Re: Bug 24457 - AES-KW can only wrap a JWK key if its serialization happens to be 8*n bytes long

Does anyone have any objections to this ?


On Mon, Mar 3, 2014 at 1:15 PM, Mark Watson <watsonm@netflix.com> wrote:

> My proposal for this is to add an *informative* note to the wrapKey method
> description as follows:
>
> "Informative note: The key wrapping operations for some algorithms place
> constraints on the payload size. For example AES-KW requires the payload to
> be a multiple of 8 bytes in length and RSA-OAEP places a restriction on the
> length. For key formats that offer flexibility in serialization of a given
> key (for example JWK), implementations may choose to adapt the
> serialization to the constraints of the wrapping algorithm."
>
> ...Mark
>
>
> On Sun, Mar 2, 2014 at 4:51 AM, Richard Barnes <rlb@ipv.sx> wrote:
>
>> Yeah, no need for normative text.  It would be helpful to have a note
>> that says "Reminder: needs to be a multiple of 8 bytes long; pad as you
>> like if you need to."
>>
>>
>> On Fri, Feb 28, 2014 at 5:49 PM, Jim Schaad <ietf@augustcellars.com>wrote:
>>
>>> I agree that this is definitely NOT normative text.
>>>
>>> The only obvious place I can think of is in the generic wrapKey
>>> description
>>> for placement.
>>>
>>> I am neutral on the proposed text and it's inclusion in the document.
>>>  It is
>>> not clear to me that it will help, but on the other hand I don't believe
>>> it
>>> is harmful in anyway.
>>>
>>> Jim
>>>
>>>
>>>
>>> From: Mark Watson [mailto:watsonm@netflix.com]
>>> Sent: Friday, February 28, 2014 8:41 AM
>>> To: public-webcrypto@w3.org
>>> Subject: Bug 24457 - AES-KW can only wrap a JWK key if its serialization
>>> happens to be 8*n bytes long
>>>
>>> https://www.w3.org/Bugs/Public/show_bug.cgi?id=24457
>>>
>>> Alexey re-opened this bug with:
>>> "A WebCrypto implementation can pad JWK with spaces for AES-KW, but the
>>> same
>>> padding can destroy the ability to wrap with RSA-OAEP, because you can
>>> run
>>> out of size limit. So, any padding should be conditional on which
>>> algorithm
>>> will be used for encryption in a later step of wrapping algorithm.
>>>
>>> I think that it would be appropriate to have normative text. But even if
>>> it's simply a note, it should be:
>>> 1. Substantially more elaborate than suggested above.
>>> 2. Added as part of this bug (so it seems like the bug should remain open
>>> until the note is added)."
>>> I would suggest that any such note be non-normative:
>>> - There has been strong objection to specifying our own padding scheme
>>>
>>> - There is no _need_ for normative specification to ensure
>>> interoperability:
>>> so long as the serialization is valid JSON, we are good.
>>>
>>> A note (I am not sure where it would be) might look something like:
>>> "Note: Some algorithms used for key wrapping place constraints on the
>>> payload size. For example AES-KW requires the payload to be a multiple
>>> of 8
>>> bytes in length and RSA-OAEP places a restriction on the length. For key
>>> formats that offer flexibility in serialization of a given key (for
>>> exmaple
>>> JWK), implementations may choose to adapt the serialization to the
>>> constraints of the wrapping algorithm."
>>> Comments ?
>>> ...Mark
>>>
>>>
>>>
>>>
>>>
>>
>