Add tooling to verify signatures with support for ERC1271

[Amxx]

SignatureChecker is a library for seamless verification of signatures with support for both EOA (ECDSA) and smart contract wallets (ERC1271).

While still being a draft, this ERC is supported by smart contract wallets such as Argent.

I believe this feature could greatly improve the compatibility of dapps that relies on message signatures with such wallets. In particular since Argent is now able to sign messages (including ERC721 typedData) through WalletConnect.

Continuation of #2459
FIxes #2535

PR Checklist

• Tests
• Documentation
• Changelog entry

[frangio]

From our recommendation in ECDSA:

openzeppelin-contracts/contracts/utils/cryptography/ECDSA.sol

Lines 20 to 24 in 5ecd2b8

	* IMPORTANT: `hash` _must_ be the result of a hash operation for the
	* verification to be secure: it is possible to craft signatures that
	* recover to arbitrary addresses for non-hashed data. A safe way to ensure
	* this is by receiving a hash of the original message (which may otherwise
	* be too long), and then calling {toEthSignedMessageHash} on it.

We should be providing some other link in the docs, but there is more info in this article.

So, is this function really safe? Isn't it vulnerable to crafting signature and hash values that will recover to the signer but which do not correspond to a real ECDSA signature?

[Amxx]

So, is this function really safe? Isn't it vulnerable to crafting signature and hash values that will recover to the signer but which do not correspond to a real ECDSA signature?

Our own ECDSA.recover doesn't enforce that. You can technically use it to recover a hash that was not properly formated. The same goes for a smart wallet 1271 implementation (the code in isValidSignature). In both cases, we cannot do anything about it (the hash might be 191, or 712, or anything not yet standardized. The best we can do is adding the warning you mentioned in the interface for 1271.

[frangio]

Ok, for some reason I thought this API was more vulnerable to misuse, but now that I'm looking at it again it I can see that it's the same.

[frangio]

LGTM!