freedoms in many circumstances. For example, a GPL'd program, or a modified

version of such a program, might need to be signed with a key or authorized

with a code in order for it to run on a particular machine and function

properly. Similarly, a program that produces digitally-restricted files might

require a decryption code in order to read the output.

The third paragraph of section 1 addresses this problem by making clear that

Complete Corresponding Source Code includes any such encryption,

authorization, and decryption codes. By requiring the inclusion of this

information whenever the GPL requires distribution of Complete Corresponding

Source Code, we thwart efforts to obstruct the goals of the GPL, and we

ensure that users will remain in control over their own machines. We

recognize an exception where use of the program normally implies that the

user already has the codes. For example, in secure systems a computer owner

might possess any keys needed to run a program, while the distributor of the

program might not have the keys.

% FIXME: installation information

%FIXME: publicly documented format

\section{Understanding License Compatibility}

\label{license-compatibility}

\section{GPLv3~\S7: Explicit Compatibility}

% FIXME:  probably mostly still right, needs some updates, though.

In GPLv3 we take a new approach to the issue of combining GPL'd code with

code governed by the terms of other free software licenses. Our view, though

it was not explicitly stated in GPLv2 itself, was that GPLv2 allowed such

combinations only if the non-GPL licensing terms permitted distribution under

the GPL and imposed no restrictions on the code that were not also imposed by

the GPL. In practice, we supplemented this policy with a structure of

exceptions for certain kinds of combinations.

% FIXME:  probably mostly still right, needs some updates, though.

Section 7 of GPLv3 implements a more explicit policy on license

compatibility. It formalizes the circumstances under which a licensee may

release a covered work that includes an added part carrying non-GPL terms. We

distinguish between terms that provide additional permissions, and terms that

place additional requirements on the code, relative to the permissions and

requirements established by applying the GPL to the code.

% FIXME:  probably mostly still right, needs some updates, though.