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RFC 8536

The Time Zone Information Format (TZif)

Pages: 34
Proposed Standard
Errata
Part 2 of 2 – Pages 17 to 34
First   Prev   None

Top   ToC   RFC8536 - Page 17   prevText

6. Security Considerations

The Time Zone Information Format contains no executable code, and it does not define any extensible areas that could be used to store such code. TZif contains counted arrays of data elements. All counts should be checked when processing TZif objects, to guard against references past the end of the object. TZif provides no confidentiality or integrity protection. Time zone information is normally public and does not call for confidentiality protection. Since time zone information is used in many critical applications, integrity protection may be required and must be provided externally.

7. Privacy Considerations

The Time Zone Information Format contains publicly available data, and it does not define any extensible areas that could be used to store private data. As discussed in Section 9 of [RFC7808], transmission of time zone data over an insecure communications channel could leak the past, current, or future location of a device or user. As such, TZif data transmitted over a public communications channel MUST be protected with a confidentiality layer such as that provided by Transport Layer Security (TLS) [RFC8446].

8. IANA Considerations

This document defines two media types [RFC6838] for the exchange of data utilizing the Time Zone Information Format.

8.1. application/tzif

Type name: application Subtype name: tzif Required parameters: none Optional parameters: none Encoding considerations: binary Security considerations: See Section 6 of RFC 8536.
Top   ToC   RFC8536 - Page 18
   Interoperability considerations:  See Section 4 of RFC 8536.

   Published specification:  This specification.

   Applications that use this media type:  This media type is designed
      for widespread use by applications that need to use or exchange
      time zone information, such as the Time Zone Information Compiler
      (zic) [ZIC] and the GNU C Library [GNU-C].  The Time Zone
      Distribution Service [RFC7808] can directly use this media type.

   Fragment identifier considerations:  N/A

   Additional information:

      Magic number(s):  The first 4 octets are 0x54, 0x5A, 0x69, 0x66

      File extensions(s):  N/A

      Macintosh file type code(s):  N/A

   Person & email address to contact for further information:
      Time Zone Database mailing list <tz@iana.org>

   Intended usage:  COMMON

   Restrictions on usage:  N/A

   Author:  See the "Authors' Addresses" section of RFC 8536.

   Change controller:  IETF

8.2. application/tzif-leap

Type name: application Subtype name: tzif-leap Required parameters: none Optional parameters: none Encoding considerations: binary Security considerations: See Section 6 of RFC 8536. Interoperability considerations: See Section 4 of RFC 8536. Published specification: This specification.
Top   ToC   RFC8536 - Page 19
   Applications that use this media type:  This media type is designed
      for widespread use by applications that need to use or exchange
      time zone information, such as the Time Zone Information Compiler
      (zic) [ZIC] and the GNU C Library [GNU-C].  The Time Zone
      Distribution Service [RFC7808] can directly use this media type.

   Fragment identifier considerations:  N/A

   Additional information:

      Magic number(s):  The first 4 octets are 0x54, 0x5A, 0x69, 0x66

      File extensions(s):  N/A

      Macintosh file type code(s):  N/A

   Person & email address to contact for further information:
      Time Zone Database mailing list <tz@iana.org>

   Intended usage:  COMMON

   Restrictions on usage:  N/A

   Author:  See the "Authors' Addresses" section of RFC 8536.

   Change controller:  IETF

9. References

9.1. Normative References

[GNU-C] "The GNU C Library (glibc)", <https://www.gnu.org/software/libc/>. [POSIX] IEEE, "Standard for Information Technology--Portable Operating System Interface (POSIX(R)) Base Specifications, Issue 7", IEEE 1003.1-2017, DOI 10.1109/IEEESTD.2018.8277153, January 2018, <http://pubs.opengroup.org/onlinepubs/9699919799/>. [RFC20] Cerf, V., "ASCII format for network interchange", STD 80, RFC 20, DOI 10.17487/RFC0020, October 1969, <https://www.rfc-editor.org/info/rfc20>. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>.
Top   ToC   RFC8536 - Page 20
   [RFC6838]   Freed, N., Klensin, J., and T. Hansen, "Media Type
               Specifications and Registration Procedures", BCP 13,
               RFC 6838, DOI 10.17487/RFC6838, January 2013,
               <https://www.rfc-editor.org/info/rfc6838>.

   [RFC7231]   Fielding, R., Ed. and J. Reschke, Ed., "Hypertext
               Transfer Protocol (HTTP/1.1): Semantics and Content",
               RFC 7231, DOI 10.17487/RFC7231, June 2014,
               <https://www.rfc-editor.org/info/rfc7231>.

