That Time Ken Thompson Wrote a Backdoor into the C Compiler

I recently wrote a deep dive exploring the famous talk "Reflections on Trusting Trust" by Ken Thompson — the one where he describes how a compiler can be tricked to insert a Trojan horse that reproduces itself even when the source is "clean".

In the post I cover:
• A walkthrough of the core mechanism (quines, compiler “training”, reproduction).
• Annotated excerpts from the original nih example (via Russ Cox) and what each part does.
• Implications today: build-tool trust, reproducible builds, supply-chain attacks.

If you’re interested in compiler internals, toolchain security, or historical hacks in UNIX/CS, I’d love your feedback or questions.

🔗 You can read it here: https://micahkepe.com/blog/thompson-trojan-horse/