Attestation Ledger

An attestation ledger is a tamper-evident record of attestations: signed statements in which one party vouches for a fact about another person, organisation, asset or piece of data. An attestation might confirm that a wallet owner passed identity checks, that a company holds certain reserves, that a document existed at a given time or that a piece of software was built from a particular source. The ledger lets anyone check who made each statement, when, and whether it has since been revoked.

Attestation ledgers are often built on public blockchains, which provide a shared, append-only record, but the idea also exists in traditional systems such as certificate transparency logs. They are related to digital identity systems, verifiable credentials and proof of reserves. An attestation differs from an audit: it records a specific claim by a named party, rather than a full independent examination.

Think of a noticeboard where people can pin signed notes like "I checked that Sam is over 18" or "I counted the gold in this vault on Monday". Anyone can read the notes, see who signed them and check that nobody has quietly changed them afterwards. If the signer later finds a mistake, they pin a new note withdrawing the old one.

The noticeboard itself does not prove the notes are true. It shows who said what and when. Whether you trust a note depends on whether you trust the person who signed it.

• Schemas. A standard format defines what an attestation contains, such as "account verified" plus a date and expiry.
• Signing. The attester signs the statement with its private key, creating a digital signature that others can verify with the attester's public key.
• Recording. The attestation, or a hash of it, is written to the ledger, often a blockchain or an append-only log built on a Merkle tree.
• Off-chain storage. Sensitive details are usually kept off-chain, with only a reference or hash recorded publicly.
• Revocation. Attesters can mark statements as revoked or expired.
• Verification. Applications and smart contracts read the ledger to check whether a valid attestation exists before allowing an action.

On Ethereum and compatible networks, the open-source Ethereum Attestation Service, launched in 2023, provides a shared registry where anyone can create schemas and attestations. Exchanges have used such systems to issue on-chain proof that a wallet belongs to a customer who passed know your customer checks, without publishing the customer's personal data. Other uses include:

• Reserve reporting. Issuers and custodians publish attestations of stablecoin reserves or exchange balances.
• Credentials. Universities, employers and professional bodies issue verifiable certificates.
• Supply chains. Inspectors attest to the origin and condition of goods.
• Software security. Transparency logs record which code was signed and released, helping detect tampering.
• Web certificates. Certificate transparency logs, used since the 2010s, publicly record website security certificates so mis-issued ones can be spotted.

Putting attestations on a public ledger creates a permanent record, which can conflict with data privacy rules and personal safety. Designers address this by keeping personal data off-chain, using one-time identifiers, and applying zero-knowledge proofs so a person can prove a fact, such as being over 18 or not on a sanctions list, without revealing anything else. Choices about who can attest, how schemas are governed and how revocation works shape how trustworthy an attestation ledger becomes.

An attestation is only as reliable as its attester. A ledger can show that a claim was made and not altered, but not that it was true; a dishonest or careless attester can still record false statements. Reserve attestations in crypto have been criticised for checking balances at a single moment without examining liabilities, which is why they are not equivalent to a full audit. Spam and fake attesters can clutter open registries, so applications must maintain lists of trusted issuers. Lost or stolen signing keys allow forged attestations, and revocation may not be noticed quickly by every application that relies on the ledger.