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

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

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.

...Mark​