A collection of circom circuits and supporting code for zero-knowledge proofs on PODs (Provable Object Data) via the GPC (General Purpose Circuits) framework. For a full introduction, see the Developer Site.

POD is a format enabling any app to flexibly create cryptographic data and make zero-knowledge proofs about it. A POD could represent your ticket to an event, a secure message, a collectible badge, or an item in a role-playing game. Using PODs, developers can create ZK-enabled apps without the effort and risk of developing their own cryptography.

ZK proofs about PODs use General Purpose Circuits (GPC) which can prove many different things about a POD without revealing it all. GPCs use human-readable configuration and pre-compiled circuits so no knowledge of circuit programming is required.

PODs and GPCs can be used in Zupass, or in your own apps without Zupass.

What's in this package?

This package implements the first prototype family of GPC circuits, named proto-pod-gpc. The primary use of the circuits in this package is via a high-level configuration interpreted by the @pcd/gpc package.

The top level circuit in the family is in proto-pod-gpc.circom. That circuit is built using a configurable number of different Modules defined in the other circom files. If you're a circom developer, you can reuse these modules to create your own circuits which prove things about PODs which the GPC configuration doesn't yet support.

Pre-compiled artifacts for these circuits at various sizes are published in the @pcd/proto-pod-gpc-artifacts package. They are stored in a dedicated repo due to their size.

Related Packages

• For information about making POD objects, see the @pcd/pod package.

• For information about making proofs about PODs, see the @pcd/gpc package.

• To interact with GPC proofs in the Zupass app, see the @pcd/gpc-pcd package.

• To find the binaries required to prove and verify, see the @pcd/proto-pod-gpc-artifacts package. Since these artifacts are large and numerous, you generally won't want to depend on this package directly.

Stability and Security

POD and GPC libraries are experimental and subject to change. We encourage devs to try them out and use them for apps, but maybe don’t rely on them for the most sensitive use cases yet.

GPC proofs are considered ephemeral (for now), primarily intended for transactional use cases. Saved proofs may not be verifiable with future versions of code. Library interfaces may also change. Any breaking changes will be reflected in the NPM versions using standard semantic versioning.

These libraries should not be considered secure enough for highly-sensitive use cases yet. The circuits are experimental and have not been audited. The proving/verification keys were generated in good faith by a single author, but are not the result of a distributed trusted setup ceremony.