Attestation

As explained in the Concepts - Attestation part, the attestation is the proof that corresponds to verifying the truth value of a statement. The attestation is then represented as a o1js's struct object.

interface IAttestation {
  // Return the attestation Poseidon hash
  hash(): Field;
  // Assert that the given hash is equal to the attestation hash
  assertEqual(hash: Field): void;
  // Check if the signature is valid
  isValidSignature(): Bool;
  // Assert that the signature is valid
  assertValidSignature(): void;
  // Check if the condition is valid
  isValidCondition: () => Bool;
  // Assert that the condition is valid
  assertValidCondition: () => void;
  // Check if the attestation is valid (signature and condition)
  isValid(): Bool;
  // Assert that the attestation is valid (signature and condition)
  assertValid(): void;
}
 
export class Attestation
  extends Struct({
    statement: ProvableStatement,
    privateData: Field,
    signature: Signature,
    address: PublicKey,
  })
  implements IAttestation {
  // ...
}

The Attestation struct contains:

the statement field as a ProvableStatement
the address field as a PublicKey of the mina account that attests the statement
the privateData field as a Field that contains the private data of the attestation
the signature field as a Signature that is the signature of the privateData by the source (statement.source)

Here's an example of how to create an attestation:

let sourceKey = "base58PublicKey"; // base58 of the public key of the Price Oracle ZAP Source
let statement = {
  sourceKey,
  route: {
    path: "/api/v1/price",
    args: {
      symbol: "ETH",
      currency: "USD",
    },
  },
  condition: {
    type: ConditionType.GT,
    targetValue: 3000,
  },
};
 
// This should be returned by the Price Oracle ZAP Source
let { signature, privateData } = {
  signature: Signature.create(sourcePrivateKey, Field(3500)),
  privateData: 3500,
};
 
let attestation = new Attestation({
  statement,
  privateData,
  signature,
  address: "base58PublicKey", // base58 of the public key of the attester
});

For an attestation to be valid, there's two steps to verify:

The signature of the private data comes from the designated source (isValidSignature)
All the rules of the statement are validated (isValidCondition)

We can use the isValid method to check if the attestation is valid. Each methods of Attestation are fully o1js circuits, so attestation can be used in smart contracts as well!

console.log(attestation.isValid()); // true

Statement Verifier Contract