Re: [dmarc-ietf] WGLC ARC-16 concern on Section 5.1.2 - cv=fail should sign greedily

[Seth Blank <[e-mail]>]

On Fri, Jul 27, 2018 at 08:24 Murray S. Kucherawy <[e-mail]>
wrote:

>  covering the ARC header fields in the failing chain, all the data in the
>> failed chain can be modified as it is not covered under the latest
>> signature.
>>
>
> I think it's weird that the body of content that gets hashed by the sealer
> in this case varies from what would normally happen.  A verifier might have
> to try two different verification algorithms if, for example, it doesn't
> determine that the chain is structurally invalid.
>
> If I receive a chain that was apparently valid at the last sealer and
> determine that it is no longer so, could we simply decline to re-seal it at
> all?
>
> -MSK
>
The verification algorithm is straightforward. If you receive a chain that
ends with cv=fail stop your evaluation, you’re done. There’s no separate
validation path here.

Additionally, I worry about the security implications of passing along a
known bad chain without terminating it. Right now, worst case, one
intermediary needs to evaluate and terminate a maliciously formed chain. If
it’s simply not Sealed, then everyone in the path must perform the
evaluation. I don’t know what new vectors this opens up, but I could
foresee some cascading issues.