To prove a derivative relationship between an original document and a revised document.

In a computer network, documents are produced, the document is hashed to produce a fingerprint, the fingerprint is encrypted to sign the document, and then, the document signature is transmitted from a user system to a secure computer system. The secure computer system creates a time stamp including the document signature and a digital time. The secure system signs the time stamp to verify its origin. The time stamp and notary's signature are transmitted from the secure system to the user's system. The user has access to the notary's public key which is used to determine whether the time stamp is authentic. Then, the document is revised, the revised document is hashed and the hash is combined with an indication that the revision is related to the original document. The indication could be a hash of the original document, the original document signature, the notary's time stamp for the original document, or the notary's signature for the original document.