The contracts package includes a generic "shield" contract which enforces on-chain verification of commitments before they are added to the on-chain merkle-tree. The logic encoded into the on-chain "verifier" contract can be custom code or a workgroup can choose to use a generic verifier (i.e. verifier may only require that a commitment is signed by each workgroup member). For convenience, a "VerifierNoop" contract is provided in the contracts package for testing a baseline workflow. The "no-op" verifier will return true for any set of arguments with the proper types.