---
title: "Solving a CTF flag checker"
url: "https://reamcp.dev/zh-tw/cases/solving-a-ctf-flag-checker-34ece1"
source: "https://rea.tools/showcase/ctf"
source_type: "website"
author: "REA team"
author_handle: "REA team"
stars: 0
category: "CTF 與學習"
categories: ["ctf-learning"]
tags: []
added: "2026-10-13T03:57:24.604Z"
updated: "2026-10-13T03:57:24.605Z"
locale: "zh-tw"
content_locale: "zh-tw"
---

# Solving a CTF flag checker

分析 DownUnderCTF 的一個執行檔，找出檢查函式、把遮罩與加總轉成方程式，並用原程式驗證解出的 flag。

## Original README

Use REA to solve DownUnderCTF's masked squares flag checker. Find the checking functions, extract the masks and compare a recovered flag with the original program.