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RE: ECC vs RSA, and Similar Conflicts

From: Da Cruz Pinto, Juan M <juan.m.da.cruz.pinto@intel.com>
Date: Wed, 30 May 2012 19:06:35 +0000
To: David McGrew <mcgrew@cisco.com>, "Richard L. Barnes" <rbarnes@bbn.com>
CC: Eric Rescorla <ekr@rtfm.com>, Anil Saldhana <Anil.Saldhana@redhat.com>, "public-webcrypto@w3.org" <public-webcrypto@w3.org>
Message-ID: <0A38A08BA24AFC4383E156B62EB0279015AEBE0D@FMSMSX107.amr.corp.intel.com>
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 Thursday, 31 May 2012 12:22:57 UTC

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