[ILUG] opinions on DKIM

[Jeroen Massar]

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paul at clubi.ie wrote:
> On Wed, 25 Apr 2007, Jeroen Massar wrote:
> 
>> The 'case against' OpenPGP according to DKIM folks and a lot of other
>> such groups:
> 
>> - No established PGP web of trust (the key distribution)
> 
> I'd expect X.509 to be the more realistic trust mechanisms..

And how exactly do you propose spreading X.509 usage to endusers?

Do recall that $grandma doesn't know what it is, and can't care less
either. And she sure is not going to change her mailsetup.

>> - hard to deploy for 100.000 clients
>>   (DKIM you simply install on the mailservers, other mail
>>    will get bounced as not being signed properly, users will need
>>    to use the upstream servers)
> 
> That's great, but see end-end. You won't be able to drop
> DKIM-bad-signature mails. If you use it for whitelisting, what's the point?

The point is that you can junk/trash/reject anything else and that those
thousands of emails being spammed onto you only get accepted when the
source domain acknowledges them. This also means that those bounces are
not going to end up at the faked domain.

>> - OpenPGP doesn't sign the headers, thus one can easily change
>>   the subject or the MIME boundaries etc. But of course parts are
>>   then not signed and one can simply choose to not accept the message
>>   or ignore those parts.
> 
> Why do you need to sign the headers?

"Subject" is a header. I personally do not care so much about it, some
other people do.

> Really, you care that the message came from the person who sent it, and
> has not been tampered with (for purposes of anti-phish at least).

I also care that somebody isn't spoofing jeroen at unfix.org with their
spamrobots or virusspreaders and then having people believe I actually
send that message. Now when the message is signed they at least know
that what send it at least had my PGP key so most likely is me.

> Neither I, nor my parents, care a flying fsck about MTA added headers
> and whether they're authentic, when deciding upon authenticity of email.

So you do not mind receiving "Paul has been fired" as a subject line,
further signed by the Linus Torvalds!? :)

> At most, a MIME section to allow MUAs to add a signature for MUA
> supplied headers - hell, a simple convention, as DKIM uses, on how to
> arrange headers+message for an HMAC.

So DKIM is a good way to solve this problem?

>> DKIM is for ISP deployment. One place, one admin, one huge amount of
>> users.
> 
> So you're saying ISPs are going to drop email based on lack of or
> failling DKIM? Or that'll maintain per-user whitelists? Course not..
> It'll be passed on for users' MUAs to do.

No. When a domain has specified a DKIM policy, the receiver will REJECT
messages which are not DKIM signed and verified to be valid.

This avoids the message even getting delivered at all.

Just as a side-example, the annoying thing about Spam is not that it
exists, but the quantities that you get them in and the amount of

> The whole "check it in the middle" idea is bogus, cause there's no
> coherent policy to apply until the *end user* gets it..

The end user doesn't need to do anything for DKIM. The ISP will do it
for them. The end user could do it also of course, but they don't need to.

>> Of course MUA's can check it next to the MTA. The place where it gets
>> checked is the place where the message can be rejected.
> 
> Why would you reject the message?

Because it is not signed by the sending domain and thus didn't come from
the originating domain and thus is faked and should not exist.

> Again, what specific, high-level *goal* are you trying to achieve?

That I don't get a daily flood of replies from all kinds of places
trying to state that they received all kinds of spam and virusses which
never where send by me, but to them did look like they where sent by me.

> Cause "ability to reject mail, somewhere, based on DKIM validation,
> according to some unspecified policy" doesnt cut it - that's just
> technology for the sake of technology. Again, not even the DKIM RFCs
> provide any real rationale, just vague, wishy-washy claims that
> domain-attestation would achieve something.

You might want to read the charter for the DKIM WG:
http://www.ietf.org/html.charters/dkim-charter.html

> Why should it /not/ be done in the MUA, the most natural place?

Because then the message is already delivered. I don't want my slow
Eircom DSL link filled with thousands of messages that are not real.

>> I have been smoking the OpenPGP crack pipe for a long time already
>> now. Still, as no large entity uses it it doesn't help much,
> 
> Help what exactly???

See above, you are repeating silly questions.

> Still awaiting /someone/ to say what actual /good/ DKIM would achieve.
> We've had the hype already with SPF, and it achieved nothing. We now
> have DKIM: SPF with some of the flaws fixed, and still /no rationale/
> for its existance, beyond:
> 
>     "Well, it would stop Paypal, Amazon, etc.., phish mail!"
> 
> Yay!
> 
> So lets all deploy DKIM just so ISPs can DKIM-whitelist big name domains.
> 
> BTW, exactly how will those DKIM whitelists be maintained?... ;)

Which whitelist? The existence of a DKIM DNS entry tells you "when mail
is not signed with DKIM it most likely does not come from here", same
thing what OpenPGP signed does. Same thing that S/MIME does.

> How many banks are there in the world again?

Enough that stupid people can't care, click on random links and give out
their credentials and their money/identity stolen.

Greets,
 Jeroen

(PGP Inline signing works with this silly ML, but I'd rather avoid it)
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