I’ve written at least twice about Ken Thompson’s Turing Award Lecture, Reflections on Trusting Trust and each time I told you to be sure to read it. It describes one of the—if not the—greatest hacks of all time. In the talk and the paper that recapitulates it, Thompson describes how he modified the C compiler to insert a backdoor into the Unix login command and arranged to have all signs of the code removed from the compiler’s source while keeping it in the binary. In a way, the paper is terrifying and after reading it, you’ll never fully trust your tools again.
If you ignored my strong urging to read the paper don’t worry. Vivek Haldar had done it for you and produced a short video describing it. Watch Haldar’s video to see how Thompson pulled off his trick but then you really should the paper itself. It’s short, easy to read, and entertaining.