Nullifiers

The definition of nullifiers used in Unirep

Attestation nullifier

• Attestation nullifiers are used to prevent an attester attests to the same epoch key twice.

• Definition:hash5(ATTESTATION_NULLIFIER_DOMAIN, identityNullifier, attesterId, epoch, epochKey)

• ATTESTATION_NULLIFIER_DOMAIN = 1

Epoch Key nullifier

• Epoch key nullifiers are used to prevent an epoch key be generated twice.

• If an epoch key is used more than once, we cannot differentiate which user receives the reputation.

• Definition:

  hash5(EPOCH_KEY_NULLIFIER_DOMAIN, identityNullifier, epoch, nonce, 0)

• nonce is used to limit the number of epoch keys, if the nonce is more than numEpochKeyNoncePerEpochthe epoch key proof will be invalid.

• EPOCH_KEY_NULLIFIER_DOMAIN = 2

Reputation nullifier

• Reputation nullifiers are used to prevent a user double spending his reputation to perform actions.

• If the same reputation nullifiers submitted to Unirep contract, the transaction will be rejected.

• Definition:hash5(REPUTATION_NULLIFIER_DOMAIN, identityNullifier, epoch, nonce, 0)

• nonce is used to limit the number of spent reputation, if the nonce is more than transitionedPosRep - transitionedNegRepthe reputation proof will be invalid.

• REPUTATION_NULLIFIER_DOMAIN = 3