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Re: [jose] [COSE] HPKE PartyU / PartyV

Ilari Liusvaara <ilariliusvaara@welho.com> Mon, 04 March 2024 08:40 UTC

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Date: Mon, 04 Mar 2024 10:33:03 +0200
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: JOSE WG <jose@ietf.org>, cose <cose@ietf.org>
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Subject: Re: [jose] [COSE] HPKE PartyU / PartyV
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On Sun, Mar 03, 2024 at 06:42:41PM +0000, lgl island-resort.com wrote:
>
> If you read the paragraph before you get more context and more
> understanding why there’s both. Seems more like efficiency / economy
> trade-off. You don’t really need both. There’s no security reason
> for one or the other.

With single message, it seems like a bad trade-off:

- aad is faster, as it is polymac instead of full-blown hash function.
- aad is much easier to implement without allocations, as it is not
  part of some larger structure.
- aad is trivially secure from definition of AEAD, but security of
  info does not trivially follow.

With multiple messages, there are reasons to use both, but I can not
come up with any actual reason to use info with a single message.




-Ilari

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