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# Count Xeno the 4th 

<!--- // TODO: bridge image --->
![](https://camo.githubusercontent.com/ef928ec6a7c319803e8bb5228eebfa54993457947e2934ad619e30b2ad605046/68747470733a2f2f75706c6f61642e77696b696d656469612e6f72672f77696b6970656469612f636f6d6d6f6e732f7468756d622f612f61662f4361726c5f4775737461665f4d616e6e65726865696d2e6a70672f3139323070782d4361726c5f4775737461665f4d616e6e65726865696d2e6a7067)

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## The problem

1. EVM only has precompile for BN-254, but much interesting cryptography can be done on other curves like BLS12 381/377.
2. Verifying aggregate BLS signatures is efficient, but typically not accountable.
<!---
// TODO: simplify
For BLS signatures, the EVM currently only has a precompile for BN-254 integrated. However, many other curves are of interest, including for security and performance reasons. This project solves verifying an aggregate BLS signature on Ethereum, where Ethereum doesn’t natively support the curves used via a precompile, such as BLS12 381 and 377. The signature scheme is accountable, and the applications are lit: having an accountable signature scheme permits use cases such as transparent DAOs (with efficient signature aggregation) and trustless bridges (since adversaries can be slashed). --->

## Solution

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Instead of aggregating signatures natively on BN-254, we perform the signature aggregation on another curve like BLS12 381 inside a zero-knowledge proof via non-native field arithmetic, and verify this proof on the EVM. We use the accountable signature aggregation implemented in https://github.com/swasilyev/snowball/pull/1 (supports both native & non-native arithmetic).

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## Applications

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<img src="https://hackmd.io/_uploads/rkrkBixVA.jpg" alt="drawing" style="width:70%;"/>

**Transparent DAOs**: can efficiently verify consensus of the DAO, while keeping signers accountable.

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![](https://assets.architecturaldigest.in/photos/63d141a75b7341ea2f9ece34/16:9/w_2240,c_limit/The%2027%20most%20beautiful%20bridges%20in%20the%20world.jpg)
**Trustless Bridges**: for another chain using BLS signatures, verify finality of blocks accountably. i.e. if validators equivocate, they can still be slashed.

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## Demo

https://github.com/w3f/ethberlin4/blob/master/count-xeno-the-4th/src/tests.rs#L87-L136

``` sh
cargo test solidity_verifier
```

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## The End
