[SC-L] Countering Trusting Trust through Diverse Double-Compiling

David A. Wheeler dwheeler at ida.org
Wed Dec 14 16:40:27 EST 2005


Everyone here should be familiar with Ken Thompson's famous
"Reflections on Trusting Trust." If not, see:
  http://www.acm.org/classics/sep95/
The "trusting trust" attack subverts the compiler binary;
if the attacker succeeds, you're doomed. Well, til now.

I've written a paper on an approach to counter this attack. See:
  "Countering Trusting Trust through Diverse Double-Compiling"
  http://www.acsa-admin.org/2005/abstracts/47.html
You can get data to reproduce this, and some related material, from
my personal site:
  http://www.dwheeler.com/trusting-trust

Here's the abstract:
"An Air Force evaluation of Multics, and Ken Thompson's famous Turing award
lecture "Reflections on Trusting Trust," showed that compilers can be subverted
to insert malicious Trojan horses into critical software, including themselves.
If this attack goes undetected, even complete analysis of a system's source code
will not find the malicious code that is running, and methods for detecting this
particular attack are not widely known. This paper describes a practical
technique, termed diverse double-compiling (DDC),
that detects this attack and some unintended compiler defects as well.
Simply recompile the purported source code twice: once with a second (trusted)
compiler, and again using the result of the first compilation.
If the result is bit-for-bit identical with the untrusted
binary, then the source code accurately represents the binary.
This technique has been mentioned informally, but its issues and
ramifications have not been identified or discussed in a
peer-reviewed work, nor has a public demonstration been made.
This paper describes the technique, justifies it, describes how
to overcome practical challenges, and demonstrates it."

I think you'll find this interesting.

(Note: I posted a similar message to Bugtraq earlier, but
I thought some of you might not have seen it.)

--- David A. Wheeler






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