This is a proposal on how to bring IBC to Ethereum. The goal of the article is to provide an overview of the technical details of this project and gather support from the Cosmos community. Let’s dive into it.
IBC works on the light client principle where the light clients of the origin and destination blockchains need to be implemented as smart contracts in order to verify cross-chain transactions.
This means that in order to connect IBC to Eth, we will need to run the tendermint light client on Ethereum as a solidity smart contract. However, this turns out to be an extremely gas expensive operation since this requires verification of hundreds of ed25519 signatures in solidity, and ed25519 pre-compiles are not available on Ethereum. One ed25519 cost 500K gas and this means that verifying a full light client headers would cost at least 50 mn gas (100 validators) and go up to 500 mn for larger cosmos chains with 1000 validators.
Hence we must find an alternative to verify these signatures cheaply on Ethereum.
We have achieved this by taking inspiration from zk-rollups. Rather than verifying the ed25519 signatures directly on Ethereum, (and performing the curve operations inside a solidity smart contract), we construct a zk-proof of signature validity and verify the proof on-chain instead.
At Electron Labs, we have built a circom-based library that allows you to generate a zk-snark proof for a batch of Ed25519 signatures. **Check out the complete implementation here
How to try this out?
We have deployed a server whose endpoints allow you to submit a batch of signatures and get the zk-proof in return. You can test this out right now using the API reference given here - Electron Server 2
Creating a Zk-prover for ed25519 is a hard problem. This is because ed25519’s twisted Edwards curve uses a finite field that is larger than that used by the altbn128 curve (used by zk-snarks). Performing large finite field operations inside a smaller field is difficult because several basic operations such as modulo and multiplication can become very inefficient in smaller fields.
To solve this problem, we were able to find 2^85 as a base over which to define our curve operations for twisted Edwards curve. Since the ed25519 prime p = 2^255 - 19 is a close multiple of 2^85, we were able to come up with efficient basic operators such as multiplication and modulo (under 25519 prime) for base2^85 numbers.
Next, we used these custom operations to define curve operations such as point addition, scalar multiplication, and signature verification inside our ZK-circuit.
It is hard to do justice to the details of the mathematics behind this in this doc, please refer to our detailed docs explaining this given here.