How to make a document modification-proof (like pdf)

Question

I'm trying to ensure no modification is allowed on a custom file format (written initially as utf8). I can't rely on OS permission, as it will be web distributed. Encryption isn't an option either, as the file must be world-readable (or with private and public key?). How could the requirements be met.

Answer 1

Sounds like you're looking for a Digital Signature. Give https://en.wikipedia.org/wiki/Digital_signature a read and see if it makes sense.