niubill's almost_impossible_can_you_crack

Author:
niubill

Language:
C/C++

Upload:
2026-07-02 06:03

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Platform:
Windows

Difficulty:
5.0

Quality:
4.0

Arch:
x86-64

Downloads:
264

Size:
24.50 KB

Writeups:
0

Comments:
4

Description

Decryption keys are split inside 3 VM layers, assembled only at runtime

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zqdev on 2026-07-02 18:37: [Click to reveal]

canberk on 2026-07-02 19:18: [Click to reveal]

kirbyyy on 2026-07-02 22:14: [Click to reveal]

999Lube on 2026-07-10 04:08: Nice 3-VM nesting: outer FSM iterates 13 rounds (states 5-8), inner FSM (states 9-13, jump table @0x140005090) applies out[i] = ROL8(bc[i],2) ^ 0x52 ^ 0x2E per byte. Bytecode at 0x140004010 -> flag = E0 05 B8 94 AC 48 91 0C 6D 6D 6D 6D 6D. Sneaky part: byte 0x0C is scanf whitespace so the intended flag is impossible to type - forces you to either patch or prove the algorithm. Anti-debug (GetWindowTextA + IsDebuggerPresent + PEB + NtQueryInformationProcess + QPC timing) all funnels into ExitProcess at 0x140001ab8, one NOP kills it. Really enjoyed this one

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niubill's almost_impossible_can_you_crack_me