Re: [W3C Web Crypto WG] about extensions to Web Crypto specification

On Thu, Aug 28, 2014 at 9:53 AM, Ryan Sleevi <sleevi@google.com> wrote:

>
> On Aug 28, 2014 9:43 AM, "Mark Watson" <watsonm@netflix.com> wrote:
> >
> >
> >
> >
> > On Wed, Aug 27, 2014 at 8:04 PM, Ryan Sleevi <sleevi@google.com> wrote:
> >>
> >>
> >>
> >>
> >> On Tue, Aug 26, 2014 at 7:51 AM, Mark Watson <watsonm@netflix.com>
> wrote:
> >>>
> >>>
> >>>
> >>>
> >>> On Mon, Aug 25, 2014 at 6:01 PM, Ryan Sleevi <sleevi@google.com>
> wrote:
> >>>>
> >>>>
> >>>>
> >>>>
> >>>> On Mon, Aug 25, 2014 at 5:49 PM, Mark Watson <watsonm@netflix.com>
> wrote:
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>> On Mon, Aug 25, 2014 at 5:31 PM, Ryan Sleevi <sleevi@google.com>
> wrote:
> >>>>>>
> >>>>>>
> >>>>>> On Mon, Aug 25, 2014 at 5:25 PM, Mark Watson <watsonm@netflix.com>
> wrote:
> >>>>>>>
> >>>>>>> All,
> >>>>>>>
> >>>>>>> Based on the lack of response to my questions below, I propose we
> close this issue as a "non-issue". As far as I can tell the specification
> contains all the extensibility that we need in the form of the ability to
> add additional algorithms.
> >>>>>>
> >>>>>>
> >>>>>> And what of SHA-3?
> >>>>>
> >>>>>
> >>>>> ​The various SHA flavors in the specification are already distinct
> algorithms. I don't see any problem adding more with the algorithm
> extensibility mechanism.​
> >>>>
> >>>>
> >>>> Apologies for not being clearer.
> >>>>
> >>>> How does SHA-3 work with RSA? With ECDSA? With HKDF? With Concat?
> With PBDKF2?
> >>>>
> >>>> I realize that your answer may very well be "I don't know", because
> no such thing exists as SHA-3 yet (beyond Keccak with some undefined set of
> parameters and uses).
> >>>>
> >>>> The point being that we don't know HOW interoperability will work in
> this case.
> >>>
> >>>
> >>> ​Hmm, the specification looks quite clear to me on this. For example,
> the RSA-SSA procedures say things like "Perform the signature generation
> operation defined in Section 8.2 of [RFC3447] with the key represented by
> the [[handle]] internal slot of key as the signer's private key and the
> contents of message as M and using the hash function specified in the hash
> attribute of the [[algorithm]] internal slot of key as the Hash option for
> the EMSA-PKCS1-v1_5 encoding method."
> >>> ​
> >>> ​So, supposing we had a WebCrypto algorithm specification for SHA-3,
> the phrase "​hash function specified in the hash attribute of the
> [[algorithm]] internal slot of key" would be well-defined and the question
> becomes one of whether RFC3447, Section 8.2, is clear on how this hash
> function should be used within the EMSA-PKCS1-v1_5 encoding method.
> Answering this question is clearly out of scope of WebCrypto. RSA-OAEP,
> RSA-PSS, HMAC, CONCAT, HKDF and PBKDF2 are similar.
> >>
> >>
> >> Apologies for not being clearer, as I hoped the issue would have been
> apparent.
> >>
> >> Consider both the importKey and exportKey methods of RSA-SSA -
> https://dvcs.w3.org/hg/webcrypto-api/raw-file/ee10c81e1141/spec/Overview.html#rsassa-pkcs1-operations
> >>
> >> These are certainly IN SCOPE of WebCrypto
> >>
> >> Or consider that these hash algorithms may not be valid with Concat,
> HKDF, or PBKDF2, whereas the current spec implies they are.
> >>
> >
> >
> > ​Thanks for clarifying. That your point was specific to import / export
> was not at all apparent from your original statements.
> >
> > For spki and pkcs8 the solution seems straightforward in that we should
> have the OIDs for the hash algorithms defined by the WebCrypto
> specification of the hash algorithm and then refer out to that from our
> algorithms. For example, RSA-OAEP would say
>
> I'll stop you here: That doesn't work. Or more aptly, it does not work to
> decouple the two aspects, nor does it logically fit a model of dependencies
> where the hash is an aspect of the algorithm, because you are instead
> treating the algorithm as an aspect of the hash.
>
​Do you mean that the OID to use for a given hash algorithm might be
specific to the main algorithm ?

So, then you need a specific notion of "Registered hash algorithms for
RSA-OAEP"​, where one has to explicitly register a new hash algorithm with
RSA-OAEP and in that process define the OID to be used in that context ?

Does that work ? It's a lot of complexity for an extension that is probably
some way away. I could argue that we should leave RSA-OAEP as is and if, in
future, someone wants to define RSA-OAEP-2 which includes more hash
algorithms, they can do so. That has the advantage that you know, when you
see that RSA-OAEP is supported, exactly which hash algorithms are supported.

It's why I didn't propose it to begin with.
>
> >
> > for exportKey:
> > "Set the algorithm object identifier to the OID
> > ​ ​
> > defined by the specification of the hash algorithm identified by the
> name attribute of the hash attribute of the [[algorithm]] internal slot of
> key".
> >
> > for importKey: "If the algorithm object identifier field of hashAlg is
> equivalent to an OID specified by a registered algorithm that supports the
> digest operation, Set hash to the name of that registered algorithm
> > ​.​
> > "
> >
> > ​For JWK, I see it is more difficult, because JWK combines the hash
> identifier into the algorithm name, e.g. "RSA-OAEP-256"​. If you remember I
> had advocated using lookup tables for this problem, in which case extension
> is simply a matter of saying that other specifications may extend the
> table. We could still do that or something similar, such as a notion of
> "registered JWK algorithms" with a requirement that each registered JWK
> algorithm consists of a tuple ( alg, name, params ), alg being the JWK alg
> string, name is the WebCrypto algorithm name and params is an object which,
> for the RSA-OAEP case, contains a single member, "hash", identifying the
> WebCrypto hash algorithm. Then, for RSA-OAEP:
> >
> > for exportKey: "If the name attribute of the hash attribute of the
> [[algorithm]] internal slot of key matches the hash attribute of the params
> attribute of a registered JWK algorithm with name
> > ​ attribute​
> > "RSA-OAEP",
> > ​s​
> > et the alg attribute of jwk to the alg attribute of that registered JWK
> algorithm."
> >
> > for importKey:
> > "If the alg field of jwk is equal to the alg attribute of a registered
> JWK algorithm, let hash be the hash attribute of the params attribute of
> that registered JWK algorithm."
> >
> > ​I'm happy to draft a detailed implementation of this if you like.
>
> I already explored your solution in the past, and believe its both
> inconsistent and illogical when carried out, which is why I didn't propose
> it, and why I still see the issue as existing.
>
​So, what's your alternative ?

Again, as above, we can have algorithms that are static and well-defined in
this respect and create new algorithms when we want to add more options.
This does not seem so bad since it keeps the discovery of what is supported
clean and ​simple, introduces new functionality in considered steps instead
of piecemeal and avoids an explosion on the permutations and combinations
of supported algorithms and parameters.

​This is in effect the status quo. In the absence of alternative proposals,
I suggest that's what we get.​

​...Mark​



>
> >
> > ...Mark​
> >
> >
>