攻防世界-lottery

得到flag要$9990000

 通过抽奖的方式获得钱，基本要7个数字都相同

 扫目录，依次点开

robots.txt中有 /.git/

用git下载，或者直接下载附件1（源码）

 然后打开api.php

API（Application Programming Interface，应用程序编程接口）是一些预先定义的函数

<?php
require_once('config.php');
header('Content-Type: application/json');

function response($resp){
	die(json_encode($resp));
}

function response_error($msg){
	$result = ['status'=>'error'];
	$result['msg'] = $msg;
	response($result);
}

function require_keys($req, $keys){
	foreach ($keys as $key) {
		if(!array_key_exists($key, $req)){
			response_error('invalid request');
		}
	}
}

function require_registered(){
	if(!isset($_SESSION['name']) || !isset($_SESSION['money'])){
		response_error('register first');
	}
}

function require_min_money($min_money){
	if(!isset($_SESSION['money'])){
		response_error('register first');
	}
	$money = $_SESSION['money'];
	if($money < 0){
		$_SESSION = array();
		session_destroy();
		response_error('invalid negative money');
	}
	if($money < $min_money){
		response_error('you don\' have enough money');
	}
}


if($_SERVER["REQUEST_METHOD"] != 'POST' || !isset($_SERVER["CONTENT_TYPE"]) || $_SERVER["CONTENT_TYPE"] != 'application/json'){
	response_error('please post json data');
}

$data = json_decode(file_get_contents('php://input'), true);
if(json_last_error() != JSON_ERROR_NONE){
	response_error('invalid json');
}

require_keys($data, ['action']);

// my boss told me to use cryptographically secure algorithm 
function random_num(){
	do {
		$byte = openssl_random_pseudo_bytes(10, $cstrong);
		$num = ord($byte);
	} while ($num >= 250);

	if(!$cstrong){
		response_error('server need be checked, tell admin');
	}
	
	$num /= 25;
	return strval(floor($num));
}

function random_win_nums(){
	$result = '';
	for($i=0; $i<7; $i++){
		$result .= random_num();
	}
	return $result;
}


function buy($req){
	require_registered();
	require_min_money(2);

	$money = $_SESSION['money'];
	$numbers = $req['numbers'];
	$win_numbers = random_win_nums();
	$same_count = 0;
	for($i=0; $i<7; $i++){
		if($numbers[$i] == $win_numbers[$i]){
			$same_count++;
		}
	}
	switch ($same_count) {
		case 2:
			$prize = 5;
			break;
		case 3:
			$prize = 20;
			break;
		case 4:
			$prize = 300;
			break;
		case 5:
			$prize = 1800;
			break;
		case 6:
			$prize = 200000;
			break;
		case 7:
			$prize = 5000000;
			break;
		default:
			$prize = 0;
			break;
	}
	$money += $prize - 2;
	$_SESSION['money'] = $money;
	response(['status'=>'ok','numbers'=>$numbers, 'win_numbers'=>$win_numbers, 'money'=>$money, 'prize'=>$prize]);
}

function flag($req){
	global $flag;
	global $flag_price;

	require_registered();
	$money = $_SESSION['money'];
	if($money < $flag_price){
		response_error('you don\' have enough money');
	} else {
		$money -= $flag_price;
		$_SESSION['money'] = $money;
		$msg = 'Here is your flag: ' . $flag;
		response(['status'=>'ok','msg'=>$msg, 'money'=>$money]);
	}
}

function register($req){
	$name = $req['name'];
	$_SESSION['name'] = $name;
	$_SESSION['money'] = 20;

	response(['status'=>'ok']);
}


switch ($data['action']) {
	case 'buy':
		require_keys($data, ['numbers']);
		buy($data);
		break;

	case 'flag':
		flag($data);
		break;

	case 'register':
		require_keys($data, ['name']);
		register($data);
		break;
	
	default:
		response_error('invalid request');
		break;
}

for($i=0; $i<7; $i++){
		if($numbers[$i] == $win_numbers[$i]){
			$same_count++;
		}
	}

关键在这，弱比较，所以可以输入ture使其和数字相等，但是数字中不能有0，否则会少一个对的数字

因为输入的数字和winning numbers是一一核对的，所以让每个数字的点都为true，就可以让7个数字都吻合