[ietf-dkim] Features that could be reconsidered: sha1 vs sha256

[Tony Hansen]

Regarding the use of sha1 vs. sha256, I did a search of messages I've
collected in the past few years that have dkim signatures.

2008	rsa-sha1	1016
2008	rsa-sha256	1525
2009	rsa-sha1	1983
2009	rsa-sha256	1932

These are just messages that have arrived in my inbox. It's just a data
point.

Regarding Steve Atkin's suggested reworded text:
    "Verifiers MUST support rsa-sha256 and MAY support rsa-sha1.
    Signers SHOULD sign using rsa-sha256 and SHOULD NOT sign using
    rsa-sha1." might provide enough wiggle room to allow existing code
    time to migrate away from SHA1.

I'm not sure we can downgrade verifier support for sha1. However, I
definitely agree that we could downgrade signing support for sha1.

	Tony Hansen
	tony at att.com