Re: [Cbor] Benjamin Kaduk's No Objection on draft-ietf-cbor-tags-oid-06: (with COMMENT)

Carsten Bormann <cabo@tzi.org> Wed, 19 May 2021 14:32 UTC

Return-Path: <cabo@tzi.org>
X-Original-To: cbor@ietfa.amsl.com
Delivered-To: cbor@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 9BC843A1215; Wed, 19 May 2021 07:32:31 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.899
X-Spam-Level:
X-Spam-Status: No, score=-1.899 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id N5oUlRqezXN4; Wed, 19 May 2021 07:32:27 -0700 (PDT)
Received: from gabriel-vm-1.zfn.uni-bremen.de (gabriel-vm-1.zfn.uni-bremen.de [134.102.50.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id EBA343A1211; Wed, 19 May 2021 07:32:23 -0700 (PDT)
Received: from [192.168.217.118] (p548dcc89.dip0.t-ipconnect.de [84.141.204.137]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by gabriel-vm-1.zfn.uni-bremen.de (Postfix) with ESMTPSA id 4Flb1J5c0gz2xNG; Wed, 19 May 2021 16:32:20 +0200 (CEST)
Content-Type: text/plain; charset="utf-8"
Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.120.23.2.6\))
From: Carsten Bormann <cabo@tzi.org>
In-Reply-To: <F32E1CFE-D37B-438C-BABF-9139F926EDA9@tzi.org>
Date: Wed, 19 May 2021 16:32:20 +0200
Cc: The IESG <iesg@ietf.org>, draft-ietf-cbor-tags-oid@ietf.org, CBOR Working Group <cbor-chairs@ietf.org>, cbor@ietf.org, Christian Amsüss <christian@amsuess.com>
X-Mao-Original-Outgoing-Id: 643127540.392779-c21e2a7a16b346244f3d0a047df6db76
Content-Transfer-Encoding: quoted-printable
Message-Id: <90BA30C5-1F1A-446A-961D-BC89003A2746@tzi.org>
References: <161783417685.27338.2878236772630764165@ietfa.amsl.com> <F32E1CFE-D37B-438C-BABF-9139F926EDA9@tzi.org>
To: Benjamin Kaduk <kaduk@mit.edu>
X-Mailer: Apple Mail (2.3608.120.23.2.6)
Archived-At: <https://mailarchive.ietf.org/arch/msg/cbor/K7K-OqEP26OG55jx_ggyTztUg6c>
Subject: Re: [Cbor] Benjamin Kaduk's No Objection on draft-ietf-cbor-tags-oid-06: (with COMMENT)
X-BeenThere: cbor@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: "Concise Binary Object Representation \(CBOR\)" <cbor.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/cbor>, <mailto:cbor-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/cbor/>
List-Post: <mailto:cbor@ietf.org>
List-Help: <mailto:cbor-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/cbor>, <mailto:cbor-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 19 May 2021 14:32:32 -0000

On 2021-04-08, at 10:00, Carsten Bormann <cabo@tzi.org> wrote:
> 
>> Section 2
>> 
>>  Tag TBD110: tags a byte string as the [X.690] encoding of a relative
>>  object identifier (also "relative OID").  Since the encoding of each
>>  number is the same as for [RFC6256] Self-Delimiting Numeric Values
>>  (SDNVs), this tag can also be used for tagging a byte string that
>>  contains a sequence of zero or more SDNVs.
>> 
>> I did not think that CBOR was prone to reusing tag values for types that
>> are semantically different but happen to have the same binary encoding
>> rules.  Should generic SDNVs get a dedicated tag?
> 
> Relative OIDs by their nature need context to interpret them.
> The same kind of context could say that they are really SDNV sequences outside the OID mechanism.
> Saying “this is an SDNV sequence but I won’t tell you how to use it” isn’t particularly useful.
> New tags could be allocated when specific non-OID SDNV usage patterns emerge.

And, after some more discussion today in the CBOR interim today, we made a small change to make this more obvious:

https://github.com/cbor-wg/cbor-oid/commit/64af0b#diff-9c4233

 Since the encoding of each
 number is the same as for {{-sdnv}} Self-Delimiting Numeric Values
 (SDNVs), this tag can also be used for tagging a byte string that
-contains a sequence of zero or more SDNVs.
+contains a sequence of zero or more SDNVs (or a more
+application-specific tag can be created for such an application).

Thank you for bringing this up; this is clearly a detail many would have missed!

Grüße, Carsten