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<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="Copyright" content="1999 Matt Newman / 2004 Starfish Systems">
<title>TLS (SSL) Tcl Commands</title>
<link rel="stylesheet" href="docs.css" type="text/css" media="all">
</head>
<body class="vsc-initialized">
<body bgcolor="#FFFFFF">
<dd><b>tls</b> - binding to <b>OpenSSL</b> toolkit.</dd>
<dd><b>package require tls</b> <em>?@@VERS@@?</em></dd>
<dd><b>package require tls</b></dd>
<dt> </dt>
<dd><b>tls::init</b> <em>?options?</em> </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::handshake</b> <em> channel</em></dd>
<dd><b>tls::status</b> <em>?-local? channel</em></dd>
<dd><b>tls::connection</b> <em>channel</em></dd>
<dd><b>tls::import</b> <em>channel ?options?</em></dd>
<dd><b>tls::unimport</b> <em>channel</em></dd>
<dt> </dt>
<dd><b>tls::ciphers</b> <em>protocol ?verbose?</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="#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>
<p><strong>tls</strong> - binding to <strong>OpenSSL</strong> library
for socket and I/O channel communications.</p>
<h3><a name="SYNOPSIS">SYNOPSIS</a></h3>
<p><b>package require Tcl 8.5</b><br>
<b>package require tls @@VERS@@</b><br>
<p><b>package require Tcl</b> <em>?<b>8.5</b>?</em><br>
<b>package require tls</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
<a href="#tls::init"><b>tls::init</b> <i>?options?</i></a><br>
<a href="#tls::socket"><b>tls::socket</b> <i>?options? host port</i><br>
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::ciphers protocol ?verbose?"><strong>tls::ciphers</strong>
<a href="#tls::protocols"><b>tls::protocols</b></a><br>
<em>protocol ?verbose?</em></a><br>
<a href="#tls::version"><b>tls::version</b></a>
<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.
<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="http://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 session.
To use TLS with an earlier version of Tcl than 8.4, please obtain
TLS 1.3.
<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>
<dt><a name="tls::init"><b>tls::init </b><i>?options?</i></a></dt>
<dd>Optional function to set the default options used by
<strong>tls::socket</strong>. 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?
<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
command except the options can also include any of the
applicable <a href="#tls::import"><strong>tls:import</strong></a>
options with one additional option:
options with one additional option:</dd>
<blockquote>
<dl>
<dt><strong>-autoservername</strong> <em>bool</em></dt>
<dd>Automatically send the -servername as the <em>host</em> argument
(default is <em>false</em>)</dd>
<dd>Automatically set the -servername argument to the <em>host</em>
argument (default is <em>false</em>).</dd>
</dl>
</blockquote>
<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 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>
<dt><strong>issuer</strong> <em>dn</em></dt>
<dd>The distinguished name (DN) of the certificate
<dt><strong>-cafile </strong><em>filename</em></dt>
<dd>Set the certificate authority (CA) certificates file. The default
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>
<dt><strong>certificate</strong> <em>n</em></dt>
<dd>The PEM encoded certificate.</dd>
<dt><strong>version</strong> <em>value</em></dt>
<dd>The protocol version used for the connection:
SSLv2, SSLv3, TLSv1, TLSv1.1, TLSv1.2, unknown</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 name of a file containing certificate to use.</dd>
<dt><strong>-cert</strong> <em>filename</em></dt>
<dd>Provide the contents of a certificate to use, as a DER encoded binary value (X.509 DER).</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>-dhparams </strong><em>filename</em></dt>
<dd>Provide a Diffie-Hellman parameters file.</dd>
<dd>Provide the private key file. (default is
<dd>Specify the private key file. (default is
value of -certfile)</dd>
<dt><strong>-key</strong> <em>filename</em></dt>
<dd>Provide the private key to use as a DER encoded value (PKCS#1 DER)</dd>
<dd>Specify the private key to use as a DER encoded value (PKCS#1 DER)</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>
<dd>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
<dd>Callback command to invoke when OpenSSL needs to obtain a password.
