Leaked Flag Checker

Show TagsShow Solved

Rows:

CHALLENGE	AUTHORS	SOLVES (CURRENT)	SOLVE RATE (AT CONTEST TIME)
Welcome Misc	admin	1351 solves	-
AlpacaHack 2100 Misc Daily AlpacaHack	admin	996 solves	-
a fact of CTF Crypto Daily AlpacaHack	xornet	625 solves	-
Simple Login Web AlpacaHack Round 2 (Web)	ark	544 solves	Top 28% = 84/300 users
Emojify Web Daily AlpacaHack	ark	441 solves	-
Leaked Flag Checker Rev Daily AlpacaHack	minaminao	414 solves	-
simpleoverflow Pwn Daily AlpacaHack	n01e0	375 solves	-
echo Pwn AlpacaHack Round 1 (Pwn)	ptr-yudai	328 solves	Top 32% = 56/174 users
hit-and-miss Misc Daily AlpacaHack	ark	282 solves	-
Integer Writer Pwn Daily AlpacaHack	mora	261 solves	-
super-tomato Crypto Daily AlpacaHack	kanon	259 solves	-
Treasure Hunt Web AlpacaHack Round 7 (Web)	ark	258 solves	Top 15% = 71/458 users
Alpaca Bank Web Daily AlpacaHack	hiikunz	258 solves	-
Read Assembly Rev Daily AlpacaHack	xrekkusu	253 solves	-
size limit Crypto Daily AlpacaHack	jp3bgy	251 solves	-
🐈 Web Daily AlpacaHack	ark	244 solves	-
qrime Crypto AlpacaHack Round 3 (Crypto)	xornet	243 solves	Top 38% = 91/239 users
Xmas Login Web Daily AlpacaHack	hiikunz	239 solves	-
Fushigi Crawler Web Daily AlpacaHack	minaminao	232 solves	-
Safe Prime Crypto Daily AlpacaHack	ptr-yudai	222 solves	-

Rows:

414 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.