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RE: ISSUE-130 (Trust Anchors): Trust Anchor Consistency Across Devices? [Techniques]

From: Luis Barriga <luis.barriga@ericsson.com>
Date: Fri, 2 Nov 2007 16:43:46 +0100
Message-ID: <1C6A13C92F510849B72272A71F9F3BCB021AAE8D@esealmw105.eemea.ericsson.se>
To: "Johnathan Nightingale" <johnath@mozilla.com>, "W3C WSC Public" <public-wsc-wg@w3.org>

The email discussions seemed to indicate the need for some sort of
non-normative recommendation. I'm afraid the we have discovered an
important issue that if dropped will remain unknown/unaddressed. The
least we could do is to raise it.

So, I agree with your proposed text raises the issue and encourages some
good practice. I would slightly rephrase it while keeping the essence:

> Web site owners operating https sites should anticipate the use of 
> those sites from mobile platforms 

We should also cover not only desktop vs phone, but even phone vs.
Phone, i.e. Web site owners operating mobile-adapted https sites.

>> which may have reduced cryptography abilities
                          ^^^^^^^^^^^^
[luis] it's more that crypto abilities, e.g. memory >> device
capabilities 

> These limitations can usually be addressed in ways that 
> preserve security without hurting the user experience on either 
> platform.  Web site owners should test the security features of their 
> site on mobile platforms, and work with their certificate provider to
                                                ^^^^^^^^^^^^^^^^^^^^ 

[luis] It could more than one certificate providers and 
       probably even trust anchor providers

> implement solutions to any problems, rather than reverting to an 
> insecure state, or blocking mobile access.

[luis] The situation today is that the user has to make the trust
decisions. 

Thus, the reformulated text would be

> Web site owners operating TLS-protected sites should anticipate the
use of 
> those sites from mobile devices which may have contrained
capabilities.
> Even mobile-adapted TLS-protected sites can be accessed from a wide
range
> of mobile devices with differing device capabilities.
> These limitations can usually be addressed in ways that 
> preserve security without hurting the user experience on either 
> device. Web site owners should test the TLS security and trust
features of
> their site on mobile devices, and work with their certificate and
trust anchor
> providers to implement solutions to any problems, rather than
reverting to an 
> insecure state, blocking mobile access, or leaving trust decisions to
the user.


-----Original Message-----
From: Johnathan Nightingale [mailto:johnath@mozilla.com] 
Sent: den 2 november 2007 15:17
To: W3C WSC Public; Luis Barriga
Subject: Re: ISSUE-130 (Trust Anchors): Trust Anchor Consistency Across
Devices? [Techniques]

On 31-Oct-07, at 11:55 AM, Luis Barriga wrote:

> Here is a summary of the discussions
>
> Issues:
> - Disjoint browsers' trust anchors in across devices
> - Non TLS-consistency mobile and desktop versions of the same web site
>
> Possible reasons
> - Memory limitatios in handled devices
> - Policy made by whoeever decide on trust anchors
> - Regional policies - some CA's are better trusted in some countries
>
> Discussed so far
> - Common set of anchors is a panacea
> - Most agree that recommendation makes sense but not normative
> - Need to agree what the recommendation would be and for whom

Thank you for the summary Luis, I think it captures things nicely.

I would point out that there are other limitations at work, notably
crypto stacks on mobile devices which don't support certain PKI  
complexities (e.g. multiple signing chains, large key sizes).   
Combined with the memory limitations you mention, they do seem to argue
that a complete cross-platform solution is out of reach at the moment.

> Proposal for recommendation

I don't want to speak in negatives, but I do have concerns with us
recommending some of these things.  I'll answer point-by-point:

> For Web Owners
> - Ensure that cert is signed by CA with wide coverage (?)
> - TLS consistency across handled and desktop versions

The good news is that I think web owners already have strong incentives
(stronger even than standards compliance! :) to use broadly deployed CAs
if they want their user experience to not be beset by nag dialogs or
error pages in modern (desktop) browsers.

Recommending that, though, seems sort of contrary to w3c principles
about openness, since it seems like a recommendation to go with
entrenched players, or at least a recommendation *against* any grass
roots "we're all going to use cacert.org until the browsers are forced
to let them in!" style web activism.  I don't know if that's a realistic
scenario or not, but I do feel that we should be careful if we seem to
be recommending against decentralized "innovation at the edges."

Consistency across handheld and desktop versions can bite you too -
maybe the best way to eliminate dialog fatigue and provide a secure
interaction for users is to deliberately diverge - to use a stronger key
or more modern protocol enhancements (e.g. OCSP with stapling) on
platforms that can handle it, but fall back to something passably good
(e.g. a vanilla, 1024-bit CA-signed key without active revocation
checking) on mobile.  Does recommending TLS consistency help here, or am
I misunderstanding the point?

> For standards org
> - Need for a protocol to manage trust anchors. Could be IETF, XKMS 
> ....

I don't think we include recommendations for other standards bodies as
part of our official work, but I might be mistaken, and certainly have
no objection to someone like the IETF working on a way to facilitate
TA-management.

> For Handled vendors
> - Allow adding trust-anchor online
> - ???

s/Handled/Handheld/?  In either event - desktop user agents do currently
support adding trust anchors but, if anything, I think we make it too
easy - point at a CA-cert url, click away some dialog boxes and you're
done.

I see from the minutes that there were a couple people proposing that
this recommendation be dropped.  If there were a way to write these
recommendations to expressly address the problem of dialog-fatigue, of
mixed messages, I think some aspect could be a reasonable
recommendation.  Maybe just a Web Author Best Practice that read
something like:

> Web site owners operating https sites should anticipate the use of 
> those sites from mobile platforms which may have reduced cryptography 
> abilities.  These limitations can usually be addressed in ways that 
> preserve security without hurting the user experience on either 
> platform.  Web site owners should test the security features of their 
> site on mobile platforms, and work with their certificate provider to 
> implement solutions to any problems, rather than reverting to an 
> insecure state, or blocking mobile access.

Is this too weak to be meaningful?  My hope is that most site operators
are not actively mobile-hostile, they just don't consider it in their QA
process, nor do they know how to cope with problems that may arise.  A
diligent admin (I think only the diligent ones would be reading our
recommendations anyhow) reading this might realize the oversight, do the
testing and, in case of problems, have some option for mitigation.

Cheers,

Johnathan

---
Johnathan Nightingale
Human Shield
johnath@mozilla.com
Received on Friday, 2 November 2007 15:44:03 GMT

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