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<meta name="Copyright" content="1999 Matt Newman / 2004 Starfish Systems">
<title>TLS (SSL) Tcl Commands</title>
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<dl>
    <dd><a href="#NAME">NAME</a>
    <dl>
        <dd><b>tls</b> - binding to <b>OpenSSL</b> toolkit.</dd>
    </dl>
    </dd>
    <dd><a href="#SYNOPSIS">SYNOPSIS</a> </dd>
    <dd><dl>
            <dd><b>package require Tcl</b> <em>?8.4?</em></dd>
            <dd><b>package require tls</b></dd>
            <dt>&nbsp;</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::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>&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="#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 8.4</b><br>
<b>package require tls</b><br>
<br>
<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>
<a href="#tls::socket"><b>tls::socket</b> <i>?-server command? ?options? port</i></a><br>
<a href="#tls::status"><b>tls::status</b> <i>?-local? channel</i></a><br>
<a href="#tls::connection"><b>tls::connection</b> <i>channel</i></a><br>
<a href="#tls::handshake"><b>tls::handshake</b> <i>channel</i></a><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>
<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 8.4 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>

<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>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>&nbsp;</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 with one additional option:
<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>
    </dl>
</blockquote>

    <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>

<blockquote>
    <dl>
        <dt><strong>-alpn</strong> <em>list</em></dt>
        <dd>List of protocols to offer during Application-Layer
	    Protocol Negotiation (ALPN). For example: h2, http/1.1, etc.</dd>
        <dt><strong>-cadir</strong> <em>dir</em></dt>
        <dd>Specify the directory containing the CA certificates. The
	    default directory is platform specific and can be set at
	    compile time. This can be overridden via the <b>SSL_CERT_DIR</b>
	    environment variable.</dd>
        <dt><strong>-cafile </strong><em>filename</em></dt>
        <dd>Specify the certificate authority (CA) file to use.</dd>
        <dt><strong>-certfile</strong> <em>filename</em></dt>
        <dd>Specify the filename containing the certificate to use. The
	    default name is <b>cert.pem</b>. This can be overridden via
	    the <b>SSL_CERT_FILE</b> environment variable.</dd>
        <dt><strong>-cert</strong> <em>filename</em></dt>
        <dd>Specify 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>List of ciphers to use. String is a colon (":") separated list
	    of ciphers or cipher suites. Cipher suites can be combined
	    using the <b>+</b> character. Prefixes can be used to permanently
	    remove ("!"), delete ("-"), or move a cypher to the end of
	    the list ("+"). Keywords <b>@STRENGTH</b> (sort by algorithm
	    key length), <b>@SECLEVEL=</b><i>n</i> (set security level to
	    n), and <b>DEFAULT</b> (use default cipher list, at start only)
	    can also be specified. See OpenSSL documentation for the full
	    list of valid values. (TLS 1.2 and earlier only)</dd>
        <dt><strong>-ciphersuites</strong> <em>string</em></dt>
        <dd>List of cipher suites to use. String is a colon (":")
	    separated list of cipher suite names. (TLS 1.3 only)</dd>
        <dt><strong>-command</strong> <em>callback</em></dt>
        <dd>Callback to invoke at several points during the handshake.
	    This is used to pass errors and tracing information, and
	    it can allow Tcl scripts to perform their own certificate
	    validation in place of the default validation provided by
	    OpenSSL. See <a href="#CALLBACK OPTIONS">CALLBACK OPTIONS</a>
	    for further discussion.</dd>
        <dt><strong>-dhparams </strong><em>filename</em></dt>
        <dd>Specify the Diffie-Hellman parameters file.</dd>
        <dt><strong>-keyfile</strong> <em>filename</em></dt>
        <dd>Specify the private key file. (default is
            value of -certfile)</dd>
        <dt><strong>-key</strong> <em>filename</em></dt>
        <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>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>Callback to invoke 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. See <a href="#CALLBACK OPTIONS">CALLBACK OPTIONS</a>
	    for further discussion.</dd>
	<dt><strong>-post_handshake</strong> <em>bool</em></dt>
	<dd>Allow post-handshake ticket updates.</dd>
        <dt><strong>-request </strong><em>bool</em></dt>
        <dd>Request a certificate from peer during SSL handshake.
            (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>
        <dt><strong>-securitylevel</strong> <em>integer</em></dt>
        <dd>Set security level. Must be 0 to 5. The security level affects
	    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>Handshake as server if true, else handshake as
            client. (default is <em>false</em>)</dd>
        <dt><strong>-servername</strong> <em>host</em></dt>
        <dd>Specify server hostname. 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>
        <dt><strong>-session_id</strong> <em>string</em></dt>
        <dd>Session id to resume session.</dd>
        <dt><strong>-ssl2</strong> <em>bool</em></dt>
        <dd>Enable use of SSL v2. (default is <em>false</em>)</dd>
        <dt><strong>-ssl3 </strong><em>bool</em></dt>
        <dd>Enable use of SSL v3. (default is <em>false</em>)</dd>
        <dt>-<strong>tls1</strong> <em>bool</em></dt>
        <dd>Enable use of TLS v1. (default is <em>true</em>)</dd>
        <dt>-<strong>tls1.1</strong> <em>bool</em></dt>
        <dd>Enable use of TLS v1.1 (default is <em>true</em>)</dd>
        <dt>-<strong>tls1.2</strong> <em>bool</em></dt>
        <dd>Enable use of TLS v1.2 (default is <em>true</em>)</dd>
        <dt>-<strong>tls1.3</strong> <em>bool</em></dt>
        <dd>Enable use of TLS v1.3 (default is <em>true</em>)</dd>
    </dl>
</blockquote>

