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<h2>Tcl Tls Extension Documentation</h2>
<dl>
<dd><a href="#NAME">NAME</a>
<dl>
<dd><b>tls</b> - binding to <b>OpenSSL</b> library
for socket and I/O channel communications.</dd>
</dl>
</dd>
<dd><a href="#SYNOPSIS">SYNOPSIS</a> </dd>
<dd><dl>
<dd><b>package require Tcl</b> <em>?8.5?</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::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::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> 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</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::protocols"><b>tls::protocols</b></a><br>
<a href="#tls::version"><b>tls::version</b></a><br>
</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> </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 the options can also include any of the
applicable <a href="#tls::import"><strong>tls:import</strong></a>
options with one additional option:</dd>
<blockquote>
<dl>
<dt><strong>-autoservername</strong> <em>bool</em></dt>
<dd>Automatically set the -servername argument to 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>Add SSL/TLS encryption to a regular Tcl channel. It need
not be a socket, but must provide bi-directional flow. Also
set 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: <em>h2</em> and
<em>http/1.1</em>, but not <em>h3</em> or <em>quic</em>.</dd>
<dt><strong>-cadir</strong> <em>dir</em></dt>
<dd>Set the CA certificates path. 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>Set the certificate authority (CA) certificates file. The default
is the cert.pem file in the OpsnSSL directory. This can also be
overridden via the <b>SSL_CERT_FILE</b> environment variable.</dd>
<dt><strong>-certfile</strong> <em>filename</em></dt>
<dd>Specify the filename with the certificate to use.</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. Ciphers 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 command 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 command to invoke when OpenSSL needs to obtain a password.
Typically used 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 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
a client connects and provides a client handshake.
(default is <em>false</em>)</dd>
<dt><strong>-servername</strong> <em>host</em></dt>
<dd>Specify server's hostname. Used to set the TLS 'Server Name
Indication' (SNI) extension. Set to the expected servername
in the server's certificate or one of the subjectAltName
alternates.</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>
<dt><strong>-validatecommand</strong> <em>callback</em></dt>
<dd>Callback command to invoke to verify or validate protocol config
parameters during the protocol negotiation phase. See
<a href="#CALLBACK OPTIONS">CALLBACK OPTIONS</a>
for further discussion.</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 encryption of a regular Tcl channel. An error
is thrown if TLS is not the top stacked channel type.</dd>
<dt> </dt>
<dt><a name="tls::handshake"><strong>tls::handshake</strong>
<em>channel</em></a></dt>
<dd>Forces handshake to take place, and returns 0 if
handshake is still in progress (non-blocking), or 1 if
the handshake was successful. If the handshake failed
this routine will throw an error.</dd>
<dt> </dt>
<dt><a name="tls::status"><strong>tls::status</strong>
<em>?</em><b>-local</b><em>? channel</em></a></dt>
<dd>Returns the current status of an SSL channel. The result is a list
of key-value pairs describing the SSL, certificate, and certificate
verification status. If the SSL handshake has not yet completed,
an empty list is returned. If <b>-local</b> 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 for the channel.</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>signatureType</strong> <em>type</em></dt>
<dd>The signature type value.</dd>
<dt><strong>verifyDepth</strong> <em>n</em></dt>
<dd>Maximum depth for the certificate chain verification.
