Omnid Docs

Install Circom

Direct Binary

You can download the latest release from https://github.com/iden3/circom/releases

From Source

Requires Rust curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

git clone https://github.com/iden3/circom
cd circom
cargo install --path . --release

Use Playground

You can also build and try out circuits on zkREPL.

https://zkrepl.dev/?gist=168c24e72f4f492d998ab00dee82e21e

Understand your Circuit

Today we will build this simple circuit that creates a zero knowledge proof of knowing the factors of a number without revealing the number.

The circuit takes three inputs, a, b, ab.
a & b are private inputs, ab is a public input.
The circuit has one output, 1 if valid, 0 if invalid.

// Example
a=10, b=11, ab=110 // Valid Inputs.
a=10, b=11, ab=100 // Invalid Inputs.

Full Circuit

CheckMult.circom

pragma circom 2.1.6;
 
template IsZero() {
    signal input in;
    signal output out;
    signal inv;
    inv <-- in!=0 ? 1/in : 0;
    out <== -in*inv +1;
    in*out === 0;
}
 
template IsEqual() {
    signal input in[2];
    signal output out;
    component isz = IsZero();
    in[1] - in[0] ==> isz.in;
    isz.out ==> out;
}
 
template CheckMult() {
    signal input a;
    signal input b;
    signal input ab;
    signal output out;
 
    component eq = IsEqual();
    eq.in[0] <== a * b;
    eq.in[1] <== ab;
    eq.out ==> out;
}
 
component main { public [ab] } = CheckMult();
 
/* INPUT = {
    "a": "5",
    "b": "77",
    "ab": "265"
} */

Setup your Project

Fork the template, https://github.com/anudit/circom-template. It simplifies the process of compiling Circom circuits in a highly customizable way.

Your project structure should look something like this.

CheckMult.circom

build.sh

checkMult.test.ts

package.json

You'll need to download the Powers of Tau file from https://storage.googleapis.com/zkevm/ptau/powersOfTau28_hez_final_20.ptau and save it inside the build directory.

You can find the other PTau files here https://github.com/iden3/snarkjs/blob/master/README.md#7-prepare-phase-2

Install the dependencies,

bun install

Build & Test your Circuit

Now the fun part.

bun run build

Your circuit files should be present in build/CheckMult directory.

bun run test

Your logs should look like this.

➜  circom-template git:(main) bun run test
$ bun test ./tests/*.test.ts
bun test v1.1.30 (7996d06b)
 
tests/checkMult.test.ts:
✓ Test Mult > Mock generate data [53.45ms]
 
 1 pass
 0 fail
 3 expect() calls
Ran 1 tests across 1 files. [269.00ms]

On-chain Verification

Your Solidity/Vyper/Fe Verifier should be present in build/CheckMult/CheckMultVerifier.(sol/vy/fe)
Tutorial on On-chain Verification

Circom