Building a ZK proof for DKIM signatures

Description

This repo takes a raw email as input and builds a ZK proof of the DKIM outputting a verifier solidity contract.

Motivation

Email providers are all centrally run entities that use any means necessary to break even/make money on an email service. Data privacy is not allowed.

Table of Contents

Installation Process Begin Compute and Compile the Witness Proving and Verification keys

Installation

Followed the ZK-Email example project

• We removed the twitter regex/inputs/outputs since we are interested in the DKIM ZKP

Guide

yarn init -y

yarn add @zk-email/circuits @zk-email/helpers @zk-email/contracts

The Process

Get a raw email (.eml)

Make sure the fs directory is correct in input2.ts

npx ts-node input2.ts

Outputs: Generates a input.json

Delete the twitter_idx_score on the bottom of the input.json output file

Compile and Compute the witness

Compile the circuit

circom -l node_modules circuits/blackbyrdverifier.circom -o --r1cs --wasm --sym --c

Outputs: blackbyrdverifier_cpp, blackbyrdverifier_js, blackbyrdverifier.r1cs, and blackbyrdverifier.sym.

This is a RAM expensive operation. I was not able to compile the 800k constraint circuit with my 16GB RAM laptop. Optionally: Add --O0. Use circom --help for more options. My circuit ended up with 2 million constraints using --O0.

Compute the witness

node blackbyrdverifier_js/generate_witness.js blackbyrdverifier_js/blackbyrdverifier.wasm input.json witness.wtns

Generating the proving and verification keys

npm install -g snarkjs

Download the phase 1 powersofTau

Fetch finalized powersofTau versions based on your circuit contraints here based on the amount of constraints your circuit has (recommended)

Or generate your own using a publically distributed phase 1. This is an example

Prepare for phase 2

snarkjs powersoftau prepare phase2 powersOfTau28_hez_final_22.ptau pot22_final.ptau -v

This is a CPU expensive operation. Has taken my laptops +8hrs to start a 4 mil constraint phase 2.

Contribute to phase 2

This step differs from the guide. I got error saying the .wasm was an incorrect input parameter. I used the command below to generate our first zkey.

snarkjs groth16 setup blackbyrdverifier.r1cs proving/pot22_final.ptau blackbyrdverifier_0000.zkey

For production applications, make sure you add your own contribution to the trusted setup phase 2!

snarkjs zkey contribute blackbyrdverifier_0000.zkey blackbyrdverifier_0001.zkey --name='1st Contributor Name' -v

Apply the final beacon

Add the final beacon to the contributed phase 2 setup zkey. This will finalize phase 2!

snarkjs zkey beacon blackbyrdverifier_0000.zkey blackbyrd_final.zkey 0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f 10 -n="Final Beacon phase2"

Export the verification key

Generate the verification key as input for verification

snarkjs zkey export verificationkey blackbyrd_final.zkey

Generate the solidity contract to deploy on-chain!

snarkjs zkey export solidityverifier blackbyrd_final.zkey verifier.sol