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rfc:rfc3797

Network Working Group D. Eastlake 3rd Request for Comments: 3797 Motorola Laboratories Obsoletes: 2777 June 2004 Category: Informational

Publicly Verifiable Nominations Committee (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 (2004).

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 (NomCom) from the pool of eligible volunteers
 is used.  Similar techniques would be applicable to other cases.

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. . . . . . . . . . . . . . .  3
    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. Handling Real World Problems. . . . . . . . . . . . . . . . . .  7
    5.1.  Uncertainty as to the Pool. . . . . . . . . . . . . . . .  7
    5.2.  Randomness Ambiguities. . . . . . . . . . . . . . . . . .  7
 6. Fully Worked Example. . . . . . . . . . . . . . . . . . . . . .  8
 7. Security Considerations . . . . . . . . . . . . . . . . . . . .  9
 8. Reference Code. . . . . . . . . . . . . . . . . . . . . . . . . 10
 Appendix A: History of NomCom Member Selection . . . . . . . . . . 16
 Appendix B: Changes from RFC 2777. . . . . . . . . . . . . . . . . 16
 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . 17

Eastlake 3rd Informational [Page 1] RFC 3797 Verifiable Random Selection June 2004

 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
    Normative References. . . . . . . . . . . . . . . . . . . . . . 17
    Informative References. . . . . . . . . . . . . . . . . . . . . 17
 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 18
 Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 19

1. Introduction

 Under the IETF rules, each year ten people are randomly selected from
 among eligible volunteers to be the voting members of the IETF
 nominations committee (NomCom).  The NomCom nominates members of the
 Internet Engineering Steering Group (IESG) and the Internet
 Architecture Board (IAB) as described in [RFC 3777].  The number of
 eligible volunteers in recent years has been around 100.
 It is highly desirable that the random selection of the voting NomCom
 be done in an unimpeachable fashion so that no reasonable charges of
 bias or favoritism can be brought.  This is as much for the
 protection of the selection administrator (currently, the appointed
 non-voting NomCom chair) from suspicion of bias as it is for the
 protection of the IETF.
 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.
 The method, in the form it appears in RFC 2777, was also used by IANA
 in February 2003 to determine the ACE prefix for Internationalized
 Domain Names [RFC 3490] so as to avoid claim jumping.

2. General Flow of a Publicly Verifiable Process

 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, determine the pool from which the selection is to be made as
 provided in [RFC 3777] or its successor.
 Volunteers are solicited by the selection administrator.  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 a reasonable
 time can be given to resolve any disputes as to who should be in the
 pool.

Eastlake 3rd Informational [Page 2] RFC 3797 Verifiable Random Selection June 2004

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,
 some public future sources of randomness such as government run
 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 pre-specified 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.  The algorithm can be run to select, in an ordered fashion,
 a larger number than are actually necessary so that if any of those
 selected need to be passed over or replaced for any reason, an
 ordered set of additional alternate selections will be available.  A
 cut off time for any complaint that the algorithm was run with the
 wrong inputs or not faithfully executed must be specified to finalize
 the output and provide a stable selection.

3. Randomness

 The crux of the unbiased nature of the selection is that it is based
 in an exact, predetermined fashion on random information which will
 be revealed in the future and thus can not be known to the person
 specifying the algorithm.  That random information will be used to
 control the selection.  The random information must be such that it
 will be publicly and unambiguously revealed in a timely fashion.
 The random sources must 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 winning lottery numbers for
 specified runnings of specified public lotteries.  Particularly for
 government run lotteries, great care is taken to see that they occur
 on time and 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.

Eastlake 3rd Informational [Page 3] RFC 3797 Verifiable Random Selection June 2004

 Other possibilities are such things as the 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 also be used.  (Experience has indicated that stock prices
 and/or volumes are a poor source of unambiguous data due trading
 suspensions, company mergers, delistings, splits, multiple markets,
 etc.)  In all cases, great care must be taken to specify exactly what
 quantities are being presumed random and what will be done if their
 issuance is cancelled, delayed, or advanced.
 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
 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 one or more sources might be
 delayed, cancelled, or just plain screwed up somehow, calling into
 play contingency provisions or, worst of all, creating a situation
 that was not anticipated.  This would either require arbitrary
 judgment by the selection administrator, defeating the randomness of
 the selection, or a re-run with a new set of sources, causing much
 delay.  Three or four would be a good number of sources.  Ten is too
 many.

3.2. Skew

 Some of the sources of randomness produce data that is not uniformly
 distributed.  This is certainly true of volumes, 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., deviate
 from a uniform distribution only by an insignificant amount.

3.3. Entropy Needed

 What we are doing is selecting 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)!