   [RFC7808]   Douglass, M. and C. Daboo, "Time Zone Data Distribution
               Service", RFC 7808, DOI 10.17487/RFC7808, March 2016,
               <https://www.rfc-editor.org/info/rfc7808>.

   [RFC8174]   Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
               2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
               May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [ZIC]       Kerrisk, M., "ZIC(8)", man-pages release 4.16, February
               2010, <http://man7.org/linux/man-pages/man8/zic.8.html>.

9.2. Informative References

[EGGERT-TZ] "History for tz", October 2018, <https://github.com/eggert/tz/commits/master/tzfile.5>. [RFC5545] Desruisseaux, B., Ed., "Internet Calendaring and Scheduling Core Object Specification (iCalendar)", RFC 5545, DOI 10.17487/RFC5545, September 2009, <https://www.rfc-editor.org/info/rfc5545>. [RFC6557] Lear, E. and P. Eggert, "Procedures for Maintaining the Time Zone Database", BCP 175, RFC 6557, DOI 10.17487/RFC6557, February 2012, <https://www.rfc-editor.org/info/rfc6557>. [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, <https://www.rfc-editor.org/info/rfc8446>. [tz-link] Eggert, P. and A. Olson, "Sources for Time Zone and Daylight Saving Time Data", 2018, <https://www.iana.org/time-zones/repository/ tz-link.html>.
Top   ToC   RFC8536 - Page 21

Appendix A. Common Interoperability Issues

This section documents common problems in implementing this specification. Most of these are problems in generating TZif files for use by readers conforming to predecessors of this specification [EGGERT-TZ]. The goals of this section are: 1. to help TZif writers output files that avoid common pitfalls in older or buggy TZif readers, 2. to help TZif readers avoid common pitfalls when reading files generated by future TZif writers, and 3. to help any future specification authors see what sort of problems arise when the TZif format is changed. When new versions of the TZif format have been defined, a design goal has been that a reader can successfully use a TZif file even if the file is of a later TZif version than what the reader was designed for. When complete compatibility was not achieved, an attempt was made to limit glitches to rarely used timestamps and allow simple partial workarounds in writers designed to generate new-version data useful even for older-version readers. This section attempts to document these compatibility issues and workarounds, as well as documenting other common bugs in readers. Interoperability problems with TZif include the following: o Some readers examine only version 1 data. As a partial workaround, a writer can output as much version 1 data as possible. However, a reader should ignore version 1 data and use version 2+ data, even if the reader's native timestamps have only 32 bits. o Some readers designed for version 2 might mishandle timestamps after a version 3 file's last transition, because they cannot parse extensions to POSIX in the TZ-like string. As a partial workaround, a writer can output more transitions than necessary, so that only far-future timestamps are mishandled by version 2 readers. o Some readers designed for version 2 do not support permanent daylight saving time -- e.g., a TZ string "EST5EDT,0/0,J365/25" denoting permanent Eastern Daylight Time (-04). As a partial workaround, a writer can substitute standard time for the next time zone east -- e.g., "AST4" for permanent Atlantic Standard Time (-04).
Top   ToC   RFC8536 - Page 22
   o  Some readers ignore the footer and instead predict future
      timestamps from the time type of the last transition.  As a
      partial workaround, a writer can output more transitions than
      necessary.

   o  Some readers do not use time type 0 for timestamps before the
      first transition, in that they infer a time type using a heuristic
      that does not always select time type 0.  As a partial workaround,
      a writer can output a dummy (no-op) first transition at an early
      time.

   o  Some readers mishandle timestamps before the first transition that
      has a timestamp not less than -2**31.  Readers that support only
      32-bit timestamps are likely to be more prone to this problem, for
      example, when they process 64-bit transitions, only some of which
      are representable in 32 bits.  As a partial workaround, a writer
      can output a dummy transition at timestamp -2**31.

   o  Some readers mishandle a transition if its timestamp has the
      minimum possible signed 64-bit value.  Timestamps less than -2**59
      are not recommended.

   o  Some readers mishandle POSIX-style TZ strings that contain "<" or
      ">".  As a partial workaround, a writer can avoid using '<' or '>'
      for time zone abbreviations containing only alphabetic characters.

   o  Many readers mishandle time zone abbreviations that contain non-
      ASCII characters.  These characters are not recommended.

   o  Some readers may mishandle time zone abbreviations that contain
      fewer than 3 or more than 6 characters, or that contain ASCII
      characters other than alphanumerics, '-', and '+'.  These
      abbreviations are not recommended.

