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rfc:rfc2550

Network Working Group S. Glassman Request for Comments: 2550 M. Manasse Category: Stinkards Track J. Mogul

                                          Compaq Computer Corporation
                                                         1 April 1999
                          Y10K and Beyond

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (1999).  All Rights Reserved.

Abstract

 As we approach the end of the millennium, much attention has been
 paid to the so-called "Y2K" problem.  Nearly everyone now regrets the
 short-sightedness of the programmers of yore who wrote programs
 designed to fail in the year 2000.  Unfortunately, the current fixes
 for Y2K lead inevitably to a crisis in the year 10,000 when the
 programs are again designed to fail.
 This specification provides a solution to the "Y10K" problem which
 has also been called the "YAK" problem (hex) and the "YXK" problem
 (Roman numerals).

1. Introduction, Discussion, and Related Work

 Many programs and standards contain, manipulate and maintain dates.
 Comparing and sorting dates is a common activity.  Many different
 formats and standards for dates have been developed and all have been
 found wanting.
 Early date formats reserved only two digits to represent the year
 portion of a date.  Programs that use this format make mistakes when
 dealing with dates after the year 2000.  This is the so-called Y2K
 problem.

Glassman, et. al. Informational [Page 1] RFC 2550 Y10K and Beyond 1 April 1999

 The most common fix for the Y2K problem has been to switch to 4-digit
 years.  This fix covers roughly the next 8,000 years (until the year
 9999) by which time, everyone seems convinced that all current
 programs will have been retired.  This is exactly the faulty logic
 and lazy programming practice that led to the current Y2K problem!
 Programmers and designers always assume that their code will
 eventually disappear, but history suggests that code and programs are
 often used well past their intended circumstances.
 The 4-digit year leads directly to programs that will fail in the
 year 10,000.  This proposal addresses the Y10K problem in a general
 way that covers the full range of date and time format issues.

1.1 Current approaches

 A large number of approaches exist for formatting dates and times.
 All of them have limitations.  The 2-digit year runs into trouble
 next year.  The 4-digit year hits the wall in the year 10,000.  A
 16-bit year runs out in the year 65,536.  A 32-bit counter for the
 number of seconds since 1970 [UNIX] wraps in 2038.  A 32-bit counter
 for the number of milli-seconds since booting crashes a Windows (TM)
 PC in 49.7 days [Microsoft].
 In this specification, we focus on the Y10K problems since they are
 most common and a large number of existing standards and protocols
 are susceptible to them (section 7).  These standards, and new
 proposals on their way, will lead to a serious world-wide problem
 unless efforts are made now to correct the computing, government, and
 business communities.
 Already, a small cottage industry is popping up to deal with the Y10K
 problem [YUCK].  We encourage these efforts and, in the coming years,
 this effort can only grow in size and importance.

1.2 A Fixed Format Y10K Fix

 At the time of this writing, only one proposal [Wilborne] directly
 deals with the Y10K problem.  In that proposal, dates are represented
 as decimal numbers with the dates compared numerically.  The proposed
 format is simply YYYYYMMDD - i.e. 5-digit years.
 To allow numerical comparison of dates, this representation requires
 a completely fixed representation for the date.  There can be no
 optional fields, the date resolution is limited to the granularity of
 one day, and this solution fails in the year 100,000 (Y100K).

Glassman, et. al. Informational [Page 2] RFC 2550 Y10K and Beyond 1 April 1999

1.2.2 Limitations of Numerical Comparison

 While sufficient for the specific Y10K problem, this solution is
 limited.  Even if extended for 6-digit years, it fails on 32-bit
 systems (and future 32-bit system emulators) after the date
 represented by the number 2147481231 (December 31, 214748) leading to
 a Y214749 problem.  Similarly, 64-bit and 128-bit systems also will
 fail, although somewhat later (after December 31, 922,337,203,685,477
 and December 31, 17,014,118,346,046,923,173,168,730,371,588,410
 respectively).

