Contracts
Semaphore contracts are designed with minimal yet essential code, enabling developers to efficiently manage on-chain groups and verify or validate zero-knowledge proofs. There are three contracts:
To use Semaphore contracts and interfaces in your project,
install the @semaphore-protocol/contracts NPM package.
SemaphoreVerifier.sol​
SemaphoreVerifier.sol is an extended version of the Groth16 verifier generated by default with SnarkJS. It contains a function for verifying proofs and a list of verification keys parameters.
Since the Semaphore circuit is compiled with a MAX_DEPTH range from 1 to 32 during the trusted setup, the verifier must contain the parameters of the verification keys of each instance.
SemaphoreGroups.sol​
SemaphoreGroups.sol is an abstract contract which contains the functions required to create on-chain groups, and add/remove/update members. Each group is assigned an admin, which can be an Ethereum account or another contract.
This contract uses the LeanIMT.sol ZK-Kit library, an optimized binary incremental Merkle tree with Poseidon.
Semaphore.sol​
Semaphore.sol inherits SemaphoreGroups.sol and adds functions to verify (verifyProof) or validate (validateProof) a Semaphore proof. The only constructor parameter is the SemaphoreVerifier.sol address, which must be deployed separately.
The verifyProof function contains code for checking whether a Semaphore proof is true or false. It is a read-only view function that in addition to verifying the proof also includes a mechanism for keeping track of proofs generated with old Merkle roots, i.e. group instances that contained fewer or different members.
The validateProof function first checks whether a proof with the same nullifier has already been validated, and then verifies the proof with the verifyProof function and saves the nullifier. This function also creates a log with the group id and the proof, which can then additionally be verified off-chain.
Semaphore contracts are deployed on the main testnets and Arbitrum One. See the deployed contracts to check the addresses.