pwb recompiled the compiler and it got 1 byte larger. again, another byte. after that they played with it until they broke the quine part. i am not sure that if they ever realized what was going on. the extra byte was my bug. On Mon, Sep 20, 2021 at 4:58 AM Douglas McIlroy < douglas.mcilroy@dartmouth.edu> wrote: > >> > It's part of my academic project to work on provable compiler > security. > >> > I tried to do it according to the "Reflections on Trusting Trust" by > Ken > >> > Thompson, not only to show a compiler Trojan horse but also to prove > that > >> > we can discover it. > >> > >> Of course it can be discovered if you look for it. What was impressive > about > >> the folks who got Thompson's compiler at PWB is that they found the > horse > >> even though they weren't looking for it. > > > I had not heard this story. Can you elaborate, please? My impression > from having > > read the paper (a long time ago now) is that Ken did the experiment > locally only. > > Ken did it locally, but a vigilant person at PWB noticed there was an > experimental > compiler on the research machine and grabbed it. While they weren't > looking for > hidden stuff, they probably were trying to find what was new in the > compiler. Ken > may know details about what they had in the way of source and binary. > > Doug >