Hash

A fixed-length fingerprint of a file, which changes completely if a single byte does.

A hash is a fixed-length value computed from data, such that the same input always produces the same output and any change to the input produces a completely different one. SHA-256 is the usual choice.

What a hash proves is narrow and useful: this is the same file. If the hash on a certificate matches the hash of the document in your hand, the document has not changed since it was recorded.

What it does not prove is anything about who made the file, who signed it, or whether they were entitled to. It is a statement about bytes. Treating a matching hash as authorisation to reveal who signed a document is a mistake — possession of a file is not entitlement to the record behind it.

Chaining extends this to a sequence. If each entry in an audit trail includes the hash of the entry before it, then altering or removing any entry breaks every hash after it. That turns a list of events into something whose integrity can be checked rather than trusted.

Last reviewed 2026-09-18. Pactlyra produces a detailed evidence record for every completed document. Electronic signature validity depends on your jurisdiction, the document type, and how the transaction is carried out; nothing here is legal advice.