   o  Some readers mishandle TZif files that specify daylight saving
      time UT offsets that are less than the UT offsets for the
      corresponding standard time.  These readers do not support
      locations like Ireland, which uses the equivalent of the POSIX TZ
      string "IST-1GMT0,M10.5.0,M3.5.0/1", observing standard time (IST,
      +01) in summer and daylight saving time (GMT, +00) in winter.  As
      a partial workaround, a writer can output data for the equivalent
      of the POSIX TZ string "GMT0IST,M3.5.0/1,M10.5.0", thus swapping
      standard and daylight saving time.  Although this workaround
      misidentifies which part of the year uses daylight saving time, it
      records UT offsets and time zone abbreviations correctly.
Top   ToC   RFC8536 - Page 23
   Some interoperability problems are reader bugs that are listed here
   mostly as warnings to developers of readers.

   o  Some readers do not support negative timestamps.  Developers of
      distributed applications should keep this in mind if they need to
      deal with pre-1970 data.

   o  Some readers mishandle timestamps before the first transition that
      has a nonnegative timestamp.  Readers that do not support negative
      timestamps are likely to be more prone to this problem.

   o  Some readers mishandle time zone abbreviations like "-08" that
      contain '+', '-', or digits.

   o  Some readers mishandle UT offsets that are out of the traditional
      range of -12 through +12 hours and so do not support locations
      like Kiritimati that are outside this range.

   o  Some readers mishandle UT offsets in the range [-3599, -1] seconds
      from UT, because they integer-divide the offset by 3600 to get 0
      and then display the hour part as "+00".

   o  Some readers mishandle UT offsets that are not a multiple of one
      hour, 15 minutes, or 1 minute.

Appendix B. Example TZif Files

The following sections contain annotated hexadecimal dumps of example TZif files. Note that these examples should only be considered informative. Although the example data entries are current as of the publication date of this document, the data will likely change in the future as leap seconds are added and changes are made to civil time.
Top   ToC   RFC8536 - Page 24

B.1. Version 1 File Representing UTC (with Leap Seconds)

