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Re: [Cbor] draft-ietf-cbor-tags-oid-00.txt

Carsten Bormann <cabo@tzi.org> Mon, 03 August 2020 05:38 UTC

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From: Carsten Bormann <cabo@tzi.org>
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Date: Mon, 03 Aug 2020 07:38:42 +0200
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To: "Dale R. Worley" <worley@ariadne.com>
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Subject: Re: [Cbor] draft-ietf-cbor-tags-oid-00.txt
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On 2020-08-03, at 09:23, Dale R. Worley <worley@ariadne.com> wrote:
> 
> Carsten Bormann <cabo@tzi.org> writes:
>> (Crypto) keys don't have to be much longer, see
>> https://tools.ietf.org/html/draft-mattsson-cose-cbor-cert-compress-01#appendix-A
>> for a worked example.
> 
> I don't know elliptic-curve crypto well enough to follow that, but it
> seems to me that you're going to have a hard time putting a 2048 bit key

That would be RSA.  Applications that care about certificate size today use ECC, with 256-bit keys (32 bytes).

> in less than about 256 octets, and the signature will need a similar
> number of octets.  So all overheads should be counted against a minimum
> of 512 octets of essentially binary data.

Five years ago, yes.  But now it is worth to use ECC as a yard stick.

Grüße, Carsten

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