KeyfileAccount should have a publicKey method

[Aviksaikat]

Overview

• It will be nice to have a account.public_key method to the KeyfileAccount or AccountAPI object.

Specification

• I have something in my mind. If I can get a green signal then I will dive right in.

Approach

• Using the keyfile property of the KeyfileAccount object I would like to implement this feature.
• Something like this

self.wallet = self.keyfile
passphrase = self._prompt_for_passphrase(default="")
# Decrypt the private key
self.private_key = Account.decrypt(self.wallet, passphrase)

# Derive the public key from the private key
self.pk = keys.PrivateKey(private_key)
self.public_key = self.pk.public_key

Dependencies

• eth_account
• eth_keys
  I believe both of them are already in use.

[fubuloubu]

Yeah, this seems fine. Implementation suggestion would be to add this property to KeyfileAccount:

class KeyfileAccount(AccountAPI):
    ...

    @property  # NOTE: consider `cached_property`
    def public_key(self) -> HexBytes:
        ... # logic you outlined above

[antazoey]

I am just perplexed that we have to decrypt an account's private key in order to obtain the public key... that just seems backwards?

[fubuloubu]

I am just perplexed that we have to decrypt an account's private key in order to obtain the public key... that just seems backwards?

Not really, and address is a keccak hash so it is not able to be obtained like this, so you need to to run the key derivation to get the public key again

But yes, you can obtain the public key during the address derivation process

[Aviksaikat]

I have made some changes to cache the public key in the keyfile please review this pr #1702