Default is -1, to check all.</dd>
<dt><strong>verifyMode</strong> <em>list</em></dt>
<dd>List of certificate verification modes.</dd>
<dt><strong>verifyResult</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 a 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>issuerUniqueID</strong> <em>string</em></dt>
<dd>The issuer unique id.</dd>
<dt><strong>subjectUniqueID</strong> <em>string</em></dt>
<dd>The subject unique id.</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>authorityKeyIdentifier</strong> <em>string</em></dt>
<dd>(AKI) Key identifier of the Issuing CA certificate that signed
the SSL certificate as a hex string. This value matches the SKI
value of the Intermediate CA certificate.</dd>
<dt><strong>subjectKeyIdentifier</strong> <em>string</em></dt>
<dd>(SKI) Hash of the public key inside the certificate as a hex
string. Used to identify certificates that contain a particular
public key.</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>ocsp</strong> <em>list</em></dt>
<dd>List of all Online Certificate Status Protocol (OCSP) URLs.</dd>
<dt><strong>certificate</strong> <em>cert</em></dt>
<dd>The PEM encoded certificate.</dd>
<dt><strong>signatureAlgorithm</strong> <em>algorithm</em></dt>
<dd>Cipher algorithm used for the certificate signature.</dd>
<dt><strong>signatureValue</strong> <em>string</em></dt>
<dd>Certificate signature as a hex string.</dd>
<dt><strong>signatureDigest</strong> <em>version</em></dt>
<dd>Certificate signing digest as a hex string.</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 a 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>Whether the certificate signature is self signed.</dd>
<dt><strong>sha1_hash</strong> <em>hash</em></dt>
<dd>The SHA1 hash of the certificate as a hex string.</dd>
<dt><strong>sha256_hash</strong> <em>hash</em></dt>
<dd>The SHA256 hash of the certificate as a 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 connection.</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_allowed</strong> <em>boolean</em></dt>
<dd>Whether protocol renegotiation is supported or not.</dd>
<dt><strong>security_level</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 is configured as a server (1) or client (0).</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>
<dt><strong>caList</strong> <em>list</em></dt>
<dd>List of Certificate Authorities (CA) for X.509 certificate.</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>algorithm_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>cipher_is_aead</strong> <em>boolean</em></dt>
<dd>Whether the cipher is Authenticated Encryption with
Associated Data (AEAD).</dd>
<dt><strong>cipher_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>
<dt><strong>handshake_digest</strong> <em>boolean</em></dt>
<dd>Digest used during handshake.</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>Whether the session can 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>binary_string</em></dt>
<dd>Unique session id for use in resuming the session.</dd>
<dt><strong>session_ticket</strong> <em>binary_string</em></dt>
<dd>Unique session ticket for use in resuming the session.</dd>
<dt><strong>ticket_app_data</strong> <em>binary_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::protocols"><strong>tls::protocols</strong></a></dt>
<dd>Returns a list of the 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
<strong>-command</strong>, <strong>-password</strong>, and
<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 and use. See below for the possible
arguments passed to the callback script. Values returned from the
callback are ignored.
<br>
<br>
<dl>
<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 type</em>
</dt>
<dd>
This form of callback is invoked by the OpenSSL function
<code>SSL_CTX_set_info_callback()</code> during connection setup
and use.
<br>
<ul>
<li>Possible values for <em>major</em> are:
<code>handshake, alert, connect, accept</code>.</li>
<li>Possible values for <em>minor</em> are:
<code>start, done, read, write, loop, exit</code>.</li>
<li>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 the context.</li>
<li>For alerts, the possible values for <em>type</em> are:
<code>warning, fatal, and unknown</code>. For others,
<code>info</code> is used.</li>
</ul>
</dd>
<dt>
<strong>message</strong> <em>channel direction version content_type data</em>
</dt>
<dd>
This form of callback is invoked by the OpenSSL function
<code>SSL_set_msg_callback()</code> whenever a message is sent or
received. It is only available when
OpenSSL is complied with the <em>enable-ssl-trace</em> option.
Where <em>direction</em> is Sent or Received, <em>version</em> is the
protocol version, <em>content_type</em> is the message content type,
and <em>data</em> is more info on the message from the <code>SSL_trace</code> API.
</dd>
<br>
<dt>
<strong>session</strong> <em>channel 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>
</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.
The callback should return the password as a string.
</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.
To reject the value and abort 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>channel 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> specified protocol common to the both the
client and server. If not, the first client specified protocol is
used. Called after hello and ALPN callbacks.
</dd>
<br>
<dt>
<strong>hello</strong> <em>channel servername</em>
</dt>
<dd>
For servers, this form of callback is invoked during client hello
message processing. It is used to select an appropriate certificate to
present, and make other configuration adjustments relevant to that
server name and its configuration. Called before SNI and ALPN callbacks.
</dd>
<br>
<dt>
<strong>sni</strong> <em>channel servername</em>
</dt>
<dd>
For servers, this form of callback is invoked when the SNI extension
from the client is received. Where <em>servername</em> is the client
provided server name from the <b>-servername</b> option. This is
used when a server supports multiple names, so the right certificate
can be used. Called after hello callback but before ALPN callback.
</dd>
<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 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 an integer representing the
current depth on the certificate chain, with
<code>0</code> as 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 an boolean representing the
validity of the current 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.</li>
<li>The <em>error</em> argument supplies the 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>, <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
<strong>-command</strong>, <strong>-password</strong>, and <strong>-validate_command</strong> options.
</p>
<p>
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.
</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 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 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
protocol versions.</p>
<h3><a name="SEE ALSO">SEE ALSO</a></h3>
<p><strong>socket</strong>, <strong>fileevent, </strong><a
href="http://www.openssl.org/"><strong>OpenSSL</strong></a></p>
<hr>
<pre>
Copyright © 1999 Matt Newman.
Copyright © 2004 Starfish Systems.
</pre>
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