Movatterモバイル変換

Network Working Group                                       S. GlassmanRequest for Comments: 2550                                   M. ManasseCategory: Stinkards Track                                      J. Mogul                                            Compaq Computer Corporation                                                           1 April 1999Y10K and BeyondStatus 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 19991.2.2 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 19992.4.2 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 99,999Glassman, 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 10**30 (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 (Y10**30)   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 Y10**30 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 19993.4.2 Space Efficient Approach for Y10**30 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') + 573.4.2.3 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') + 7333.4.2.4 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            /980001013.6 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     A99999999990000000000000Glassman, et. al.            Informational                      [Page 9]

RFC 2550                    Y10K and Beyond                 1 April 19994 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 Profilerfc2326: Real Time Streaming Protocol (RTSP)rfc2311: ODETTE File Transfer Protocolrfc2280: Routing Policy Specification Language (RPSL)rfc2259: Simple Nomenclator Query Protocol (SNQP)rfc2244: ACAP -- Application Configuration Access Protocolrfc2167: Referral Whois (RWhois) Protocol V1.5rfc2065: Domain Name System Security Extensionsrfc2060: Internet Message Access Protocol - Version 4rev1rfc1922: Chinese Character Encoding for Internet Messagesrfc1912: Common DNS Operational and Configuration Errorsrfc1903: 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 SMIv2rfc1514: Host Resources MIB   The following ISO standard is affected:     ISO8601: International Date Format8 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 Equationhttp://www.umsl.edu/~bwilking/assign/drake.html   [Microsoft] SNMP SysUpTime Counter Resets After 49.7 Dayshttp://support.microsoft.com/support/kb/articles/Q169/8/47.asp   [Mike]      Y1Khttp://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 Timeshttp://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 Issueshttp://www.rdrop.com/users/caf/y2k.htmlGlassman, et. al.            Informational                     [Page 12]

RFC 2550                    Y10K and Beyond                 1 April 1999   [Wilborne]  PktCDateLighttp://www3.gamewood.net/mew3/pilot/pocketc/pktcdate/index.html   [YUCK]      Y10K Unlimited Consulting Knowledgebasehttp://www.loyd.net/y10k/index.html   [Zebu]      The Search for H0http://zebu.uoregon.edu/1997/ph410/l6.html11 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.comGlassman, et. al.            Informational                     [Page 13]

RFC 2550                    Y10K and Beyond                 1 April 199912.  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]