[cabfpub] More changes to proposed policy update

[王文正]

Rob,

Believe it or not. Even the Name Constraints extension is marked non-critical, there still exist dumb clients that will explode when encountering it.
Dumb clients might explode simply because they never saw this kind of extensions rather than because they are marked critical.
In that situations, what can you do?

Currently, if major browsers/operating systems all can live peacefully with "Critical" Name Constraints extensions, why bother making the BR inconsistent with RFC5280?

Wen-Cheng Wang

________________________________
From: Rob Stradling [rob.stradling at comodo.com]
Sent: Friday, May 25, 2012 9:56 PM
To: 王文正
Cc: Ryan Hurst; Steve Roylance; 'Chris Palmer'; public at cabforum.org
Subject: Re: [cabfpub] More changes to proposed policy update

On 25/05/12 14:41, 王文正 wrote:
<snip>
 > On the contrary, I think marking the Name Constraints extension
 > critical is the way to provide the motive power. If dumb clients
 > explode, their users will ask the implementers to support it.

I don't think that that is what would happen.  I think the actual
scenario would be closer to this...

Dumb client explodes when encountering a Critical Name Constraints
extension.  User complains to the Certificate Holder that the
certificate is broken.  Certificate Holder complains to the CA.  CA
blames the dumb client software, but neither the Certificate Holder nor
the User accepts this explanation (even though the explanation is
correct!)  Certificate Holder asks for a refund and then obtains a new
certificate from a different CA that doesn't use the Name Constraints
extension.  Very quickly every CA realizes that it is not commercially
viable to use Critical Name Constraints.  Back to square one.

