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Verifying foreign event

This example demonstrates the validation of a Transfer Event from an ERC-20 contract on the Sepolia network using an event proof on the Chiado network. The proof is retrieved via an API call and provided to a custom contract to be deployed on Chiado. The contract utilizes the HashiProver helper library to verify the proof against the latest block header recorded in Hashi.

Setting the scene

What we have:

A ERC20 Transfer Event emitted in Sepolia USDC contract.

What we need:

The verification on Chiado chain of the actual Sepolia Transfer event.

How Hashi enables the Event verification:

With HashiAPI: a offchain component used to retrieve the Event Proof for the specific Sepolia Event emitted.
With HashiProver: a onchain contract provided by Hashi which can verify the block proof provided by HashiAPI. HashiProver must be deployed on the target chain (Chiado in this case) and can be used in a custom contract which can use the Event proof verification provided by HashiProver itself.

Steps followed in this example:

Fetch the event proof for Transfer event from Sepolia.
Deploy a custom contract on Chiado that will verify the event proof using HashiProver.
Submitting the proof to the custom contract.

Getting the Event Proof

The first step is to fetch the Event Proof from Sepolia. An important parameter is the block number which ensures that Hashi can verify the proof against the block header stored on Chiado. This is possible if the block header related the emitted event on the origin chain (Sepolia in this case) has already been propagated to the target chain (Chiado in this case). To check the block propagation status is possible to use the Hashi Explorer.

Fetching the Proof

Use the following curl command to fetch the account and storage proof for the following ERC20 Transaction : tx-example.

curl --location --request POST 'https://jsonrpc.hashi-explorer.xyz/v1'

chainId: 11155111 (Sepolia).
txHash: The tx-hash that emitted the Transfer Event on Sepolia: .
logIndex: The log index for the event.

This curl command / script returns the Event Proof for the Transfer Event on Sepolia, which will be used for verification on Chiado.

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Validating your statements

Once the proof has been fetched, we can verify it using a custom contract on Chiado. The contract will use the HashiProver helper library to check the proof against the block header stored on Chiado.

Deploying the Custom Verification Contract on Chiado

Here is a custom contract that deployed on Chiado can be used to read and verify the Transfer event on Sepolia:

Deployment:

Getting the Event Proof

Fetching the Proof

Use the following curl command to fetch the account and storage proof for the following ERC20 Transaction : tx-example.

curl --location --request POST 'https://jsonrpc.hashi-explorer.xyz/v1'

chainId: 11155111 (Sepolia).
txHash: The tx-hash that emitted the Transfer Event on Sepolia: .
logIndex: The log index for the event.

This curl command / script returns the Event Proof for the Transfer Event on Sepolia, which will be used for verification on Chiado.

References

Setting the scene

What we have:

A ERC20 Transfer Event emitted in Sepolia USDC contract.

What we need:

The verification on Chiado chain of the actual Sepolia Transfer event.

How Hashi enables the Event verification:

With HashiAPI: a offchain component used to retrieve the Event Proof for the specific Sepolia Event emitted.
With HashiProver: a onchain contract provided by Hashi which can verify the block proof provided by HashiAPI. HashiProver must be deployed on the target chain (Chiado in this case) and can be used in a custom contract which can use the Event proof verification provided by HashiProver itself.

Steps followed in this example:

Fetch the event proof for Transfer event from Sepolia.
Deploy a custom contract on Chiado that will verify the event proof using HashiProver.
Submitting the proof to the custom contract.

check that the proof chainID matches the origin chain chainId (Sepolia in this case).
The verifyForeignEvent function validates the event proof against the block header stored on Chiado, which was relayed from Sepolia.
check that rlpEncodedEvent returned from HashiProver.verifyForeignEvent matches the expectedRlpEncodedEvent that we passed as the function argument. This is useful to check that the Event infos encoded in the proof just verified actually match the Event we expect.
If the proof is valid, the contract emits the TransferEventVerified event. You may define your own logic after the proof has been verified.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import { HashiProver } from "./HashiProver.sol";

contract MockERC20Prover {

    event TransferEventVerified(uint256 indexed chainID, bytes rlpEncodedEvent);

    HashiProver public hashiProver;
    address public erc20Contract;
    uint256 public chainID;

    constructor(address shoyuBashi_, address erc20Contract_, uint256 chainID_) {
        hashiProver = HashiProver(shoyuBashi_);
        erc20Contract = erc20Contract_;
        chainID = chainID_;
    }

    function verifyTransferEvent(HashiProver.ReceiptProof calldata proof, bytes memory expectedRlpEncodedEvent) external {
        require(proof.chainId == chainID, "Invalid chain id"); 

        bytes memory rlpEncodedEvent = hashiProver.verifyForeignEvent(proof);

        require(keccak256(rlpEncodedEvent) == keccak256(expectedRlpEncodedEvent), "invalid event");
        emit TransferEventVerified(proof.chainId , rlpEncodedEvent);

        // TODO: Define custom logic here

    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import { HashiProver } from "./HashiProver.sol";

contract MockERC20Prover {

    event TransferEventVerified(uint256 indexed chainID, bytes rlpEncodedEvent);

    HashiProver public hashiProver;
    address public erc20Contract;
    uint256 public chainID;

    constructor(address shoyuBashi_, address erc20Contract_, uint256 chainID_) {
        hashiProver = HashiProver(shoyuBashi_);
        erc20Contract = erc20Contract_;
        chainID = chainID_;
    }

    function verifyTransferEvent(HashiProver.ReceiptProof calldata proof, bytes memory expectedRlpEncodedEvent) external {
        require(proof.chainId == chainID, "Invalid chain id"); 

        bytes memory rlpEncodedEvent = hashiProver.verifyForeignEvent(proof);

        require(keccak256(rlpEncodedEvent) == keccak256(expectedRlpEncodedEvent), "invalid event");
        emit TransferEventVerified(proof.chainId , rlpEncodedEvent);

        // TODO: Define custom logic here

    }
}

Verifying foreign event

Setting the scene

Getting the Event Proof

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Validating your statements

hashtagDeployment:

Getting the Event Proof

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Verifying foreign event

Setting the scene

Validating your statements

hashtagDeployment:

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Deployment:

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Deployment:

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