Implement signed-type data

[arboleya]

This should allow applications to request the signature of any arbitrary bytecode, encoded using the schema provided by the DApp, then hashed and prefixed by fixed data. In the case of ETH, Ethereum Signed Message:\n.

• https://eips.ethereum.org/EIPS/eip-191

[luizstacio]

We can go on the route of changing the prefix text to Fuel Signed Message:\n.

[petertonysmith94]

1. Do we want to hash using keccak256 as per the specification or continue using sha256?
2. Do we also want to add the same prefix text for the existing implementation (of a UTF8 string)? (A breaking change)

Pros:

• Consistent hashing between messages
• Less confusion for users about signature format

Cons:

• Pre-existing hashes will be invalidated (contracts, predicates, etc)

---

I have gone with using keccak256 and adding the prefix for all hashes:

• feat: enable arbitrary data signing #3720

[arboleya]

As per a quick conversation I had with @luizstacio:

1. Let's go with sha256
2. No, ideally, it should not be breaking but a hybrid / opt-in approach.

// all pseudo code to illustrate

signMessage('string' || bytes) // default/existent method
signMessage({ raw: .... }) // using EIP19

Could we also have an extra parameter, maybe? Not sure. We could also look at Viem, as they use a similar approach from which we could draw inspiration.

[petertonysmith94]

Implemented the changes, one small comment questioning the raw property.