What Is a Merkle Tree?

A Merkle tree hashes data in pairs up to a single root hash, so any change to any leaf changes the root. That lets a verifier confirm a specific item belongs to a set, and that the set has not been altered, by checking a short path rather than the whole set. Certificate Transparency (RFC 6962) uses it for append-only logs — the same structure the estate’s checkpoint format publishes over its sealed claims.

Root property

Any leaf change changes the root

Standard

RFC 6962 (Certificate Transparency)

Estate use

A checkpoint tree head over sealed claims

Proving membership without the whole set

An inclusion proof is the list of sibling hashes along the path from a leaf to the root. A verifier recomputes the root from the leaf and that short path; if it matches the published root, the item was in the set and the set is intact. The work is logarithmic in the size of the set, which is what makes a transparency log over millions of entries practical.

The estate publishes exactly such a tree head over the claims it seals, so a stranger can prove a record was logged at a point in time without trusting the operator.

Related standards

RFC 6962 — Certificate Transparency

Questions

Why not just hash the whole set?

A single hash proves the set is intact but cannot prove one item belongs without revealing everything; a Merkle path proves membership with a short, private proof.

Is a Merkle tree a blockchain?

No. A blockchain uses Merkle trees internally, but the structure long predates it and is used wherever append-only, verifiable logs are needed.