tls - binding to OpenSSL toolkit.
package require Tcl 8.2
package require tls 1.5
tls::socket ?options? host port
tls::socket ?-server command? ?options? port
tls::status ?-local? channel
tls::import channel ?options?
tls::ciphers protocol ?verbose?
This extension provides a generic binding to OpenSSL, utilizing the 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. To use TLS with an earlier version of Tcl than 8.2, please obtain TLS 1.3. Please note that there are known limitations with the stacked channel implementation prior to 8.3.2, so it is recommended that TLS is used with an 8.3.2+ interpreter. The current version of TLS will work with Tcl 8.2+, it is just more stable with 8.3.2+.
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.
- 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.
- sbits n
- The number of bits used for the session key.
- -cadir dir
- Provide the directory containing the CA certificates.
- -cafile filename
- Provide the CA file.
- -certfile filename
- Provide the certificate to use.
- -cipher string
- Provide the cipher suites to use. Syntax is as per OpenSSL.
- -command callback
- 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. The callback should return an integer whose interpretation depends on context.
See CALLBACK OPTIONS for further discussion.
- -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.
- -password callback
- If supplied, this callback will be invoked when OpenSSL needs to obtain a password, typically for a certificate. The callback should return a string which represents the password to be used.
See CALLBACK OPTIONS for further discussion.
- -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)
- -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)
As indicated above, individual channels can be given their own callbacks to handle intermediate processing by the OpenSSL library, using the -command and -password options passed to either of tls::socket or tls::import.
Reference implementations of these callbacks are provided in the distribution as tls::callback and tls::password. Note that these are sample implementations only. In a more realistic deployment you would substitute your own callbacks, typically by configuring the -command and -password options on each channel with scripts to be executed when the callbacks are invoked.
The default behavior when the -command option is not specified is for TLS to process the associated library callbacks internally. The default behavior when the -password option is not specified is for TLS to process the associated library callbacks by attempting to call tls::password. The difference between these two behaviors is a consequence of maintaining compatibility with earlier implementations. The use of implied callbacks is not recommended.
The tls::debug variable provides some additional control over the default commands. Its value is zero by default. Higher values produce more diagnostic output. Setting this value greater than zero will also force the default verify method in tls::callback to accept the certificate, even if it is invalid.
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/]
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.
socket, fileevent, OpenSSL
Copyright © 1999 Matt Newman.