tamper evidence

The standard mechanism is a log that is added to and never rewritten, built on a Merkle tree — a structure of hashes in which each one covers those beneath it. RFC 9162 describes such logs for TLS certificates. What it calls the append-only property is achieved using Merkle trees, which can prove that any instance of the log is a superset of any previous instance. Consistency proofs establish that property, and inclusion proofs show that a particular record is in the log its operator published. Altering an earlier entry changes every hash above it, so the change is visible rather than silent.

Time is the other half, and a separate standard. RFC 3161 defines a time-stamp protocol whose service supports assertions of proof that a datum existed before a particular time. A chain of hashes proves the order things were written in; it does not by itself prove when.

For a record of somebody else's endpoints the point is narrow. Anybody can publish a table of what endpoints were doing last month. What separates evidence from assertion is whether a reader can check that the rows were written when they claim, and have not been edited since. That has to be built into how the record is kept, because it cannot be added afterwards. A payment receipt is the paid party's own account of one transaction. A dated series of outside readings is a different kind of record, and this property is what makes it checkable — rather than the care of whoever kept it.