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Re: [jose] [COSE] COSE/JOSE elliptic curves and their relationship with key types

Michael Richardson <mcr+ietf@sandelman.ca> Tue, 13 July 2021 16:06 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: Benjamin Kaduk <kaduk@mit.edu>, cose@ietf.org, jose@ietf.org
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Date: Tue, 13 Jul 2021 12:06:17 -0400
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Subject: Re: [jose] [COSE] COSE/JOSE elliptic curves and their relationship with key types
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Benjamin Kaduk <kaduk@mit.edu> wrote:
    >> It also seems that we might also be thinking that there might be other
    >> ways to encode the keys (into bytes), but that mostly it is the case
    >> that we have a single encoding that we stick to.

    > But for a protocol don't we kind of only want a single encoding anyway?

As the thread between Neil and Ilari shows, there were reasons to make
different choices.

My take, being intentionally not intimate with such issues, is that the best
encoding for using the key may not be the best encoding for transmitting the
key.   That the translation between the two forms might sometimes fail, and
so it's a protocol decision as to which to transmit, which to sign (in a
certificate), etc.
(And that this was the entire lwig-curves document's point)

    >> (Why did we call it "EC2". Huh)

    > I feel like I used to know this, but am drawing a blank.  Maybe that
    > there are two coordinates included?

I have always been blissfully ignorant.




--
Michael Richardson <mcr+IETF@sandelman.ca>   . o O ( IPv6 IøT consulting )
           Sandelman Software Works Inc, Ottawa and Worldwide

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