DownUnderCTF 2025 — rocky (100 pts)

Description

An underdog boxer gets a once-in-a-lifetime shot at the world heavyweight title and proves his worth through sheer determination.

Solution

We were given a 64-bit ELF binary. Running it asks for user input; wrong answers return Hash mismatch :(.

Static analysis in IDA revealed:

1. Program accepts up to 16 characters and strips newlines
2. Computes MD5 hash of input against a hardcoded target
3. Target hash (little-endian): 70924d0cf669f9d23ccabd561202351f
4. Upon a match, reverses the input and runs a decryption routine

Looking up the hash on CrackStation returns the matching string immediately. The binary then decrypts and prints the flag.

Flag

DUCTF{In_the_land_of_cubicles_lined_in_gray_Where_the_clock_ticks_loud_by_the_light_of_day}