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Re: crypto-ISSUE-30 (where is the key ?): How does the application know where the key is stored ? [Web Cryptography API]

From: Ryan Sleevi <sleevi@google.com>
Date: Fri, 7 Sep 2012 11:55:35 -0700
Message-ID: <CACvaWvaJF4p-GuuLBfgpsdKM8_sUCdkVYjknyUTCrRGc8Sz5FQ@mail.gmail.com>
To: Seetharama Rao Durbha <S.Durbha@cablelabs.com>
Cc: Vijay Bharadwaj <Vijay.Bharadwaj@microsoft.com>, Lu HongQian Karen <karen.lu@gemalto.com>, Ali Asad <Asad.Ali@gemalto.com>, GALINDO Virginie <Virginie.GALINDO@gemalto.com>, "public-webcrypto@w3.org" <public-webcrypto@w3.org>
On Fri, Sep 7, 2012 at 8:02 AM, Seetharama Rao Durbha
<S.Durbha@cablelabs.com> wrote:
> On 9/7/12 12:00 AM, "Vijay Bharadwaj" <Vijay.Bharadwaj@microsoft.com> wrote:
>
>   I would like to agree with you. But that is assuming that a user has only
> one identity tied to an application  not always true. We all have multiple
> accounts with the same providers. Some identities may be stronger than
> others  the user may have some in the browser, and some in smart card(s).
>
>
>
> It does not follow that the user must be required to select keys. A
> well-designed application would present the user with a choice of
> identities, and do key selection based on that.
>
> I guess the UI for selecting keys is an altogether different topic. Yes, (as
> was also suggested by Anders Rundgren recently), the UI for selecting
> keys/identities should be different from the current nerdy interface. Thus,
> a user may not realize they are selecting a 'key' (nerdy term), they might
> just be presented with 'identities' that are tied to a key.

Just as a point of reference - such selection *MUST* be user agent
controlled, because it's about making a security decision. Exposing
the keys to the web application, in order to allow the web application
to present an interface that the user then selects which keys to
authorize for the web application, is a fundamentally flawed and
inherently insecure operation.

>
>
>
>   Whether a key is acceptable or not may not be possible to do on the
> client side, so the client-side app will have to communicate all key details
> to the back-end to determine which key is what it is looking for. Having an
> attribute on the key could help the application make choices on the
> client-side. Of course, as repeated so many times, this does not mean that
> the server does not do its own validations on the key  it still has to do
> those validations. The reason people do client-side validation of forms in
> JS is because of expediency  does not mean that server does not do those
> same checks.
>
>
>
> I think we all agree with this statement. However, it seems that youre
> using it to justify client-side checks that, almost by definition, cannot be
> repeated on the server. A server cannot possibly check what provider a key
> is stored in; its going to do cryptographic checks like looking for a
> certificate. Why not have the app do the same check on the client as well?
>
> Again, I agree with you. Yes, the same logic that the server uses can be
> used on the client side. It is just burdensome. The server will have to
> expose its different trust anchors to the client and client will have to
> iterate through each of them for each key. Again going back to form
> validations done in JS, note that JS validations are not the only
> validations the server does, the server could do many more validations. All
> of them are not implemented on the client-side.
> I guess the question is the relative merits of exposing this attribute  vs
> having the client implement trust-anchor logic.

Originally, we were talking in terms of discovery/authorization. Such
UI is necessarily *only* in the user agent, and cannot be (securely)
exposed to arbitrary web applications.

So when we say "the client well have to iterate through each of them
for each key", I think it should be clarified that we're talking about
the client being "the user agent" *not* "the web application"
Received on Friday, 7 September 2012 18:56:02 GMT

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