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<title>TLS (SSL) Tcl Commands</title>
</head>

<body bgcolor="#FFFFFF">

<dl>
    <dd><a href="#NAME">NAME</a> <dl>
            <dd><strong>tls</strong> - binding to <strong>OpenSSL</strong>
                toolkit.</dd>
        </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><em>?@@VERS@@?</em></dd>
            <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><i>?options?</i> </dd>
            <dd><b>tls::socket </b><em>?options? host port</em></dd>
            <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::import</b><em> channel ?options?</em></dd>
            <dd><b>tls::unimport</b><em> channel</em></dd>
            <dd><b>tls::ciphers </b><em>protocol ?verbose?</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 @@VERS@@</b><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>
<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>
<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>
<a href="#tls::ciphers protocol ?verbose?"><strong>tls::ciphers</strong>
<em>protocol ?verbose?</em></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
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<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>
    <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
            (<strong>default</strong>: <em>false</em>)</dd>
            (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 security status of an SSL channel. The
    <dd>Returns the current certificate 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>
    <dl>
        <dt><strong>version</strong> <em>value</em></dt>
        <dd>The certification version</dd>
        <dt><strong>signature_algorithm</strong> <em>algorithm</em></dt>
        <dd>Cipher algorithm used for certificate signature.</dd>
        <dt><strong>digest</strong> <em>version</em></dt>
        <dd>Certificate signature digest.</dd>
        <dt><strong>public_key_algorithm</strong> <em>algorithm</em></dt>
        <dd>Certificate signature public key algorithm.</dd>
        <dt><strong>issuer</strong> <em>dn</em></dt>
        <dd>The distinguished name (DN) of the certificate
            issuer.</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.</dd>
        <dt><strong>sha256_hash</strong> <em>hash</em></dt>
        <dd>The SHA256 hash of the certificate.</dd>
        <dt><strong>subject</strong> <em>dn</em></dt>
        <dd>The distinguished name (DN) of the certificate
            subject.</dd>
        <dd>The distinguished name (DN) of the certificate subject.</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 expiry date for the certificate.</dd>
        <dt><strong>serial</strong> <em>n</em></dt>
        <dd>The serial number of the certificate.</dd>
        <dt><strong>certificate</strong> <em>cert</em></dt>
        <dd>The PEM encoded certificate.</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>peername</strong> <em>name</em></dt>
        <dd>The peername from the certificate.</dd>
        <dt><strong>sbits</strong> <em>n</em></dt>
        <dd>The number of bits used for the session key.</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>
        <dt><strong>verification<em>result</em></dt>
        <dd>The number of bits used for the session key.</dd>
        <dt><strong>certificate</strong> <em>cert</em></dt>
        <dd>The PEM encoded certificate.</dd>
        <dd>Certificate verification result.</dd>
        <dt><strong>sha1_hash</strong> <em>hash</em></dt>
        <dd>The SHA1 hash of the certificate.</dd>
        <dt><strong>sha256_hash</strong> <em>hash</em></dt>
        <dd>The SHA256 hash of the certificate.</dd>
        <dt><strong>alpn</strong> <em>protocol</em></dt>
        <dd>The protocol selected after Application-Layer Protocol
	    Negotiation (ALPN).</dd>
        <dt><strong>version</strong> <em>value</em></dt>
        <dt><strong>protocol</strong> <em>value</em></dt>
        <dd>The protocol version used for the connection:
	  SSLv2, SSLv3, TLSv1, TLSv1.1, TLSv1.2, TLSv1.3, unknown</dd>
	  SSLv2, SSLv3, TLSv1, TLSv1.1, TLSv1.2, TLSv1.3, or unknown</dd>
        <dt><strong>signature_hash</strong> <em>string</em></dt>
        <dd>The signature hash value.</dd>
        <dt><strong>signature_type</strong> <em>type</em></dt>
        <dd>The signature type value.</dd>
        <dt><strong>ca_names</strong> <em>list</em></dt>
        <dd>List of the Certificate Authorities used to create the certificate.</dd>
    </dl>
</blockquote>