On 25/05/12 14:41, 王文正 wrote:
> Dear Rob, Steve, Ryan and Chris,
>
> Thank you all for your patience in explain your logic.
>
> Now I understand your rationale goes like this: If we turn the Name Constraints extension into an 'informative' extension first by marking it non-critical, hopefully it will become a real constraint-type extension in the end.
>
> Making it as an informative extension is better than nothing. Maybe you are right. However, my guess is it will stay as an informative extension forever. I do not believe allowing the non-critical Name Constraints extension can help pushing the world to reach the desired end state (I mean all clients become supporting the critical Name Constraints extension.). Since it is non-critical, it will not provide the motive power to push those dumb clients to change themselves because they can simply ignore it. On the contrary, I think marking the Name Constraints extension critical is the way to provide the motive power. If dumb clients explode, their users will ask the implementers to support it. Otherwise, the users will switch to more smart clients. I do understand that if we goes this way, the process to reach the desired end state might be bloody. If your goal is to reach the desired end state, this is the way that can really accelerate the process.
>
> If the forum finally decide to approve the motion of allowing non-critical Name Constraints extension, then we should ask ourselves a question: when will we turn back to change the BR to require marking the Name Constraints extension as critical? Until 100% of clients become smart? Or 95% (whatever) is acceptable? Can we really reach the so-called "desired end state" in this way?
>
> Wen-Cheng Wang
>
> -----Original Message-----
> From: Rob Stradling [mailto:rob.stradling at comodo.com]
> Sent: Friday, May 25, 2012 7:12 PM
> To: 王文正
> Cc: Ryan Hurst; 'Chris Palmer'; public at cabforum.org
> Subject: Re: [cabfpub] More changes to proposed policy update
>
> On 25/05/12 11:43, 王文正 wrote:
>> I do not get the logic here.
>
> I think Ryan's post explained the logic clearly and succinctly.
>
> You're looking only at the "desired end state".  Please consider the "transition problem".
>
> Security versus Usability.  If we can't ever Use it in practice, we won't ever benefit from the Security it offers.
>
> Today, Critical Name Constraints are considered undeployable by many CAs, because too much relying party software would break.  Therefore, using the Name Constraints extension _at all_ is not an option for us.
>
> Non-critical Name Constraints are better than No Name Constraints!
>
> The "desired end state" is...
> 1. Name Constraints always Critical.
> 2. Name Constraints actually used!
>
> If you can suggest an alternative way to solve the "transition problem"
> so that we can reach the "desired end state", we would love to hear it!
>
> Nobody is suggesting that CAs should be prohibited from setting the Name Constraints extension to Critical.  All we are saying is that CAs should be allowed to use non-critical Name Constraints instead of No Name Constraints at all.
>
>> Since the purpose of adding the Name Constraints extension is to technically constrain the name space the externally-operated subordinate CA is allowed to issue subsequent certificates, I do not see how this purpose can be accomplished if we allow clients to ignore the Name Constraints extension (by marking it non-critical).
>>
>> To those smart clients, marking the Name Constraints extension critical cause no problem because that extension is recognized. To those dumb clients, if they do not understand the meaning of the Name Constraints extension, it is dangerous for them to blindly accept the certificate. It comes naturally that those dumb clients should reject constrained certificate they do not understand. I do not see why allowing clients to blindly accept certificates which may be out of the allowed name space can materially reduce the risk of those that rely on us.
>>
>> I do not oppose the use of the Name Constraints extension, but I want that extension to be used in the correct way.
>>
>> Wen-Cheng Wang
>>
>> -----Original Message-----
>> From: Ryan Hurst [mailto:ryan.hurst at globalsign.com]
>> Sent: Friday, May 25, 2012 6:15 AM
>> To: 'Chris Palmer'; 王文正
>> Cc: public at cabforum.org
>> Subject: RE: [cabfpub] More changes to proposed policy update
>>
>> I agree with Chris and others on this topic.
>>
>> The intent of a standard is to document the desired end state, only sometimes do they bother themselves with the transition problem (which is why so many never really get fully deployed IMHO).
>>
>> In this case the only downside of doing this is not complying with a clause in some document, the upside is materially reducing the risk of those that rely on us.
>>
>> We are actively moving our customers to this model.
>>
>> Ryan
>>
>> -----Original Message-----
>> From: public-bounces at cabforum.org [mailto:public-bounces at cabforum.org]
>> On Behalf Of Chris Palmer
>> Sent: Thursday, May 24, 2012 1:38 PM
>> To: 王文正
>> Cc: public at cabforum.org
>> Subject: Re: [cabfpub] More changes to proposed policy update
>>
>> On Thu, May 24, 2012 at 6:42 AM, 王文正<wcwang at cht.com.tw>   wrote:
>>
>>> For the criticality of the Name Constraints extension, the text in
>>> the ITU-T X.509 standard reads "It is recommended that it be flagged critical; otherwise, a certificate user may not check that subsequent certificates in a certification path are located in the constrained name spaces intended by the issuing CA."
>>
>> Sure, but otherwise-acceptable certificate chains fail in some clients when the client sees critical fields it doesn't understand. That effectively stops us from deploying name-constrained certificates without an Internet Flag Day where everyone fixes their clients. Since that is not going to happen, the way to get incremental improvement is to allow non-critical name constraints, and for the vendors of smart clients to enforce them where present.
>>
>> That is, to smart clients they will be effectively critical, but dumb clients at least won't explode. That's not ideal, but it is significantly Better Than Nothing. Name constraints are so wonderfully good that it's still very nice to get their benefits in some clients, even if not in all clients.
>>
>> So Google would most likely vote for it and implement it.
>>
>>
>> --
>> If it's not safe, is it really usable?
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>
> --
> Rob Stradling
> Senior Research&  Development Scientist
> COMODO - Creating Trust Online
> Office Tel: +44.(0)1274.730505
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>
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--
Rob Stradling
Senior Research & Development Scientist
COMODO - Creating Trust Online
Office Tel: +44.(0)1274.730505
Office Fax: +44.(0)1274.730909
www.comodo.com<http://www.comodo.com/>

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   3rd Floor, 26 Office Village, Exchange Quay,
   Trafford Road, Salford, Manchester M5 3EQ

This e-mail and any files transmitted with it are confidential and
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