Subject: RE: [ietf-dkim] draft-ietf-dkim-base-02 // Parent signing securityconsiderations

From: <[email-masked]>
Date: Thu, 1 Jun 2006 14:57:49 -0400

Doug,
Just so that I can understand clearly,
TLD offers signing ability to those who don't want to develop or buy
their own. 
So bar.com offers to sign for [email-masked]
However by bringing cetificated messages frm [email-masked] you are assigning
a reputation to that signature that DKIM presents. That is not a valid
assumption as plenty of bar.com's for a fee would be happy to sign for
any spammer that shows up with cash. This is inevitable.

Bill Oxley 
Messaging Engineer 
Cox Communications, Inc. 
Alpharetta GA 
404-847-6397 
[email-masked] 

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]] On Behalf Of Douglas Otis
Sent: Thursday, June 01, 2006 2:44 PM
To: william(at)elan.net
Cc: IETF-DKIM
Subject: Re: [ietf-dkim] draft-ietf-dkim-base-02 // Parent signing
securityconsiderations

On Jun 1, 2006, at 11:33 AM, william(at)elan.net wrote:

>
> On Thu, 1 Jun 2006, Douglas Otis wrote:
>
>> There should be a security consideration mentioning an unintended  
>> consequence when a different entity controls sub-domains of a high  
>> level domain.  This could be viewed as an ICANN, ARIN, APNIC,  
>> LACNIC, AfricNIC, RIPE NCC,
>
> Could you explain what the ip registries (ARIN, APNIC, LACNIC,  
> AfriNIC,
> RIPE) have to do with domain-based authentication protocol?
>
> Note: they do indirectly if somebody hijacks ip address of dns  
> server, but
> the what Doug is talking about does not seem to be it.

The current obligations are strictly related to domain delegations,  
as you suggest.  However DKIM introduces new business opportunities  
for these organizations.  Only regulatory bodies would be in a  
position to establish any requisite limitations regarding the use of  
sub-domains as related to DKIM within their domain.

Parent signing introduces currently non-existent contractual  
obligations and liabilities related to the publishing of DKIM keys.   
Simple prohibition of any such publishing by global and regional  
Internet Registries would be the simplest solution.  Whether these  
organizations view publishing DKIM keys within their prerogative may  
depend upon whether there is a business model that exploits their  
control of domains considered authoritative for all email-addresses  
below this domain.

Speculating on the possible business model, outbound SMTP services  
could be offered to those able to authenticates with a certificate  
from a recognized CA that identifies their email-address, for  
example.  These messages could then be signed by the TLD domain where  
the i= parameter would indicate the identity found within the  
certificate.  These TLD signed messages could then be considered an  
elite assurance that the message will not be abusive.  The location  
of these keys however introduces the possibility of catastrophic  
failure which should involve regulatory oversight.

-Doug
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---

From: Douglas Otis <[email-masked]>
Date: Thu, 1 Jun 2006 12:28:28 -0700

On Jun 1, 2006, at 11:57 AM, <[email-masked]>  
<[email-masked]> wrote:
>
> Just so that I can understand clearly, TLD offers signing ability  
> to those who don't want to develop or buy their own.
>

No.

Imagine a TLD wants to promote use of certificates for exchanging  
emails.  These outbound services could only be used for email- 
addresses within their domain for the email-address to be marked as  
verified (included within the i= parameter).  A TLD of .foo could  
sign a message that validates any email-address within the foo  
domain.  This could be [email-masked] that uses a signature  
with i=[email-masked] d=foo.

> However by bringing cetificated messages frm [email-masked] you are  
> assigning a reputation to that signature that DKIM presents.

Assume DKIM becomes the more widely adopted convention used for  
verifying signed messages.  The certificate would be used only to  
gain access to the TLD's outbound servers.  Reputation would likely  
be based upon the foo signing domain, as you seem to be suggesting.

It is unlikely a reputation service will create reputations for  
individual email-addresses.  The basis for identifying a culpable  
entity seems too weak to risk possible litigation.  Reputation  
services may report specific messages to the signing domain for  
confirmation and resolution.  (The Opaque-Identifier revocation  
option was intended to provide a scalable and timely method for  
curtailing abuse of this type.)

Contrary to the base draft claim of relying upon the email-address,  
receivers are more likely to focus upon the signing domain with  
respect to messages acceptance.  Aggregating more email-addresses  
behind a common signing domain introduces the issue of greater  
collateral blocking.  Although parent signing will simplify the  
handling of email-addresses received with wildcard MX records, this  
convenience for the transmitter increases the burden on the  
receiver.  This added burden for the receiver is highly counter  
productive when abating abuse.

> That is not a valid assumption as plenty of bar.com's for a fee  
> would be happy to sign for any spammer that shows up with cash.  
> This is inevitable.

Agreed.  It makes the TLD and CA money, while also introducing  
conflicts with respect to who is really authoritative.  Many criminal  
spammers already hide by utilizing shared resources.  Allowing the  
parent to be authoritative will also increase the number of these  
shared hiding places. : (

-Doug