+-------+---------------+------------------+------------------------+ | File | Data Octets | Record Name / | Field Value | | Offset| (hexadecimal) | Field Name | | +-------+---------------+------------------+------------------------+ | 000 | 54 5a 69 66 | magic | "TZif" | | 004 | 00 | version | 0 (1) | | 005 | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 | | | | 020 | 00 00 00 01 | isutccnt | 1 | | 024 | 00 00 00 01 | isstdcnt | 1 | | 028 | 00 00 00 1b | isleapcnt | 27 | | 032 | 00 00 00 00 | timecnt | 0 | | 036 | 00 00 00 01 | typecnt | 1 | | 040 | 00 00 00 04 | charcnt | 4 | | | | | | | | | localtimetype[0] | | | 044 | 00 00 00 00 | utcoff | 00:00 | | 048 | 00 | isdst | 0 (no) | | 049 | 00 | desigidx | 0 | | | | | | | 050 | 55 54 43 00 | designations[0] | "UTC" | | | | | | | | | leapsecond[0] | | | 054 | 04 b2 58 00 | occurrence | 78796800 | | | | | (1972-06-30T23:59:60Z) | | 058 | 00 00 00 01 | correction | 1 | | | | | | | | | leapsecond[1] | | | 062 | 05 a4 ec 01 | occurrence | 94694401 | | | | | (1972-12-31T23:59:60Z) | | 066 | 00 00 00 02 | correction | 2 | | | | | | | | | leapsecond[2] | | | 070 | 07 86 1f 82 | occurrence | 126230402 | | | | | (1973-12-31T23:59:60Z) | | 074 | 00 00 00 03 | correction | 3 | | | | | | | | | leapsecond[3] | | | 078 | 09 67 53 03 | occurrence | 157766403 | | | | | (1974-12-31T23:59:60Z) | | 082 | 00 00 00 04 | correction | 4 | | | | | |
Top   ToC   RFC8536 - Page 25
   |       |               | leapsecond[4]    |                        |
   | 086   | 0b 48 86 84   | occurrence       | 189302404              |
   |       |               |                  | (1975-12-31T23:59:60Z) |
   | 090   | 00 00 00 05   | correction       | 5                      |
   |       |               |                  |                        |
   |       |               | leapsecond[5]    |                        |
   | 094   | 0d 2b 0b 85   | occurrence       | 220924805              |
   |       |               |                  | (1976-12-31T23:59:60Z) |
   | 098   | 00 00 00 06   | correction       | 6                      |
   |       |               |                  |                        |
   |       |               | leapsecond[6]    |                        |
   | 102   | 0f 0c 3f 06   | occurrence       | 252460806              |
   |       |               |                  | (1977-12-31T23:59:60Z) |
   | 106   | 00 00 00 07   | correction       | 7                      |
   |       |               |                  |                        |
   |       |               | leapsecond[7]    |                        |
   | 110   | 10 ed 72 87   | occurrence       | 283996807              |
   |       |               |                  | (1978-12-31T23:59:60Z) |
   | 114   | 00 00 00 08   | correction       | 8                      |
   |       |               |                  |                        |
   |       |               | leapsecond[8]    |                        |
   | 118   | 12 ce a6 08   | occurrence       | 315532808              |
   |       |               |                  | (1979-12-31T23:59:60Z) |
   | 122   | 00 00 00 09   | correction       | 9                      |
   |       |               |                  |                        |
   |       |               | leapsecond[9]    |                        |
   | 126   | 15 9f ca 89   | occurrence       | 362793609              |
   |       |               |                  | (1981-06-30T23:59:60Z) |
   | 130   | 00 00 00 0a   | correction       | 10                     |
   |       |               |                  |                        |
   |       |               | leapsecond[10]   |                        |
   | 134   | 17 80 fe 0a   | occurrence       | 394329610              |
   |       |               |                  | (1982-06-30T23:59:60Z) |
   | 138   | 00 00 00 0b   | correction       | 11                     |
   |       |               |                  |                        |
   |       |               | leapsecond[11]   |                        |
   | 142   | 19 62 31 8b   | occurrence       | 425865611              |
   |       |               |                  | (1983-06-30T23:59:60Z) |
   | 146   | 00 00 00 0c   | correction       | 12                     |
   |       |               |                  |                        |
   |       |               | leapsecond[12]   |                        |
   | 150   | 1d 25 ea 0c   | occurrence       | 489024012              |
   |       |               |                  | (1985-06-30T23:59:60Z) |
   | 154   | 00 00 00 0d   | correction       | 13                     |
   |       |               |                  |                        |
   |       |               | leapsecond[13]   |                        |
   | 158   | 21 da e5 0d   | occurrence       | 567993613              |
   |       |               |                  | (1987-12-31T23:59:60Z) |
Top   ToC   RFC8536 - Page 26
   | 162   | 00 00 00 0e   | correction       | 14                     |
   |       |               |                  |                        |
