Hash chain
Definition
A hash chain is a sequence of records in which every entry contains the cryptographic hash (e.g. SHA-256) of its predecessor. If an old entry is modified later, all subsequent hashes stop matching - tampering becomes mathematically provable. Hash chains make logs tamper-evident without requiring a blockchain.
For approval evidence this is the difference between "we have a log" and "we can prove the log is complete and unmodified". A verification recomputes the chain and confirms integrity - a result that belongs on the cover page of every audit report.
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