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Zero-Knowledge Standards

zkInterface

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An open standard, designed and built by QEDIT, for interoperability between zero-knowledge proof systems — letting circuits written in one framework be proved by another.

What zkInterface is

zkInterface is an open standard for interoperability between zero-knowledge proof systems. Zero-knowledge tooling is fragmented: circuits are written in many different frontends — libsnark, ZoKrates, jsnark, Snarky, Bellman, and others — and consumed by many different proving backends, each with its own formats and conventions. zkInterface defines a common, framework-agnostic way to describe a constraint system and its witness, so a circuit built in one framework can be proved by another.

QEDIT designed and implemented zkInterface, and contributed it to the ZKProof standardization effort as a reference for zero-knowledge interoperability.

How it works

zkInterface specifies a small, purely functional, message-based interface built around rank-1 constraint systems (R1CS), independent of any particular proving system.

  • Frontends and backends. Frontends produce R1CS constraint systems; backends consume them to generate and verify proofs. zkInterface sits between the two, so any compliant frontend can talk to any compliant backend.
  • Messages. Interaction happens by exchanging read-only messages — Circuit, Constraints, and Witness. These are defined with a FlatBuffers schema, which fixes a precise byte-level layout and generates read/write code for many languages (C++ and Rust among them). Because messages are self-contained and size-prefixed, they can be streamed through files, pipes, sockets, or shared memory, and concatenated in a single byte stream.
  • Gadgets. The same interface lets a large circuit be decomposed into reusable gadgets that can be engineered separately, each exchanging Circuit messages with the caller in a control flow analogous to a function call. This makes it possible to combine gadgets written in different frameworks inside one constraint system.
  • Instance and witness reduction. Constructing the constraint system (instance reduction) and assigning concrete values to its variables (witness reduction) are handled as separate, explicitly-requested steps, so the interface supports proving systems both with and without preprocessing.

Why it matters

Interoperability is a precondition for a healthy zero-knowledge ecosystem. It lets developers choose the best frontend for expressing a circuit and the best backend for proving it, reuse low-level building blocks across projects, and build shared benchmarks. By standardizing the boundary between frontends and backends, zkInterface reduces lock-in and makes advanced cryptography more composable — the same philosophy behind QEDIT's broader work on zero-knowledge standardization.

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