Prajwal's Blog

So I had this little idea of building an entire custom CPU instruction set architecture called Rune ISA from scratch - 42-bit instructions, 24-bit registers, a full VM in Python, an assembler, and a text-based RPG called Unknown Runes as a reversing challenge for ISSessions CTF 2026. It felt like the ISA needed more, so I uh made something.

So I was doing my internship at Trend Micro, and during my free time I was looking around at CTF challenges for ideas cause I was also a CTF Dev for ISSessions CTF 2026. One day, I asked a colleague of mine if he had any cool ideas and he showed me an article about a DEFCON challenge that had participants reversing a completely custom instruction set. I can't for the life of me find the link or even remember the challenge name (believe me I've tried finding it since), but the concept stuck with me like glue. A fully custom ISA, no documentation, just raw bytes and vibes, a true nightmare for the players ^w^.