HW03: Family wealth management

Problem statement

Implement a smart contract for shared wealth management for couples.

• The contract should store the two addresses of the couple.
• The contract should store the funds of the couple in ether.
• Only the couple can access the funds.
• There is a limit of 1 ether for single withdraws.
• Any withdraw over the limit needs to be approved by both people, i.e. such transactions require two signatures.

Example scenario

Alice and Bob create a contract with 10 ether initial balance. Every time they receive their salary, they transfer it to the contract. Every time they need money, they withdraw money from the contract, knowing that normally they can only withdraw 1 ether at a time.

One day, Bob needs to withdraw 10 ether. After they have discussed this, Alice approves a single withdraw over the limit setting 10 ether as the maximum withdraw amount. Bob can now withdraw 1 ether. If Bob tries to withdraw over the limit again, he will fail.

Contract interface

• constructor: function WealthManager(address partner2) payable

  • The creator of the contract (msg.sender) is the first partner.
  • partner2 is the second partner.

• withdraw: function withdraw(uint256 amount)

  • Sends amount wei to the sender of the transaction.
  • Succeeds only if the sender is one of the partners and amount is not over the associated withdraw limit or the other partner has approved this transaction.
  • A successful withdrawal of any amount will clear any signatures/approvals.

• sign: function sign(uint256 maxAmount)

  • If sent by the first partner, this will allow the second partner a one time withdraw of at most maxAmount wei.
  • If sent by the second partner, this will allow the first partner a one time withdraw of at most maxAmount wei.
  • Succeeds only if there are no open approvals (i.e. if the first partner has signed a transaction that has not yet been withdrawn, the second partner cannot sign a new transaction).

• fallback: function () payable

  • Receives ether from any address.

Contract skeleton

pragma solidity ^0.4.21;

contract WealthManager {

    // <contract_variables>

    // </contract_variables>

    function WealthManager(address partner2) public payable {
        // TODO
    }

    function withdraw(uint256 amount) public {
        // TODO
    }

    function sign(uint256 maxAmount) public {
        // TODO
    }

    function () public payable {
        // TODO
    }

}