Possible Duplicate:
What security policies exist in place for packages and scripts?
Originally I want(ed) to know how the Ubuntu update process is being secured against tampering of packages by a man in the middle. I asked this question: Are Virus/rootkits via Ubuntu updates possible? [closed]
It was closed as a duplicate, but the supposed duplicates cover some quite different topics (like how cd/flashdrive autorun etc affects safety etc.). So I've reposted my specific question. How is the update process secured against a man in the middle attack?
I feel this question is not really covered by:
How is the system kept secure? (covers more the aspect of gaining root access)
What security policies exist in place for packages and scripts? (covers the aspect of deb safety files being autorun)