Withdrawal addr should be able to call logout

Issue

Currently, a validator must call logout using their validation key. If the validator loses their validation key, they can never get their deposit back. Allowing logout to be called from the validator’s withdrawal addr provides a backup in case of any issue that might arise with their validation key.

This is a simple addition that will ultimately provide a better validator experience and will likely encourage validation through reduced risk.

Proposed Implementation

• change logout to assert that either ‘the msg sender is withdrawal_addr’ or ‘logout_msg is signed by the validators validation key’
• add tests demonstrating both of these methods (including when both!)

Code should look something like the following:

@public
def logout(logout_msg: bytes <= 1024):
    sighash: bytes32 = extract32(raw_call(self.SIGHASHER, logout_msg, gas=self.SIGHASHER_GAS_LIMIT, outsize=32), 0)
    values = RLPList(logout_msg, [int128, int128, bytes])
    validator_index: int128 = values[0]
    epoch: int128 = values[1]
    sig: bytes <= 1024 = values[2]

    assert self.current_epoch >= epoch

    from_withdrawal: bool = msg.sender == self.validators[validator_index].withdrawal_addr
    assert msg.sender == from_withdrawal or self.validate_signature(sighash, sig, validator_index)
    
    ...

[gabririgo]

This is also a more secure way and a better experience for users looking to interact with casper through smart contracts (i.e. multisigs or vaults), as it enable to run a validator and manage the funds with completely separate logics and keys. I like it.

[hrishikeshio]

@paulhauner No worries. I have stopped working on it. You can claim the bounty.