NAME
tls - binding to OpenSSL toolkit.
SYNOPSIS
package require tls ?1.3?
 
tls::init ?options?
tls::socket ?options? host port
tls::socket ?-server command? ?options? port
tls::handshake channel
tls::status channel
tls::import channel ?options?
tls::ciphers protocol ?verbose?
COMMANDS
CONFIGURATION OPTIONS
HTTPS EXAMPLE
SPECIAL CONSIDERATIONS
SEE ALSO

NAME

tls - binding to OpenSSL toolkit.

SYNOPSIS

package require tls ?1.3?

tls::init ?options?
tls::socket ?options? host port
tls::socket ?-server command? ?options? port
tls::status channel
tls::handshake channel

tls::import channel ?options?
tls::ciphers protocol ?verbose?

DESCRIPTION

This extension provides a generic binding to OpenSSL, utilizing the Trf Channel Stacking patch for Tcl 8.[01] and the new Tcl_StackChannel API for Tcl 8.2 and higher. The sockets behave exactly the same as channels created using Tcl's built-in socket command with additional options for controlling the SSL session.

COMMANDS

Typically one would use the tls::socket command which provides compatibility with the native Tcl socket command. In such cases tls::import should not be used directly.

tls::init ?options?
This routine sets the default options used by tls::socket and is optional. If you call tls::import directly this routine has no effect. Any of the options that tls::socket accepts can be set using this command, though you should limit your options to only TLS related ones.
 
tls::socket ?options? host port
tls::socket ?-server command? ?options? port
This is a helper function that utilizes the underlying commands (tls::import). It behaves exactly the same as the native Tcl socket command except that the options can include any of the applicable tls:import options.
 
tls::handshake channel
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.
 
tls::status channel
Returns the current security status of a SSL channel. The result is a list of key value pairs describing the connected peer. If the result is an empty list then the SSL handshake has not yet completed.
issuer dn
The distinguished name (DN) of the certificate issuer.
subject dn
The distinguished name (DN) of the certificate subject.
notBefore date
The begin date for the validity of the certificate.
notAfter date
The expiry date for the certificate.
serial n
The serial number of the certificate.
cipher cipher
The current cipher in use between the client and server channels.
tls::import channel ?options?
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.
-cafile filename
Provide the CA file.
-cadir dir
Provide the directory containing the CA certificates.
-certfile filename
Provide the certificate to use.
-cipher string
Provide the cipher suites to use. Syntax is as per OpenSSL.
-command callback
This callback is invoked to pass errors, tracing information and to allow Tcl scripts to perform additional verification of the certificate, which can override the default validation in OpenSSL.
-keyfile filename
Provide the private key file. (default: value of -certfile)
-model channel
This will force this channel to share the same SSL_CTX structure as the specified channel, and therefore share callbacks etc.
-request bool
Request a certificate from peer during SSL handshake. (default: true)
-require bool
Require a valid certificate from peer during SSL handshake. If this is set to true then -request must also be set to true. (default: false)
-server bool
Handshake as server if true, else handshake as client.(default: false) [Not available to tls::socket]
-ssl2 bool
Enable use of SSL v2. (default: true unless -DNO_PATENTS was specified in build)
-ssl3 bool
Enable use of SSL v3. (default: true)
-tls1 bool
Enable use of TLS v1. (default: false)
tls::ciphers protocol ?verbose?
Returns list of supported ciphers based on the protocol you supply, which must be one of ssl2, ssl3, or tls1. If verbose 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.

CONFIGURATION OPTIONS

In addition to the options listed above you can set the tls::debug flag to a non-zero value to see the output from the default command callback (tls::callback) which shows the progression of the SSL handshake. Setting this value to greated than 1 will cause the default verify method in tls::callback to always accept the certificate, even if it is invalid.

In a real-world deployment you should substitute your own callback in place of tls::callback, via the -command option to tls::socket or tls::import.

When the TLS layer needs to obtain a password, typically for a certificate, the software will invoke a Tcl command called tls::password, which should return a string which represents the password to be used. A default implementation is provided, which simply returns "secret" - you should redefine this procedure after issuing the package require tls.

HTTPS EXAMPLE

This example requires a patch to the http module that ships with Tcl - this patch has been submitted for inclusion in Tcl 8.2.1, but is also provided in the tls directory if needed. A sample server.pem is provided with the TLS release, courtesy of the OpenSSL project.

package require http
package require tls

http::register https 443 [list ::tls::socket -require 1 -cafile ./server.pem]

set tok [http::geturl https://developer.netscape.com/]

SPECIAL CONSIDERATIONS

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 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 http://www.openssl.org/ for more information on the whole issue of patents and US export restrictions.

SEE ALSO

socket, fileevent, OpenSSL


Copyright  1999 Matt Newman.