    <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>
    <dt>&nbsp;</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>&nbsp;</dt>
    <dt><a name="tls::status"><strong>tls::status</strong>
    <em>?-local? channel</em></a></dt>
    <dd>Returns the current status of the certificate for an SSL
	channel. The result is a list of key-value pairs describing
	the certificate. If the result is an empty list then the
        SSL handshake has not yet completed. If <em>-local</em> is
	specified, then the local certificate is used.</dd>
<blockquote>
	<b>SSL Status</b>
    <dl>
        <dt><strong>alpn</strong> <em>protocol</em></dt>
        <dd>The protocol selected after Application-Layer Protocol
	    Negotiation (ALPN).</dd>
        <dt><strong>cipher</strong> <em>cipher</em></dt>
        <dd>The current cipher in use between the client and
            server channels.</dd>
        <dt><strong>peername</strong> <em>name</em></dt>
        <dd>The peername from the certificate.</dd>
        <dt><strong>protocol</strong> <em>version</em></dt>
        <dd>The protocol version used for the connection:
	    SSL2, SSL3, TLS1, TLS1.1, TLS1.2, TLS1.3, or unknown.</dd>
        <dt><strong>sbits</strong> <em>n</em></dt>
        <dd>The number of bits used for the session key.</dd>
        <dt><strong>signatureHashAlgorithm</strong> <em>algorithm</em></dt>
        <dd>The signature hash algorithm.</dd>
        <dt><strong>signature_type</strong> <em>type</em></dt>
        <dd>The signature type value.</dd>
        <dt><strong>verification</strong> <em>result</em></dt>
        <dd>Certificate verification result.</dd>
        <dt><strong>ca_names</strong> <em>list</em></dt>
        <dd>List of the Certificate Authorities used to create the certificate.</dd>
    </dl>
</blockquote>
<blockquote>
	<b>Certificate Status</b>
    <dl>
        <dt><strong>all</strong> <em>string</em></dt>
        <dd>Dump of all certificate info.</dd>

        <dt><strong>version</strong> <em>value</em></dt>
        <dd>The certificate version.</dd>
        <dt><strong>serialNumber</strong> <em>n</em></dt>
        <dd>The serial number of the certificate as hex string.</dd>
        <dt><strong>signature</strong> <em>algorithm</em></dt>
        <dd>Cipher algorithm used for certificate signature.</dd>
        <dt><strong>issuer</strong> <em>dn</em></dt>
        <dd>The distinguished name (DN) of the certificate issuer.</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 expiration date for the certificate.</dd>
        <dt><strong>subject</strong> <em>dn</em></dt>
        <dd>The distinguished name (DN) of the certificate subject.
	    Fields include: Common Name (CN), Organization (O), Locality
	    or City (L), State or Province (S), and Country Name (C).</dd>

