circomlibjs VS tornado-core

The advantage of SMT over the general Merkle tree is that it not only allows us to provide an inclusion proof but also an exclusion proof. This means that we can prove that a tree does not contain a value for the given key. Thanks to this, we can prove any operation (insert, delete, update), which will be a very important property of our rollup. Fortunately, Circomlib (and CircomlibJS) includes an SMT implementation, so we do not need to implement this ourselves.

Circomlib has a JS implementation that can be used for this. Let’s install it:

This is the repo we’re going to look at: Tornado core.

The method that I’m using is the same as what is used by Tornado Cash. Tornado Cash is a non-custodial Ethereum and ERC20 privacy solution based on zkSNARKs.

Tornado Cash is a great learning resource on how to build a real-world zk-app with Circom circuits. I strongly recommend going through the 3-page-long white paper, as well as Gubsheep's breaking down Tornado Cash session from the 0xparc course, plus Porter's overview of the white paper.

This was my very short tutorial on using zk-SNARK in JavaScript. It’s not a full course, and you probably have many questions, but I hope I helped you to start your journey. Circom and snarkjs are well documented, and you can also learn a lot from existing projects like Tornado Cash.

This is the MerkleTree contract, and the problem is on lines 58 and 59, I cannot understand why would you need to veryfy that the hash of a number has to be less than FIELD_SIZE.