I said it before: Mr. Rosenstein is in denial of the true state of things.
Here's the fact: Anyone can encrypt their own files with (practically) unbreakable encryption. The tools are out there, sometimes built in OSs, and even if they weren't, the math and algorithms are out there to be used (one can self-teach enough coding in short time. It's not that hard).
What this means is that one CANNOT catch criminals that are smart enough easier by outlawing encryption – i.e., the planners, the masterminds, the ones who run the show behind the scenes, the ones who you want to catch.
Because you cannot make "encryption" a criminal act on the same level as the criminal acts those people want to hide – murder, terrorism, child porn etc. To illegally encrypt will always be the lesser crime compared to anything else.
For us non-criminals, these attempts at stupid lawmaking are easy to fight: Encrypt the hell out of everything. Even the most trivial piece of data.