Tag: Flag Checker

Flag Checker

Flag checkers are a common type of challenge in the Reverse Engineering category.

An executable or script called a flag checker takes the player's input and outputs whether that input matches the flag.

These challenges may also be called "crackmes" in a broader sense. (automatically translated from Japanese)

·Updated May 3, 2026

Flag Checker Challenges

Leaked Flag Checker

Daily AlpacaHackTopic: C, Flag CheckerReleased: Dec 4, 2025

632 solves

minaminao

Tags

flag checker everyone loves

Beginner Hint

This challenge is in the Rev (Reverse Engineering) category.
Flag checkers are a common theme in Rev problems.
A flag checker executable or script accepts player input and tells you whether it matches the flag.
The provided files are the C source challenge.c and its Ubuntu 24.04 binary build challenge.
In challenge.c, the flag-related string xor_flag has been edited out and hidden.
The goal is to use challenge.c as a reference and find an input (the flag) that makes the challenge binary print Correct.
Typically Rev problems don't include source code. You usually analyze only the binary. This one can also be solved without the source.