trusting trust considered harmful

http://cm.bell-labs.com/who/ken/trust.html
Ken Thompson, creator of UNIX
"You can't trust code that you did not totally create yourself."
C compiler could put an invisible backdoor in the Unix login command when it noticed that the login program was being compiled
C compiler could also add this feature undetectably to future compiler versions upon their compilation as well.
"I picked on the C compiler. I could have picked on any program-handling program such as an assembler, a loader, or even hardware microcode. As the level of program gets lower, these bugs will be harder and harder to detect. A well installed microcode bug will be almost impossible to detect."
"No amount of source-level verification or scrutiny will protect you from using untrusted code."

>>15
But when an IC has state it can pretend to be anything.

Also, assuming that two or more ICs are conspiring against you, they have at least two other modes of communication: whisper over the same wire signals at a lower voltage level that fits in the logic family's tolerances, or with intentional EMI, one chip can radio back and forth with another chip.