1.2.3 Granularity Issues

 The granularity problems of a fixed format date can be improved by
 extending the date format to include greater precision in the date.
 However, since numerical comparison of dates requires a fixed
 representation date, an extended format can not provide sufficient
 resolution for all foreseeable needs.
 For instance, if the precision were extended to the femto-second
 range the date format would become YYYYYMMDDHHMMSSmmmuuunnnpppfff
 (year, month, day, hour, minute, second, milli-second, micro-second,
 nano-second, pico-second, and femto-second).  The additional 21
 digits of this format limit the set of representable dates.  Compared
 to 1.2.2, the 32-bit and 64-bit forms of the date are instantly
 exceeded, while the 128-bit version would be viable - expiring on
 December 31, 17,014,118,346,046.

1.2.3.1 Extrapolation of Future Granularity Issues

 However, a simple extrapolation of Moore's law shows that even
 femto-second resolution will soon be inadequate.  Projecting current
 CPU clock speeds forward, a femto-second clock speed will be achieved
 in only 30 years.  And, by the year 10,000 the projected clock speed
 of the Intel Pentium MMDCLXVI (TM) will be approximately 10 ** (-
 1609) seconds.
 This discussion clearly shows that any fixed-format, integer
 representation of a date is likely to be insufficiently precise for
 future uses.

1.2.3.2 Floating Point Is No Solution

 The temptation to use floating point numbers to represent dates
 should be avoided.  Like the longer fixed-format, integer
 representations of the date, floating point representations merely
 delay the inevitable time when their range is exceeded.  In addition,

Glassman, et. al. Informational [Page 3] RFC 2550 Y10K and Beyond 1 April 1999

 the well known problems of real numbers - rounding, de-normalization,
 non-uniform distribution, etc. - just add to the problems of dealing
 with dates.

2 Structure of Y10K Solution

 Any Y10K solution should have the following characteristics.

2.1 Compatibility

 The format must be compatible with existing 4-digit date formats.
 Y2K compliant programs and standards must continue to work with Y10K
 dates before the year 10,000.  Y10K compliant programs can gradually
 be developed over time and coexist with non-Y10K compliant programs.

2.2 Simplicity and Efficiency

 Y10K dates must allow dates after 10,000 to be easily identified.
 Within a program, there must be a simple procedure for recognizing
 the Y10K dates and distinguishing them from legacy dates.

2.3 Lexical Sorting

 Y10K dates must be sortable lexically based on their ASCII
 representation.  The dates must not require specialized libraries or
 procedures.

2.4 Future Extensibility

 Y10K dates must support arbitrary precision dates, and should support
 dates extending arbitrarily far into the future and past.  Y10K dates
 from different eras and with different precisions must be directly
 comparable and sortable.

2.4.1 Environmental Considerations

 The known universe has a finite past and future.  The current age of
 the universe is estimated in [Zebu] as between 10 ** 10 and 2 * 10 **
 10 years.  The death of the universe is estimated in [Nigel] to occur
 in 10 ** 11 - years and in [Drake] as occurring either in 10 ** 12
 years for a closed universe (the big crunch) or 10 ** 14 years for an
 open universe (the heat death of the universe).
 In any case, the prevailing belief is that the life of the universe
 (and thus the range of possible dates) is finite.

Glassman, et. al. Informational [Page 4] RFC 2550 Y10K and Beyond 1 April 1999

2.4.2 Transcending Environmental Considerations

 However, we might get lucky.  So, Y10K dates are able to represent
 any possible time without any limits to their range either in the
 past or future.
 Y10K compliant programs MAY choose to limit the range of dates they
 support to those consistent with the expected life of the universe.
 Y10K compliant systems MUST accept Y10K dates from 10 ** 12 years in
 the past to 10 ** 20 years into the future.  Y10K compliant systems
 SHOULD accept dates for at least 10 ** 29 years in the past and
 future.

