feat(forge): Cheatcode to receive public key of private key

[pmerkleplant]

Component

Forge

Describe the feature you would like

Forge provides a cheatcode to receive the address of a private key, see forge-std/Vm.sol::addr(uint)(address).

It would be great if we could get a cheatcode to receive the public key too. The public key should be returned in affine coordinates, e.g. vm.pubKey(uint privkey)(uint xCoordinate, unit yCoordinate).

To receive the public key of a private key, you currently either have to implement an ecMul function in solidity, quickly leading to out-of-gas errors or use ffi, leading to big overhead and long-running testsuites.

Additional context

Issue initially opened in forge-std repo: foundry-rs/forge-std#356

[mds1]

Thanks! This is a good idea. What do you think of generalizing this a bit to something like this:

struct Wallet {
  address addr;
  uint256 publicKeyX;
  uint256 publicKeyY;
  uint256 privateKey;
}

// New cheats below:

// Derives a private key from the name, labels the account with that name, and returns the wallet
function createWallet(string calldata name) external returns (Wallet);

// Generates a wallet from the private key and returns the wallet
function createWallet(uint256 privateKey) external returns (Wallet);

// Generates a wallet from the private key, labels the account with that name, and returns the wallet
function createWallet(uint256 privateKey, string calldata name) external returns (Wallet);

[pmerkleplant]

This looks great!

There are two more functions I can think of that may benefit from being implemented for such a Wallet type:

function sign(uint256 privateKey, bytes32 digest) external pure returns (uint8 v, bytes32 r, bytes32 s);
function getNonce(address account) external view returns (uint64 nonce);

// For Wallet:
function sign(Wallet calldata wallet, bytes32 digest) external pure returns (uint8, bytes32, bytes32);
function getNonce(Wallet calldata wallet) external pure returns (unit);

This is probably more of an issue for forge-std though. StdWallet.sol sounds intriguing ;)

[mds1]

This is probably more of an issue for forge-std though. StdWallet.sol sounds intriguing ;)

Actually per #3782 we'll end up upstreaming most of those things, and this does feel like a good simple one to upstream from the start. Those extra cheats/overloads make sense to me though

cc'ing @jameswenzel since you might be interested in this discussion per foundry-rs/forge-std#331

[drewstone]

I guess the hacky way to get the pubkey would be to sign something and recover the pubkey with ecrecover. Though, I'm looking forward to this feature!

[pmerkleplant]

recover the pubkey with ecrecover.

That's the issue, ecrecover does not return the signer's public key but its Ethereum address, see here.

[drewstone]

Gotcha ok, mis-spoke.

…

On Tue, Jun 13, 2023 at 12:44 AM merkleplant ***@***.***> wrote: recover the pubkey with ecrecover. That's the issue, ecrecover does not return the signer's public key but its Ethereum address, see here <https://www.evm.codes/precompiled#0x01?fork=shanghai>. — Reply to this email directly, view it on GitHub <#4790 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ADELLF36TONKK5PPPMQ4CM3XLAK7TANCNFSM6AAAAAAXG724V4> . You are receiving this because you commented.Message ID: ***@***.***>