Document Hash
A document hash is a fixed-length cryptographic digest computed from a document's contents, serving as a unique fingerprint that changes detectably if the document is altered in any way.
What it means
When a document is signed, the signature is applied to the hash of the document, not the document itself. This makes signing efficient (hashes are small, documents can be large) and tamper-evident. Any modification to the document — even a single character — produces a different hash, causing signature verification to fail and alerting recipients to potential tampering.
Why it matters for e-signatures
SignOwl embeds the SHA-256 document hash in every signature. When you or a recipient verifies a signed document, SignOwl recomputes the hash and compares it to the signed value — instantly confirming the document is unchanged since signing.
Related terms
Frequently asked questions
Can a document hash be used to verify a document without the original signature?
You need both the hash and the original signer's certificate to verify authenticity. The hash alone confirms integrity; the certificate confirms identity.
What if I need to add a page to a signed document?
Adding a page after signing changes the document hash and invalidates the original signature. Use PDF incremental updates or resign the amended document through SignOwl.
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