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neutralizing laws that prohibit free software — but not forbidding drm

you're probably familiar with the digital restrictions mismanagement (drm) on dvds and other media. you're probably also familiar with the laws that make it illegal to write your own tools to bypass those restrictions, like the digital millennium copyright act and the european union copyright directive. nobody should be able to stop you from writing any code that you want, and gplv3 protects this right for you.

it's always possible to use gpled code to write software that implements drm. however, if someone does that with code protected by gplv3, section 3 says that the system will not count as an effective technological "protection" measure. this means that if you break the drm, you'll be free to distribute your own software that does that, and you won't be threatened by the dmca or similar laws.

as usual, the gnu gpl does not restrict what people do in software; it just stops them from restricting others.

protecting your right to tinker

tivoization is a dangerous attempt to curtail users' freedom: the right to modify your software will become meaningless if none of your computers let you do it. gplv3 stops tivoization by requiring the distributor to provide you with whatever information or data is necessary to install modified software on the device. this may be as simple as a set of instructions, or it may include special data such as cryptographic keys or information about how to bypass an integrity check in the hardware. it will depend on how the hardware was designed—but no matter what information you need, you must be able to get it.

this requirement is limited in scope. distributors are still allowed to use cryptographic keys for any purpose, and they'll only be required to disclose a key if you need it to modify gpled software on the device they gave you. the gnu project itself uses gnupg to prove the integrity of all the software on its ftp site, and measures like that are beneficial to users. gplv3 does not stop people from using cryptography; we wouldn't want it to. it only stops people from taking away the rights that the license provides you—whether through patent law, technology, or any other means.

stronger protection against patent threats

in the 17 years since gplv2 was published, the software patent landscape has changed considerably, and free software licenses have developed new strategies to address them. gplv3 reflects these changes too. whenever someone conveys software covered by gplv3 that they've written or modified, they must provide every recipient with any patent licenses necessary to exercise the rights that the gpl gives them. in addition to that, if any licensee tries to use a patent suit to stop another user from exercising those rights, their license will be terminated.

what this means for users and developers is that they'll be able to work with gplv3-covered software without worrying that a desperate contributor will try to sue them for patent infringement later. with these changes, gplv3 affords its users more defenses against patent aggression than any other free software license.

clarifying license compatibility

if you found some code and wanted to incorporate it into a gpled project, gplv2 said that the license on the other code was not allowed to have any restrictions that were not already in gplv2. as long as that was the case, we said the license was gpl-compatible.

however, some licenses had requirements that weren't really restrictive, because they were so easy to comply with. for example, some licenses say that they don't give you permission to use certain trademarks. that's not really an additional restriction: if that clause wasn't there, you still wouldn't have permission to use the trademark. we always said those licenses were compatible with gplv2, too.

now, gplv3 explicitly gives everyone permission to use code that has requirements like this. these new terms should help clear up misunderstandings about which licenses are gpl-compatible, why that is, and what you can do with gpl-compatible code.

new compatible licenses

in addition to clarifying the rules about licenses that are already gpl-compatible, gplv3 is also newly compatible with a few other licenses. the apache license 2.0 is a prime example. lots of great free software is available under this license, with strong communities surrounding it. we hope that this change in gplv3 will foster more cooperation and sharing within the free software community. the chart below helps illustrate some common compatibility relationships between different free software licenses: