VSEC's VSEC Challenger Num #5

Author:
VSEC

Language:
C/C++

Upload:
2026-10-20 04:29

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Platform:
Windows

Difficulty:
6.0

Quality:
5.0

Arch:
x86-64

Downloads:
68

Size:
2.99 MB

Writeups:
0

Comments:
5

Description

Challenge Rules 1.You are allowed to use artificial intelligence to help solve the challenge. 2.You may patch the binary, but you must comment the correct flag. Submissions without the correct flag commented will not be accepted. 3.You can recover the program key by reverse-engineering the algorithm (the algorithm is reversible). 4.After solving the challenge, you may optionally explain your solution method. 5.The program is obfuscated only at the OEP by my private obfuscator/packer [ not commercial ], other parts obfuscated/virtualized at source code level. 6.For compression file packed with UPX Good luck!

Labels ?

String / data encryption XOR Substitution / table Packer UPX Self-modifying / runtime decrypt Crypto / hash algorithm Other / custom hash Code virtualization / VM Control-flow obfuscation Spaghetti / junk-branch Exception / interrupt-based Indirect / computed jumps & calls State machine / dispatcher Control-flow flattening (CFF) Return-address / stack-based Anti-disassembly Junk / garbage bytes Opaque predicates Overlapping / misaligned instructions Jump-based desync Custom / generic obfuscation

Comments (5)
Writeups (0)

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sacredgravel44 on 2026-10-20 19:34: [Click to reveal]

VSEC on 2026-10-20 20:17: @sacredgravel44 Sure , as i said only comment when you get correct flag please don't spam. If I could, I would definitely send you a video of how the program functions correctly when it receives the right key.

VSEC on 2026-10-20 20:43: @sacredgravel44 as a hint , Correct flag should start with CMO

sacredgravel44 on 2026-10-20 22:28: The check compares only 32 bits (fin == 0x9BE0807A), but the flag's ChaCha key uses the full 64-bit state. Any brute-forced collision, e.g. VSEC___________lpybU, prints Correct with a garbage flag. Can you fix the check to cover the whole state? Otherwise the only shortcut to the flag is your key itself.

VSEC on 2026-10-20 22:37: @sacredgravel44 The key is generated based on cryptography, which is completely reversible. Therefore, by studying the algorithm, you can generate the exact same key. And that is precisely the point: there is no need to blindly guess the key. You must find the algorithm, deobfuscate (or clarify) it, and generate the key. You can use the algorithm to generate hundreds of keys that will lead to a successful message.

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crackmes.one

crackmes.one

VSEC's VSEC Challenger Num #5