Gift List

This exercise demonstrates how you can use the Merkle tree to check if a data item is in a set without having to store the set.

In order to do this, the root of the Merkle tree is calculated and stored on the server. The client generates a proof that an element is in the set and sends it along with the element to be verified. The server calculates the root using the given proof and checks if it's equal to the stored root.

Results

For this project, a typescript cryptography module was created with the following functions:

function hashMessage(message: string) : Uint8Array

async function signMessage(message: string, privateKey: Uint8Array) : Promise<[string, number]>

function getAddress(publicKey: Uint8Array): string

function recoverKey(message: string, signature: string, recoveryBit: number): Uint8Array

function authenticate(message: string, signature: string, recoveryBit: number): [boolean, string]

// Added
type Proof = { data: string; left: boolean };

type HexProof = { data: Uint8Array; left: boolean };

class MerkleTree {
  leaves: Uint8Array[];
  
  getRoot() : string

  getProof(index: number, layer : Uint8Array[] = this.leaves, proof: Proof[] = []): Proof[]
}

function verifyProof(proof: Proof[], leaf: string, root: string) : boolean

The objective of the module is to provide the UI and the server with the same cryptographic functions so that they can communicate securely.

Get Started

To get started with the repository, clone it and then run npm install in the top-level directory to install the depedencies.

There are three folders in this repository:

Client

You can run the client from the top-level directory with node client/index. This file is a script which will send an HTTP request to the server.

Think of the client as the prover here. It needs to prove to the server that some name is in the MERKLE_ROOT on the server.

Server

You can run the server from the top-level directory with node server/index. This file is an express server which will be hosted on port 1225 and respond to the client's request.

Think of the server as the verifier here. It needs to verify that the name passed by the client is in the MERKLE_ROOT. If it is, then we can send the gift!

Utils

There are a few files in utils:

• The niceList.json which contains all the names of the people who deserve a gift this year (this is randomly generated, feel free to add yourself and others to this list!)
• The example.js script shows how we can generate a root, generate a proof and verify that some value is in the root using the proof. Try it out from the top-level folder with node/example.js
• The MerkleTree.js should look familiar from the Merkle Tree module! This one has been modified so you should not have to deal with any crypto type conversion. You can import this in your client/server
• The verifyProof.js should also look familiar. This was the last stage in the module. You can use this function to prove a name is in the merkle root, as show in the example.