I am reminded of a (bottle of wine induced) argument I once had with dan geer over whether a buffer overflow is a bug or a flaw. We ultimately realized that I was sitting in the app code looking at strcpy() and dan was thinking of language architecture on a machine with innane memory layout. We were both right...kind of. Thing is, when it comes to misuse of really pathetic string functions in C, most developers make bugs...
Of course there is a deep relation between bugs and flaws. Unfortunately, most software security discourse these days is stuck in the Web app bugs only mud. Any acknowledgement of higher level thinking is a good thing. gem company www.cigital.com podcast www.cigital.com/silverbullet blog www.cigital.com/justiceleague book www.swsec.com Sent from my treo. -----Original Message----- From: Crispin Cowan [mailto:[EMAIL PROTECTED] Sent: Monday, June 11, 2007 05:50 PM Eastern Standard Time To: Gary McGraw Cc: Blue Boar; SC-L@securecoding.org Subject: Re: [SC-L] Harvard vs. von Neumann Gary McGraw wrote: > Though I don't quite understand computer science theory in the same way that > Crispin does, I do think it is worth pointing out that there are two major > kinds of security defects in software: bugs at the implementation level, and > flaws at the design/spec level. I think Crispin is driving at that point. > Kind of. I'm saying that "specification" and "implementation" are relative to each other: at one level, a spec can say "put an iterative loop here" and implementation of a bunch of x86 instructions. At another level, specification says "initialize this array" and the implementation says "for (i=0; i<ARRAY_SIZE;i++){...". At yet another level the specification says "get a contractor to write an air traffic control system" and the implementation is a contract :) So when you advocate automating the implementation and focusing on specification, you are just moving the game up. You *do* change properties when you move the game up, some for the better, some for the worse. Some examples: * If you move up to type safe languages, then the compiler can prove some nice safety properties about your program for you. It does not prove total correctness, does not prove halting, just some nice safety properties. * If you move further up to purely declarative languages (PROLOG, strict functional languages) you get a bunch more analyzability. But they are still Turing-complete (thanks to Church-Rosser) so you still can't have total correctness. * If you moved up to some specification form that was no longer Turing complete, e.g. something weaker like predicate logic, then you are asking the compiler to contrive algorithmic solutions to nominally NP-hard problems. Of course they mostly aren't NP-hard because humans can create algorithms to solve them, but now you want the computer to do it. Which begs the question of the correctness of a compiler so powerful it can solve general purpose algorithms. > If we assumed perfection at the implementation level (through better > languages, say), then we would end up solving roughly 50% of the software > security problem. > The 50% being rather squishy, but yes this is true. Its only vaguely what I was talking about, really, but it is true. Crispin -- Crispin Cowan, Ph.D. http://crispincowan.com/~crispin/ Director of Software Engineering http://novell.com AppArmor Chat: irc.oftc.net/#apparmor _______________________________________________ Secure Coding mailing list (SC-L) SC-L@securecoding.org List information, subscriptions, etc - http://krvw.com/mailman/listinfo/sc-l List charter available at - http://www.securecoding.org/list/charter.php SC-L is hosted and moderated by KRvW Associates, LLC (http://www.KRvW.com) as a free, non-commercial service to the software security community. _______________________________________________
