Glossary
What is a hash-chained external anchor?
A hash-chained external anchor commits a chain’s checkpoints to a separate append-only substrate outside the chain. It is what makes wholesale chain replacement detectable, protecting the record against a silent reset.
§ 01 Definition
Hash-chaining protects entries. Anchoring protects the chain.
External anchoring is not tamper-proofing. A determined actor can still attempt to alter a chain and re-anchor a substitute.
What changes is the shape of the attack: the substitute chain does not match the anchor already committed to the external substrate, and any party who reads the anchor sees the mismatch.
§ 02 Questions
External anchoring, answered.
How is external anchoring different from standalone hash-chaining?
External anchoring is a separate property: it binds the chain itself, or a checkpoint of the chain, to a substrate outside the chain, so that the chain cannot be replaced wholesale without breaking the external commitment.
What does the external anchor need to be?
It needs to be append-only and outside the operator’s full control. Common shapes: a public timestamping service (RFC 3161 time-stamping authority), a partner-held signed receipt (counter-signed by a counterparty), or a separately-operated append-only log.
How does external anchoring relate to independent verification?
The anchor is what makes independent verification possible at all. The scope of what can be independently verified is bounded by the anchor’s cadence and coverage: verification runs from the most recent anchor forward.
§ 03 Related