is due to the lack of a common cross
platform database of Certificate Authority (CA) provided certificates to
validate against. Many Linux systems natively support OpenSSL and thus have
these certificates installed as part of the OS, but MacOS and Windows do not.
In order to use the <b>-require</b> option, one of the following must be true:</p>
<ul>
<li>On Linux and Unix systems with OpenSSL already installed, if the CA
certificates are stored in the standard locations, or the <b>SSL_CERT_DIR</b>
or <b>SSL_CERT_FILE</b> env vars are set, then no other options are needed.</li>

<li>If OpenSSL is not installed in the default location, or when using Mac OS
or Windows and OpenSSL is installed, the <b>SSL_CERT_DIR</b> and/or 
<b>SSL_CERT_FILE</b> env vars or the <b>-cadir</b> and/or <b>-cafile</b>
 options must be defined.</li>

<li>On Windows, starting in OpenSSL 3.2, it is now possible to access the
built-in Windows Certificate Store from OpenSSL. This can be achieved by
setting the <b>-castore</b> option to "<b>org.openssl.winstore://</b>".</li>

<li>If OpenSSL is not installed, the CA certificates must be downloaded and
installed with the user software. The CURL team makes them available at
<a href="https://curl.se/docs/caextract.html">CA certificates extracted
from Mozilla</a>. Look for the <b>cacert.pem</b> file. You must then either
set the <b>SSL_CERT_DIR</b> and/or <b>SSL_CERT_FILE</b> env vars or the
<b>-cadir</b> or <b>-cafile</b> options must be set to the file's install
location. It is your responsibility to keep this file up to date.</li>
</ul>
<br>

<hr>

<h3><a name="CALLBACK OPTIONS">CALLBACK OPTIONS</a></h3>

<p>
As indicated above, individual channels can be given their own callbacks
to handle intermediate processing by the OpenSSL library, using the
<strong>-command</strong>, <strong>-password</strong>, and
<strong>-validate_command</strong> options passed to either of
<strong>tls::socket</strong> or <strong>tls::import</strong>.
Unlike previous versions of TCL TLS, only if the callback generates an error,
will the <b>bgerror</b> command will be invoked with the error information.
</p>

<dl>
    <dt><strong>-command</strong> <em>callback</em></dt>
    <dd>
	Invokes the specified <em>callback</em> script at several points
	during the OpenSSL handshake and use. See below for the possible

<p>
<em>
The use of the reference callbacks <strong>tls::callback</strong>,
<strong>tls::password</strong>, and <strong>tls::validate_command</strong>
is not recommended. They may be removed from future releases.
</em>
</p>
<br>

<hr>

<h3><a name="DEBUG">DEBUG</a></h3>

<p>For most debugging needs, the <b>-callback</b> option can be used to provide
sufficient insight and information on the TLS handshake and progress. If further
troubleshooting insight is needed, the compile time option <b>--enable-debug</b>
can be used to get detailed execution flow status.</p>

<p>TLS key logging can be enabled by setting the environment variable
<b>SSLKEYLOGFILE</b> to the name of the file to log to. Then whenever TLS
key material is generated or received it will be logged to the file. This
is useful for logging key data for network logging tools to use to
decrypt the data.</p>

<p>The <strong>tls::debug</strong> variable provides some additional
control over these reference callbacks. Its value is zero by default.
Higher values produce more diagnostic output, and will also force the
verify method in <strong>tls::callback</strong> to accept the
certificate, even when it is invalid if the <b>tls::validate_command</b>
callback is used for the <b>-validatecommand</b> option.</p>



<p><em>The use of the variable <strong>tls::debug</strong> is not recommended.
It may be removed from future releases.</em></p>



<h4><a name="DEBUG_EXAMPLES">Debug Examples</a></h4>

<p>These examples use the default Unix platform SSL certificates. For standard
installations, -cadir and -cafile should not be needed. If your certificates
are in non-standard locations, update -cadir or use -cafile as needed.</p>
<br>

array set conn [tls::connection $ch]
array set chan [chan configure $ch]
close $ch
parray status
parray conn
parray chan
</code></pre>
<br>

<hr>

<h3><a name="HTTPS EXAMPLE">HTTPS EXAMPLE</a></h3>

<p>These examples use the default Unix platform SSL certificates. For standard
installations, -cadir and -cafile should not be needed. If your certificates

set ch [open $filename wb]
set token [::http::geturl $url -blocksize 65536 -channel $ch]

# Cleanup
close $ch
::http::cleanup $token
</code></pre>
<br>

<hr>

<h3><a name="SPECIAL CONSIDERATIONS">SPECIAL CONSIDERATIONS</a></h3>

<p>The capabilities of this package can vary enormously based upon how the
linked to OpenSSL library was configured and built. New versions may obsolete