3 Syntax Overview

 The syntax of Y10K dates consists of simple, printable ASCII
 characters.  The syntax and the characters are chosen to support a
 simple lexical sort order for dates represented in Y10K format.  All
 Y10K dates MUST conform to these rules.
 Every Y10K date MUST begin with a Y10K year.  Following the year,
 there MAY be an arbitrary sequence of digits.  The digits are
 interpreted as MMDDHHMMSSmmmuuunnnpppfff...  (month, day, hour,
 minute, second, milli-second, micro-second, nano-second pico-second,
 femto-second, etc. - moving left to right in the date, digits always
 decrease in significance).
 All dates and times MUST be relative to International Atomic Time
 (TAI) [NRAO].
 When comparing dates, a date precedes every other date for which it
 is a prefix.  So, the date "19990401000000" precedes the date
 "19990401000000000".  In particular, dates with the format YYYYMMDD
 are interpreted to represent the exact instant that the day begins
 and precede any other date contained in that day.

3.1 Years 1 - 9999

 The current 4-digit year syntax covers all years from 1000 - 9999.
 These years are represented as 4 decimal digits.  Leading 0's MUST be
 added to the years before 1000 to bring the year to 4 digits.  Files
 containing legacy pre-Y1K [Mike] dates will have to be converted.

3.2 Years 10,000 through 99,999

 Four digits are not sufficient to represent dates beyond the year
 9999.  So, all years from 10,000 - 99,999 are represented by 5 digits
 preceded by the letter 'A'.  So, 10,000 becomes "A10000" and 99,999

Glassman, et. al. Informational [Page 5] RFC 2550 Y10K and Beyond 1 April 1999

 becomes "A99999".  Since 'A' follows '9' in the ASCII ordering, all
 dates with 5-digit years will follow all dates with 4-digit years
 (for example, "A10000" will sort after "9999").  This gives us the
 sort and comparison behaviour we want.

3.3 Years 100,000 up to 10 30 By a simple generalization of 3.2, 6-digit years are preceded by the letter 'B', 7-digit years by 'C', etc. Using just the 26 upper-case ASCII characters, we can cover all years up to 1030 (the last year

 representable is "Z999999999999999999999999999999").  Again, since
 the ASCII characters are sorted alphabetically, all dates sort
 appropriately.

3.4 Years 10 30 and beyond (Y1030)

 As discussed in 2.4.1, the end of the universe is predicted to occur
 well before the year 10 ** 30.  However, if there is one single
 lesson to be learned from the current Y2K problems, it is that
 specifications and conventions have a way of out living their
 expected environment.  Therefore we feel it is imperative to
 completely solve the date representation problem once and for all.

3.4.1 Naive Approach for Y1030 Problem The naive solution is to prepend a single '^' (caret) - caret sorts after all letters in the ASCII order) before all years from 10 30

 to 10 ** 56.  Thus the year "Z999999999999999999999999999999" is
 followed by the year "^A1000000000000000000000000000000".  Similarly,
 all years from 10 ** 56 to 10 ** 82 get one more caret.  So, the year
 "^Z99999999999999999999999999999999999999999999999999999999" is
 followed by the year
 "^^A100000000000000000000000000000000000000000000000000000000".  This
 scheme can be extended indefinitely by prepending one addition caret
 for each additional factor of 10 ** 26 in the range of the year.
 In this approach, the number of digits in a date that are used to
 represent the year is simply:
    26 * <number of '^'> + ASCII(<prefix letter>) - ASCII('A') + 5
 Note: this algorithm is provided for informational purposes only and
 to show the path leading to the true solution.  Y10K dates MUST NOT
 use this format.  They MUST use the format in the next section.

