ZK Gadget Standard Interface

zkInterface is a standard tool for zero-knowledge interoperability.

The spec can be found here.

How to contribute

• In a frontend, implement a feature to export the circuits or gadgets to ZkInterface format.
• In a proving system, support loading circuits from ZkInterface buffers or files.

See the implementation guide section in the spec above for more details, and check out the existing implementations below.

Implementations

	Proving System	Export Circuits	Import Circuits
Bellman (Groth16)	Yes	No	Yes
Dalek (Bulletproofs)	Yes	No	No
ZoKrates	-	Yes	No
Libsnark	PGHR	Yes	No

See also the WebAssembly modules and the live demo.

Structure of this repo

zkInterface.pdf	The interface specification
zkinterface.fbs	The gadget interface definition using FlatBuffers
rust/src/zkinterface_generated.rs	Generated Rust code
rust/src/reading.rs	Rust helpers to read messages
rust/src/writing.rs	Rust helpers to write messages
rust/src/cpp_gadget.rs	Rust helpers to interact with C++
rust/src/examples.rs	Example messages for a simple test circuit
cpp/zkinterface_generated.h	Generated C++ code
cpp/gadget_example.cpp	Example gadget in C++
build.rs	Generate Rust and C++ code from zkinterface.fbs, and compile the C++ example
cpp/libsnark_integration.hpp	Libsnark support
cpp/libsnark_example.cpp	Libsnark gadget example

Test

In the rust directory:

cargo test

This will generate and compile Rust and C++ code, and run a test of both sides communicating through the standard interface.

cargo run --bin example > example.zkif
cargo run --bin print   < example.zkif

This will generate and print a file containing the messages Circuit, R1CSConstraints, and Witness for a toy circuit.

Generated code

Generated C++ and Rust code is included.

For other languages, install the FlatBuffers code generator (flatc). One way is to compile it with the following:

git clone https://github.com/google/flatbuffers.git
cd flatbuffers
cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=Release
make

Then run: flatc --LANGUAGE zkinterface.fbs