Richard Stallman, author of the GNU General Public License - the most widely used open source licence - has said that the upcoming GPL version 3 would not be "huge".

Speaking at FOSDEM (Free and Open Source Software Developers' European Meeting) held in Brussels last Saturday, Stallman outlined the ways the revised GPL will attempt to combat threats to free (as in "freedom") software that have emerged over the last 10 years.

Stallman said: "There is no big change in GNU GPL version 3. There can't be and must never be. The basic idea will always be the same." Nevertheless, those changes have proven controversial so far, not least amongst developers currently using the GPL v2, such as Linus Torvalds. Stallman said the new licence will be completed in October or early in 2007.

Two of the most important changes are designed to head off problems posed by copy-restriction systems (DRM, or digital rights management) and software patents, Stallman said. He said systems such as Advanced Access Content System (AACS), the DRM standard adopted for Blu-Ray and HD-DVD discs, will cause problems for users because of the restrictions they impose, such as disallowing analogue outputs.

Moreover, they threaten to cripple open-source software, because programs that have been modified won't be able to open certain files or, in some cases, run at all, Stallman said. "What they want to do is distribute to the public software which theoretically is free and practically speaking is not," he said.

The current GPL would allow companies to distribute software giving the user the ability to modify the program, but which might not run if modifications are made, Stallman said. "We came to the conclusion that that is not really respecting the user's freedom to change and share software," he said.

To fix the problem, the GPL v3 will require distributors to supply authorisation signature keys to users in some cases, Stallman said. This won't apply to companies that sign programs merely to ensure their authenticity, but will apply to programs that won't run without an authorised signature, Stallman said. "They must give you the signature key so that you can authorise your version at least to run on your machine," he said.

The provision goes too far for many, including Torvalds, who said he was unlikely to adopt the new GPL for the Linux kernel. "I think it's insane to require people to make their private signing keys available, for example. I wouldn't do it," he said in a recent posting to the Linux kernel mailing list. "So I don't think the GPL v3 conversion is going to happen for the kernel."

The licence will add a provision explicitly granting patent rights in some cases, Stallman said. However, large companies that have blanket cross-licensing agreements, and thus don't "knowingly" use a particular licence, won't be affected, he said.

"We don't want to impose a requirement on, say, IBM, to do something for other people when IBM doesn't even know that it has a patent licence for a certain patent," Stallman said.

The GPL will be made compatible with various licences that it doesn't currently work with. That means a program covered under the GPL v3 will be able to have parts licensed under a wider variety of licences, for example imposing certain conditions that aren't allowed under the GPL v2.

Among the newly allowed conditions will be patent retaliation clauses, which say that if the user sues for software patent infringement, he loses the right to use the program. The GPL v3 will allow only particular types of these clauses in compatible licences, Stallman said.

A transcript of Stallman's speech was made available by Ciaran O'Riordan of the Free Software Foundation Europe (FSF Europe), the European branch of the organisation Stallman founded in 1985.