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<meta name="Copyright" content="1999 Matt Newman.">
<title>TLS (SSL) Tcl Commands</title>
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<dl>
<dd><a href="#NAME">NAME</a> <dl>
<dd><strong>tls</strong> - binding to <strong>OpenSSL</strong>
toolkit.</dd>
</dl>
</dd>
<dd><a href="#SYNOPSIS">SYNOPSIS</a> </dd>
<dd><dl>
<dd><b>package require Tcl </b><em>?8.2?</em></dd>
<dd><b>package require tls </b><em>?1.4?</em></dd>
<dt> </dt>
<dd><b>tls::init </b><i>?options?</i> </dd>
<dd><b>tls::socket </b><em>?options? host port</em></dd>
<dd><b>tls::socket</b><em> ?-server command?
?options? port</em></dd>
<dd><b>tls::handshake</b><em> channel</em></dd>
<dd><b>tls::status </b><em>?-local? channel</em></dd>
<dd><b>tls::import</b><em> channel ?options?</em></dd>
<dd><b>tls::ciphers </b><em>protocol ?verbose?</em></dd>
<dd><b>tls::version</b></dd>
</dl>
</dd>
<dd><a href="#COMMANDS">COMMANDS</a></dd>
<dd><a href="#CALLBACK OPTIONS">CALLBACK OPTIONS</a></dd>
<dd><a href="#HTTPS EXAMPLE">HTTPS EXAMPLE</a></dd>
<dd><a href="#SEE ALSO">SPECIAL CONSIDERATIONS</a></dd>
<dd><a href="#SEE ALSO">SEE ALSO</a></dd>
</dl>
<hr>
<h3><a name="NAME">NAME</a></h3>
<p><strong>tls</strong> - binding to <strong>OpenSSL</strong>
toolkit.</p>
<h3><a name="SYNOPSIS">SYNOPSIS</a></h3>
<p><b>package require Tcl 8.2</b><br>
<b>package require tls 1.4</b><br>
<br>
<a href="#tls::init"><b>tls::init </b><i>?options?</i><br>
</a><a href="#tls::socket"><b>tls::socket </b><em>?options? host
port</em><br>
<b>tls::socket</b><em> ?-server command? ?options? port</em><br>
</a><a href="#tls::status"><b>tls::status </b><em>?-local? channel</em><br>
</a><a href="#tls::handshake"><b>tls::handshake</b><em> channel</em></a><br>
<br>
<a href="#tls::import"><b>tls::import </b><i>channel ?options?</i></a><br>
<a href="#tls::ciphers protocol ?verbose?"><strong>tls::ciphers</strong>
<em>protocol ?verbose?</em></a><br>
<a href="#tls::version"><b>tls::version</b></a>
</p>
<h3><a name="DESCRIPTION">DESCRIPTION</a></h3>
<p>This extension provides a generic binding to <a
href="http://www.openssl.org/">OpenSSL</a>, utilizing the
<strong>Tcl_StackChannel</strong>
API for Tcl 8.2 and higher. The sockets behave exactly the same
as channels created using Tcl's built-in <strong>socket</strong>
command with additional options for controlling the SSL session.
To use TLS with an earlier version of Tcl than 8.2, please obtain
TLS v1.3. Please note that there are known limitations with the
stacked channel implementation prior to 8.3.2, so it is recommended
that TLS is used with an 8.3.2+ interpreter. TLS v1.4 will work
with 8.2+, it is just more stable with 8.3.2+.
</p>
<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>
command. In such cases <strong>tls::import</strong> should not be
used directly.</p>
<dl>
<dt><a name="tls::init"><b>tls::init </b><i>?options?</i></a></dt>
<dd>This routine sets the default options used by <strong>tls::socket</strong>
and is <em>optional</em>. If you call <strong>tls::import</strong>
directly this routine has no effect. Any of the options
that <strong>tls::socket</strong> accepts can be set
using this command, though you should limit your options
to only TLS related ones.</dd>
<dt> </dt>
<dt><a name="tls::socket"><b>tls::socket </b><em>?options?
