2022 Paradigm CTF：RIDDLE-OF-THE-SPHINX题解（writeup）

题目

   同上一题，只是这次的环境不是 evm ，而是cairo.

   riddle-of-the-sphinx对应合约 代码 ，贴在后面。

实现&分析

flag 返回前提

还是一样的流程，flag返回前提变化：

async def checker(client: AccountClient, riddle_contract: Contract, player_address: int) -> bool:
    solution = (await riddle_contract.functions["solution"].call()).solution

    return to_bytes(solution).lstrip(b"\x00") == b"man"

关键返回内容转字符串后等于man。

思路

合约代码：

from starkware.cairo.common.cairo_builtins import HashBuiltin

@storage_var
func _solution() -> (res : felt):
end

@external
func solve{
    syscall_ptr : felt*,
    pedersen_ptr : HashBuiltin*,
    range_check_ptr,
}(solution : felt):
    _solution.write(solution)
    return ()
end

@view
func solution{
    syscall_ptr : felt*,
    pedersen_ptr : HashBuiltin*,
    range_check_ptr,
}() -> (solution : felt):
    let (solution) = _solution.read()
    return (solution)
end

调用 solution 方法查看_solution的值，调用solve方法写_solution，所以答案很明显了，调用solve传入值为man的数值即可。

题目内代码基本都有所有的调用方法，abi获取从remix编译后跳转可以查看。

调用值设定 类  似evm，不能用call，要用invoke，max_fee也要设置才行，具体实现见writeup。

writeup

from starknet_py.net.networks import *
from starknet_py.net.gateway_client import *
from starknet_py.net.http_client import *
from starknet_py.net import AccountClient,KeyPair
from starknet_py.contract import *
from starkware.python.utils import *
from starknet_py.net.full_node_client import FullNodeClient
from starknet_py.net import AccountClient
from starknet_py.cairo.felt import *
from starkware.crypto.signature.signature import private_to_stark_key
import threading,asyncio
from starkware.starknet.services.api.messages import StarknetMessageToL1, StarknetMessageToL2
from starkware.starknet.core.os.contract_address.contract_address import \
    calculate_contract_address_from_hash

uuid = "xxxx"
url = "xxxx"
pkey = xxxx
contract = xxxx
ticket = "xxxx"

config1 = {"abi":
    [
        {
            "name": "solve",
            "type": "function",
            "inputs": [
                {
                    "name": "solution",
                    "type": "felt"
                }
            ],
            "outputs": []
        },
        {
            "name": "solution",
            "type": "function",
            "inputs": [],
            "outputs": [
                {
                    "name": "solution",
                    "type": "felt"
                }
            ],
            "stateMutability": "view"
        }

]
}

async def getSolution():
    client = GatewayClient(url, TESTNET)
    pubkey = private_to_stark_key(pkey)
    fullNodeClient = AccountClient(
        client=client,
        address=calculate_contract_address_from_hash(
                salt=20,
                class_hash=1803505466663265559571280894381905521939782500874858933595227108099796801620,
                constructor_calldata=[pubkey],
                deployer_address=0,
            ),
        key_pair=KeyPair(
            private_key=pkey, public_key=private_to_stark_key(pkey)
        ),
        chain=StarknetChainId.TESTNET,
    )
    riddleContract = Contract(address=contract, abi=config1["abi"], client=fullNodeClient)

    result = (await riddleContract.functions['solve'].invoke(0x6d616e,max_fee=int(1e16)))
    print(result)
    solution = (await riddleContract.functions["solution"].call()).solution
    print("solution")
    print(solution)


asyncio.get_event_loop().run_until_complete(getSolution())





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