Re: [Dcrup] stronger crypto, I-D Action: draft-ietf-dcrup-dkim-usage-02.txt

Eric Rescorla <ekr@rtfm.com> Mon, 12 June 2017 09:30 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Mon, 12 Jun 2017 10:30:00 +0100
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To: Martin Thomson <martin.thomson@gmail.com>
Cc: John Levine <johnl@taugh.com>, dcrup@ietf.org
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Subject: Re: [Dcrup] stronger crypto, I-D Action: draft-ietf-dcrup-dkim-usage-02.txt
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Yes, I think we should do hashed-<everything>, for obvious reasons.

-Ekr


On Mon, Jun 12, 2017 at 10:26 AM, Martin Thomson <martin.thomson@gmail.com>
wrote:

> On 12 June 2017 at 00:13, John Levine <johnl@taugh.com> wrote:
> >>1156 is better, but I was hoping for a bit higher than that.  I would
> >>include text that suggests this (explaining the limitations you set
> >>out regarding the whitespace and so forth), but note that the
> >>additional security margin is, well, marginal.
> >
> > Of course it is.  My draft has two approaches to stronger crypto in
> > 256 bytes of TXT.  One is key hashes with the key in the signature,
> > the other is elliptic crypto.
> >
> > At this point it seems likely that we'll do the elliptic crypto so I'm
> > inclined to skip the key hashes.
>
> This is an odd angle to take here.
>
> Key hashes would remove the limit entirely.  I appreciate that you
> think that 1024-1156 is of marginal benefit, but the benefit of key
> hashes is that you can use the existing, certified, and tested
> primitives AND keys that you have already.  It's a much smaller
> increment.  That makes me inclined to think that hashed-RSA has some
> value.
>
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