Concise Binary Object Representation (CBOR) Tags for DateMicrosoftmbj@microsoft.comhttps://self-issued.info/Independentnadalin@prodigy.netpdv Financial Software GmbHjoerg.richter@pdv-fs.de
Applications
CBOR Working GroupCompact Binary Object RepresentationCBORTagDate
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
.
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
Provisions Relating to IETF Documents
() in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
document must include Simplified BSD License text as described in
Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Simplified BSD License.
Table of Contents
Introduction
The Concise Binary Object Representation (CBOR)
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 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.
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 those in RFC 3339 .
The time zones and actual times of these events are intentionally not represented in the calendar date.
The epoch chosen for the second tag, which represents days since the
Gregorian calendar date 1970-01-01, is related to the IEEE Std
1003.1, 2013 Edition time epoch
1970-01-01T00:00:00Z UTC only insofar as both contain the date 1970-01-01.
This should not be construed as indicating that dates using this tag
represent either a specific time of day and/or time zone.
The day of the week (Sunday, Monday, Tuesday, etc.) is not explicitly represented
in either of these date formats.
However, deterministic algorithms that are beyond the scope of this specification
can be used to derive the day of the week in the Gregorian calendar
from dates represented in both of these formats.
Example Date Representations
This table contains example representations for dates using both tags.
Date
Tag 1004
Tag 100
October 9, 1940
"1940-10-09"
-10676
December 8, 1980
"1980-12-08"
3994
Comparing Dates
Comparison of dates in full-date format can be accomplished by
normal string comparison, since, by design, the digits representing the date are in fixed format
and ordered from most significant to least significant.
Comparison of numeric dates representing days since 1970-01-01 can be performed by
normal integer comparison.
Comparison of dates in other formats or using other calendars require conversions
that are beyond the scope of this specification.
Note that different dates may correspond to the same moment in time,
depending upon the time zone in which the date was determined.
For instance, at many times of the day, a conference call occurring
on a particular date in Japan will simultaneously occur
on the previous date in Hawaii;
at many times of the day, Japan's Friday corresponds with Hawaii's Thursday.
Comparing Dates and Date/Time Values
Comparing dates with date/time values, which represent a particular moment in time,
is beyond the scope of this specification.
That said, if a date is augmented with a time zone and time of day,
a specific date/time value can be determined, and
comparing that date/time value to others becomes possible.
For instance, if one were to augment John Lennon's birth date
of October 9, 1940 with the time of day and time zone of his birth,
then it would be possible to derive a date/time at which he was born
that could be compared with other date/time values.
IANA ConsiderationsConcise Binary Object Representation (CBOR) Tags Registrations
This section registers the following values in the
IANA "Concise Binary Object Representation (CBOR) Tags" registry .
Tag:
1004
Data Item:
UTF-8 text string
Semantics:
full-date string
Reference:
RFC 8943
Tag:
100 (ASCII 'd')
Data Item:
Unsigned or negative integer
Semantics:
Number of days since the epoch date 1970-01-01
Reference:
RFC 8943
Security Considerations
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.
Similarly, it would be inappropriate to use only a date to trigger certificate expiration,
since a date corresponds to a range of times worldwide
rather than a specific point in time that is independent of geographic location.
ReferencesNormative ReferencesDate and Time on the Internet: TimestampsThis document defines a date and time format for use in Internet protocols that is a profile of the ISO 8601 standard for representation of dates and times using the Gregorian calendar.Concise Binary Object Representation (CBOR)The Concise Binary Object Representation (CBOR) 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. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack.Informative ReferencesConcise Binary Object Representation (CBOR) TagsIANAThe Open Group Base Specifications Issue 7IEEE2013 EditionConcise Binary Object Representation (CBOR) Tags for Time, Duration, and PeriodUniversitaet Bremen TZIWell-TypedFraunhofer SIT 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 (RFC3339 time) and tag
1 (Posix time [TIME_T], int or float). Since then, additional
requirements have become known. The present document defines a CBOR
tag for time that allows a more elaborate representation of time, and
anticipates the definition of related CBOR tags for duration and time
period. It is intended as the reference document for the IANA
registration of the CBOR tags defined.
Work in ProgressAcknowledgements
Thanks to for supporting creation of this specification.
Parts of the explanatory text in this specification come from .
Thanks to these people for reviews of the specification:
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
and
.
Authors' AddressesMicrosoftmbj@microsoft.comhttps://self-issued.info/Independentnadalin@prodigy.netpdv Financial Software GmbHjoerg.richter@pdv-fs.de