Network Working Group D. Eastlake 3rd
Request for Comments: 2777 Motorola
Category: Informational February 2000
Publicly Verifiable Nomcom Random Selection
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 (2000). All Rights Reserved.
Abstract
This document describes a method for making random selections in such
a way that the unbiased nature of the choice is publicly verifiable.
As an example, the selection of the voting members of the IETF
Nominations Committee from the pool of eligible volunteers is used.
Similar techniques would be applicable to other cases.
Acknowledgement
Matt Crawford made major contributions to this document.
Table of Contents
1. Introduction............................................2
2. General Flow of a Publicly Verifiable Process...........2
2.1 Determination of the Pool..............................2
2.2 Publication of the Algorithm...........................2
2.3 Publication of Selection...............................3
3. Randomness..............................................3
3.1 Sources of Randomness..................................3
3.2 Skew...................................................4
3.3 Entropy Needed.........................................4
4. A Suggested Precise Algorithm...........................5
5. Fully Worked Example....................................6
6. Security Considerations.................................7
7. Reference Code.........................................8
Appendix: History of NomCom Member Selection..............14
References................................................15
Author's Address..........................................15
Full Copyright Statement..................................16
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RFC 2777 Verifiable Random Selection February 2000
1. Introduction
Under the IETF rules, each year 10 persons are randomly selected from
among the eligible persons who volunteer to be the voting members of
the nominations committee (NomCom) to nominate members of the
Internet Engineering Steering Group (IESG) and the Internet
Architecture Board (IAB) [RFC 2727]. The number of eligible
volunteers in recent years has varied in the approximate range of 40
to 60.
It is highly desireable that the random selection of the voting
NomCom be done in a unimpeachable fashion so that no reasonable
charges of bias or favoritism can be brought. This is for the
protection of the IETF from bias and protection of the administrator
of the selection (currently, the appointed non-voting NomCom chair)
from suspicion of bias.
A method such that public information will enable any person to
verify the randomness of the selection meets this criterion. This
document gives an example of such a method.
2. General Flow of a Publicly Verifiable Process
In general, a selection of NomCom members publicly verifiable as
unbiased or similar selection could follow the three steps given
below.
2.1 Determination of the Pool
First, you need to determine the pool from which the selection is to
be made.
Volunteers are solicited by the appointed (non-voting) NomCom chair.
Their names are then passed through the IETF Secretariat to check
eligibility. (Current eligibility criteria relate to IETF meeting
attendance, records of which are maintained by the Secretariat.) The
full list of eligible volunteers is made public early enough that
there is a reasonable time to resolve any disputes as to who should
be in the pool, probably a week to ten days before the selection.
2.2 Publication of the Algorithm
The exact algorithm to be used, including the public future sources
of randomness, is made public. For example, the members of the final
list of eligible volunteers are ordered by publicly numbering them,
several public future sources of randomness such as government run
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lotteries are specified, and an exact algorithm is specified whereby
eligible volunteers are selected based on a strong hash function [RFC
1750] of these future sources of randomness.
2.3 Publication of Selection
When the prespecified sources of randomness produce their output,
those values plus a summary of the execution of the algorithm for
selection should be announced so that anyone can verify that the
correct randomness source values were used and the algorithm properly
executed. A cut off time for any complaint that the algorithm was
run with the wrong inputs or not faithfully executed should be
specified to finalize the output and provide a stable NomCom.
3. Randomness
The crux of the unbiased nature of the selection is that it is based
exactly on random information which will be revealed in the future
and thus can not be known to the person specifying the algorithm by
which that random information will be used to select the NomCom
members. The random information must be such that it will be
publicly revealed in a timely fashion.
The random sources should not include anything that any reasonable
person would believe to be under the control or influence of the IETF
or its components, such as IETF meeting attendance statistics,
numbers of documents issued, or the like.
3.1 Sources of Randomness
Examples of good information to use are lottery winning numbers for
specified runnings of specified lotteries. Particularly for
government run lotteries, great care is usually taken to see that
they produce random quantities. Even in the unlikely case one were
to have been rigged, it would almost certainly be in connection with
winning money in the lottery, not in connection with IETF use.
Other possibilities are such things as the closing price of a stock
on a particular day, daily balance in the US Treasury on a specified
day, the volume of trading on the New York Stock exchange on a
specified day, etc. (However, the reference code given below will not
handle integers that are too large.) Sporting events can be used but
only with care to specify exactly what quantities are being presumed
random and what will be done if they are cancelled or delayed.
