Concise Binary Object Representation (CBOR) Tags for Date
RFC 8943

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Internet Engineering Task Force (IETF)                          M. Jones
Request for Comments: 8943                                     Microsoft
Category: Standards Track                                     A. Nadalin
ISSN: 2070-1721                                              Independent
                                                              J. Richter
                                             pdv Financial Software GmbH
                                                           November 2020

       Concise Binary Object Representation (CBOR) Tags for Date

Abstract

   The Concise Binary Object Representation (CBOR), as specified in 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 (date/time string as
   per RFC 3339) and tag 1 (POSIX "seconds since the epoch").  Since
   then, additional requirements have become known.  This specification
   defines a CBOR tag for a date text string (as per RFC 3339) for
   applications needing a textual date representation within the
   Gregorian calendar without a time.  It also defines a CBOR tag for
   days since the date 1970-01-01 in the Gregorian calendar for
   applications needing a numeric date representation without a time.
   This specification is the reference document for IANA registration of
   the CBOR tags defined.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8943.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (https://trustee.ietf.org/license-info) in effect on the date of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
     1.1.  Calendar Dates
       1.1.1.  Example Date Representations
     1.2.  Comparing Dates
     1.3.  Comparing Dates and Date/Time Values
   2.  IANA Considerations
     2.1.  Concise Binary Object Representation (CBOR) Tags
           Registrations
   3.  Security Considerations
   4.  References
     4.1.  Normative References
     4.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   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.  Per RFC
   3339, this represents a date within the Gregorian calendar.

   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
   Gregorian calendar 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 40587.

   Note that since both tags are for dates without times, times of day,
   time zones, and leap seconds are not applicable to these values.
   These tags are both for representations of Gregorian calendar dates.

1.1.  Calendar Dates

   Calendar dates are used for numerous human use cases, such as marking
   the dates of significant events.  For instance, John Lennon was born
   on October 9, 1940 and died on December 8, 1980.  One such use case
   is driver's licenses, which typically include a date of birth.  The
   dates used in this specification use the Gregorian calendar, as do