Control Flow Flattening

LYKNCTF 2026’s crack track (reverse engineering) was built around a repeating pattern: build a small cipher out of well-known cryptographic primitives, wrap it in obfuscation that looks harder than it is, then bake a .text-derived self-hash into the state so that any patch or debugger attach silently produces wrong output without changing the error message. Nine challenges, nine variations on that theme, from a simple string-import inspection in a Tauri desktop app all the way to a four-layer keygen whose master key mixes account name, license key, SHA-256(.text), and an anti-debug byte. ...

Platform THEM?! CTF 2026 Difficulty Mixed (Easy → Hard) OS Jeopardy (Reverse, Crypto) Tags CHIP-8 emulation, x86-64 PE reverse engineering, Unicorn dynamic emulation, FNV-1a hash recovery, custom bytecode VMs, control-flow flattening, DES weak-key parity, XOR-chain cryptanalysis, modular arithmetic over 10^155 THEM?! CTF 2026 is a large jeopardy event with 85 total challenges across the usual categories. This writeup covers the seven challenges I personally solved, all from the reverse-engineering and cryptography tracks — every one demanded a real RE or cryptanalytic technique end-to-end. The reverse picks range from a CHIP-8 ROM that paints its flag onto a 64×32 screen across ~2⁴⁰ encoder steps per round, to a Windows binary whose VM mutates its own register state during dispatch. The crypto picks are the same shape — three challenges that look obscure on the surface and reduce to a clean number-theory or XOR-algebra invariant once you read carefully. ...