It is important that the last source of randomness, chronologically,
produce a substantial amount of the entropy needed. If most of the
randomness has come from the earlier of the specified sources, and
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someone has even limited influence on the final source, they might do
an exhaustive analysis and exert such influence so as to bias the
selection in the direction they wanted. Thus it is best for the last
source to be an especially strong and unbiased source of a large
amount of randomness such as a government run lottery.
It is best not to use too many different sources. Every additional
source increases the probability that it might be delayed or
cancelled calling into play contingency plans or, worst of all,
possibly creating a situation that was not anticipated. This would
either require arbitrary judgement by the Nomcom chair, defeating the
randomness of the selection, or a re-run with a new set of sources,
causing much delay. Probably a good number of sources is three.
3.2 Skew
Many of the sources of randomness suggested above produce data which
is not uniformly distributed. This is certainly true of stock prices
and horse race results, for example. However, use of a strong mixing
function [RFC 1750] will extract the available entropy and produce a
hash value whose bits, remainder modulo a small divisor, etc., are
uniformly distributed.
3.3 Entropy Needed
What we are doing is selection N items without replacement from a
population of P items. The number of different ways to do this is as
follows, where "!" represents the factorial function:
P!
-------------
N! * (P - N)!
To do this in a completely random fashion requires as many random
bits as the logarithm base 2 of that quantity. Some sample
calculated approximate number of random bits for the selection of 10
nomcom members from various pool sizes is given below:
Random Selection of Ten Items From Pool
Pool size 20 25 30 35 40 50 60 75 100
Bits needed 18 22 25 28 30 34 37 40 44
Using an inadequate number of bits means that not all of the possible
selections would be available. For a substantially inadequate amount
of entropy, there would be substantial correlations between the
selection of two members of the pool, for example. However, as a
practical matter, for pool sizes likely to be encountered in IETF
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nomcom membership selection, 40 bits of entropy should always be
adequate. Even if there is a large pool and theoretically more bits
are needed for complete randomness, 40 bits of entropy will assure
that the probability of selection of each pool member differs from
that of other pool members, the correlation between the selection of
any pair of pool members, etc., differs only insignificantly from
that for completely random selection.
An MD5 [RFC 1321] hash has 128 bits and therefore can produce no more
than that number of bits of entropy. However, this is three times
what is likely to ever been needed for IETF nomcom membership
selection.
4. A Suggested Precise Algorithm
It is important that a precise algorithm be given for mixing the
random sources specified and making the selection based thereon.
Sources suggested above each produce either a single positive number
(i.e., closing price for a stock) or a small set of positive numbers
(many lotteries provide 6 numbers in the range of 1 through 40 or the
like, a sporting event could produce the scores of two teams, etc.).
A sample precise algorithm is as follows:
For each source producing multiple numeric values, represent each as
a decimal number terminated by a period (or with a period separating
the whole from the fractional part) and without leading zeroes
(except for a single leading zero if the integer part is zero) or
trailing zeroes after the period. Order them from smallest to the
largest and concatenate them and follow the results by a "/". For
each source producing a single number, simply represent it as above
with a trailing "/". At this point you have a string for each
source, say s1/, s2/, ... Concatenate these strings in a pre-
specified order and represent each character as its ASCII code
producing s1/s2/.../.
You can then produce a sequence of random values derived from a
strong mixing of these sources by calculating the MD5 hash [RFC 1321]
of this string prefixed and suffixed with a zero byte for the first
value, the string prefixed and suffixed by a 0x01 byte for the second
value, etc. Treat each of these derived random values as a positive
multiprecision integer. If there are P eligible volunteers, select
the first voting member by dividing the first derived random value by
P and using the remainder plus one as the position of the selectee in
the ordered list or volunteers. Select the second voting member by
dividing the second derived random value by P-1 and using the
remainder plus one as the position of the selectee in the list with
the first selectee eliminated. Etc.
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It is recommended that alphanumeric random sources be avoided due to
the greater difficulty in canonicalizing them in an independently
repeatable fashion; however, if any are used, all white space,
punctuation, and special characters should be removed and all letters
set to upper case. This will leave only an unbroken sequence of
letters A-Z and digits 0-9 which can be treated as a canonicalized
number above and suffixed with a "/".