   |       |               | leapsecond[14]   |                        |
   | 166   | 25 9e 9d 8e   | occurrence       | 631152014              |
   |       |               |                  | (1989-12-31T23:59:60Z) |
   | 170   | 00 00 00 0f   | correction       | 15                     |
   |       |               |                  |                        |
   |       |               | leapsecond[15]   |                        |
   | 174   | 27 7f d1 0f   | occurrence       | 662688015              |
   |       |               |                  | (1990-12-31T23:59:60Z) |
   | 178   | 00 00 00 10   | correction       | 16                     |
   |       |               |                  |                        |
   |       |               | leapsecond[16]   |                        |
   | 182   | 2a 50 f5 90   | occurrence       | 709948816              |
   |       |               |                  | (1992-06-30T23:59:60Z) |
   | 186   | 00 00 00 11   | correction       | 17                     |
   |       |               |                  |                        |
   |       |               | leapsecond[17]   |                        |
   | 190   | 2c 32 29 11   | occurrence       | 741484817              |
   |       |               |                  | (1993-06-30T23:59:60Z) |
   | 194   | 00 00 00 12   | correction       | 18                     |
   |       |               |                  |                        |
   |       |               | leapsecond[18]   |                        |
   | 198   | 2e 13 5c 92   | occurrence       | 773020818              |
   |       |               |                  | (1994-06-30T23:59:60Z) |
   | 202   | 00 00 00 13   | correction       | 19                     |
   |       |               |                  |                        |
   |       |               | leapsecond[19]   |                        |
   | 206   | 30 e7 24 13   | occurrence       | 820454419              |
   |       |               |                  | (1995-12-31T23:59:60Z) |
   | 210   | 00 00 00 14   | correction       | 20                     |
   |       |               |                  |                        |
   |       |               | leapsecond[20]   |                        |
   | 214   | 33 b8 48 94   | occurrence       | 867715220              |
   |       |               |                  | (1997-06-30T23:59:60Z) |
   | 218   | 00 00 00 15   | correction       | 21                     |
   |       |               |                  |                        |
   |       |               | leapsecond[21]   |                        |
   | 222   | 36 8c 10 15   | occurrence       | 915148821              |
   |       |               |                  | (1998-12-31T23:59:60Z) |
   | 226   | 00 00 00 16   | correction       | 22                     |
   |       |               |                  |                        |
   |       |               | leapsecond[22]   |                        |
   | 230   | 43 b7 1b 96   | occurrence       | 1136073622             |
   |       |               |                  | (2005-12-31T23:59:60Z) |
   | 234   | 00 00 00 17   | correction       | 23                     |
   |       |               |                  |                        |
Top   ToC   RFC8536 - Page 27
   |       |               | leapsecond[23]   |                        |
   | 238   | 49 5c 07 97   | occurrence       | 1230768023             |
   |       |               |                  | (2008-12-31T23:59:60Z) |
   | 242   | 00 00 00 18   | correction       | 24                     |
   |       |               |                  |                        |
   |       |               | leapsecond[24]   |                        |
   | 246   | 4f ef 93 18   | occurrence       | 1341100824             |
   |       |               |                  | (2012-06-30T23:59:60Z) |
   | 250   | 00 00 00 19   | correction       | 25                     |
   |       |               |                  |                        |
   |       |               | leapsecond[25]   |                        |
   | 254   | 55 93 2d 99   | occurrence       | 1435708825             |
   |       |               |                  | (2015-06-30T23:59:60Z) |
   | 258   | 00 00 00 1a   | correction       | 26                     |
   |       |               |                  |                        |
   |       |               | leapsecond[26]   |                        |
   | 262   | 58 68 46 9a   | occurrence       | 1483228826             |
   |       |               |                  | (2016-12-31T23:59:60Z) |
   | 266   | 00 00 00 1b   | correction       | 27                     |
   |       |               |                  |                        |
   | 270   | 00            | UT/local[0]      | 0 (local)              |
   |       |               |                  |                        |
   | 271   | 00            | standard/wall[0] | 0 (wall)               |
   +-------+---------------+------------------+------------------------+

