tls - binding to OpenSSL toolkit.
package require Tcl 8.2
package require tls 1.4
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 v1.3. 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. TLS v1.4 will work with 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.
- -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)
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.
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.