
# Why do we need Zero Knowledge to scale

So I recently did a talk on **Why Zero Knowledge is a game changer** in the context of scaling at a conference called Next Blockchain Expo. Here’s a picture.

![talk on stage](/images/posts/why_zk_scale/Untitled.png)

Quick disclaimer…we’re not going to talk about how Zero Knowledge proofs are generated, Plonk, Halo2, KZG commits all that stuff. That is for later. As a matter of fact, even in the context of **Scaling**, there is a buttload to cover. So the way we’re peeling off Zero Knowledge Proofs(ZKP) is by starting at the top and then diving in, one layer at a time. **It’s story time.**

## What is Zero Knowledge…

Well in one sentence:

> **I can prove this is true, but i don’t (need to) and won’t show you the data**
> 

If this seems unclear, check out my [last post](https://www.razacodes.com/blog/zero-knowledge-principles).

## Story Time

In a land far far away, there lives a King and he has one rule. Every citizen of this country needs to show the King all the receipts for every purchase, sale or any other transfer they made.

![king and citizen](/images/posts/why_zk_scale/Screenshot_2023-06-13_at_21.27.21.png)

The thing is…checking on all those transactions takes a whole lot of time and the King’s time is expensive. Needless to say, the King is not happy.

![king not happy](/images/posts/why_zk_scale/Screenshot_2023-06-13_at_21.32.11.png)

So the King hires an accountant, who has one job. Check on all those transactions, making sure the receipts are there. Once the accountant is done, he produces a report. If the report has the special stamp, everything is OK. No stamp, not OK.

![accountant that checks transactions](/images/posts/why_zk_scale/Screenshot_2023-06-13_at_21.34.31.png)

Now the King doesn’t want create a single point of failure. That’s the accountant right now. What if the accountant is corrupt! So he gives the accountant a computer, that is programmed to process the transactions. The computer has a list of all the citizens, so the accountant has a fixed list to go through. The stamp is only generated if for every transaction there is a valid receipt and all the citizens are processed.

![computer helping accountant](/images/posts/why_zk_scale/Screenshot_2023-06-13_at_21.45.28.png)

Now, all citizens are checked, all transactions are verified by an independent system and the King spends a fraction of his time. Ladies and Gentleman, the King is happy.

![king is happy](/images/posts/why_zk_scale/Screenshot_2023-06-13_at_21.46.29.png)

## What is Zero Knowledge…again

Now let’s take a closer look at what a protocol utilising a **Zero Knowledge Proof** is. 

> A **zero-knowledge protocol** is a method by which one party (the prover) can prove to another party (the verifier) that a given statement is true while the prover avoids conveying any additional information apart from the fact that the statement is indeed true.
> 

Now let’s take a look at our story. In this case, the **user** provides the transactions. The accountant, or his computer, is the prover and generates the proof, the report. Finally the King is the verifier.

![explaining through story how zkp works](/images/posts/why_zk_scale/Screenshot_2023-06-13_at_21.48.39.png)

Let’s look at it differently. In the context of scaling, the King represents Ethereum and the Accountant represents a Layer 2 (L2), like Scroll. All the users interact on the L2. The Prover (the computer the accountant uses) makes sure the transactions are sound. Then the batch of transactions (report) together with the stamp (the ZKP) are send to the King (L1 - Ethereum).

![explaining through story how zkp works in context of scaling](/images/posts/why_zk_scale/Screenshot_2023-06-13_at_22.18.27.png)

## Zero - Knowledge Rollups

In essence this is how a ZK Rollup works. Now before anyone gets a heart attack, looking at the researchers, obviously there is more to it. But you get the gist of it. We have another layer where all the transactions happen, like Scroll. Ethereum needs to know that these transactions are valid. So a proof is generated by Scroll and provided to Ethereum together with the transactions.

## Why ZK Rollups

ZK Rollups are Layer 2’s (L2’s) that scale Ethereum. Lower gas fees, higher throughput. 

## The Problem

A ZK Rollup aims to solve the scalability problem. Ethereum has an inherent limitation caused by the blockchain trilemma. If you’re not familiar with the trilemma, it’s a whole blog post on it’s own. [This one](https://vitalik.ca/general/2021/04/07/sharding.html) by Vitalik is a good one to read.

The TLDR is, Ethereum focuses on being a secured and decentralised chain, but at the cost of being scalable. Thus it’s expensive for users to transact on Ethereum. Layer 2’s aim to solve this.

## The rise of L2’s

We’ve seen many L2’s come up, trying to solve this problem and have seen some successes, like optimistic rollups. So…problem solved? Well not necessarily. Optimistic rollups are great. They provide the same developer experience as Ethereum (provided they run an EVM), lower gas fees, higher throughput. However the major downside is the **one-week challenge period.** During this period, the user can’t withdraw funds back to Ethereum if they would want to. In other words, for one week your funds are trapped on the L2. 

Quote from [this article](https://ethereum.org/en/developers/docs/scaling/optimistic-rollups/):

> Users must wait for the one-week challenge period to expire before withdrawing funds back to Ethereum.
> 

I’ll leave a link [here](https://ethereum.org/en/developers/docs/scaling/optimistic-rollups/), that explains more about this.

## Enter ZK Rollups

Just like any other rollup, users interact and transact on the L2. If the L2 is build on Ethereum (ie it inherits security from, settles data on Ethereum, has an Ethereum Virtual Machine, etc.), transactions are committed in batches on Ethereum. And, like I explained before, a proof is committed within minutes that the transactions are valid. No more waiting for a week!

> Note: proving times is a whole other topic which we’ll dive into later
> 

## Diving in a bit deeper

Let’s take a look at the transaction lifecycle, which is just a fancy way of saying, where the fuck is my NFT bro…you get it. Here’s a visual example of how it works with Scroll. I stole this from my colleague [Orest](https://twitter.com/OrestTa) and will not credit him.

![Scroll architexture](/images/posts/why_zk_scale/Screenshot_2023-06-14_at_11.08.43.png)

 This is the TLDR process:

1. You login to your wallet, go to a bridge like [this one](https://scroll.io/portal) and transfer ETH from Ethereum to Scroll.
2. Now you got **monaay** to pay for gas fees on an L2. Yes, gas fees are still paid in ETH, BUT they are much cheaper than they are on L1. Benefit number uno.
3. Now you send transactions on L2 and the **Sequencer** starts working really hard.
4. The Sequencer creates a batch of transactions and sends it to the **Prover Network,** the Prover network is just a bunch of Provers connected to each other….ow yeah and a Prover is just a node or computer that generates the proof (remember our story!). 
5. Proof is generated and then send back to the Sequencer
6. Both the batch of transactions and Proof are send to Ethereum and stored in a Smart Contract on Ethereum. In the picture above it’s called a **Rollup Contract**.
7. Now if you WANT you could transfer or “bridge” your assets (eth, token, nft) from the L2 back to Ethereum.

Now I bet there are lots of questions:

- What type of data gets stored?
- What are the proving times?
- What are the differences between all these ZK Rollups?

And many many more questions. Sigh. Yes, there is a LOT to cover. To be quite honest, all the information is out there. I’m just learning and telling it you my way. There is too much to cover and like I said, we’re starting at the top and peeling our way to the core or bottom.

This post is already a bit long. Keep an eye out for my next one.