   To determine TAI corresponding to 2000-01-01T00:00:00Z
   (UNIX time = 946684800), the following procedure would be followed:

   1.  Find the latest leap-second occurrence prior to the time of
       interest (leapsecond[21]) and note the correction value
       (LEAPCORR = 22).

   2.  Add LEAPCORR + 10 to the time of interest to yield TAI of
       2000-01-01T00:00:32.
Top   ToC   RFC8536 - Page 28

B.2. Version 2 File Representing Pacific/Honolulu

+--------+--------------+------------------+------------------------+ | File | Hexadecimal | Record Name / | Field Value | | Offset | Octets | Field Name | | +--------+--------------+------------------+------------------------+ | 000 | 54 5a 69 66 | magic | "TZif" | | 004 | 32 | version | '2' (2) | | 005 | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 | | | | 020 | 00 00 00 06 | isutccnt | 6 | | 024 | 00 00 00 06 | isstdcnt | 6 | | 028 | 00 00 00 00 | isleapcnt | 0 | | 032 | 00 00 00 07 | timecnt | 7 | | 036 | 00 00 00 06 | typecnt | 6 | | 040 | 00 00 00 14 | charcnt | 20 | | | | | | | 044 | 80 00 00 00 | trans time[0] | -2147483648 | | | | | (1901-12-13T20:45:52Z) | | 048 | bb 05 43 48 | trans time[1] | -1157283000 | | | | | (1933-04-30T12:30:00Z) | | 052 | bb 21 71 58 | trans time[2] | -1155436200 | | | | | (1933-05-21T21:30:00Z) | | 056 | cb 89 3d c8 | trans time[3] | -880198200 | | | | | (1942-02-09T12:30:00Z) | | 060 | d2 23 f4 70 | trans time[4] | -769395600 | | | | | (1945-08-14T23:00:00Z) | | 064 | d2 61 49 38 | trans time[5] | -765376200 | | | | | (1945-09-30T11:30:00Z) | | 068 | d5 8d 73 48 | trans time[6] | -712150200 | | | | | (1947-06-08T12:30:00Z) | | | | | | | 072 | 01 | trans type[0] | 1 | | 073 | 02 | trans type[1] | 2 | | 074 | 01 | trans type[2] | 1 | | 075 | 03 | trans type[3] | 3 | | 076 | 04 | trans type[4] | 4 | | 077 | 01 | trans type[5] | 1 | | 078 | 05 | trans type[6] | 5 | | | | | | | | | localtimetype[0] | | | 079 | ff ff 6c 02 | utcoff | -37886 (-10:21:26) | | 083 | 00 | isdst | 0 (no) | | 084 | 00 | desigidx | 0 | | | | | |
Top   ToC   RFC8536 - Page 29
   |        |              | localtimetype[1] |                        |
   | 085    | ff ff 6c 58  | utcoff           | -37800 (-10:30)        |
   | 089    | 00           | isdst            | 0 (no)                 |
   | 090    | 04           | desigidx         | 4                      |
   |        |              |                  |                        |
   |        |              | localtimetype[2] |                        |
   | 091    | ff ff 7a 68  | utcoff           | -34200 (-09:30)        |
   | 095    | 01           | isdst            | 1 (yes)                |
   | 096    | 08           | desigidx         | 8                      |
   |        |              |                  |                        |
   |        |              | localtimetype[3] |                        |
   | 097    | ff ff 7a 68  | utcoff           | -34200 (-09:30)        |
   | 101    | 01           | isdst            | 1 (yes)                |
   | 102    | 0c           | desigidx         | 12                     |
   |        |              |                  |                        |
   |        |              | localtimetype[4] |                        |
   | 103    | ff ff 7a 68  | utcoff           | -34200 (-09:30)        |
   | 107    | 01           | isdst            | 1 (yes)                |
   | 108    | 10           | desigidx         | 16                     |
   |        |              |                  |                        |
   |        |              | localtimetype[5] |                        |
   | 109    | ff ff 73 60  | utcoff           | -36000 (-10:00)        |
   | 113    | 00           | isdst            | 0 (no)                 |
   | 114    | 04           | desigidx         | 4                      |
   |        |              |                  |                        |
   | 115    | 4c 4d 54 00  | designations[0]  | "LMT"                  |
   | 119    | 48 53 54 00  | designations[4]  | "HST"                  |
   | 123    | 48 44 54 00  | designations[8]  | "HDT"                  |
   | 127    | 48 57 54 00  | designations[12] | "HWT"                  |
   | 131    | 48 50 54 00  | designations[16] | "HPT"                  |
   |        |              |                  |                        |
   | 135    | 00           | UT/local[0]      | 1 (UT)                 |
   | 136    | 00           | UT/local[1]      | 0 (local)              |
   | 137    | 00           | UT/local[2]      | 0 (local)              |
   | 138    | 00           | UT/local[3]      | 0 (local)              |
   | 139    | 01           | UT/local[4]      | 1 (UT)                 |
   | 140    | 00           | UT/local[5]      | 0 (local)              |
   |        |              |                  |                        |
   | 141    | 00           | standard/wall[0] | 1 (standard)           |
   | 142    | 00           | standard/wall[1] | 0 (wall)               |
   | 143    | 00           | standard/wall[2] | 0 (wall)               |
   | 144    | 00           | standard/wall[3] | 0 (wall)               |
   | 145    | 01           | standard/wall[4] | 1 (standard)           |
   | 146    | 00           | standard/wall[5] | 0 (wall)               |
   |        |              |                  |                        |
   | 147    | 54 5a 69 66  | magic            | "TZif"                 |
   | 151    | 32           | version          | '2' (2)                |
Top   ToC   RFC8536 - Page 30
   | 152    | 00 00 00 00  |                  |                        |
   |        | 00 00 00 00  |                  |                        |
   |        | 00 00 00 00  |                  |                        |
   |        | 00 00 00     |                  |                        |
   | 167    | 00 00 00 06  | isutccnt         | 6                      |
   | 171    | 00 00 00 06  | isstdcnt         | 6                      |
   | 175    | 00 00 00 00  | isleapcnt        | 0                      |
   | 179    | 00 00 00 07  | timecnt          | 7                      |
