Re: mail signing history, was Call for Community Feedback: Retiring IETF FTP Service

[Stephen Farrell <[e-mail]>]

Hiya,

On 18/11/2020 21:51, Michael Thomas wrote:
> 
> On 11/18/20 1:45 PM, John R Levine wrote:
>> On Wed, 18 Nov 2020, Ned Freed wrote:
>>> That said, a mechanism for publishing/expiring DKIM private keys is 
>>> something
>>> the IETF might want to standardize.
>>
>> I've started to publish my old private keys since I rotate every month 
>> but I agree a standard way to tell people where to look would be nice.
>>
> Why isn't just deleting/replacing the selector sufficient? It's not as 
> definitive but it's a lot simpler.

Publishing the private key enables various forms of
denyability - if someone claims msg1 is original
anyone with access to the private can produce a
msg2 that seems as cryptographically correct but
is clearly bogus (e.g. containing lottery numbers
that post-date message timestamps).

Yes an adversary could have gotten an independent
signed timestamp on msg1 before the private was
published but that seems low probability.

I'd support development of such a standard if it
had a good chance of deployment as I think it'd
also encourage key rotation.

S.

> 
> Mike
>