This reads as extremely bizarre. I mean, reading the fifth amendment makes it pretty clear - no one should be compelled to witness against oneself. However, it looks like the current executive and judicial are thinking "well, those Founders were just idiots for putting such an amendment in, clearly it'd be much easier to prosecute people if we could compel them to witness against themselves, so why don't we just igno…
It's not bizarre at all. "To be a witness against himself" is not metaphorical or ye olde English. It literally means what it says--the government can't force someone to testify against himself ( i.e. to provide a confession). If the Founders had meant to say that the government can't compel someone to cooperate in an investigation at all , they would have said that.
If the government can't compel someone to say when, where and how they disposed of the bodies, then they also can't make someone explain how they encrypted some files.
In case they can confirm the existence of files some other way I guess you could make the case that the government can force someone to produce those files. Of course this won't tell them anything they didn't know already (which is kind of the point). Making someone produce files that may or may not exist is the same as making them testify that those files exist and that they have access to them, which I would argue falls under the 5th amendment.