Hi Laurence,

When you say below that this is the code size, what exactly is included in the 
measurement?

FWIW I agree with you statement that making the KEM ID mandatory simplifies 
decoding.

Ciao
Hannes

From: COSE <[email protected]> On Behalf Of Laurence Lundblade
Sent: Thursday, December 1, 2022 11:01 PM
To: cose <[email protected]>
Subject: [COSE] Code size of Ilari's proposal vs Laurence's

x86 code bytes from rough implementations for t_cose using QCBOR:

          Laurence    Ilari  Ilari-kem-id-not-optional
Encode       141       120         115
Decode       123       194         169
Total        264       314         284

Not a very big difference. I’m fine with either.

If we take Ilari’s, I’d like the KEM ID to not be optional. It will only add 
one or two bytes to what is transmitted and it will simplify decoding. It 
probably removes some ambiguity and error conditions too.

LL


In Laurence’s, t_cose works on a linked list of parameters including HPKE 
parameters that are encoded/decoded by the already-existing parameter 
processor. For Ilari’s the CBOR decoder is called to encode/decode the array 
in/out of a COSE parameter.



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