Re: [Dcrup] Review of draft-ietf-dcrup-dkim-crypto-03

[Jim Fenton <[e-mail]>]

On Jul 7, 2017, at 4:24 PM, Salz, Rich <[e-mail]> wrote:

>> For what it's worth, I agree with Jim and Ekr. Hashing is just fine.
> 
> Is it fine, or is it a required or just good?
> 
> Nobody is saying there is anything wrong with hashing.  Several are saying that, given the limitations of some DNS deployments, it is useful to avoid the indirection and just put the key when we can.

What DNS deployment limitation would be adversely affected by the use of a hash? I can't think of any.

"Avoid the indirection" makes it sound like more network round-trips would be required if a hash is used. No more network traffic is involved; the verifier only needs to compute the hash of the key included in the message and compare that with the fingerprint included in the key lookup response from DNS. The verifier can even check the signature prior to receiving the DNS response, if it wants.

I'm supporting publishing key fingerprints because I think it's slightly more future-proof, and having been burned by that once already, I don't want to make the same mistake again. But if rough consensus decides otherwise, we go with that of course.

I still haven't heard an answer to the following question I posed about the fingerprints, though: Will the fingerprints always be sha256, or do we need to specify the fingerprint algorithm in the DNS record? In other words, will we assume that sha256 will be strong enough for the life of this protocol?

-Jim