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.


Question: form save progress indication
Answer: 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.