host port</em></a></dt>
<dt><b>tls::socket</b><em> ?-server command? ?options? port</em></dt>
<dd>This is a helper function that utilizes the underlying
commands (<strong>tls::import</strong>). It behaves
exactly the same as the native Tcl <strong>socket</strong>
command except that the options can include any of the
applicable <a href="#tls::import"><strong>tls:import</strong></a>
options.</dd>
<dt> </dt>
<dt><a name="tls::handshake"><strong>tls::handshake</strong> <em>channel</em></a></dt>
<dd>Forces handshake to take place, and returns 0 if
handshake is still in progress (non-blocking), or 1 if
the handshake was successful. If the handshake failed
this routine will throw an error.</dd>
<dt> </dt>
<dt><a name="tls::status"><strong>tls::status</strong>
<em>?-local? channel</em></a></dt>
<dd>Returns the current security status of a SSL channel. The
result is a list of key value pairs describing the
connected peer. If the result is an empty list then the
SSL handshake has not yet completed.
If <em>-local</em> is given, then the certificate information
is the one used locally.</dd>
</dl>
<blockquote>
<dl>
<dt><strong>issuer</strong> <em>dn</em></dt>
<dd>The distinguished name (DN) of the certificate
issuer.</dd>
<dt><strong>subject</strong> <em>dn</em></dt>
<dd>The distinguished name (DN) of the certificate
subject.</dd>
<dt><strong>notBefore</strong> <em>date</em></dt>
<dd>The begin date for the validity of the certificate.</dd>
<dt><strong>notAfter</strong> <em>date</em></dt>
<dd>The expiry date for the certificate.</dd>
<dt><strong>serial</strong> <em>n</em></dt>
<dd>The serial number of the certificate.</dd>
<dt><strong>cipher</strong> <em>cipher</em></dt>
<dd>The current cipher in use between the client and
server channels.</dd>
<dt><strong>sbits</strong> <em>n</em></dt>
<dd>The number of bits used for the session key.</dd>
</dl>
</blockquote>
<dl>
<dt><a name="tls::import"><b>tls::import </b><i>channel
?options?</i></a></dt>
<dd>SSL-enable a regular Tcl channel - it need not be a
socket, but must provide bi-directional flow. Also
setting session parameters for SSL handshake.</dd>
</dl>
<blockquote>
<dl>
<dt>-<strong>cadir</strong> <em>dir</em></dt>
<dd>Provide the directory containing the CA certificates.</dd>
<dt><strong>-cafile </strong><em>filename</em></dt>
<dd>Provide the CA file.</dd>
<dt><strong>-certfile</strong> <em>filename</em></dt>
<dd>Provide the certificate to use.</dd>
<dt><strong>-cipher </strong><em>string</em></dt>
<dd>Provide the cipher suites to use. Syntax is as per
OpenSSL.</dd>
<dt><strong>-command</strong><em> callback</em></dt>
<dd>If specified, this callback will be invoked at several points
during the OpenSSL handshake. It can pass errors and tracing
information, and it can allow Tcl scripts to perform
their own validation of the certificate in place of the
default validation provided by OpenSSL.
The callback should return an integer whose interpretation
depends on context.
<br>
See <a href="#CALLBACK OPTIONS">CALLBACK OPTIONS</a> for
further discussion.</dd>
<dt><strong>-keyfile</strong> <em>filename</em></dt>
<dd>Provide the private key file. (<strong>default</strong>:
value of -certfile)</dd>
<dt><strong>-model</strong> <em>channel</em></dt>
<dd>This will force this channel to share the same <em><strong>SSL_CTX</strong></em>
structure as the specified <em>channel</em>, and
therefore share callbacks etc.</dd>
<dt><strong>-password</strong><em> callback</em></dt>
<dd>If supplied, this callback will be invoked when OpenSSL needs
to obtain a password, typically for a certificate.
The callback should return a string which represents the
password to be used.
<br>
See <a href="#CALLBACK OPTIONS">CALLBACK OPTIONS</a> for
further discussion.</dd>
<dt><strong>-request </strong><em>bool</em></dt>
<dd>Request a certificate from peer during SSL handshake.
