In my opinion, When user submits form by clicking 'Submit button' instead of making that button disabled, show the 'progress bar' in that button. This will not break user's focus and attention. 

form save progress indication
I want to provide a service that encrypts and decrypts documents and I want to provide the users with proof that I haven't stolen their secret key and read their documents.

I know I can prove when a document was last modified with cryptographic timestamping.  Is it possible to prove a document was or was not encrypted/decrypted in a given time period?

Off the top of my head, I'm thinking maybe there's some way to arrange that some kind of proof-of-work would be needed to encrypt/decrypt a document, but I'm not comfortable with inventing my own crypto.