   | 183    | 00 00 00 06  | typecnt          | 6                      |
   | 187    | 00 00 00 14  | charcnt          | 20                     |
   |        |              |                  |                        |
   | 191    | ff ff ff ff  | trans time[0]    | -2334101314            |
   |        | 74 e0 70 be  |                  | (1896-01-13T22:31:26Z) |
   | 199    | ff ff ff ff  | trans time[1]    | -1157283000            |
   |        | bb 05 43 48  |                  | (1933-04-30T12:30:00Z) |
   | 207    | ff ff ff ff  | trans time[2]    | -1155436200            |
   |        | bb 21 71 58  |                  | (1933-05-21T21:30:00Z) |
   | 215    | ff ff ff ff  | trans time[3]    | -880198200             |
   |        | cb 89 3d c8  |                  | (1942-02-09T12:30:00Z) |
   | 223    | ff ff ff ff  | trans time[4]    | -769395600             |
   |        | d2 23 f4 70  |                  | (1945-08-14T23:00:00Z) |
   | 231    | ff ff ff ff  | trans time[5]    | -765376200             |
   |        | d2 61 49 38  |                  | (1945-09-30T11:30:00Z) |
   | 239    | ff ff ff ff  | trans time[6]    | -712150200             |
   |        | d5 8d 73 48  |                  | (1947-06-08T12:30:00Z) |
   |        |              |                  |                        |
   | 247    | 01           | trans type[0]    | 1                      |
   | 248    | 02           | trans type[1]    | 2                      |
   | 249    | 01           | trans type[2]    | 1                      |
   | 250    | 03           | trans type[3]    | 3                      |
   | 251    | 04           | trans type[4]    | 4                      |
   | 252    | 01           | trans type[5]    | 1                      |
   | 253    | 05           | trans type[6]    | 5                      |
   |        |              |                  |                        |
   |        |              | localtimetype[0] |                        |
   | 254    | ff ff 6c 02  | utcoff           | -37886 (-10:21:26)     |
   | 258    | 00           | isdst            | 0 (no)                 |
   | 259    | 00           | desigidx         | 0                      |
   |        |              |                  |                        |
   |        |              | localtimetype[1] |                        |
   | 260    | ff ff 6c 58  | utcoff           | -37800 (-10:30)        |
   | 264    | 00           | isdst            | 0 (no)                 |
   | 265    | 04           | desigidx         | 4                      |
   |        |              |                  |                        |
   |        |              | localtimetype[2] |                        |
   | 266    | ff ff 7a 68  | utcoff           | -34200 (-09:30)        |
   | 270    | 01           | isdst            | 1 (yes)                |
   | 271    | 08           | desigidx         | 8                      |
Top   ToC   RFC8536 - Page 31
   |        |              |                  |                        |
   |        |              | localtimetype[3] |                        |
   | 272    | ff ff 7a 68  | utcoff           | -34200 (-09:30)        |
   | 276    | 01           | isdst            | 1 (yes)                |
   | 277    | 0c           | desigidx         | 12                     |
   |        |              |                  |                        |
   |        |              | localtimetype[4] |                        |
   | 278    | ff ff 7a 68  | utcoff           | -34200 (-09:30)        |
   | 282    | 01           | isdst            | 1 (yes)                |
   | 283    | 10           | desigidx         | 16                     |
   |        |              |                  |                        |
   |        |              | localtimetype[5] |                        |
   | 284    | ff ff 73 60  | utcoff           | -36000 (-10:00)        |
   | 288    | 00           | isdst            | 0 (no)                 |
   | 289    | 04           | desigidx         | 4                      |
   |        |              |                  |                        |
   | 290    | 4c 4d 54 00  | designations[0]  | "LMT"                  |
   | 294    | 48 53 54 00  | designations[4]  | "HST"                  |
   | 298    | 48 44 54 00  | designations[8]  | "HDT"                  |
   | 302    | 48 57 54 00  | designations[12] | "HWT"                  |
   | 306    | 48 50 54 00  | designations[16] | "HPT"                  |
   |        |              |                  |                        |
   | 310    | 00           | UT/local[0]      | 0 (local)              |
   | 311    | 00           | UT/local[1]      | 0 (local)              |
   | 312    | 00           | UT/local[2]      | 0 (local)              |
   | 313    | 00           | UT/local[3]      | 0 (local)              |
   | 314    | 01           | UT/local[4]      | 1 (UT)                 |
   | 315    | 00           | UT/local[5]      | 0 (local)              |
   |        |              |                  |                        |
   | 316    | 00           | standard/wall[0] | 0 (wall)               |
   | 317    | 00           | standard/wall[1] | 0 (wall)               |
   | 318    | 00           | standard/wall[2] | 0 (wall)               |
   | 319    | 00           | standard/wall[3] | 0 (wall)               |
   | 320    | 01           | standard/wall[4] | 1 (standard)           |
   | 321    | 00           | standard/wall[5] | 0 (wall)               |
   |        |              |                  |                        |
   | 322    | 0a           | NL               | '\n'                   |
   | 323    | 48 53 54 31  | TZ string        | "HST10"                |
   |        | 30           |                  |                        |
   | 328    | 0a           | NL               | '\n'                   |
   +--------+--------------+------------------+------------------------+
Top   ToC   RFC8536 - Page 32
   To determine the local time in this time zone corresponding to
   1933-05-04T12:00:00Z (UNIX time = -1156939200), the following
   procedure would be followed:

