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

Christian Amsüss <> Thu, 16 March 2023 11:54 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id 1C14BC151717 for <>; Thu, 16 Mar 2023 04:54:22 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -2.599
X-Spam-Status: No, score=-2.599 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_ZEN_BLOCKED_OPENDNS=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001] autolearn=unavailable autolearn_force=no
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id PRpwYPFdF55c for <>; Thu, 16 Mar 2023 04:54:20 -0700 (PDT)
Received: from ( [IPv6:2a02:b18:500:a515::f455]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by (Postfix) with ESMTPS id 27347C1516FF for <>; Thu, 16 Mar 2023 04:54:14 -0700 (PDT)
Received: from ([IPv6:2a02:b18:c13b:8010:a800:ff:fede:b1bd]) by (8.17.1/8.17.1) with ESMTPS id 32GBrktX088875 (version=TLSv1.2 cipher=ECDHE-ECDSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 16 Mar 2023 12:53:47 +0100 (CET) (envelope-from
X-Authentication-Warning: Host [IPv6:2a02:b18:c13b:8010:a800:ff:fede:b1bd] claimed to be
Received: from ( []) by (Postfix) with ESMTP id 598A31D343; Thu, 16 Mar 2023 12:53:46 +0100 (CET)
Received: from ( []) by (Postfix) with ESMTPSA id D26861F738; Thu, 16 Mar 2023 12:53:45 +0100 (CET)
Received: (nullmailer pid 12570 invoked by uid 1000); Thu, 16 Mar 2023 11:53:44 -0000
Date: Thu, 16 Mar 2023 12:53:44 +0100
From: Christian Amsüss <>
To: Giuseppe Fioccola <>
Cc: Marco Tiloca <>, "" <>
Message-ID: <>
References: <> <> <>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="PbPN02FkXowWH80L"
Content-Disposition: inline
In-Reply-To: <>
Archived-At: <>
Subject: Re: [core] Review of draft-fz-core-coap-pm-03
X-Mailman-Version: 2.1.39
Precedence: list
List-Id: "Constrained RESTful Environments \(CoRE\) Working Group list" <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Thu, 16 Mar 2023 11:54:22 -0000

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.

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).

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