Reply to your edit:

That's what the first exception in the DMCA itself is for. It provides that:

1. You can manually decrypt DRM'd content if it's software you own a legal copy of and you need to run it.

2. You can make an automated tool that does step 1.

3. You can share that tool with anyone as long as they respect 1.

The DMCA DRM clauses only care about that, the DRM itself. Not whether you make a new copy of the content.