Re: [Cbor] 7049bis: The concept of "optional tagging" is not really used in practice #126
Henk Birkholz <henk.birkholz@sit.fraunhofer.de> Sun, 03 November 2019 21:07 UTC
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To: Laurence Lundblade <lgl@island-resort.com>, Carsten Bormann <cabo@tzi.org>
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From: Henk Birkholz <henk.birkholz@sit.fraunhofer.de>
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Subject: Re: [Cbor] 7049bis: The concept of "optional tagging" is not really used in practice #126
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Well there is this for starters > https://tools.ietf.org/html/rfc8610#appendix-D On 03.11.19 22:02, Laurence Lundblade wrote: > OK. I understand. To use it one of these new types in CDDL, > particularly those with a internal structure, you make a pair of CDDL > headers, one for tagged and one for untagged that describe it like COSE > did (from 8152): > > COSE_Messages = COSE_Untagged_Message / COSE_Tagged_Message > > COSE_Untagged_Message = COSE_Sign / COSE_Sign1 / > COSE_Encrypt / COSE_Encrypt0 / > COSE_Mac / COSE_Mac0 > > COSE_Tagged_Message = COSE_Sign_Tagged / COSE_Sign1_Tagged / > COSE_Encrypt_Tagged / COSE_Encrypt0_Tagged / > COSE_Mac_Tagged / COSE_Mac0_Tagged > > > .... > > > COSE_Sign1_Tagged = #6.18(COSE_Sign1) > > > COSE_Sign1 = [ > Headers, > payload : bstr / nil, > signature : bstr > ] > > > Would be cool if there were standard CDDL definitions ready for > normative reference for all the “tagged” data types defined in 7049 / > 7049bis. > > LL > > >> On Nov 3, 2019, at 8:59 AM, Carsten Bormann <cabo@tzi.org >> <mailto:cabo@tzi.org>> wrote: >> >> Hi Laurence, >> >> CDDL does not describe behavior, but the shape of data. >> >>> Maybe a key question here is whether you can say in CDDL “this next >>> item must always be interpreted as a date even though it will never >>> have a date tag”. >> >> CDDL can say “this item is a number”. It does not tell you how to >> “interpret” things, that would be the job of a language that >> transforms the data just received into data that is used by an >> application. >> >>> If CDDL doesn’t have than, then you can’t describe some >>> CBOR-protocols with it. >> >> You sure can “describe” the shape of data in CBOR protocols, but you >> will also need some information about how you plan to interpret the data. >> >>> CWT would be one of those protocols as it forbids adding the tag to >>> dates. >> >> (For the exp, nbf, and iat claims, or claim numbers 4 to 6:) Yes, the >> CWT RFC (RFC 8392) tells you that the value here is a number, not a >> tagged date. >> >>> The designer of a protocol using a new data type will indicate in >>> their protocol for each occurrence of it whether the tag must be >>> present or not (never saying the tag may or may not be present). The >>> designer will typically require the tag only when necessary to >>> disambiguate the type of the data item. >> >> Right. If you need to register for CWT a new claim that could either >> take a number (such as the longitude of the satellite that this claim >> is about) or a date/time (such as the time the satellite was >> launched), then a tag could be useful to make that distinction. >> >> That example is a bit contrived, because it’s just not as usual to >> have a choice between a number and a date. More likely might be a >> choice between a date/time represented as a Tag 1 and a Tag 1001. The >> encoding could choose to leave off the tag from the number that is the >> enclosed item of Tag 1, so you would have a choice between a number >> and a Tag 1001. >> >>> The implementor of a general purpose library to generate one of these >>> new data item types must give the caller the option to include or not >>> include the tag. Maybe this is just by never automatically outputting >>> the tag and having a distinct output tag function. >>> >>> The implementor of a general purpose library to decode one of these >>> new data types must allow the caller to say that the next data item >>> should be decoded as this new data type whether or not it is tagged. >>> Maybe it even errors out if it is tagged for the cases where the >>> protocol document says no tag should be used. >> >> Right. >> >>> What I don’t know is whether CDDL can describe all this desired behavior. >> >> CDDL can describe the shape of the data interchanged, but it can’t >> describe the mapping to application semantics. It can provide hints, >> and that’s one of the things that the unwrap operator is good for: >> When you apply it to a tag, this is a hint that you do not just want >> the data shape of that tag’d enclosed item, but also its semantics. >> >> Grüße, Carsten >> >> > > > _______________________________________________ > CBOR mailing list > CBOR@ietf.org > https://www.ietf.org/mailman/listinfo/cbor >
- [Cbor] 7049bis: The concept of "optional tagging"… Carsten Bormann
- Re: [Cbor] 7049bis: The concept of "optional tagg… Carsten Bormann
- Re: [Cbor] 7049bis: The concept of "optional tagg… Christophe Lohr
- Re: [Cbor] 7049bis: The concept of "optional tagg… Laurence Lundblade
- Re: [Cbor] 7049bis: The concept of "optional tagg… Carsten Bormann
- Re: [Cbor] 7049bis: The concept of "optional tagg… Henk Birkholz
- Re: [Cbor] 7049bis: The concept of "optional tagg… Christophe Lohr
- Re: [Cbor] 7049bis: The concept of "optional tagg… Laurence Lundblade
- Re: [Cbor] 7049bis: The concept of "optional tagg… Carsten Bormann
- Re: [Cbor] 7049bis: The concept of "optional tagg… Carsten Bormann
- Re: [Cbor] 7049bis: The concept of "optional tagg… Henk Birkholz
- Re: [Cbor] 7049bis: The concept of "optional tagg… Henk Birkholz
- Re: [Cbor] 7049bis: The concept of "optional tagg… Jim Schaad
- Re: [Cbor] 7049bis: The concept of "optional tagg… Carsten Bormann
- Re: [Cbor] 7049bis: The concept of "optional tagg… Laurence Lundblade
- Re: [Cbor] 7049bis: The concept of "optional tagg… Carsten Bormann
- Re: [Cbor] 7049bis: The concept of "optional tagg… Laurence Lundblade