[Cryptography] PRISM-Proofing and PRISM-Hardening

Viktor Dukhovni cryptography at dukhovni.org
Tue Sep 17 17:31:21 EDT 2013

On Tue, Sep 17, 2013 at 05:01:12PM -0400, Perry E. Metzger wrote:

> (Note that this assumes no cryptographic breakthroughs like doing
> discrete logs over prime fields easily or (completely theoretical
> since we don't really know how to do it) sabotage of the elliptic
> curve system in use.)
> Given that many real organizations have hundreds of front end
> machines sharing RSA private keys, theft of RSA keys may very well be
> much easier in many cases than broader forms of sabotage.

There is also I suspect a lot of software with compiled-in EDH
primes (RFC 5114 or other).  Without breaking EDH generally, perhaps
they have better precomputation attacks that were effective against
the more popular groups.

I would certainly recommend that each server generate its own EDH
parameters, and change them from time to time.  Sadly when choosing
between a 1024-bit or a 2048-bit EDH prime you get one of
interoperability or best-practice security but not both.

And indeed the FUD around the NIST EC curves is rather unfortunate.
Is secp256r1 better or worse than 1024-bit EDH?


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