5. Fully Worked Example
Assume the following ordered list of 25 eligible volunteers is
published in advance of selection:
1. John 11. Pollyanna 21. Pride
2. Mary 12. Pendragon 22. Sloth
3. Bashful 13. Pandora 23. Envy
4. Dopey 14. Faith 24. Anger
5. Sleepy 15. Hope 25. Kasczynski
6. Grouchy 16. Charity
7. Doc 17. Love
8. Sneazy 18. Longsuffering
9. Handsome 19. Chastity
10. Cassandra 20. Smith
Assume the following (fake example) ordered list of randomness
sources:
1. The People's Democracy of Betastani State Lottery six winning
numbers (ignoring the seventh "extra" number) for 1 October 1998.
2. Numbers of the winning horses at Hialeia for all races for the
first day on or after x September 1998 on which at least two
races are run.
3. The Republic of Alphaland State Lottery daily number for 1
October 1998 treated as a single four digit integer.
4. Closing price of Example Corporation stock on the Lunar Stock
Exchange for the first business day after x September 1998 when
it trades.
Randomness publicly produced:
Source 1: 9, 18, 26, 34, 41, 45
Source 2: 2, 5, 12, 8, 10
Source 3: 9319
Source 4: 13 11/16
Resulting key string:
9.18.26.34.41.45./2.5.8.10.12./9319./13.6875/
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The table below gives the hex of the MD5 of the above key string
bracketed with a byte whose value is successively 0x00, 0x01, 0x02,
through 0x09. The divisor for the number size of the remaining pool
at each stage is given and the index of the selectee as per the
original number of those in the pool.
index hex value of MD5 div selected
1 746612D0A75D2A2A39C0A957CF825F8D 25 -> 12 <-
2 95E31A4429ED5AAF7377A15A8E10CD9D 24 -> 6 <-
3 AFB2B3FD30E82AD6DC35B4D2F1CFC77A 23 -> 8 <-
4 06821016C2A2EA14A6452F4A769ED1CC 22 -> 3 <-
5 94DA30E11CA7F9D05C66D0FD3C75D6F7 21 -> 2 <-
6 2FAE3964D5B1DEDD33FDA80F4B8EF45E 20 -> 24 <-
7 F1E7AB6753A773EFE46393515FDA8AF8 19 -> 11 <-
8 700B81738E07DECB4470879BEC6E0286 18 -> 19 <-
9 1F23F8F8F8E5638A29D332BC418E0689 17 -> 15 <-
10 61A789BA86BF412B550A5A05E821E0ED 16 -> 22 <-
Resulting selection, in order selected:
1. Pendragon (12) 6. Anger (24)
2. Grouchy (6) 7. Pollyanna (11)
3. Sneazy (8) 8. Chastity (19)
4. Bashful (3) 9. Hope (15)
5. Mary (2) 10. Sloth (22)
6. Security Considerations
Careful choice of should be made of randomness inputs so that there
is no reasonable suspicion that they are under the control of the
administrator. Guidelines given above to use a small number of
inputs with a substantial amount of entropy from the last shoud be
followed. And equal care needs to be given that the algorithm
selected is faithfully executed with the designated inputs values.
Publication of the results and a week or so window for the community
of interest to duplicate the calculations should give a reasonable
assurance against implementation tampering.
To maintain the unpredictable character of selections, should a
member of the nomcom need to be replaced due to death, resignation,
expulsion, etc., new publicly announced future random sources should
be used for the selection of their replacement.
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7. Reference Code
This code makes use of the MD5 reference code from [RFC 1321] ("RSA
Data Security, Inc. MD5 Message-Digest Algorithm"). The portion of
the code dealing with multiple floating point numbers was written by
Matt Crawford.
