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<meta name="Author"
content="Matt Newman <matt@novadigm.com>">
<meta name="Copyright" content="1999 Matt Newman.">
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<meta name="Copyright" content="1999 Matt Newman / 2004 Starfish Systems">
<title>TLS (SSL) Tcl Commands</title>
</head>
<body bgcolor="#FFFFFF">
<dl>
<dd><a href="#NAME">NAME</a> <dl>
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<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>
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<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 an 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>
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<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.
<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.
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<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.
<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 to unlock the private key of
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.
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<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.
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
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<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>
<blockquote>
<dl>
<dt><strong>-command</strong> <em>callback</em></dt>
<dd>
Invokes the specified <em>callback</em> script at
several points during the OpenSSL handshake.
Except as indicated below, values returned from the
callback are ignored.
Arguments appended to the script upon callback take one of the
following forms:
<br>
<br>
<dl>
<!-- This form of callback is disabled.
<dt>
<strong>error</strong> <em>channel message</em>
</dt>
<dd>
The <em>message</em> argument contains an error message generated
by the OpenSSL function
<code>ERR_reason_error_string()</code>.
</dd>
<br>
-->
<dt>
<strong>info</strong> <em>channel major minor message</em>
</dt>
<dd>
This form of callback is invoked by the OpenSSL function
<code>SSL_CTX_set_info_callback()</code>.
<br>
The <em>major</em> and <em>minor</em> arguments are used to
represent the state information bitmask.
<dl>
<dt>Possible values for <em>major</em> are:</dt>
<dd><code>handshake, alert, connect, accept</code>.</dd>
<dt>Possible values for <em>minor</em> are:</dt>
<dd><code>start, done, read, write, loop, exit</code>.</dd>
</dl>
The <em>message</em> argument is a descriptive string which may
be generated either by
<code>SSL_state_string_long()</code> or by
<code>SSL_alert_desc_string_long()</code>,
depending on context.
</dd>
<br>
<dt>
<strong>verify</strong> <em>channel depth cert status error</em>
</dt>
<dd>
This form of callback is invoked by the OpenSSL function
<code>SSL_set_verify()</code>.
<br>
The <em>depth</em> argument is an integer representing the
current depth on the certificate chain, with
<code>0</code> as the subject certificate and higher values
denoting progressively more indirect issuer certificates.
<br>
The <em>cert</em> argument is a list of key-value pairs similar
to those returned by
<a href="#tls::status"><strong>tls::status</strong></a>.
<br>
The <em>status</em> argument is an integer representing the
current validity of the certificate.
A value of <code>0</code> means the certificate is deemed invalid.
A value of <code>1</code> means the certificate is deemed valid.
<br>
The <em>error</em> argument supplies the message, if any, generated
by
<code>X509_STORE_CTX_get_error()</code>.
<br>
<br>
The callback may override normal validation processing by explicitly
returning one of the above <em>status</em> values.
</dd>
</dl>
</dd>
<br>
<dt><strong>-password</strong> <em>callback</em></dt>
<dd>
Invokes the specified <em>callback</em> script when OpenSSL needs to
obtain a password. The callback should return a string which
represents the password to be used.
No arguments are appended to the script upon callback.
</dd>
</dl>
</blockquote>
<p>
Reference implementations of these callbacks are provided in the
distribution as <strong>tls::callback</strong> and
<strong>tls::password</strong> respectively. Note that these are
<em>sample</em> implementations only. In a more realistic deployment
you would specify your own callback scripts on each TLS channel
using the <em>-command</em> and <em>-password</em> options.
</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.
</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.
</p>
<p>
<em>
The use of the reference callbacks <strong>tls::callback</strong> and
<strong>tls::password</strong> is not recommended. They may be removed
from future releases.
</em>
</p>
<p>
<em>
The use of the variable <strong>tls::debug</strong> is not recommended.
It may be removed from future releases.
</em>
</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>
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<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>
</body>
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<p><strong>socket</strong>, <strong>fileevent, </strong><a
href="http://www.openssl.org/"><strong>OpenSSL</strong></a></p>
<hr>
<pre>
Copyright © 1999 Matt Newman.
Copyright © 2004 Starfish Systems.
</pre>
</body>
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