Re: [Webpush] Eric Rescorla's Discuss on draft-ietf-webpush-vapid-03: (with DISCUSS and COMMENT)

Ben Campbell <ben@nostrum.com> Wed, 16 August 2017 02:31 UTC

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From: Ben Campbell <ben@nostrum.com>
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Date: Tue, 15 Aug 2017 21:31:36 -0500
Cc: Martin Thomson <martin.thomson@gmail.com>, "webpush@ietf.org" <webpush@ietf.org>, draft-ietf-webpush-vapid <draft-ietf-webpush-vapid@ietf.org>, webpush-chairs@ietf.org, The IESG <iesg@ietf.org>, Phil Sorber <sorber@apache.org>
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To: Eric Rescorla <ekr@rtfm.com>
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Subject: Re: [Webpush] Eric Rescorla's Discuss on draft-ietf-webpush-vapid-03: (with DISCUSS and COMMENT)
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> On Aug 15, 2017, at 9:04 PM, Eric Rescorla <ekr@rtfm.com>; wrote:
> 
> 
> 
>> On Tue, Aug 15, 2017 at 6:56 PM, Martin Thomson <martin.thomson@gmail.com>; wrote:
>>> On 16 August 2017 at 09:42, Eric Rescorla <ekr@rtfm.com>; wrote:
>>> > Ultimately, this is a WG decision, but given that there are designs
>>> > with much better security properties, I'd like to know that the WG
>>> > considered and rejected this kind of design alternative before
>>> > we advance the weaker design.
>>> 
>> We discussed the implications of the bearer token design and concluded
>> that this was acceptable. 
> 
> That's a much easier discussion to have without an alternative.
> 
>  
>> We didn't discuss additionally signing
>> messages in this way.  Another alternative is to describe how token
>> binding could be used to prevent token theft.
>> 
>> One complaint I get about webpush is the amount of overhead crypto
>> adds to sending messages.  Mostly from a complexity standpoint.  It's
>> a real implementation barrier.  We've forced people to jump through a
>> lot of hoops and that has made them pretty annoyed.  Deploying this as
>> a required extension could be additionally annoying, not to mention
>> incompatible with the existing deployed code.
>> 
> The flippant thing to say would be that I-Ds come with a big disclaimer
> for exactly this reason. More seriously, the future is bigger than the past
> and given that (as you observe) the vapid token is used to identify
> what you support, it seems like deploying the new thing would be
> straightforward.
> 
> I'm not terribly sympathetic to the complexity point: this is a very modest
> amount of crypto.
> 
> 
> 
>> What is nice about the specific design you describe (and my flippant
>> tokbind suggestion as well coincidentally) is that it can be
>> incrementally added to this scheme without a complete overhaul,
>> probably without even changing the scheme name, suggestions below
>> notwithstanding.
>> 
>> It could be an optional increment, if we could decide that the push
>> service doesn't require this additional protection and it was
>> primarily for the benefit of application servers.  Yes, there are
>> benefits that accrue to push services and user agents alike, but we
>> might decide that they don't gain any certainty about these benefits.
>> That suggests a second, though less satisfying, path: a new draft
>> describing the enhancement.
>> 
> I agree that that's possible, but it's kind of unsatisfying to be publishing
> a draft with this kind of known deficiency.
> 
> Maybe the chairs or ART ADs would like to weigh in here?
> 
> 

Weighing in as an irresponsible (for this draft) ART AD:

My knee jerk response is to agree with Ekr. But it’s worth discussing how big of an incompatibility with existing code people are talking about. Are there a lot of deployed services that support vapid? Do people think that existing implementors will choose not to implement/deploy the additional protection?

Ben.

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