| CBOR Working Group | M. Jones |
| Internet-Draft | A. Nadalin |
| Intended status: Standards Track | Microsoft |
| Expires: January 2, 2021 | J. Richter |
| pdv Financial Software GmbH | |
| July 1, 2020 |
Concise Binary Object Representation (CBOR) Tags for Date
draft-ietf-cbor-date-tag-03
The Concise Binary Object Representation (CBOR, RFC 7049) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation.
In CBOR, one point of extensibility is the definition of CBOR tags. RFC 7049 defines two tags for time: CBOR tag 0 (RFC 3339 date/time string) and tag 1 (Posix "seconds since the epoch"). Since then, additional requirements have become known. This specification defines a CBOR tag for an RFC 3339 date text string, for applications needing a textual date representation without a time. It also defines a CBOR tag for days since the Posix epoch, for applications needing a numeric date representation without a time. These tags are both for representations of calendar dates. It is intended as the reference document for the IANA registration of the CBOR tags defined.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 2, 2021.
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The Concise Binary Object Representation (CBOR) [RFC7049] provides for the interchange of structured data without a requirement for a pre-agreed schema. RFC 7049 defines a basic set of data types, as well as a tagging mechanism that enables extending the set of data types supported via an IANA registry.
This specification defines a CBOR tag for a text string representing a date without a time. The tagged text string is represented as specified by the RFC 3339 [RFC3339] full-date production.
This specification also defines a CBOR tag for an integer representing a date without a time. The tagged integer is an unsigned or negative value indicating the number of days since the IEEE Std 1003.1, 2013 Edition epoch date 1970-01-01. As an implementation note, this value has a constant offset from the Modified Julian Date value (which is defined by the Smithsonian Astrophysical Observatory as the number of days since November 17, 1858); this value is the Modified Julian Date minus 40,587.
Note that since both tags are for dates without times, time zones and leap seconds are not applicable to these values. These tags are both for representations of calendar dates.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
This section registers the following values in the IANA "Concise Binary Object Representation (CBOR) Tags" registry [IANA.cbor-tags].
The security considerations of RFC 7049 apply; the tags introduced here are not expected to raise security considerations beyond those.
A date, of course, has significant security considerations; these include the exploitation of ambiguities where the date is security relevant or where the date is used in access control decisions. When using a calendar date for decision making, for example access control, it needs to be noted that since calendar dates do not represent a specific point in time, the results of the evaluation can differ depending upon where the decision is made. For instance, a person may have reached their 21st birthday in Japan while simultaneously being a day short of their 21st birthday in Hawaii.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC3339] | Klyne, G. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002. |
| [RFC7049] | Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, October 2013. |
| [RFC8174] | Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017. |
| [IANA.cbor-tags] | IANA, "Concise Binary Object Representation (CBOR) Tags" |
| [POSIX.1] | IEEE, "The Open Group Base Specifications Issue 7", IEEE Std 1003.1, 2013 Edition, 2013. |
Thanks to Carsten Bormann for supporting creation of this specification. Parts of the explanatory text in this specification come from draft-bormann-cbor-time-tag-02.
Thanks to these people for reviews of the specification: Henk Birkholz, Carsten Bormann, Thiago Macieira, Michael Richardson, Jim Schaad, Juergen Schoenwaelder, and Dale Worley.
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