W3C home > Mailing lists > Public > public-webcrypto@w3.org > June 2012

Re: ECC vs RSA, and Similar Conflicts

From: Ryan Sleevi <sleevi@google.com>
Date: Fri, 1 Jun 2012 10:45:39 -0700
Message-ID: <CACvaWva67n=7RuGFzq9duD6uC9WPNx5ZPwyChCWpZ3jTkOrAEA@mail.gmail.com>
To: Seetharama Rao Durbha <S.Durbha@cablelabs.com>
Cc: "Da Cruz Pinto, Juan M" <juan.m.da.cruz.pinto@intel.com>, David McGrew <mcgrew@cisco.com>, "Richard L. Barnes" <rbarnes@bbn.com>, Eric Rescorla <ekr@rtfm.com>, Anil Saldhana <Anil.Saldhana@redhat.com>, "public-webcrypto@w3.org" <public-webcrypto@w3.org>
On Fri, Jun 1, 2012 at 8:45 AM, Seetharama Rao Durbha <
S.Durbha@cablelabs.com> wrote:

>
> I am not completely convinced how PKCS#11 is applicable to a JavaScript
> Crypto API provided by a browser.
>
> In case of PKCS#11 usage, keys are built-in through a trusted mechanism
> (manufacturing time or through a
> trusted process). In case of browser, keys are not built-in, and there is
> no way to get the keys into a browser in a way that the server can trust.
> Put another way, the ultimate beneficiary of any assurance we can provide
> on the browser side, is actually the server, so that the server can be
> assured that a client key is secure and not compromised, thus allow access
> to some services exposed by the server.
>

I don't think this is an accurate characterization of PKCS#11. While
PKCS#11 certainly permits pre-provisioned keys, I don't think that's the
only use case. Certainly, at it's core, it's an extensible crypto API,
allowing both implementations and mechanisms to be plugged in.

It's certainly not the only one - again, CDSA/CSSM and CryptoAPI/CNG are
two other examples of APIs that are both modular and extensible. The
advantage PKCS#11 has here is that it's not directly tied to the platform,
unlike


>
> But given the nature of HTTP and web, I am not sure server can be given
> that assurance. Take two cases - one where I have developed very secure
> implementation of a JS using the crypto API. Another where I am a rogue
> client that will mimic whatever the JS will do (including any user
> authentication). In the first case, my keys are secure in the browser, and
> in the second case, my keys are known to my rogue client. The question is
> how can the server be assured that one client is based on a secure browser
> implementation and the other is not?
>
> Also, as more and more services are exposed as web services, there is a
> need to support multiple client types (browser as well as custom client).
>

And I don't think we necessarily want to support this use case, at least
not in any FPWD. Key attestation (that a key really is stored in a
particular module) is orthogonal to providing a crypto API, and while
useful for crypto *systems *(such as GlobalPlatform), it's not necessary to
actually build a useful API.

In short - the server cannot have any assurances of secure browser, secret
keys, or anything like that. However, that doesn't prohibit using opaque
keys / key handles / non-exportable keys on the client - it's just that
it's a client protection mechanism, not a server protection mechanism.


>
>
> Consider a related case - installing certificates in the browser. There is
> no secret sauce to the protocol, thus any custom client (not a browser)
> can mimic the browser. The assurance to the server does not actually come
> from technology, per se, but from the user - user is expected to treat
> this certificate as securely as possible, otherwise, it is their account
> that will get compromised.
>
>
> Seetharama
>
> On 5/30/12 1:06 PM, "Da Cruz Pinto, Juan M"
> <juan.m.da.cruz.pinto@intel.com> wrote:
>
> >Keep in mind that PKCS#11 defines an API for accessing crypto operations,
> >one which does not require the caller to have direct access to key
> >material. For instance, most HSM (Hardware Security Modules) vendors
> >provide a PKCS#11 library for developers to integrate with.
> >
> >This means that if you are using a PKCS#11 module, then you don't really
> >need to have safe/unsafe sections of the API when using ,e.g., RSA.
> >Moreover, if you are using a smartcard thru a PKCS#11 module, then you
> >most probably will not be able to access the key material at all.
> >
> >Developers try to avoid manipulating private key material in code for
> >several reasons (it's difficult, security concerns, etc.). Developers
> >might need to access public key material (e.g. in cases where they might
> >need to package signatures and certificates in custom protocols), but not
> >typically private key material.
> >
> >Marcelo.
> >
> >-----Original Message-----
> >From: David McGrew [mailto:mcgrew@cisco.com]
> >Sent: Tuesday, May 29, 2012 17:55
> >To: Richard L. Barnes
> >Cc: Eric Rescorla; Anil Saldhana; public-webcrypto@w3.org
> >Subject: Re: ECC vs RSA, and Similar Conflicts
> >
> >Hi Richard,
> >
> >On May 25, 2012, at 3:39 PM, Richard L. Barnes wrote:
> >
> >> How about this as a compromise:  Split the API into two halves, safe
> >>and unsafe.  The safe methods preserve key isolation, have been reviewed
> >>by Dan, etc.  The unsafe methods might leak key material.
> >>
> >
> >I think this dichotomy makes sense.   It seems technically feasible, and
> >as a direction it allows the development of both safe and unsafe APIs in
> >parallel.
> >
> >Disclaimer: I am not an expert in API security.  It would be good to hear
> >from someone who has been analyzing PKCS#11.
> >
> >David
> >
> >> You can imagine a couple of ways this could be useful...
> >> -- Browsers through big red flags when an app tries to use unsafe
> >> stuff (especially if JS arrived over HTTP)
> >> -- Web sites could publish over HTTPS a manifest of whether they
> >> intend to be safe/unsafe
> >> -- Code/security reviews could focus on unsafe sections of the API
> >>
> >> At the very least, if we enforce the discipline of marking methods as
> >>safe or not, then it allows us to move ahead with the API, optionally
> >>kicking out the unsafe methods later.
> >>
> >> --Richard
> >>
> >>
> >>
> >>
> >> On May 22, 2012, at 11:54 AM, Eric Rescorla wrote:
> >>
> >>> On Tue, May 22, 2012 at 2:23 AM, David McGrew <mcgrew@cisco.com>
> wrote:
> >>>> On May 10, 2012, at 10:36 AM, Anil Saldhana wrote:
> >>>>
> >>>>> Giving direct access to private keys to the JS api is trouble.
> >>>>>
> >>>>> I support David's thoughts on just allowing references to IDs of
> >>>>>Private Keys.
> >>>>
> >>>> +1
> >>>>
> >>>> It will also be important that the API itself not allow
> >>>> manipulations of the secret and private keys that allow an attacker
> >>>> to cause one of those keys to be revealed by executing a (possibly
> >>>> convoluted) sequence of operations on it, as has been shown to be
> >>>> the case for PKCS#11 (see for instance
> >>>> <http://www.lsv.ens-cachan.fr/~steel/pkcs11/>)
> >>>
> >>> David,
> >>>
> >>> I think this is actually an argument *against* key isolation.
> >>>
> >>> As soon as protecting the keys becomes a system invariant, then the
> >>> introduction of any new API call requires extensive cryptographic
> >>> review. As I've been putting it lately, "every time you want to add a
> >>> new API point, you need to call Dan Boneh".
> >>>
> >>> This isn't to say that there is no use for key isolation, but that
> >>> making it a security guarantee of the system is quite expensive in
> >>> terms of design cost.
> >>>
> >>> -Ekr
> >>>
> >>
> >
> >
> >
> >
>
>
>
Received on Friday, 1 June 2012 17:46:10 GMT

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