   1.  Find the latest time transition prior to the time of interest
       (trans time[1]).

   2.  Reference the corresponding transition type (trans type[1]) to
       determine the local time type index (2).

   3.  Reference the corresponding local time type (localtimetype[2]) to
       determine the offset from UTC (-09:30), the daylight saving
       indicator (1 = yes), and the index into the time zone designation
       strings (8).

   4.  Look up the corresponding time zone designation string
       (designations[8] = "HDT").

   5.  Add the UTC offset to the time of interest to yield a local
       daylight saving time of 1933-05-04T02:30:00-09:30 (HDT).

   To determine the local time in this time zone corresponding to
   2019-01-01T00:00:00Z (UNIX time = 1546300800), the following
   procedure would be followed:

   1.  Find the latest time transition prior to the time of interest
       (there is no such transition).

   2.  Look up the TZ string in the footer ("HST10"), which indicates
       that the time zone designation is "HST" year-round, and the
       offset to UTC is 10:00.

   3.  Subtract the UTC offset from the time of interest to yield a
       standard local time of 2018-12-31T14:00:00-10:00 (HST).
Top   ToC   RFC8536 - Page 33

B.3. Truncated Version 3 File Representing Asia/Jerusalem

The following TZif file has been truncated to start on 2038-01-01T00:00:00Z. +--------+--------------+------------------+------------------------+ | File | Hexadecimal | Record Name / | Field Value | | Offset | Octets | Field Name | | +--------+--------------+------------------+------------------------+ | 000 | 54 5a 69 66 | magic | "TZif" | | 004 | 33 | version | '3' (3) | | 005 | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 | | | | 020 | 00 00 00 00 | isutccnt | 0 | | 024 | 00 00 00 00 | isstdcnt | 0 | | 028 | 00 00 00 00 | isleapcnt | 0 | | 032 | 00 00 00 00 | timecnt | 0 | | 036 | 00 00 00 00 | typecnt | 0 | | 040 | 00 00 00 00 | charcnt | 0 | | | | | | | 044 | 54 5a 69 66 | magic | "TZif" | | 048 | 33 | version | '3' (3) | | 049 | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 00 | | | | | 00 00 00 | | | | 064 | 00 00 00 03 | isutccnt | 1 | | 068 | 00 00 00 03 | isstdcnt | 1 | | 072 | 00 00 00 00 | isleapcnt | 0 | | 076 | 00 00 00 03 | timecnt | 1 | | 080 | 00 00 00 03 | typecnt | 1 | | 084 | 00 00 00 08 | charcnt | 4 | | | | | | | 088 | 00 00 00 00 | trans time[0] | 2145916800 | | | 7f e8 17 80 | | (2038-01-01T00:00:00Z) | | | | | | | 096 | 00 | trans type[0] | 0 | | | | | | | | | localtimetype[0] | | | 097 | 00 00 1c 20 | utcoff | 7200 (+02:00) | | 101 | 00 | isdst | 0 (no) | | 102 | 00 | desigidx | 0 | | | | | | | 103 | 49 53 54 00 | designations[0] | "IST" | | | | | | | 107 | 01 | UT/local[0] | 1 (UT) |
Top   ToC   RFC8536 - Page 34
   |        |              |                  |                        |
   | 108    | 01           | standard/wall[0] | 1 (standard)           |
   |        |              |                  |                        |
   | 109    | 0a           | NL               | '\n'                   |
   | 110    | 49 53 54 2d  | TZ string        | "IST-2IDT,             |
   |        | 32 49 44 54  |                  | M3.4.4/26,M10.5.0"     |
   |        | 2c 4d 33 2e  |                  |                        |
   |        | 34 2e 34 2f  |                  |                        |
   |        | 32 36 2c 4d  |                  |                        |
   |        | 31 30 2e 35  |                  |                        |
   |        | 2e 30        |                  |                        |
   | 136    | 0a           | NL               | '\n'                   |
   +--------+--------------+------------------+------------------------+

Acknowledgments

The authors would like to thank the following individuals for contributing their ideas and support for writing this specification: Michael Douglass, Ned Freed, Guy Harris, Eliot Lear, and Alexey Melnikov.

Authors' Addresses

Arthur David Olson Email: arthurdavidolson@gmail.com Paul Eggert University of California, Los Angeles Email: eggert@cs.ucla.edu Kenneth Murchison FastMail US LLC Email: murch@fastmailteam.com