[farmdawgnation]

However, I think that in the case of a password or passphrase (e.g. something that you know) that would trigger decryption of such a spreadsheet you can refuse to give that up under the Fifth Amendment under current caselaw.

With a physical key, you couldn't do that.

[spiralpolitik]

I think that part is up in the air and will probably be decided by the supreme court sometime in the next few years.

Encryption on a per file basis is somewhat interesting. You've provided the item requested but do you have to provide it in an understandable format ? An interesting analogy would be if you had a document written in a language (say shorthand) only you could understand, could you be compelled to provide a translation ?