Glassman, et. al. Informational [Page 6] RFC 2550 Y10K and Beyond 1 April 1999

3.4.2 Space Efficient Approach for Y1030 Problem The solution in 3.4.1 is not a space efficient format for giving the number of digits in the year. The length of the prefix grows linearly in the length of the year (which, itself, grows logarithmically over time). Therefore, Y10K format dates use an improved, more compact encoding of the number of digits in the year. 3.4.2.1 Years 10 30 to 10 56 As in 3.4.1, a single '^' and letter precede the year. 3.4.2.2 Years 10 56 to 10 732 The year is preceded by two carets ("^^") and two letters. The letters create a two digit, base 26 number which is the number of digits in the year minus 57. So, the year "^Z99999999999999999999999999999999999999999999999999999999" is followed by the year "^^AA100000000000000000000000000000000000000000000000000000000". The last representable year with two carets is the year (10 732) - 1

 and is "^^ZZ999..999" (i.e. two carets and two Z's, followed by 732
 consecutive 9's).
 The formula for the number of digits in the year is, based on the two
 digit prefix is:
  26 * (ASCII(<prefix letter1>) - ASCII('A')) +
        ASCII(<prefix letter2>) - ASCII('A') + 57

3.4.2.3 Years 10 732 to 10 18308

 The next block of years has the number of digits given by three
 carets ("^^^") followed by three letters forming a three-digit, base
 26 number.  The number of digits in the year is given by the formula:
  676 * (ASCII(<prefix letter1>) - ASCII('A')) +
   26 * (ASCII(<prefix letter2>) - ASCII('A')) +
         ASCII(<prefix letter3>) - ASCII('A') + 733

3.4.2.4 General Format for Y10K Dates

 In general, if there is at least one letter in a Y10K year, the
 number of the digits in the year portion of the date is given by the
 formula:
     base26(fib(n) letters) + y10k(n)

Glassman, et. al. Informational [Page 7] RFC 2550 Y10K and Beyond 1 April 1999

 Where "n" is the number of leading carets and the fig, base26 and
 y10k functions are defined with the following recurrence relations:
    fib(n) is the standard Fibonacci sequence with:
    fib(0) = 1
    fib(1) = 1
    fib(n+2) = fib(n) + fib(n+1)
    base26(m letters) is the base 26 number represented by m letters
    A-Z:
    base26(letter) =  ASCII(<letter>) - ASCII('A')
    base26(string letter) = 26 * base26(string) + base26(letter)
    y10k(n) is the necessary fudge factor to align the sequences
    properly:
    y10k(0) = 5
    y10k(n+1) = 26 ** fib(n) + y10k(n)
 If the year does not have at least one letter in the year, then the
 number of digits in the year is:
     4
 This year format is space-efficient.  The length of the prefix giving
 number of digits in the year only grows logarithmically with the
 number of digits in the year.  And, the number of carets preceding
 the prefix only grows logarithmically with the number of digits in
 the prefix.

3.5 B.C.E. (Before Common Era) Years

 Now that have a format for all of the years in the future, we'll take
 on the "negative" years.  A negative year is represented in "Y10K-
 complement" form.  A Y10K-complement year is computed as follows:
  1) Calculate the non-negative Y10K year string as in 3.4.2.4.
  2) Replace all letters by their base 26 complement.  I.E. A -> Z, B
     -> Y, ... Z -> A.
  3) Replace all digits in the year portion of the date by their base
     10 complement.  I.E. 0 -> 9, 1 -> 8, ... 9 -> 0.
  4) Replace carets by exclamation points ('!').
  5) Four-digit years are pre-pended with a slash ('/')

Glassman, et. al. Informational [Page 8] RFC 2550 Y10K and Beyond 1 April 1999

  6) Years that don't now begin with an exclamation point or slash are
     pre-pended with a star ('*').  (This rule covers the negative 5-
     31 digit years).
 For example, the year 1 BCE is represented by "/9998".  The
 conversion is accomplished by applying rules:
  1) Calculate the non-negative Y10K year ("1" -> "0001")
  2) Complement the digits ("0001" -> "9998")
  3) Four-digit numbers get a leading slash.
 The earliest four-digit BCE year (9999 BCE) becomes "/0000" and the
 year before that (10000 BCE) becomes "*Z89999".  The earliest 5-digit
 BCE year (99999 BCE) is "*Z00000".  And the year before that (100000
 BCE) is "*Y899999".  And so on.
 These rules give the desired sort order for BCE dates.  For example,
 the following dates get translated and sorted as:
   Jun 6, 200 BCE            /97990606
   199 BCE                   /9800
   Jan 1, 199 BCE            /98000101

