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

[Michael Thomas <[e-mail]>]

On 11/18/20 1:19 PM, John Levine wrote:
> In article <[e-mail]> you write:
>> More specifically, we developed DKIM/DMARC as an anti-phishing measure for
>> commerical email. It was never intedned to be used for personal email, but
>> Yahoo deployed it in the personal email space and others have followed suit on
>> a massive scale. As a result a significant and growing percentage of email is
>> now signed, to the point where privacy experts are calling for DKIM key release
>> after rotation to at least partially mitigate the damage we have done.
> Urrgh. We correctly expected DKIM to be used for all sorts of mail,
> but without expecting the DKIM domain to match the From (other than
> the experimental and unused ADSP extension.) DMARC made "aligned"
> signatures treated specially, but the signatures didn't change.
>
> What we didn't anticipate is that large mail systems would never
> rotate their keys and use the same DKIM signing key for many years, so
> you can easily check old messages with old signatures. I suppose it is
> kind of a surprise that people use them for non-repudiation, but since
> the signatures aren't technically very different from S/MIME or PGP
> signatures, it shouldn't be that surprising.

It was certainly our intention that it was at least for enterprise since 
that's the use case we were most interested in at Cisco. But Ned is 
right that a lot of our motivation at Cisco was driven by spear 
phishing. We didn't ultimately succeed because there were just too many 
things emitting mail in closets from 386 servers everybody was afraid to 
turn off. I hope it's a different situation now after 15 years.

The funny thing about this non-repudiation issue is that I don't recall 
anybody bringing it up, and that's probably because it was a non-issue 
then because submission authentication was pretty rare. DKIM couldn't 
prove anything beyond that it was the domain that sent it which is 
pretty ho-hum for say a gmail. Only changing policies about submission 
authentication closed the loop. I've always wondered whether DKIM had a 
part in that policy change, or whether it was just in the water to clean 
up lax email provider policies.

I frankly see non-repudiation as an unexpected benefit. The internet is 
forever. Film at 11.

Mike