> On Dec 10, 2022, at 11:53 AM, Ilari Liusvaara <[email protected]>
> wrote:
>
> On Sat, Dec 10, 2022 at 09:48:04AM -0700, Laurence Lundblade wrote:
>> +1 for HPKE-v1-BASE
>>
>> Re title the draft "HPKE Base Mode for COSE” or similar because it’s
>> not a definition of all of HPKE for COSE
>>
>> Use a fixed array for the sender info that is tied to HPKE-v1-BASE.
>> If there becomes a need to change the array, then we’ll use.an
>> algorithm identifier different from HPKE-v1-BASE. For example, we
>> could have a different array for HPKE-v1-AUTH (if/when someone gets
>> around to it and there is actual need for it to be different).
>
> However, parameters with short identifers are not cheap. So if both
> are to have short parameter identifier, one needs to be able to reuse
> the same parameter for both.
>
> (The reason why my proposal was written in a bit odd way is to enable
> that sort of reuse. Yes, I realize this is a bit controversal.)
Hi Ilari,
I assume you mean registered COSE header parameters with ID’s between -24 and
24 are not cheap. Initially, we’ll only require one. I assume HPKE is important
enough that we’ll easily get one for the sender info for HPKE-v1-BASE and then
another later for HPKE-v1-AUTH if needed.
From a first glance, it looks the ID(s) should be from the COSE Header
Algorithm Parameters
<https://www.iana.org/assignments/cose/cose.xhtml#header-algorithm-parameters>
range (-1 to -65536). There are 16 free here now (-19 to -4) and HPKE is
important, so I expect little objection from experts to us using 2 if needed.
Even if we discover in a few years, we defined sender info wrong for
HPKE-v1-BASE and need a sender info v2, I think we’ll be OK. I’m also confident
we can get it right now.
And even if we can’t get the one-byte ID, a two-byte ID is only one more byte.
There are hundreds of two-byte IDs available.
Parameter IDs don't seem like a critical resource that constrains what we do
now. So, I don’t see this as a reason for making the sender info array variable.
LL
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