/****************************************************************
*
* Reference code for
* "Publicly Verifiable Nomcom Random Selection"
* Donald E. Eastlake 3rd
*
****************************************************************/
#include <limits.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "global.h"
#include "MD5.h"
/* local prototypes */
int longremainder ( unsigned char divisor,
unsigned char dividend[16] );
int getinteger ( char *string );
double NPentropy ( int N, int P );
/* limited to 16 inputs of up to sixteen integers each */
/****************************************************************/
main ()
{
int i, j, k, k2, err, keysize, pool, selection;
unsigned char unch, uc16[16], remaining, *selected;
long int temp, array[16];
MD5_CTX ctx;
char buffer[257], key [800], sarray[16][256];
pool = getinteger ( "Type size of pool:\n" );
if ( pool > 255 )
{
printf ( "Pool too big.\n" );
exit ( 1 );
}
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selected = (unsigned char *) malloc ( pool );
if ( !selected )
{
printf ( "Out of memory.\n" );
exit ( 1 );
}
selection = getinteger ( "Type number of items to be selected:\n" );
if ( selection > pool )
{
printf ( "Pool too small.\n" );
exit ( 1 );
}
if ( selection == pool )
{
printf ( "All of the pool is selected.\n" );
exit ( 0 );
}
err = printf ( "Approximately %.1f bits of entropy needed.\n",
NPentropy ( selection, pool ) + 0.1 );
if ( err <= 0 ) exit ( 1 );
for ( i = 0, keysize = 0; i < 16; ++i )
{
if ( keysize > 500 )
{
printf ( "Too much input.\n" );
exit ( 1 );
}
/* get the "random" inputs. echo back to user so the user may
be able to tell if truncation or other glitches occur. */
err = printf (
"\nType #%d randomness or 'end' followed by new line.\n"
"Up to 16 integers or the word 'float' followed by up\n"
"to 16 x.y format reals.\n", i+1 );
if ( err <= 0 ) exit ( 1 );
gets ( buffer );
j = sscanf ( buffer,
"%ld%ld%ld%ld%ld%ld%ld%ld%ld%ld%ld%ld%ld%ld%ld%ld",
&array[0], &array[1], &array[2], &array[3],
&array[4], &array[5], &array[6], &array[7],
&array[8], &array[9], &array[10], &array[11],
&array[12], &array[13], &array[14], &array[15] );
if ( j == EOF )
exit ( j );
if ( !j )
if ( buffer[0] == 'e' )
break;
else
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{ /* floating point code by Matt Crawford */
j = sscanf ( buffer,
"float %ld.%[0-9]%ld.%[0-9]%ld.%[0-9]%ld.%[0-9]"
"%ld.%[0-9]%ld.%[0-9]%ld.%[0-9]%ld.%[0-9]"
"%ld.%[0-9]%ld.%[0-9]%ld.%[0-9]%ld.%[0-9]"
"%ld.%[0-9]%ld.%[0-9]%ld.%[0-9]%ld.%[0-9]",
&array[0], sarray[0], &array[1], sarray[1],
&array[2], sarray[2], &array[3], sarray[3],
&array[4], sarray[4], &array[5], sarray[5],
&array[6], sarray[6], &array[7], sarray[7],
&array[8], sarray[8], &array[9], sarray[9],
&array[10], sarray[10], &array[11], sarray[11],
&array[12], sarray[12], &array[13], sarray[13],
&array[14], sarray[14], &array[15], sarray[15] );
if ( j == 0 || j & 1 )
printf ( "Bad format." );
else {
for ( k = 0, j /= 2; k < j; k++ )
{
/* strip trailing zeros */
for ( k2=strlen(sarray[k]); sarray[k][--k2]=='0';)
sarray[k][k2] = '\0';
err = printf ( "%ld.%s\n", array[k], sarray[k] );
if ( err <= 0 ) exit ( 1 );
keysize += sprintf ( &key[keysize], "%ld.%s",
array[k], sarray[k] );
}
keysize += sprintf ( &key[keysize], "/" );
}
}
else
{ /* sort values, not a very efficient algorithm */
for ( k2 = 0; k2 < j - 1; ++k2 )
for ( k = 0; k < j - 1; ++k )
if ( array[k] > array[k+1] )
{
temp = array[k];
array[k] = array[k+1];
array[k+1] = temp;
}
for ( k = 0; k < j; ++k )
{ /* print for user check */
err = printf ( "%ld ", array[k] );
if ( err <= 0 ) exit ( 1 );
keysize += sprintf ( &key[keysize], "%ld.", array[k] );
}
keysize += sprintf ( &key[keysize], "/" );
}
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} /* end for i */
/* have obtained all the input, now produce the output */
err = printf ( "Key is:\n %s\n", key );
if ( err <= 0 ) exit ( 1 );
for ( i = 0; i < pool; ++i )
selected [i] = i + 1;
printf ( "index hex value of MD5 div selected\n" );
