GPT-6 Cracks HellGates, a Custom CPU Challenge That Stumped Humans and LLMs for a Year
HellGates, custom CPU gate-level challenge
In 2025, I built HellGates: a custom 32-bit CPU in VHDL with encrypted, bit-addressable memory, multiple obfuscation layers, and anti-debug traps. For a year, no human or LLM solved it—until GPT-6 cracked it in under 30 minutes on SRE-Bench. The fatal flaw was weak homebrew crypto protecting the CPU state, which GPT-6 exploited via differential analysis to decrypt the entire 1GB memory.
I actually left this on purpose because if I used real cryptography, the logic gates count would have increased to a larger number and I thought nobody would see the side-channel anyway and so moved on because I needed to test my design rapidly after synthesis. I was wrong, this mistake cost me a lot.