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

Re: ACTION-22: Key export

From: Ryan Sleevi <sleevi@google.com>
Date: Mon, 13 Aug 2012 15:10:47 -0700
Message-ID: <CACvaWvZvJu5gk-YMW2fuKOqPBQveXwszskoKs_K6YbkFqjz_aQ@mail.gmail.com>
To: Vijay Bharadwaj <Vijay.Bharadwaj@microsoft.com>
Cc: "public-webcrypto@w3.org" <public-webcrypto@w3.org>
On Mon, Aug 13, 2012 at 7:54 AM, Vijay Bharadwaj
<Vijay.Bharadwaj@microsoft.com> wrote:
> Weve gone around on this a few times, including at the f2f, so here is a
> concrete proposal. Im trying to find a balance between extensibility and
> not loading up the API with a bunch of stuff, so feedback is welcome.
>
>
>
> I see the following use cases for key import/export:
>
> -          Create session key object from derived key bytes (using either
> KDF or secret agreement): this would require raw key import
>
> -          Create key object from public key received from peer (for
> asymmetric encryption or signature verification): this would require public
> key import, where the public key is likely ASN.1 encoded in many apps
>
> -          Export/import (wrapped) content encryption key for data
> encryption: this could be just the wrapped key or something like a PKCS#7
> RecipientInfo (which is ASN.1 encoded). Import/export requires a handle to
> the wrapping key.
>
> -          Export/import of private keys for distribution, with formats like
> PKCS#8.
>
>
>
> From an API perspective, supporting export seems to be straightforward. The
> Key object needs an export (or wrap) method, which takes a target format and
> potentially a wrapping key as parameters.
>
>
>
> It seems to me there are two API models to support import. Either have an
> ability to create an empty Key object, then invoke an import method on that
> object, or make it part of the construction of the Key object. I propose the
> latter, so that we dont complicate the state model of the Key object.
>
>
>
> So in WebIDL,
>
>
>
> interface Crypto {
>
>
>
>  other stuff 
>
>
>
> KeyGenerator importKey(DOMString format, ArrayBuffer keyBlob, optional Key
> wrappingKey=null);
>
> }
>
>
>
> interface Key {
>
>
>
>  other stuff 
>
>
>
> KeyExporter exportKey(DOMString format, optional Key wrappingKey=null);
>
> }
>
>
>
> Where KeyExporter is exactly like KeyGenerator but returns a value instead
> of a Key object.
>
>
>
> One big issue is what key formats should be supported. For symmetric keys it
> makes sense to support a raw format, but for asymmetric keys things are more
> complex. As has been brought up on other threads, many commonly-used formats
> are ASN.1 based and so it seems like supporting that would really help
> interoperability. However, Id like to avoid a repeat of the mandatory
> algorithms discussion. Any ideas here are welcome.

Hi Vijay,

Thanks for writing this up. A few questions:

1) What do you imagine the "Format" to contain? Something like "ASN.1"
vs "JOSE"? Some registered mime type? Something else entirely?

2) With key wrapping, you're only taking a key - so what algorithm is
being used for key wrap? It would seem that for key wrap/unwrap, a
full AlgorithmIdentifier specification would be needed here.

3) The asymmetry of the API seems rather unfortunate
(crypto.importKey, key.exportKey). I'm wondering whether it makes more
sense to have them both on the crypto interface. This would mean
key.exportKey takes a key as an input parameter, but has the advantage
of symmetry with the other 'primitive' operations (en/decrypt,
sign/verify). What are your thoughts on this?
Received on Monday, 13 August 2012 22:11:16 UTC

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