Eastlake 3rd Informational [Page 4] RFC 3797 Verifiable Random Selection June 2004

 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 completely
 random 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  120
   Bits needed   18   22   25   28   30   34   37   40   44   47
 Using an inadequate number of bits means that not all of the possible
 sets of ten selected items would be available.  For a substantially
 inadequate amount of entropy, there could be a significant
 correlation between the selection of two different members of the
 pool, for example.  However, as a practical matter, for pool sizes
 likely to be encountered in IETF NomCom membership selection, 40 bits
 of entropy should always be adequate.  Even if there is a large pool
 and more bits are needed for perfect randomness, 40 bits of entropy
 will assure only an insignificant deviation from completely random
 selection for the difference in probability of selection of different
 pool members, the correlation between the selection of any pair of
 pool members, etc.
 An MD5 [RFC 1321] hash has 128 bits and therefore can produce no more
 than that number of bits of entropy.  However, this is more than
 three times what is likely to ever be needed for IETF NomCom
 membership selection.  A even stronger hash, such as SHA-1
 [RFC 3174], can be used if desired.

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 produce either a single positive number
 (i.e., NY Stock Exchange volume in thousands of shares) 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 suggested precise algorithm is as
 follows:
    1. 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), without
       leading zeroes (except for a single leading zero if the integer
       part is zero), and without trailing zeroes after the period.

Eastlake 3rd Informational [Page 5] RFC 3797 Verifiable Random Selection June 2004

    2. Order the values from each source from smallest to the largest
       and concatenate them and suffix the result with a "/".  For
       each source producing a single number, simply represent it as
       above with a suffix "/".  (This sorting is necessary because
       the same lottery results, for example, are sometimes reported
       in the order numbers were drawn and sometimes in numeric order
       and such things as the scores of two sports teams that play a
       game has no inherent order.)
    3. At this point you have a string for each source, say s1/, s2/,
       ...  Concatenate these strings in a pre-specified order, the
       order in which the sources were listed if not otherwise
       specified, and represent each character as its ASCII code
       [ASCII] producing "s1/s2/.../".
 You 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 an all zeros two byte sequence
 for the first value, the string prefixed and suffixed by 0x0001 for
 the second value, etc., treating the two bytes as a big endian
 counter.  Treat each of these derived "random" MD5 output values as a
 positive 128-bit multiprecision big endian integer.
 Then totally order the pool of listed volunteers as follows: If there
 are P volunteers, select the first by dividing the first derived
 random value by P and using the remainder plus one as the position of
 the selectee in the published list.  Select the second by dividing
 the second derived random value by P-1 and using the remainder plus
 one as the position in the list with the first selected person
 eliminated.  Etc.
 It is STRONGLY recommended that alphanumeric random sources be
 avoided due to the much greater difficulty in canonicalizing them in
 an independently repeatable fashion; however, if you choose to ignore
 this advice and use an ASCII or similar Roman alphabet source or
 sources, all white space, punctuation, accents, 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 "./".  If you choose to not just ignore but flagrantly flout
 this advice and try to use even more complex and harder to
 canonicalize internationalized text, such as UNICODE, you are on your
 own.

Eastlake 3rd Informational [Page 6] RFC 3797 Verifiable Random Selection June 2004

5. Handling Real World Problems

 In the real world, problems can arise in following the steps and flow
 outlined in Sections 2 through 4 above.  Some problems that have
 actually arisen are described below with recommendations for handling
 them.

5.1. Uncertainty as to the Pool

 Every reasonable effort should be made to see that the published pool
 from which selection is made is of certain and eligible persons.
 However, especially with compressed schedules or perhaps someone
 whose claim that they volunteered and are eligible has not been
 resolved by the deadline, or a determination that someone is not
 eligible which occurs after the publication of the pool, it may be
 that there are still uncertainties.
 The best way to handle this is to maintain the announced schedule,
 INCLUDE in the published pool all those whose eligibility is
 uncertain and to keep the published pool list numbering IMMUTABLE
 after its publication.  If someone in the pool is later selected by
 the algorithm and random input but it has been determined they are
 ineligible, they can be skipped and the algorithm run further to make
 an additional selection.  Thus the uncertainty only effects one
 selection and in general no more than a maximum of U selections where
 there are U uncertain pool members.
 Other courses of action are far worse.  Actual insertion or deletion
 of entries in the pool after its publication changes the length of
 the list and totally scrambles who is selected, possibly changing
 every selection.  Insertion into the pool raises questions of where
 to insert: at the beginning, end, alphabetic order, ... Any such
 choices by the selection administrator after the random numbers are
 known destroys the public verifiability of fair choice.  Even if done
 before the random numbers are known, such dinking with the list after
 its publication just smells bad.  There should be clear fixed public
 deadlines and someone who challenges their absence from the pool
 after the published deadline should have their challenge
 automatically denied for tardiness.

