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

Seth Blank <seth@sethblank.com> Fri, 27 July 2018 17:29 UTC

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From: Seth Blank <seth@sethblank.com>
Date: Fri, 27 Jul 2018 10:29:26 -0700
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Subject: Re: [dmarc-ietf] WGLC ARC-16 concern on Section 5.1.2 - cv=fail should sign greedily
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On Fri, Jul 27, 2018 at 10:21 AM, Murray S. Kucherawy <superuser@gmail.com>
wrote:

> On Fri, Jul 27, 2018 at 8:35 AM, Seth Blank <seth@sethblank.com> wrote:
>
>> 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.
>>
>
> Then why bother signing anything when you affix "cv=fail"?
>

Because adding your ARC Seal over the chain guarantees that the receiver
has a complete list of everyone who modified the message up until the
failure. Without this signature any failures cannot be localized, and any
ARC data in a failed chain could not be trusted. This data is crucial for
analysis, understanding the experiment, and reporting back accurate and
untampered information.

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