I haven't seen such an option in the S3 store, but its implementation
should be quite simple to look at. Which means that it should be quite
simple to implement a custom S3 store that encrypts/decrypts files.
Note that this now turns your "trust" problem into a
key-management problem. Check what you're protecting yourself from,
and if this encryption helps (I'm not saying it doesn't - just check upfront)
