Document integrity

Document integrity is the guarantee that content has not changed since a reference moment - the property that turns a digital file into evidence. It is achieved by hashing the content and signing or timestamping the hash: any later change, down to a single byte, makes the check fail visibly.

Integrity is one of the three assurances that signatures and seals bundle, next to authenticity (who) and non-repudiation (undeniably so). It is also a standalone need: a qualified timestamp alone proves integrity-since-then for logs, archives and evidence files, without anyone signing.