----- Forwarded message from Andy Isaacson <adi@hexapodia.org> ----- Date: Fri, 6 Sep 2013 12:34:54 -0700 From: Andy Isaacson <adi@hexapodia.org> To: liberationtech <liberationtech@lists.stanford.edu> Subject: Re: [liberationtech] Random number generation being influenced - rumors User-Agent: Mutt/1.5.20 (2009-06-14) Reply-To: liberationtech <liberationtech@lists.stanford.edu> On Fri, Sep 06, 2013 at 10:45:46AM -0700, Joe Szilagyi wrote:

Does anyone put any stock into the rumors floating lately that the government may have influenced Intel and/or AMD into altering in subtle ways that CPUs handle random number generation? I keep seeing this possible FUD floating around in comments here and there on other articles.

I agree with some of your premises, but disagree with the conclusion you seem to be drawing. Yes, it's just a fear of uncertainty. We do not have evidence, nor even a claim based on knowledge, that HWRNG backdooring has occurred. However, I claim that the fear is well founded and should be taken into account by all threat models. HWRNG is a nearly-uniquely difficult security problem to crack. By definition it is impossible to prove that a black-box HWRNG is safe. This is different from the security properties of a blackbox AES or MODMUL accelerator, which can be demonstrated to conform to a known specification. If your AES instructions don't do AES, then testing against a software implementation will show it! The AES logic unit will have a hard time leaking the AES keybits since there's nowhere nondeterministic to put them. etc. By contrast, a properly functioning HWRNG cannot be tested in a way that distinguishes it from the output of a stream cipher seeded with a backdoor key. And there's no way to test the behavior of HWRNG on an ongoing basis; even if you had a test to run, it might switch to "stream cipher mode" under the covers. This is not to say that RdRand is completely unusable. Putting RdRand entropy into a software pool implementation like /dev/urandom (or preferably, a higher-assurance multipool design like Fortuna) is a cheap way to prevent a putative backdoor from compromising your system state. Now, there is a way that we can learn that a backdoor was included; if someone does a tear-down of a HWRNG and finds circuitry that has no purpose other than being a backdoor, that would be conclusive. AFAIK nobody has tried that experiment. Weighing towards distrusting HWRNG we have the fact that NSA is reported (yesterday) to have intentionally backdoored Dual_EC_DRBG, and to have spent significant amounts of money to backdoor chip implementations, with enough success that they brag about it in administrative summaries. So, I put a lot of credence in distrusting HWRNG black box implementations. But unfortunately we need a lot more reliable entropy. A fully open source, nothing up my sleeve hardware entropy source would be a huge improvement. -andy -- Liberationtech is a public list whose archives are searchable on Google. Violations of list guidelines will get you moderated: https://mailman.stanford.edu/mailman/listinfo/liberationtech. Unsubscribe, change to digest, or change password by emailing moderator at companys@stanford.edu. ----- End forwarded message ----- -- Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org ______________________________________________________________ ICBM: 48.07100, 11.36820 http://ativel.com http://postbiota.org AC894EC5: 38A5 5F46 A4FF 59B8 336B 47EE F46E 3489 AC89 4EC5