Typically used to unlock the private key of a certificate. The
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>
(default is <em>true</em>)</dd>
(default is <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. (default is <em>false</em>)</dd>
<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, or platform
default must be provided in order to validate against.
(default is <em>false</em>)</dd>
<dt><strong>-security_level</strong> <em>integer</em></dt>
<dd>Set security level. Must be 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.
Level 3 and higher disable support for session tickets and only
accept cipher suites that provide forward secrecy.</dd>
<dt><strong>-server</strong> <em>bool</em></dt>
<dd>Set to act as a server and respond with a server handshake when
<dd>Handshake as server if true, else handshake as
client.(default is <em>false</em>)</dd>
a client connects and provides a client handshake.
(default is <em>false</em>)</dd>
<dt><strong>-servername</strong> <em>host</em></dt>
<dd>Only available if the OpenSSL library the package is linked
against supports the TLS hostname extension for 'Server Name
Indication' (SNI). Use to name the logical host we are talking
to and expecting a certificate for</dd>
<dl>
<dt><a name="tls::unimport"><b>tls::unimport</b> <i>channel</i></a></dt>
<dd>Provided for symmetry to <strong>tls::import</strong>, this
unstacks the SSL-enabling of a regular Tcl channel. An error
is thrown if TLS is not the top stacked channel type.</dd>
</dl>
<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>
<dd>Returns the version string defined by OpenSSL.</dd>
<dd>Returns the OpenSSL version string.</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
<strong>-command</strong>, <strong>-password</strong>, and
<em>-command</em> and <em>-password</em> options passed to either of
<strong>-validate_command</strong> options passed to either of
<strong>tls::socket</strong> or <strong>tls::import</strong>.
If the callback generates an error, the <b>bgerror</b> command will be
invoked with the error information.
</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
Invokes the specified <em>callback</em> script at several points
during the OpenSSL handshake and use. See below for the possible
arguments passed to the callback script. Values returned from the
callback are ignored.
Arguments appended to the script upon callback take one of the
following forms:
<!-- This form of callback is disabled.
<strong>error</strong> <em>channel message</em>
<strong>error</strong> <em>channelId message</em>
</dt>
<dd>
This form of callback is invoked whenever an error occurs during the
The <em>message</em> argument contains an error message generated
by the OpenSSL function
<code>ERR_reason_error_string()</code>.
initial connection, handshake, or I/O operations. The <em>message</em>
argument can be from the Tcl_ErrnoMsg, OpenSSL function
<code>ERR_reason_error_string()</code>, or a custom message.
</dd>
<br>
-->
<strong>info</strong> <em>channel major minor message</em>
<strong>info</strong> <em>channelId major minor message type</em>
</dt>
<dd>
This form of callback is invoked by the OpenSSL function
<code>SSL_CTX_set_info_callback()</code>.
<code>SSL_set_info_callback()</code> during the initial connection
and handshake operations. The <em>type</em> argument is new for
TLS 1.8. The arguments are:
<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.
<br>
<strong>verify</strong> <em>channel depth cert status error</em>
<strong>message</strong> <em>channelId direction version content_type message</em>
</dt>
<dd>
This form of callback is invoked by the OpenSSL function
<code>SSL_set_verify()</code>.
<code>SSL_set_msg_callback()</code> whenever a message is sent or
<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.
<br>
</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. See below for the possible arguments passed to
the callback script. See below for valid return values.
<br>
<br>
<dl>
<dt>
<strong>password</strong> <em>rwflag size</em>
</dt>
<dd>
Invoked when loading or storing a PEM certificate with encryption.
Where <em>rwflag</em> is 0 for reading/decryption or 1 for
writing/encryption (can prompt user to confirm) and
<em>size</em> is the max password length in bytes.
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.
The callback should return the password as a string.
Both arguments are new for TLS 1.8.
</dd>
</dd>
<br>
<dt><strong>-validatecommand</strong> <em>callback</em></dt>
<dd>
Invokes the specified <em>callback</em> script during handshake in
order to validate the provided value(s). See below for the possible
arguments passed to the callback script. If not specified, OpenSSL
will accept valid certificates and extensions.
