alt Hacker Newsin the NIST Curve arena, I think DJB's main concern is engineering implementation - from an online slide deck he published:
We’re writing a document “Security dangers of the NIST curves”
Focus on the prime-field NIST curves
DLP news relevant to these curves? No
DLP on these curves seems really hard
So what’s the problem?
Answer: If you implement the NIST curves, chances are you’re doing it wrong
Your code produces incorrect results for some rare curve points
Your code leaks secret data when the input isn’t a curve point
Your code leaks secret data through branch timing
Your code leaks secret data through cache timing
Even more trouble in smart cards: power, EM, etc.
Theoretically possible to do it right, but very hard
Can anyone show us software for the NIST curves done right?
Replies
cryptonector • today at 12:32 AM
Well, DJB also focused on "nothing up my sleeve" design methodology for curves. The implication was that any curves that were not designed in such a way might have something nefarious going on.
He does a motte-and-bailey thing with the P-curves. I don't know if it's intentional or not.
Curve25519 was a materially important engineering advance over the state of the art in P-curve implementations when it was introduced. There was a window of time within which Curve25519 foreclosed on Internet-exploitable vulnerabilities (and probably a somewhat longer period of time where it foreclosed on some embedded vulnerabilities). That window of time has pretty much closed now, but it was real at the time.
But he also does a handwavy thing about how the P-curves could have been backdoored. No practicing cryptgraphy engineer I'm aware of takes these arguments seriously, and to buy them you have to take Bernstein's side over people like Neil Koblitz.
The P-curve backdoor argument is unserious, but the P-curve implementation stuff has enough of a solid kernel to it that he can keep both arguments alive.