In Summer 2025, the author published Hell Gates, a crackme featuring a custom 32-bit CPU designed in VHDL with multiple layers of obfuscation, anti-tamper, timing checks, and anti-debug protections. Synthesized to a gate-level netlist, the challenge defeated humans and LLMs like Claude, ChatGPT, and DeepSeek for over a year. Then in September 2026, GPT-6 solved it in under 20-30 minutes on SRE-Bench, credited to Zhuo Zhang.

The breakthrough came because the crypto protecting the CPU's state was poorly implemented. GPT-6 used a side-channel/differential analysis attack that made runs replayable after stripping all obfuscation layers. The model identified hints on the encryption, decrypted and re-encrypted registers, ran the netlist properly, and dumped all decrypted 1GB of memory data.

Hell Gates features a custom CPU with 16 32-bit general purpose registers and special registers including overflow flags, condition flags, a program counter, and a pseudo-random state. The architecture supports integer, memory, branch, and jump operations with basic ALU functions. Despite extensive obfuscation techniques, the lazily implemented encryption ultimately proved to be the challenge's weakest link.