https://github.com/onflow/flow-cadence-eth-utils
https://github.com/onflow/flow-cadence-eth-utils
Last synced: 9 months ago
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- Host: GitHub
- URL: https://github.com/onflow/flow-cadence-eth-utils
- Owner: onflow
- Created: 2023-08-01T18:33:22.000Z (over 2 years ago)
- Default Branch: main
- Last Pushed: 2023-10-31T23:17:17.000Z (about 2 years ago)
- Last Synced: 2025-01-09T10:16:31.531Z (11 months ago)
- Language: Cadence
- Size: 165 KB
- Stars: 3
- Watchers: 3
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# Ethereum Signature Verification with Cadence
This guide will show you how to generate a public key, a signature, and a message that can be passed into a Cadence smart contract. This can be achieved using Ethereum JavaScript libraries such as ethers.js or any other Web3 API.
## Requirements
This function depends on the following libraries:
- `ethers.js`: Ethereum's JavaScript library used for interacting with Ethereum's network and its smart contracts.
- `@onflow/fcl`: Flow's JavaScript library used for interacting with Flow's network and its smart contracts.
## Example
```js
try {
const provider = new ethers.providers.Web3Provider(window.ethereum, "any");
// Send a request to access the user's Ethereum accounts
await provider.send("eth_requestAccounts", []);
const signer = provider.getSigner();
// Define a string message to be signed
const toSign = `Hello Cadence World!`
const ethSig = await signer.signMessage(toSign);
// Remove the '0x' prefix from the signature string
const removedPrefix = ethSig.replace(/^0x/, '');
// Construct the sigObj object that consists of the following parts
let sigObj = {
r: removedPrefix.slice(0, 64), // first 32 bytes of the signature
s: removedPrefix.slice(64, 128), // next 32 bytes of the signature
recoveryParam: parseInt(removedPrefix.slice(128, 130), 16), // the final byte (called v), used for recovering the public key
};
// Combine the 'r' and 's' parts to form the full signature
const signature = sigObj.r + sigObj.s;
// Construct the Ethereum signed message, following Ethereum's \x19Ethereum Signed Message:\n convention.
// The purpose of this convention is to prevent the signed data from being a valid Ethereum transaction
const ethMessageVersion = `\x19Ethereum Signed Message:\n${toSign.length}${toSign}`;
// Compute the Keccak-256 hash of the message, which is used to recover the public key
const messageHash = ethers.utils.keccak256(ethers.utils.toUtf8Bytes(ethMessageVersion));
const pubKeyWithPrefix = ethers.utils.recoverPublicKey(messageHash, ethSig);
// Remove the prefix of the recovered public key
const pubKey = pubKeyWithPrefix.slice(4);
// The pubKey, toSign, and signature can now be used to interact with Cadence
} catch (err) {
console.error(err); // Log any errors
}
```
This function does the following:
1. **Set up an Ethereum provider**: Uses window.ethereum, which is provided by MetaMask or other Ethereum wallet extensions.
2. **Request account access**: Asks the user to unlock their Ethereum wallet.
3. **Get a signer**: A signer is an Ethereum account that can sign transactions and messages.
4. **Create a message to sign**: For this example, the message is Hello Cadence World!.
5. **Sign the message**: The signer signs the message.
6. **Clean up the signature**: Removes the '0x' prefix from the signature string.
7. **Create a signature object**: Constructs an object with the signature components.
8. **Create the full signature**: Combines the 'r' and 's' components to form the full signature.
9. **Format the message**: Follows Ethereum's signed message convention to prevent the signed data from being a valid Ethereum transaction.
10. **Hash the message**: Computes the Keccak-256 hash of the message, which will be used to recover the public key.
11. **Recover the public key**: Uses the hashed message and the signature to recover the public key.
12. **Clean up the public key**: Removes the prefix of the recovered public key.
## Usage
You can use this function in any situation where you need to authenticate and verify an Ethereum account in Cadence.
```js
await fcl.query({
cadence: `
import ETHUtils from
pub fun main(hexPublicKey: String, hexSignature: String, message : String): Bool {
return ETHUtils.verifySignature(hexPublicKey: hexPublicKey, hexSignature: hexSignature, message: message)
}
`,
args: (arg, t) => [arg(pubKey, t.String), arg(signature, t.String), arg(toSign, t.String)],
});
```
This example queries a Cadence smart contract to verify the Ethereum signature.