Re: [Cfrg] Dual_EC_DRBG ... [was RE: Requesting removal of CFRG co-chair]

Dan Brown <> Fri, 27 December 2013 20:44 UTC

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From: Dan Brown <>
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Thread-Topic: [Cfrg] Dual_EC_DRBG ... [was RE: Requesting removal of CFRG co-chair]
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Date: Fri, 27 Dec 2013 20:43:56 +0000
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Subject: Re: [Cfrg] Dual_EC_DRBG ... [was RE: Requesting removal of CFRG co-chair]
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> -----Original Message-----
> From: Adam Back []
> Sent: Friday, December 27, 2013 2:09 PM
> Dan Brown wrote:
> > [...]
> > 8. All considered, I don't see how the ANSI and NIST standards for
> > Dual_EC_DRBG can be viewed as a subverted standard, per se.
> Of course they're subverted.   

> We have Ferguson et al show how they could
> be backdoored.  
Repeating myself, nobody showed how the alternative P&Q could be backdoored.

In other words, even if subversion were attempted, it was effectively caught
and thwarted, at least in 800-90A and X9.82-3, by two things: (a) the
alternative points, and (b) the highly publicized potential backdoor.  Of
course, (b) is outside the standard, which is why I referred to naïve and
malicious implmenters.

Arguably, the specs do not do enough to warn naïve implementers of the
backdoor.  So, I went back to look at SP 800-90A.

Section 10.3.1, first paragraph states that Dual_EC_DRBG depends on it hard
to find a such that Q=aP.  On the same page, Figure 13 outlines the
Dual_EC_DRBG, using the same notation P and Q.

So, even if a naïve implementer hadn't heard of Ferguson et al., these two
parts of the spec together spell out to the implementer the need to ensure
that a is secret, no?

In other words, the specs are fairly clear to a thorough implementer.  

I admit that the specs could be made even clearer: they could have said that
there is a potential "backdoor".  

I would even want them to clearer. 

> We have internal NSA documents reported as talking about
> the subversion.  
Reported, yes.  But AFAIK, not published.

> We have confirmation of RSA (inadvertently or not)
> accepting money to put a EC_DRBG as a default.  

My conclusion was regarding the standards, per se, not about
implementations. I was not drawing any conclusions about implementations.

> You yourself just said the
> validation labs are demanding the backdoored P & Q be used (and rejecting
> the provably uncooked implemented chosen parameters presumably).  

 Yes, I should clarify, I was referring to the NIST SP 800 90A and ANSI
X9.82-4 as not being subverted.  I am only vaguely familiar with CAVP and
CMVP, and was not drawing any conclusions about them.  Aside: I do not deals
with labs personally, so have nothing to say about them.

> put the standard forward (inadvertently or not) from NSA input.

Hmm, I'm biased towards to mainly looking at documents in a context-free
manner: i.e. what they say, not who is saying it.  The way I read the specs,
nothing is being is hidden.  
> I am non-plussed at what you could be trying to say with the above
> statement.
Hope my response helps you.  

I am anticipating it is too narrow.

I am a bit perplexed too: I see many statements about Dual_EC_DRBG that seem
too broad.  

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