Gift List

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.

Solution

In this solution, the client generates a proof for the name it wants to prove is in the merkle root. It then sends this proof to the server. The server then verifies the proof using the MERKLE_ROOT stored in the server and if it is valid, it sends the gift.

It is important to notice that the server only needs to store the MERKLE_ROOT and not the entire merkle tree. This is because the merkle tree is a binary tree and the proof is a path from the leaf to the root. This means that the server can reconstruct the merkle tree from the proof and the root.