circom-helper

circom-helper allows developers to test circom circuits quickly and easily.

It uses circom version 2, which has better performance than the previous version. Note that circuits written for the previous version of circom must be slightly modified to be compatible with circom 2.

To use the old version of circom, install circom-helper 0.1.0 or 0.2.0 via NPM.

It compiles circuits and exposes a JSON-RPC API which allows developers to generate witnesses and access signal values without writing command-line glue scripts.

Installation

npm i circom-helper

To build from source:

git clone [e-mail]:weijiekoh/circom-helper.git && \
cd circom-helper && \
npm i && \
npm run build

Install OS dependencies

On Debian, Ubuntu, or derivatives:

sudo apt-get install libgmp-dev nlohmann-json3-dev nasm g++

On openSUSE or derivatives:

sudo zypper install gmp-devel nlohmann_json-devel nasm g++

User guide

1. Create a config file. Use config.example.json as a reference.

   • The circuitDirs field should be an array of directories which contain the circom files you wish to compile. Note that there should not be any filename collisions, even across directories.
   • The circom field should be a path to the circom binary, relative to the config file's path.
   • The snarkjs field should be a path to the build/cli.cjs in a snarkjs node_modules package.

2. Create a compiled/ and temp/ directory for compiled circuits and tempoary files.

3. Run the server:

    npm run serve
   

4. Run the internal test suite for the server:

    npm run test-server
   

5. Run a test suite for the example circuit under example/:

    npm run test-snarks
   

JSON-RPC API

gen_witness

Generates a witness given a circuit name and public inputs.

Inputs:

• circuit: the name of the circuit. For example, if test.circom is in one of the circuitDirs, and you want to generate a witness for inputs to this circuit, set this value as test.
• inputs: the public inputs to the circuit (as a JS object). For example: { left: '1', right: '2' }. The number values should be strings as the JS safe integer limit is lower than the group order for BN254 and other elliptic curves used for ZK proofs.

Returns:

• witness: an array of strings (e.g. [1, 3, 1, 2]).

To find the index of any signal (e.g. main.out), use get_signal_index. With this index, you can then look up this array and get the value of the signal.

get_signal_index

Inputs:

• circuit: the name of the circuit.
• name: the signal name (e.g. main.out).

Returns:

• index: a numeric value as a string.