To reject the value and abort the connection, the callback should return 0.
To accept the value and continue the connection, it should return 1.
To reject the value, but continue the connection, it should return 2.
<br>
<br>
<dl>
<dt>
<strong>alpn</strong> <em>channelId protocol match</em>
</dt>
<dd>
For servers, this form of callback is invoked when the client ALPN
extension is received. If <em>match</em> is true, <em>protocol</em>
is the first <b>-alpn</b> option specified protocol common to both
the client and server. If not, the first client specified protocol is
used. It is called after the hello and ALPN callbacks.
This callback is new for TLS 1.8.
</dd>
<br>
<dt>
<strong>hello</strong> <em>channelId servername</em>
</dt>
<dd>
For servers, this form of callback is invoked during client hello
message processing. The purpose is so the server can select the
appropriate certificate to present to the client, and to make other
configuration adjustments relevant to that server name and its
configuration. It is called before the SNI and ALPN callbacks.
This callback is new for TLS 1.8.
</dd>
<br>
<dt>
<strong>sni</strong> <em>channelId servername</em>
</dt>
<dd>
For servers, this form of callback is invoked when the Server Name
Indication (SNI) extension is received. The <em>servername</em>
argument is the client provided server name in the <b>-servername</b>
option. The purpose is so when a server supports multiple names, the
right certificate can be used. It is called after the hello callback
but before the ALPN callback.
This callback is new for TLS 1.8.
</dd>
<br>
<dt>
<strong>verify</strong> <em>channelId depth cert status error</em>
</dt>
<dd>
This form of callback is invoked by OpenSSL when a new certificate
is received from the peer. It allows the client to check the
certificate verification results and choose whether to continue
or not. It is called for each certificate in the certificate chain.
<ul>
<li>The <em>depth</em> argument is the integer depth of the
certificate in the certificate chain, where 0 is the peer certificate
and higher values going up to the Certificate Authority (CA).</li>
<li>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>.</li>
<li>The <em>status</em> argument is the boolean validity of the
current certificate where 0 is invalid and 1 is valid.</li>
<li>The <em>error</em> argument is the error message, if any, generated
by <code>X509_STORE_CTX_get_error()</code>.</li>
</ul>
</dd>
<br>
</dl>
</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
distribution as <strong>tls::callback</strong>, <strong>tls::password</strong>,
and <strong>tls::validate_command</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.
you would specify your own callback scripts on each TLS channel using the
<strong>-command</strong>, <strong>-password</strong>, and <strong>-validate_command</strong> 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 default behavior when the <strong>-command</strong> and <strong>-validate_command</strong>
options are not specified is for TLS to process the associated library callbacks
internally. The default behavior when the <strong>-password</strong> 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>
<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>
<h3><a name="DEBUG">DEBUG</a></h3>
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>
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.
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 reference callbacks <strong>tls::callback</strong> and
<strong>tls::password</strong> is not recommended. They may be removed
from future releases.
<p>
<em>
The use of the variable <strong>tls::debug</strong> is not recommended.
It may be removed from future releases.
</em>
</p>
<p>This example uses a sample server.pem provided with the TLS release,
courtesy of the <strong>OpenSSL</strong> project.</p>
set tok [http::geturl https://core.tcl-lang.org/]
<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
<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
older protocol versions, add or remove ciphers, change default values, etc.
Use the <strong>tls::protocols</strong> commands to obtain the supported
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>
<p><strong>socket</strong>, <strong>fileevent</strong>, <a
href="http://www.openssl.org/"><strong>OpenSSL</strong></a></p>
<p><strong>socket</strong>, <strong>fileevent</strong>, <strong>http</strong>,
<a href="http://www.openssl.org/"><strong>OpenSSL</strong></a></p>
<hr>
<pre>
Copyright © 1999 Matt Newman.
Copyright © 2004 Starfish Systems.
Copyright © 2023 Brian O'Hagan.
</pre>
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