3.6 Restrictions on Y10K Dates

 There are no restrictions on legal values for Y10K dates.  Y10K
 compliant programs MUST accept any syntactically legal Y10K date as a
 valid date.  A '0' can be appended to the end of any Y10K date,
 yielding an equivalent date that sorts immediately after the original
 date and represents the instant after the original date.
 The following are all valid representations (in sorted order) of the
 first instant of A10000:
   A1
   A10000
   A1000001
   A100000101000000
   A1000001010000000000000000000000
 Similarly, the following are all valid Y10K dates (in sorted order)
 for the time after the last instant of the A99999 and before the
 first instant of B100000:
   A999991231250000
   A999991232
   A999992
   A9999999999
   A99999999990000000000000

Glassman, et. al. Informational [Page 9] RFC 2550 Y10K and Beyond 1 April 1999

4 ABNF

 The following ABNF [Crocker] gives the formal syntax for Y10K years.
 The initial characters definitions are given in their lexical
 collation (ASCII) order.
 exclamation = '!'
 star        = '*'
 slash       = '/'
 digit       =  0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
 letter      =  A | B | C | D | E | F | G | H | I | J | K | L | M |
                 N | O | P | Q | R | S | T | U | V | W | X | Y | Z
 caret       = '^'
 year     = [*(caret | exclamation) | star | slash ] [ *letter ]
           *digit
 month    = 2digit
 day      = 2digit
 hour     = 2digit
 minute   = 2digit
 second   = 2digit
 fraction = *digit
 date     = year [ month [ day [ hour [ minute [ second [ fraction
           ]]]]]]

5 Open Issues

 There are a number date comparison problems that are beyond the scope
 of this specification.
 1) Dates from different calendar systems can not be directly
    compared.  For instance, dates from the Aztec, Bhuddist, Jewish,
    Muslim, and Hittite calendars must be converted to a common
    calendar before comparisons are possible.
 2) Future re-numberings of years are not covered.  If, and when, a
    new "Year 0" occurs and comes into general use, old dates will
    have to be adjusted.
 3) Continued existence of Earth-centric time periods (year, day,
    etc.) are problematical past the up-coming destruction of the
    solar system (5-10 billion years or so).  The use of atomic-time
    helps some since leap seconds are no longer an issue.

Glassman, et. al. Informational [Page 10] RFC 2550 Y10K and Beyond 1 April 1999

 4) Future standards and methods of synchronization for inter-
    planetary and inter-galactic time have not been agreed to.
 5) Survivability of dates past the end of the universe is uncertain.

6 Affected Standards

 A number of standards currently and RFCs use 4-digit years and are
 affected by this proposal:
   rfc2459: Internet X.509 Public Key Infrastructure
            Certificate and CRL Profile
   rfc2326: Real Time Streaming Protocol (RTSP)
   rfc2311: ODETTE File Transfer Protocol
   rfc2280: Routing Policy Specification Language (RPSL)
   rfc2259: Simple Nomenclator Query Protocol (SNQP)
   rfc2244: ACAP -- Application Configuration Access Protocol
   rfc2167: Referral Whois (RWhois) Protocol V1.5
   rfc2065: Domain Name System Security Extensions
   rfc2060: Internet Message Access Protocol - Version 4rev1
   rfc1922: Chinese Character Encoding for Internet Messages
   rfc1912: Common DNS Operational and Configuration Errors
   rfc1903: Textual Conventions for Version 2 of the
            Simple Network Management Protocol (SNMPv2)
   rfc1521: MIME (Multipurpose Internet Mail Extensions) Part One:
   rfc1123: Requirements for Internet hosts - application and support
 The following standards internally represent years as 16-bit numbers
 (0..65536) and are affected by this proposal:
   rfc2021: Remote Network Monitoring Management Information Base
            Version 2 using SMIv2
   rfc1514: Host Resources MIB
 The following ISO standard is affected:
   ISO8601: International Date Format

8 Security Considerations

 Y10K dates will improve the security of all programs where they are
 used.  Many errors in programs have been tracked to overflow while
 parsing illegal input.  Programs allocating fixed size storage for
 dates will exhibit errors when presented with larger dates.  These
 errors can be exploited by wily hackers to compromise the security of
 systems running these programs.  Since Y10K dates are arbitrary
 length strings, there is no way to make them overflow.

