Blockchain_CA3

Introduction

In this task, we will create a K Framework rule that enforces access control on a withdraw() function in a Solidity smart contract. The rule will ensure that only the contract owner can execute the withdraw() function, preventing unauthorized users from withdrawing funds.

We will:

1. Write a vulnerable Solidity contract with a withdraw() function.
2. Write a K rule to enforce that only the contract owner can call the withdraw() function.
3. Provide a sample README file to document how to set up and use the K Framework to verify this rule.

Step 1: Vulnerable Solidity Contract

Here is an example of a vulnerable Solidity contract where any user can call the withdraw() function, potentially leading to unauthorized fund withdrawals.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract VulnerableWallet {
    address public owner;
    uint256 public balance;
    
    constructor() {
        owner = msg.sender;
    }
    
    function deposit() public payable {
        balance += msg.value;
    }
    
    function withdraw(uint256 amount) public {
        require(balance >= amount, "Insufficient balance");
        payable(msg.sender).transfer(amount);
        balance -= amount;
    }
}

In this contract, the withdraw() function can be called by anyone who has a balance. This is a vulnerability because it lacks a restriction for the contract owner. Now, we need to create a K rule to ensure only the contract owner can execute the withdraw() function.

Step 2: K Rule for Access Control

In the K Framework, we define rules using the K syntax, which is a formal specification language for describing the semantics of programming languages. The K rule will enforce that only the contract owner can call the withdraw() function.

Step 3: K Rule for Verifying Access Control

Let's now refine the rule to include the owner check:

module ACCESS_CONTROL
  syntax Exp ::= "withdraw" "(" Exp "," Exp ")" [function]
  rule <k> withdraw(Amt, _) => . ... </k>
       <env> .[msg.sender] = owner </env>
endmodule

Code for the K Framework Implementation:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract SecureWallet {
    address public owner;
    uint256 public balance;
    
    constructor() {
        owner = 0x70997970C51812dc3A010C7d01b50e0d17dc79C8;
    }
    
    modifier onlyOwner() {
        require(msg.sender == owner, "Not authorized");
        _;
    }
    
    function deposit() public payable {
        balance += msg.value;
    }
    
    function withdraw(uint256 amount) public onlyOwner {
        require(balance >= amount, "Insufficient balance");
        payable(msg.sender).transfer(amount);
        balance -= amount;
    }
}

Conclusion

In this guide, we created a vulnerable Solidity contract with an unprotected withdraw() function, then demonstrated how to use the K Framework to enforce that only the contract owner can access this function. The K rule checks that msg.sender is the contract owner before proceeding with the withdrawal, which ensures proper access control.

Make sure to test the contract and the K rules thoroughly to prevent unauthorized access and enhance the security of your smart contracts!