This repository contains code examples demonstrating concepts from Ken Thompson's 1984 Turing Award lecture Reflections on Trusting Trust. These quines illustrate the ideas behind self-propagating code. Thompson shared the concept of a self-propagating compiler backdoor that could survive indefinitely without leaving evidence in the source code.

1. Self-Producing Program (Quine): Program that outputs its own source code
2. "Trojanized" Quine: Self-producing program that inject purposeful modifications
3. Obfuscated "Trojan" Quine: Simple obfuscation to hide the injected modifications

gcc quine.c -o quine
./quine

gfortran fort_quine.f90 -o fort_quine
./fort_quine

Demonstrates payload injection by replacing the word "right" with "wrong" in its output.

gcc trojan_quine.c -o trojan_quine
./trojan_quine

gcc obfuscated_trojan_quine.c -o obfuscated_trojan_quine
./obfuscated_trojan_quine

Verify that the quines work correctly by comparing their output to their source:

# Test basic quine
./quine > output.c
diff quine.c output.c

# Test trojan quine (will show differences due to "right" -> "wrong" replacement)
./trojan_quine > trojan_output.c
diff trojan_quine.c trojan_output.c