Incremental Authentication of Tree-Structured Documents

A new message authentication code (MAC) is described that exploits the tree structure present in many modern document formats, e.g. SGML and XML. The new code supports incremental updating of the cryptographic checksum in the process of making incremental changes to the document. Theoretical bounds on the probability of a successful substitution attack are derived. Through experimental results we demonstrate that for randomly chosen messages the success probability of such an attack will be smaller and is easily identified.