(<strong>default</strong>: <em>true</em>)</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. (<strong>default</strong>: <em>false</em>)</dd>
<dt><strong>-server</strong> <em>bool</em></dt>
<dd>Handshake as server if true, else handshake as
client.(<strong>default</strong>: <em>false</em>)</dd>
<dt><strong>-ssl2</strong> <em>bool</em></dt>
<dd>Enable use of SSL v2. (<strong>default</strong>: <em>true</em>
unless -DNO_PATENTS was specified in build)</dd>
<dt><strong>-ssl3 </strong><em>bool</em></dt>
<dd>Enable use of SSL v3. (<strong>default</strong>: <em>true</em>)</dd>
<dt>-<strong>tls1</strong> <em>bool</em></dt>
<dd>Enable use of TLS v1. (<strong>default</strong>: <em>false</em>)</dd>
</dl>
</blockquote>
<dl>
<dt><a name="tls::ciphers protocol ?verbose?"><strong>tls::ciphers</strong>
<em>protocol ?verbose?</em></a></dt>
<dd>Returns list of supported ciphers based on the <em>protocol</em>
you supply, which must be one of <em>ssl2, ssl3, or tls1</em>.
If <em>verbose</em> is specified as true then a verbose,
semi-human readable list is returned providing additional
information on the nature of the cipher support. In each
case the result is a Tcl list.</dd>
</dl>
<dl>
<dt><a name="tls::version"><strong>tls::version</strong></a></dt>
<dd>Returns the version string defined by OpenSSL.</dd>
</dl>
<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
<em>-command</em> and <em>-password</em> options passed to either of
<strong>tls::socket</strong> or <strong>tls::import</strong>.
</p>
<p>
Reference implementations of these callbacks are provided in the distribution
as <strong>tls::callback</strong> and <strong>tls::password</strong>.
Note that these are <em>sample</em> implementations only. In a more realistic
deployment you would substitute your own callbacks, typically by configuring
the <em>-command</em> and <em>-password</em> options on each channel with
scripts to be executed when the callbacks are invoked.
</p>
<p>
The default behavior when the <em>-command</em> option is not specified is for
TLS to process the associated library callbacks internally.
The default behavior when the <em>-password</em> option is not specified is for
TLS to process the associated library callbacks by attempting to call
<strong>tls::password</strong>.
The difference between these two behaviors is a consequence of maintaining
compatibility with earlier implementations. The use of implied callbacks
is not recommended.
</p>
<p>
The <strong>tls::debug</strong> variable provides some additional control
over the default commands. Its value is zero by default. Higher values
produce more diagnostic output. Setting this value greater than zero
will also force the default verify method in <strong>tls::callback</strong>
to accept the certificate, even if it is invalid.
</p>
<h3><a name="HTTPS EXAMPLE">HTTPS EXAMPLE</a></h3>
<p>This example requires a patch to the <strong>http</strong>
module that ships with Tcl - this patch has been submitted for
inclusion in Tcl 8.2.1, but is also provided in the tls directory
if needed. A sample server.pem is provided with the TLS release,
courtesy of the <strong>OpenSSL</strong> project.</p>
<pre><code>package require http
package require tls
http::register https 443 [list ::tls::socket -require 1 -cafile ./server.pem]
set tok [http::geturl https://developer.netscape.com/]
</code></pre>
<h3><a name="SPECIAL CONSIDERATIONS">SPECIAL CONSIDERATIONS</a></h3>
<p>The capabilities of this package can vary enormously based
upon how your OpenSSL library was configured and built. At the
most macro-level OpenSSL supports a "no patents" build,
which disables RSA, IDEA, RC(2,4,5) and SSL2 - if your OpenSSL is
configured this way then you will need to build TLS with the
-DNO_PATENTS option - and the resultant module will function
correctly and also support ADH certificate-less encryption,
however you will be unable to utilize this to speak to normal Web
Servers, which typically require RSA support. Please see <a
href="http://www.openssl.org/">http://www.openssl.org/</a> for
more information on the whole issue of patents and US export
restrictions. </p>
<h3><a name="SEE ALSO">SEE ALSO</a></h3>
<p><strong>socket</strong>, <strong>fileevent, </strong><a
href="http://www.openssl.org/"><strong>OpenSSL</strong></a></p>
<hr>
<pre>
Copyright © 1999 Matt Newman.
</pre>
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