Implementing Zero-Knowledge Proofs In Blockchain

Intro to Zero-Knowledge Proofs

Zero-Knowledge Proofs (ZKPs) are complex cryptographic protocols aimed at maintaining privacy and security in blockchain operations. These protocols allow one party to prove to another that certain information is true, without revealing any details about the information itself. As blockchains evolve, there is an increasing need for privacy-conscious and scalable solutions — this is where Zero-Knowledge Proofs come into play. Here, we will unravel a way to implement a Zero-Knowledge Proof system on Ethereum blockchain using Solidity.

The zk-SNARKs Approach

Ethereum uses a type of ZKP called zk-SNARKs (Zero-Knowledge Succinct Non-Interactive Argument of Knowledge). This scheme is succinct and non-interactive, allowing for efficient exchanges of proofs.

Prerequisites

• Install Node.js and npm (Node.js package manager).
• Install Truffle: Truffle is a popular development framework for Ethereum blockchain.

npm install -g truffle

• Install Ganache: Ganache is a personal blockchain for rapid Ethereum DApp development and testing.
• Some familiarity with Solidity programming language.

Code Implementation

Let's create a new truffle project.

$ mkdir ZKP-demo && cd ZKP-demo
$ truffle init

Next, install the zk-SNARKs library for Solidity — snarkjs and circom compiler.

$ npm install -D snarkjs circom

Now, create a simple circuit file circuit.circom.

$ touch circuit.circom

Open the circuit.circom file and put this code:

template Multiplier() {
  signal private input a;
  signal private input b;
  signal output c;

  var z = a*b;
  c <== z;
}
component main = Multiplier();

This simple circuit will multiply two private inputs and provide the output.

Now we'll compile this circuit using circom.

$ npx circom circuit.circom --r1cs --wasm --sym

This will generate three files: circuit.r1cs, circuit.wasm, circuit.sym.

Next, generate the zk-SNARKs trusted setup using snarkjs.

$ npx snarkjs setup

This will generate two more files: proving_key.json, verification_key.json.

Now, let's generate the proof and public signals.

$ npx snarkjs calculatewitness --input '{"a": 3, "b": 21}'
$ npx snarkjs proof

The last command generates proof.json and public.json.

Finally, we can verify the proof.

$ npx snarkjs verify

Conclusion

Implementing Zero-Knowledge Proofs in Blockchain is an exciting topic as it provides a pathway to securing information and preserving privacy in decentralized systems. Incorporating ZKP's especially zk-SNARKs in Ethereum smart contracts can expand the utility of blockchain applications by a significant margin.