Re: [Last-Call] [secdir] Secdir last call review of draft-ietf-dnsop-server-cookies-04

On Wed, Dec 2, 2020 at 10:32 AM Ondřej Surý <ondrej@isc.org> wrote:

> Stephen,
>
> ad 1) the performance is crucial for DNS over UDP and PRF such as SipHash
> is more efficient than HMACs. No, it wasn’t consulted with CFRG, and I
> can’t speak for Willem, but I am confident enough to make the decision.
> SipHash is widely used for hash tables virtually anywhere now.
>

Well hash tables are an application with somewhat different security
properties than MACs, so I don't think this is dispositive.

I concur with Stephen that CFRG should sign off on the use of SipHash here.
With that said, how does SipHash compare to GMAC in terms of performance?

-Ekr

> ad 2) we need a value that’s synchronized well enough and monotonic. I
> honestly don’t see any value in using 64-bit value here. Using unixtime has
> a value in itself, it’s a well-known and there’s a little room for any
> implementor to make a mistake in an implementation. The interoperability is
> more important than the actual value of the counter. It’s write only
> counter, nobody is going to interpret it after it has been generated, and
> it’s wide enough to prevent brute forcing.
>
> Cheers,
> Ondřej
> --
> Ondřej Surý — ISC (He/Him)
>
> > On 2. 12. 2020, at 18:47, Stephen Farrell via Datatracker <
> noreply@ietf.org> wrote:
> >
> > Reviewer: Stephen Farrell
> > Review result: Has Issues
> >
> > I see two issues here worth checking:
> >
> > 1. I don't recall SipHash being used as a MAC in
> > any IETF standard before. We normally use HMAC,
> > even if truncated. Why make this change and was
> > that checked with e.g. CFRG? (And the URL given
> > in the reference gets me a 404.)
> >
> > 2. Is it really a good idea to use a 32 bit seconds
> > since 1970-01-01 in 2020? I'd have thought that e.g.
> > a timestamp in hours since then or seconds since
> > some date in 2020 would be better.
> >
> > Here's a couple of nits too:
> > - section 1: what's a "strong cookie"?
> > - "gallimaufry" - cute! but not sure it'll help readers to learn that
> word.
> >
> >
> >
> >
>
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