<dl>
    <dt><a name="tls::import"><b>tls::import </b><i>channel
    <dt><a name="tls::connection"><strong>tls::connection</strong>
        ?options?</i></a></dt>
    <dd>SSL-enable a regular Tcl channel - it need not be a
    <em>channel</em></a></dt>
        socket, but must provide bi-directional flow. Also
        setting session parameters for SSL handshake.</dd>
</dl>
    <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>
    <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>
        <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>Provide the directory containing the CA certificates. The
	default directory is platform specific and can be set at
        <dd>The protocol version used for the connection:
	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>Provide the CA file.</dd>
        <dt><strong>-certfile</strong> <em>filename</em></dt>
	    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 allowed or disallowed.</dd>
        <dt><strong>securitylevel</strong> <em>level</em></dt>
        <dd>Provide the name of a file containing certificate to use.
	The default name is cert.pem. This can be overridden via the
	<b>SSL_CERT_FILE</b> environment variable.</dd>
        <dt><strong>-cert</strong> <em>filename</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>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>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>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>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>
        <dt><strong>-keyfile</strong> <em>filename</em></dt>
        <dd>Provide the private key file. (<strong>default</strong>:
            value of -certfile)</dd>
        <dt><strong>-key</strong> <em>filename</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>Provide 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>
            structure as the specified <em>channel</em>, and
            therefore share callbacks etc.</dd>
        <dt><strong>-password</strong> <em>callback</em></dt>
        <dd>The OpenSSL cipher id.</dd>
        <dt><strong>description</strong> <em>string</em></dt>
        <dd>A text description of the cipher.</dd>
        <dt><strong>alpn</strong> <em>protocol</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.
        <dd>The protocol selected after Application-Layer Protocol
            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>
	    Negotiation (ALPN).</dd>
        <dt><strong>resumable</strong> <em>boolean</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>Can the session be resumed or not.</dd>
        <dt><strong>start_time</strong> <em>seconds</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>Time since session started in seconds since epoch.</dd>
        <dt><strong>timeout</strong> <em>seconds</em></dt>
        <dd>Handshake as server if true, else handshake as
            client.(<strong>default</strong>: <em>false</em>)</dd>
        <dt><strong>-servername</strong> <em>host</em></dt>
        <dd>Max duration of session in seconds before time-out.</dd>
        <dt><strong>lifetime</strong> <em>seconds</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>
        <dt><strong>-ssl2</strong> <em>bool</em></dt>
        <dd>Enable use of SSL v2. (<strong>default</strong>: <em>false</em>)</dd>
        <dt><strong>-ssl3 </strong><em>bool</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>Enable use of SSL v3. (<strong>default</strong>: <em>false</em>)</dd>
        <dt>-<strong>tls1</strong> <em>bool</em></dt>
        <dd>Unique session ticket application data.</dd>
        <dt><strong>master_key</strong> <em>binary_string</em></dt>
        <dd>Enable use of TLS v1. (<strong>default</strong>: <em>true</em>)</dd>
        <dt>-<strong>tls1.1</strong> <em>bool</em></dt>
        <dd>Unique session master key.</dd>
        <dt><strong>compression</strong> <em>mode</em></dt>
        <dd>Enable use of TLS v1.1 (<strong>default</strong>: <em>true</em>)</dd>
        <dt>-<strong>tls1.2</strong> <em>bool</em></dt>
        <dd>Enable use of TLS v1.2 (<strong>default</strong>: <em>true</em>)</dd>
        <dt>-<strong>tls1.3</strong> <em>bool</em></dt>
        <dd>Compression method.</dd>
        <dt><strong>expansion</strong> <em>mode</em></dt>
        <dd>Expansion method.</dd>
        <dt><strong>session_cache_mode</strong> <em>mode</em></dt>
        <dd>Enable use of TLS v1.3 (<strong>default</strong>: <em>true</em>)</dd>
        <dd>Server cache mode (client, server, or both).</dd>
    </dl>
</blockquote>

<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
    <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>
        case the result is a Tcl list.</dd>
</dl>
	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>
<dl>

    <dt><a name="tls::version"><strong>tls::version</strong></a></dt>
    <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
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	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 -alpn 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>.
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	  <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 the OpenSSL function
	  <code>SSL_set_verify()</code>.
	  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