Glassman, et. al. Informational [Page 11] RFC 2550 Y10K and Beyond 1 April 1999

 In addition, positive Y10K dates are easy to compare and less error-
 prone for humans.  It is easier to compare the three projected end of
 the universe dates - "H100000000000", "I1000000000000" and
 "K100000000000000" - by looking at the leading letter than by
 counting the 0's.  This will reduce inadvertent errors by people.
 This advantage will become more noticeable when large dates are more
 common.
 Unfortunately, negative Y10K dates are a bit more difficult to
 decipher.  However, by comparing the current age of the universe to
 its projected end, it is obvious that there will be many more
 positive dates than negative dates.  And, while the number of
 negative dates for human history is currently greater than the number
 of positive dates, the number of negative dates is fixed and the
 number of positive dates is unbounded.

9 Conclusion

 It is not too early to aggressively pursue solutions for the Y10K
 problem.  This specification presents a simple, elegant, and
 efficient solution to this problem.

10 References

 [Crocker]   Crocker, D. and P. Overell, "Augmented BNF for Syntax
             Specifications: ABNF", RFC 2234, November 1997.
 [Drake]     Review for the Drake Equation
             http://www.umsl.edu/~bwilking/assign/drake.html
 [Microsoft] SNMP SysUpTime Counter Resets After 49.7 Days
             http://support.microsoft.com/support/kb/articles/Q169/
             8/47.asp
 [Mike]      Y1K http://lonestar.texas.net/~mdlvas/y1k.htm
 [Nigel]     Nigel's (en)lighening tour of Thermodynamics for
             Economists ;-) http://www.santafe.edu/~nigel/thermo-
             primer.html
 [NRAO]      Astronomical Times
             http://sadira.gb.nrao.edu/~rfisher/Ephemerides/times.html
 [RFC]       Here are all the online RFCs. Note: this is a LONG menu.
             http://info.internet.isi.edu/1s/in-notes/rfc/files
 [UNIX]      Year 2000 Issues http://www.rdrop.com/users/caf/y2k.html

Glassman, et. al. Informational [Page 12] RFC 2550 Y10K and Beyond 1 April 1999

 [Wilborne]  PktCDateLig
             http://www3.gamewood.net/mew3/pilot/pocketc/pktcdate/
             index.html
 [YUCK]      Y10K Unlimited Consulting Knowledgebase
             http://www.loyd.net/y10k/index.html
 [Zebu]      The Search for H0
             http://zebu.uoregon.edu/1997/ph410/l6.html

11 Authors' Addresses

 Steve Glassman
 Compaq Systems Research Center
 130 Lytton Avenue
 Palo Alto, CA 94301 USA
 Phone: +1 650-853-2166
 EMail: steveg@pa.dec.com
 Mark Manasse
 Compaq Systems Research Center
 130 Lytton Avenue
 Palo Alto, CA 94301 USA
 Phone: +1 650-853-2221
 EMail: msm@pa.dec.com
 Jeff Mogul
 Compaq Western Resarch Lab
 250 University Avenue
 Palo Alto, CA 94301 USA
 Phone: +1 650-617-3300
 EMail: mogul@pa.dec.com

Glassman, et. al. Informational [Page 13] RFC 2550 Y10K and Beyond 1 April 1999

12. Full Copyright Statement

 Copyright (C) The Internet Society (1999).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Glassman, et. al. Informational [Page 14]

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