8. Reputation proof

Generate a reputation proof

See 4. Epoch key proof to know how to generate a current user state.

Specify what will be included in the reputation proof:

1. Prove the minimum posRep-negRep that an attester gives: minRep

2. Prove the reputation nullifiers: nonceList

3. Prove the graffiti pre-image: graffitiPreImage

User should also specify the attesterId and epochKeyNonce to generate an output epoch key.

const attesterID = await contract.attesters(attester.address)
const epkNonce = 0
const rep = userState.getRepByAttester(BigInt(attesterId))
const minRep = Number(rep.posRep) - Number(rep.negRep)
const proveGraffiti = 0 // 0 then it will not prove the pre-image
const nonceList = 0 // 0 or [-1,..,-1] with length 'maxReputationBudget' means the proof will not generate reputation nullifiers.

const proof = await userState.genProveReputationProof(
    attesterId,
    epkNonce,
    minRep,
    proveGraffiti,
    graffitiPreImage,
    nonceList
)

Spend reputation

Call the spendReputation in UniRep smart contract

const tx = await contract.spendReputation(
    proof.publicSignals,
    proof.proof,
    {
        value: attestingFee,
    }
)

Get the proof index

const fromIndex = await contract.getProofIndex(
    proof.hash()
)

Use the reputation proof to attest others. To construct another attestation, epochKey, and index, see 5. Attest

const tx = await unirepContract
    .connect(attester)
    .submitAttestation(
        attestation, 
        epochKey, 
        index, 
        fromIndex, 
        {
            value: attestingFee,
        }
    )

Verify the proof

with UniRep smart contract:

const isValid = await contract.verifyReputation(
    proof.publicSignals,
    proof.proof
)

with a prover:

const isValid = await proof.verify()

Verify UniRep state

Check global state tree root exits.

const isGSTRootExisted = await unirepState.GSTRootExists(
    proof.globalStateTree,
    proof.epoch
)
console.log(isGSTRootExisted) // false then the proof will be invalid

Verify reputation nullifiers.

const repNullifiers = proof.repNullifiers.map((i) => i.toString())
for (const nullifier of repNullifiers) {
    if (await unirepState.nullifierExist(nullifier)) {
        return false // then the proof will be invalid
    }
}