[Cryptography] how reliably do audits spot backdoors?

[Benjamin Kreuter]

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On Tue, 24 Dec 2013 17:42:33 +1000
"James A. Donald" <jamesd at echeque.com> wrote:
 
> I find C quite intuitive, possibly as a result of having done a bit
> of code review.
>
> What you would call counterintuitive, I read as idiomatic, and what
> is undefined, I read as unidiomatic.

So the fact that it is possible for the sum of two positive integers to
be a negative number is idiomatic?  C has many of the features that make
writing reliable (let alone secure) code difficult, and almost none of
the features that make it easy.

> So, the underhanded C examples would have failed code review, not 
> because their terribly sneaky measures would have been detected in
> code review, but for being unidiomatic, obfuscated, uglified, or
> complexified.

Nonsense.  The UCC entries win points for not be obfuscated or
uglified or complicated.  That is the entire point of the contest.
There is a sufficient amount of undefined behavior in C to make such
things possible, which is part of the problem.

> The code review would have come to an end, and the developer ordered
> to do a rewrite, before the trick had been detected.

So what do we do when we are asked to check an already completed
program for back doors?  This conversation started with the common
suggestion that open source software is more secure because we can
check the code for problems.  Rewriting the Linux kernel or OpenSSL is
not typically considered to be something that is on the table.

Now, if it is on the table, then I do not see any reason why it would
be desirable to choose C over a more well-defined language.  If a
complete rewrite is something we can undertake, then even if *none* of
the languages available now fit the bill, why not just create a new
one?  Why not just identify that subset of C that is "good" and write a
compiler for that language, without any undefined behavior?  Why not
create a new language that we can audit more easily if something like
OCaml is "too slow" (or whatever reason people are giving for avoiding
high-level languages these days)?

- -- Ben



- -- 
Benjamin R Kreuter
KK4FJZ

- --

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