On-chain attestation

An on-chain attestation is a statement recorded on a blockchain network and associated with an issuer, subject and data schema. Its origin and status can be verified under the protocol. A signature or record establishes who made a claim, not whether it is true.

Written by Pablo Gómez

Founder & CEO at Metlabs · Reviewed on October 11, 2026

A schema defines the statement’s fields. An issuer may claim, for example, to have verified a subject attribute. The record supports querying the attestation and any protocol-supported revocation or expiry.

Trust depends on the issuer and how information was obtained. Recording a statement does not independently prove its truth.

Attestations can contain personal data or enable inference by linking addresses and attributes. Publishing only a hash does not automatically eliminate privacy risks.

Sources

Ethereum Attestation Service: Documentation

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On-chain attestation

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Merkle rootA Merkle root is the single hash at the top of a Merkle tree that cryptographically summarizes the entire set of leaf data, so that one value, typically 32 bytes, commits to an arbitrary number of elements and acts as the integrity fingerprint of the set.
Merkle treeA Merkle tree is a tree data structure where each leaf is the hash of a data block and each internal node is the hash of its children, so the top node (the Merkle root) is a compact commitment to the entire set: any change to a single piece of data alters the root.
NullifierA nullifier is a unique, deterministic public marker published when a private note or commitment is spent, used to prevent double-spending without revealing which specific commitment is being consumed or the identity of the user spending it.
Pedersen commitmentA Pedersen commitment is a cryptographic scheme for committing to a value so that the commitment reveals nothing about it (perfectly hiding) and cannot be altered afterward (computationally binding), with the key property of being additively homomorphic, the basis of confidential transactions.
PLONKPLONK is a zk-SNARK with a universal and updatable trusted setup: a single initial ceremony serves any circuit up to a given size, making it flexible for zk-rollups where circuits change, at the cost of proofs somewhat larger than those of Groth16.
Polynomial commitmentA polynomial commitment is a cryptographic primitive that lets a prover commit to a polynomial with a short string and later prove the value the polynomial takes at a chosen point, without revealing the whole polynomial and with a compact proof.

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