tl; dr: You already heard of Tornado Cash? And Halo2? Great! Here we’re going to mix those 2 and re-write the Tornado Cash circuits from Circom to Halo2.

Ok, let’s have a bit of a better intro…

“Zero Knowledge” is definitely a scary word (or 2 words)! When I started learning about it a few months ago I couldn’t understand anything 🤯

Recently I started to learn about Halo2, and after reading a bit of code and a few tutorials I tried to write my own circuit but was completely stuck: I had no idea how to do it...

That’s why I decided to write this article: to learn how to write a circuit, and teach some other people at the same time. Hopefully you’ll learn something from it.

This article may need to be corrected, or some things I’m saying might be completely wrong. If so: please message me so I can fix it (and improve myself at the same time 😄).

Let’s review where I am when starting this project:

• read a few Halo2 tutorials
• I think I understand what Chips and Circuits are, I have no idea what Layouter and Regions are for
• I don’t know how to write my own circuit
• I definitely don’t understand how things work “underneath”. Like how the proof is generated from the “halo2 board”

This is “part 1”. We’re going to start easy with an implementation as simple as possible, and the next parts will improve on it. I haven’t written part 2 (or 3, or…) yet, so if you’re here a few weeks/months from now and they are not published, it means I gave up 🥲 so you’re allowed to send me a twitter message and tell me you’re disappointed.

Here’s our plan for today:

• i’ll give you a quick reminder on how tornado cash works
• what is halo2?