        <dt><strong>num_extensions</strong> <em>n</em></dt>
        <dd>Number of certificate extensions.</dd>
        <dt><strong>extensions</strong> <em>list</em></dt>
        <dd>List of certificate extension names.</dd>
        <dt><strong>subjectKeyIdentifier</strong> <em>string</em></dt>
        <dd>Hash of the public key inside the certificate.</dd>
        <dt><strong>subjectAltName</strong> <em>list</em></dt>
        <dd>List of all of the alternative domain names, sub domains,
	    and IP addresses that are secured by the certificate.</dd>

	<dt><strong>certificate</strong> <em>cert</em></dt>
        <dd>The PEM encoded certificate.</dd>

        <dt><strong>signatureDigest</strong> <em>version</em></dt>
        <dd>Certificate signing digest.</dd>
        <dt><strong>publicKeyAlgorithm</strong> <em>algorithm</em></dt>
        <dd>Certificate signature public key algorithm.</dd>
        <dt><strong>publicKey</strong> <em>string</em></dt>
        <dd>Certificate signature public key as hex string.</dd>
        <dt><strong>bits</strong> <em>n</em></dt>
        <dd>Number of bits used for certificate signature key</dd>
        <dt><strong>self_signed</strong> <em>boolean</em></dt>
        <dd>Is certificate signature self signed.</dd>

        <dt><strong>sha1_hash</strong> <em>hash</em></dt>
        <dd>The SHA1 hash of the certificate as hex string.</dd>
        <dt><strong>sha256_hash</strong> <em>hash</em></dt>
        <dd>The SHA256 hash of the certificate as hex string.</dd>
    </dl>
</blockquote>

    <dt><a name="tls::connection"><strong>tls::connection</strong>
    <em>channel</em></a></dt>
    <dd>Returns the current connection status of an SSL channel. The
        result is a list of key-value pairs describing the
        connected peer.</dd>
<blockquote>
	<b>SSL Status</b>
    <dl>
        <dt><strong>state</strong> <em>state</em></dt>
        <dd>State of the connection.</dd>
        <dt><strong>servername</strong> <em>name</em></dt>
        <dd>The name of the connected to server.</dd>
        <dt><strong>protocol</strong> <em>version</em></dt>
        <dd>The protocol version used for the connection:
	    SSL2, SSL3, TLS1, TLS1.1, TLS1.2, TLS1.3, or unknown.</dd>
        <dt><strong>renegotiation</strong> <em>state</em></dt>
        <dd>Whether protocol renegotiation is supported or not.</dd>
        <dt><strong>securitylevel</strong> <em>level</em></dt>
        <dd>The security level used for selection of ciphers, key size, etc.</dd>
        <dt><strong>session_reused</strong> <em>boolean</em></dt>
        <dd>Whether the session has been reused or not.</dd>
        <dt><strong>is_server</strong> <em>boolean</em></dt>
        <dd>Whether the connection configured as a server or client (false).</dd>
        <dt><strong>compression</strong> <em>mode</em></dt>
        <dd>Compression method.</dd>
        <dt><strong>expansion</strong> <em>mode</em></dt>
        <dd>Expansion method.</dd>
    </dl>
</blockquote>
<blockquote>
	<b>Cipher Info</b>
    <dl>
        <dt><strong>cipher</strong> <em>cipher</em></dt>
        <dd>The current cipher in use for the connection.</dd>
        <dt><strong>standard_name</strong> <em>name</em></dt>
        <dd>The standard RFC name of cipher.</dd>
        <dt><strong>bits</strong> <em>n</em></dt>
        <dd>The number of processed bits used for cipher.</dd>
        <dt><strong>secret_bits</strong> <em>n</em></dt>
        <dd>The number of secret bits used for cipher.</dd>
        <dt><strong>min_version</strong> <em>version</em></dt>
        <dd>The minimum protocol version for cipher.</dd>
        <dt><strong>id</strong> <em>id</em></dt>
        <dd>The OpenSSL cipher id.</dd>
        <dt><strong>description</strong> <em>string</em></dt>
        <dd>A text description of the cipher.</dd>
    </dl>
</blockquote>
<blockquote>
	<b>Session Info</b>
    <dl>
        <dt><strong>alpn</strong> <em>protocol</em></dt>
        <dd>The protocol selected after Application-Layer Protocol
	    Negotiation (ALPN).</dd>
        <dt><strong>resumable</strong> <em>boolean</em></dt>
        <dd>Can the session be resumed or not.</dd>
        <dt><strong>start_time</strong> <em>seconds</em></dt>
        <dd>Time since session started in seconds since epoch.</dd>
        <dt><strong>timeout</strong> <em>seconds</em></dt>
        <dd>Max duration of session in seconds before time-out.</dd>
        <dt><strong>lifetime</strong> <em>seconds</em></dt>
        <dd>Session ticket lifetime hint in seconds.</dd>
        <dt><strong>session_id</strong> <em>string</em></dt>
        <dd>Unique session id for use in resuming the session.</dd>
        <dt><strong>session_ticket</strong> <em>string</em></dt>
        <dd>Unique session ticket for use in resuming the session.</dd>
        <dt><strong>ticket_app_data</strong> <em>string</em></dt>
        <dd>Unique session ticket application data.</dd>
        <dt><strong>master_key</strong> <em>binary_string</em></dt>
        <dd>Unique session master key.</dd>
        <dt><strong>session_cache_mode</strong> <em>mode</em></dt>
        <dd>Server cache mode (client, server, or both).</dd>
    </dl>
</blockquote>

