Leaked Flag Checker

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Rows:

CHALLENGE	AUTHORS	SOLVES (CURRENT)	SOLVE RATE (AT CONTEST TIME)
AlpacaHack 2100 Misc Daily AlpacaHack	admin	1650 solves	-
Welcome Misc	admin	1546 solves	-
a fact of CTF Crypto Daily AlpacaHack	xornet	884 solves	-
Simple Login Web AlpacaHack Round 2 (Web)	ark	612 solves	Top 28% = 84/300 users
Emojify Web Daily AlpacaHack	ark	597 solves	-
Leaked Flag Checker Rev Daily AlpacaHack	minaminao	571 solves	-
simpleoverflow Pwn SECCON Beginners CTF 2024	n01e0	510 solves	Top 73% = 683/928 teams
super-tomato Crypto Daily AlpacaHack	kanon	393 solves	-
hit-and-miss Misc Daily AlpacaHack	ark	388 solves	-
echo Pwn AlpacaHack Round 1 (Pwn)	ptr-yudai	357 solves	Top 32% = 56/174 users
Xmas Login Web Daily AlpacaHack	hiikunz	356 solves	-
Fushigi Crawler Web Daily AlpacaHack	minaminao	347 solves	-
Alpaca Bank Web Daily AlpacaHack	hiikunz	332 solves	-
Integer Writer Pwn Daily AlpacaHack	mora	328 solves	-
size limit Crypto Daily AlpacaHack	jp3bgy	320 solves	-
Encoding Basics Misc Crypto Daily AlpacaHack	kurenaif	320 solves	-
Read Assembly Rev Daily AlpacaHack	xrekkusu	315 solves	-
🐈 Web Daily AlpacaHack	ark	313 solves	-
Bars Web Daily AlpacaHack	kakur41	302 solves	-
108 Misc Daily AlpacaHack	admin	296 solves	-

Rows:

571 solves

Author:

minaminao

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.