Re: [core] Review of draft-fz-core-coap-pm-03

Giuseppe Fioccola <> Fri, 17 March 2023 16:13 UTC

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From: Giuseppe Fioccola <>
To: Christian Amsüss <>
CC: Marco Tiloca <>, "" <>
Thread-Topic: [core] Review of draft-fz-core-coap-pm-03
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Date: Fri, 17 Mar 2023 16:13:24 +0000
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Subject: Re: [core] Review of draft-fz-core-coap-pm-03
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Hi Christian,
Please see inline [GF]



-----Original Message-----
From: Christian Amsüss <> 
Sent: Thursday, March 16, 2023 12:54 PM
To: Giuseppe Fioccola <>
Cc: Marco Tiloca <>;
Subject: Re: [core] Review of draft-fz-core-coap-pm-03

On Fri, Mar 10, 2023 at 03:34:24PM +0000, Giuseppe Fioccola wrote:
> > * When using OSCORE, having the PM option as inner or outer does not
> I don't think that option should be Class-I. The option is hop-by-hop 
> now, and may be legitimately terminated at proxies. If it were 
> Class-I, a proxy's operation would make the requests fail.
> [GF]: Yes, in case of collaborating proxies, the option is terminated 
> at proxies and Class E is ok. But, in case of non-collaborating and 
> non-caching proxies an implementation may consider the option as 
> Safe-to-Forward in order to implement measurements. In this corner 
> case, Class-I can be considered to enable hop-by-hop.

You can't just switch around an option between Class-I and Class-U depending on details of the deployment scenario. If there is any disagreement between client and server about an option's class, encryption will fail in practically impossible-to-debug ways.

[GF]: I agree that the option must be of a specific class to avoid compatibility issues. I will remove this ambiguity in the next revision.

The benefits to using it Class-I are fringe benefits. If you want to measure both in the end-to-end stacks and enable use with proxies, just place it outer (Class-U) and inner (Class-E).

[GF]: Yes, the outer option should be of Class-U to allow the on-path measurements.

And I say that as someone who is a big fan of Class-I options.


To use raw power is to make yourself infinitely vulnerable to greater powers.
  -- Bene Gesserit axiom