[cyphar]

If you don't have a system that takes away your freedom with tivoisation, then yes you can have free software that implements DRM. But there's no purpose to that software because it cannot be used to restrict your users (the whole point of DRM). In addition, the software is actually not effectively free because you cannot exercise any of the freedoms because you might get DMCA'd (especially freedoms #1 and #3 -- where modification involves removing the digital handcuffs).

So, practically speaking, you can't have free DRM software. But you can have "open source" DRM software, because there's no part of the OSI that classifies software that acts like such a trap as being immoral. The GPLv3 essentially ensures that a user is not threatened by legal threats about breaking DRM in a piece of free software. It's the only software license that ensures this AFAIK, so I'm a bit sad more people don't use it for firmware and other places where defence against tivoisation matters.