    <dt><a name="tls::ciphers"><strong>tls::ciphers</strong>
    <em>protocol ?verbose? ?supported?</em></a></dt>
    <dd>Returns a list of supported ciphers available for <em>protocol</em>,
        where protocol must be one of <b>ssl2, ssl3, tls1, tls1.1,
	tls1.2,</b> or <b>tls1.3</b>. If <em>verbose</em> is specified as
	true then a verbose, human readable list is returned with
	additional information on the cipher. If <em>supported</em>
	is specified as true, then only the ciphers supported for protocol
	will be listed.</dd>

    <dt><a name="tls::protocols"><strong>tls::protocols</strong></a></dt>
    <dd>Returns a list of supported protocols. Valid values are:
	<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><a name="tls::version"><strong>tls::version</strong></a></dt>
    <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
<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>

	<dt>
	  <strong>alpn</strong> <em>protocol</em>
	</dt>
	<dd>
	  For servers, this form of callback is invoked when the client ALPN
	  header is received and the first <b>-alpn</b> specified protocol common
	  to the both the client and server is selected. If none, the first
	  client specified protocol is used.
	</dd>

	<br>

<!--	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>hello</strong> <em>servername</em>
	</dt>
	<dd>
	  For servers, this form of callback is invoked during client hello
	  message processing.
	</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>session</strong> <em>session_id ticket lifetime</em>
	</dt>
	<dd>
	  This form of callback is invoked by the OpenSSL function
	  <code>SSL_CTX_sess_set_new_cb()</code>.
	  Where <em>session_id</em> is the current session identifier,
	  <em>ticket</em> is the session ticket info, and <em>lifetime</em>
	  is the the ticket lifetime in seconds.
	</dd>

	<br>

	<dt>
	  <strong>sni</strong> <em>servername</em>
	</dt>
	<dd>
	  For servers, this form of callback is invoked when the SNI header
	  from the client is received. Where <i>servername</i> is the client
	  specified servername. This is used when a server supports multiple
	  names, so the right certificate can be used.
	</dd>

	<br>
	<br>

	<dt>
	  <strong>verify</strong> <em>channel 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 result and choose whether to continue or not.
	  <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="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.

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

<p>This example uses a sample server.pem 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 -autoservername true -require true -cadir /etc/ssl/certs]

set tok [http::geturl https://www.tcl.tk/]
</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 &quot;no patents&quot; 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 &copy; 1999 Matt Newman.
Copyright &copy; 2004 Starfish Systems.
</pre>
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