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Contract API

Constructor​

Contract ABI:

constructor(uint8 _treeLevels, uint232 _firstExternalNullifier)

  • _treeLevels: The depth of the identity tree.
  • _firstExternalNullifier: The first identity nullifier to add.

The depth of the identity tree determines how many identity commitments may be added to this contract: 2 ^ _treeLevels. Once the tree is full, further insertions will fail with the revert reason IncrementalMerkleTree: tree is full.

The first external nullifier will be added as an external nullifier to the contract, and this external nullifier will be active once the deployment completes.

Add, deactivate, or reactivate external nullifiiers​

Contract ABI:

addExternalNullifier(uint232 _externalNullifier)

Adds an external nullifier to the contract. Only the owner can do this. This external nullifier is active once it is added.

  • _externalNullifier: The new external nullifier to set.

deactivateExternalNullifier(uint232 _externalNullifier)

  • _externalNullifier: The existing external nullifier to deactivate.

Deactivate an external nullifier. The external nullifier must already be active for this function to work. Only the owner can do this.

reactivateExternalNullifier(uint232 _externalNullifier)

Reactivate an external nullifier. The external nullifier must already be inactive for this function to work. Only the owner can do this.

  • _externalNullifier: The deactivated external nullifier to reactivate.

Insert identities​

Contract ABI:

function insertIdentity(uint256 _identityCommitment)

  • _identity_commitment: The user's identity commitment, which is the hash of their public key and their identity nullifier (a random 31-byte value). It should be the output of a Pedersen hash. It is the responsibility of the caller to verify this.

Off-chain libsemaphore helper functions:

Use genIdentity() to generate an Identity object, and genIdentityCommitment(identity: Identity) to generate the _identityCommitment value to pass to the contract.

To convert identity to a string and back, so that you can store it in a database or somewhere safe, use serialiseIdentity() and unSerialiseIdentity().

See the Usage section on inserting identities for more information.

Broadcast signals​

Contract ABI:

broadcastSignal(
    bytes memory _signal,
    uint256[8] memory _proof,
    uint256 _root,
    uint256 _nullifiersHash,
    uint232 _externalNullifier
)
  • _signal: the signal to broadcast.
  • _proof: a zk-SNARK proof (see below).
  • _root: The root of the identity tree, where the user's identity commitment is the last-inserted leaf.
  • _nullifiersHash: A uniquely derived hash of the external nullifier, user's identity nullifier, and the Merkle path index to their identity commitment. It ensures that a user cannot broadcast a signal with the same external nullifier more than once.
  • _externalNullifier: The external nullifier at which the signal is broadcast.

Off-chain libsemaphore helper functions:

Use libsemaphore's genWitness(), genProof(), genPublicSignals() and finally genBroadcastSignalParams() to generate the parameters to the contract's broadcastSignal() function.

See the Usage section on broadcasting signals for more information.