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 (C) The Internet Society (1999). All Rights Reserved.
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
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
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
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
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).
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
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.
220.127.116.11 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 ** (-
This discussion clearly shows that any fixed-format, integer
representation of a date is likely to be insufficiently precise for
18.104.22.168 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,
the well known problems of real numbers - rounding, de-normalization,
non-uniform distribution, etc. - just add to the problems of dealing
2 Structure of Y10K Solution
Any Y10K solution should have the following characteristics.
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
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.
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
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
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
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
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
followed by the year
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:
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.
3.4.2 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.
22.214.171.124 Years 10 ** 30 to 10 ** 56
As in 3.4.1, a single '^' and letter precede the year.
126.96.36.199 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
followed by the year
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
The formula for the number of digits in the year is, based on the two
digit prefix is:
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:
y10k(n) is the necessary fudge factor to align the sequences
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:
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
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 188.8.131.52.
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 ('/')
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:
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:
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 ]
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.
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.
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
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.
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.
[Crocker] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[Drake] Review for the Drake Equation
[Microsoft] SNMP SysUpTime Counter Resets After 49.7 Days
[Zebu] The Search for H0
11 Authors' Addresses
Compaq Systems Research Center
130 Lytton Avenue
Palo Alto, CA 94301 USA
Phone: +1 650-853-2166
Compaq Systems Research Center
130 Lytton Avenue
Palo Alto, CA 94301 USA
Phone: +1 650-853-2221
Compaq Western Resarch Lab
250 University Avenue
Palo Alto, CA 94301 USA
Phone: +1 650-617-3300
12. Full Copyright Statement
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