for ( unch = 0, remaining = pool;
unch < selection;
++unch, --remaining )
{
MD5Init ( &ctx );
MD5Update ( &ctx, &unch, 1 );
MD5Update ( &ctx, (unsigned char *)key, keysize );
MD5Update ( &ctx, &unch, 1 );
MD5Final ( uc16, &ctx );
k = longremainder ( remaining, uc16 );
/* printf ( "Remaining = %d, remainder = %d.\n", remaining, k ); */
for ( j = 0; j < pool; ++j )
if ( selected[j] )
if ( --k < 0 )
{
printf ( "%2d "
"%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X "
"%2d -> %2d <-\n",
unch+1, uc16[0],uc16[1],uc16[2],uc16[3],uc16[4],uc16[5],uc16[6],
uc16[7],uc16[8],uc16[9],uc16[10],uc16[11],uc16[12],uc16[13],uc16[14],
uc16[15], remaining, selected[j] );
selected[j] = 0;
break;
}
}
printf ( "\nDone, type any character to exit.\n" );
getchar ();
return 0;
}
/* prompt for an integer input */
/****************************************************************/
int getinteger ( char *string )
{
int i, j;
char tin[257];
while ( 1 )
{
printf ( string );
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printf ( "(or 'exit' to exit) " );
gets ( tin );
j = sscanf ( tin, "%d", &i );
if ( ( j == EOF )
|| ( !j && ( ( tin[0] == 'e' ) || ( tin[0] == 'E' ) ) )
)
exit ( j );
if ( j == 1 )
return i;
} /* end while */
}
/* get remainder of dividing a 16 byte unsigned int
by a small positive number */
/****************************************************************/
int longremainder ( unsigned char divisor,
unsigned char dividend[16] )
{
int i;
long int kruft;
if ( !divisor )
return -1;
for ( i = 0, kruft = 0; i < 16; ++i )
{
kruft = ( kruft << 8 ) + dividend[i];
kruft %= divisor;
}
return kruft;
} /* end longremainder */
/* calculate how many bits of entropy it takes to select N from P */
/****************************************************************/
/* P!
log ( ----------------- )
2 N! * ( P - N )!
*/
double NPentropy ( int N, int P )
{
int i;
double result = 0.0;
if ( ( N < 1 ) /* not selecting anything? */
|| ( N >= P ) /* selecting all of pool or more? */
)
return 1.0; /* degenerate case */
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for ( i = P; i > ( P - N ); --i )
result += log ( i );
for ( i = N; i > 1; --i )
result -= log ( i );
/* divide by [ log (base e) of 2 ] to convert to bits */
result /= 0.69315;
return result;
} /* end NPentropy */
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Appendix: History of NomCom Member Selection
For reference purposes, here is a list of the IETF Nominations
Committee member selection techniques and chairs so far:
YEAR CHAIR SELECTION METHOD
1993/1994 Jeff Case Clergy
1994/1995 Fred Baker Clergy
1995/1996 Guy Almes Clergy
1996/1997 Geoff Huston Spouse
1997/1998 Mike St.Johns Algorithm
1998/1999 Donald Eastlake 3rd This Algorithm
1999/2000 Avri Doria This Alogrithm
Clergy = Names were written on pieces of paper, placed in a
receptacle, and a member of the clergy picked the Nomcom members.
Spouse = Same as Clergy except chair's spouse made the selection.
Algorithm = Algorithmic selection based on the same concepts as
documented herein.
This Algorithm = Algorithmic selection using the algorithm and
reference code (but not the fake example sources of randomness)
described herein.
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References
RFC 1321 Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992.
RFC 1750 Eastlake, D., 3rd, Crocker, S. and J. Schiller, "Randomness
Recommendations for Security", RFC 1750, December 1994.
RFC 2727 Galvin, J., "IAB and IESG Selection, Confirmation, and
Recall Process: Operation of the Nominating and Recall
Committees", BCP 10, RFC 2727, February 2000.
Author's Address
Donald E. Eastlake, 3rd
Motorola
65 Shindegan Hill Road, RR #1
Carmel, NY 10512 USA
Phone: +1-914-276-2668 (h)
+1-508-261-5434 (w)
Fax: +1-508-261-4447 (w)
EMail: Donald.Eastlake@motorola.com
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Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved.
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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