5.2. Randomness Ambiguities

 The best good faith efforts have been made to specify precise and
 unambiguous sources of randomness.  These sources have been made
 public in advance and there has not been objection to them.  However,
 it has happened that when the time comes to actually get and use this
 randomness, the real world has thrown a curve ball and it isn't quite
 clear what data to use.  Problems have particularly arisen in

Eastlake 3rd Informational [Page 7] RFC 3797 Verifiable Random Selection June 2004

 connection with stock prices, volumes, and financial exchange rates
 or indices.  If volumes that were published in thousands are
 published in hundreds, you have a rounding problem.  Prices that were
 quoted in fractions or decimals can change to the other.  If you take
 care of every contingency that has come up in the past, you can be
 hit with a new one.  When this sort of thing happens, it is generally
 too late to announce new sources, an action which could raise
 suspicions of its own.  About the only course of action is to make a
 reasonable choice within the ambiguity and depend on confidence in
 the good faith of the selection administrator.  With care, such cases
 should be extremely rare.
 Based on these experiences, it is again recommended that public
 lottery numbers or the like be used as the random inputs and stock
 prices and volumes avoided.

6. 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. Lee
       8. Sneazy       18. Longsuffering
       9. Handsome     19. Chastity
      10. Cassandra    20. Smith
 Assume the following (fake example) ordered list of randomness
 sources:
 1. The Kingdom of Alphaland State Lottery daily number for 1 November
    2004 treated as a single four digit integer.
 2. Numbers of the winning horses at Hialeia for all races for the
    first day on or after 13 October 2004 on which at least two races
    are run.
 3. The People's Democratic Republic of Betastani State Lottery six
    winning numbers (ignoring the seventh "extra" number) for 1
    November 2004.
 Hypothetical randomness publicly produced:
     Source 1:  9319
     Source 2:  2, 5, 12, 8, 10
     Source 3:  9, 18, 26, 34, 41, 45

Eastlake 3rd Informational [Page 8] RFC 3797 Verifiable Random Selection June 2004

 Resulting key string:
     9319./2.5.8.10.12./9.18.26.34.41.45./
 The table below gives the hex of the MD5 of the above key string
 bracketed with a two byte string that is successively 0x0000, 0x0001,
 0x0002, through 0x0010 (16 decimal).  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  990DD0A5692A029A98B5E01AA28F3459  25  -> 17 <-
  2  3691E55CB63FCC37914430B2F70B5EC6  24  ->  7 <-
  3  FE814EDF564C190AC1D25753979990FA  23  ->  2 <-
  4  1863CCACEB568C31D7DDBDF1D4E91387  22  -> 16 <-
  5  F4AB33DF4889F0AF29C513905BE1D758  21  -> 25 <-
  6  13EAEB529F61ACFB9A29D0BA3A60DE4A  20  -> 23 <-
  7  992DB77C382CA2BDB9727001F3CDCCD9  19  ->  8 <-
  8  63AB4258ECA922976811C7F55C383CE7  18  -> 24 <-
  9  DFBC5AC97CED01B3A6E348E3CC63F40D  17  -> 19 <-
 10  31CB111C4A4EBE9287CEAE16FE51B909  16  -> 13 <-
 11  07FA46C122F164C215BBC72793B189A3  15  -> 22 <-
 12  AC52F8D75CCBE2E61AFEB3387637D501  14  ->  5 <-
 13  53306F73E14FC0B2FBF434218D25948E  13  -> 18 <-
 14  B5D1403501A81F9A47318BE7893B347C  12  ->  9 <-
 15  85B10B356AA06663EF1B1B407765100A  11  ->  1 <-
 16  3269E6CE559ABD57E2BA6AAB495EB9BD  10  ->  4 <-
 Resulting first ten selected, in order selected:
       1. Lee (17)           6. Envy (23)
       2. Doc (7)            7. Sneazy (8)
       3. Mary (2)           8. Anger (24)
       4. Charity (16)       9. Chastity (19)
       5. Kasczynski (25)   10. Pandora (13)
 Should one of the above turn out to be ineligible or decline to
 serve, the next would be Sloth, number 22.

7. 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 should be
 followed.  And equal care needs to be given that the algorithm
 selected is faithfully executed with the designated inputs values.

Eastlake 3rd Informational [Page 9] RFC 3797 Verifiable Random Selection June 2004

 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.

8. 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.  The original code in RFC 2777 could only handle pools
 of up to 255 members and was extended to 2**16-1 by Erik Nordmark.
 This code has been extracted from this document, compiled, and
 tested.  While no flaws have been found, it is possible that when
 used with some compiler on some system some flaw will manifest
 itself.
 /****************************************************************
   *
   *  Reference code for
   *      "Publicly Verifiable Random Selection"
   *          Donald E. Eastlake 3rd
   *              February 2004
   *
   ****************************************************************/
  #include <limits.h>
  #include <math.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  /* From RFC 1321 */
  #include "global.h"
  #include "MD5.h"
  /* local prototypes */
  int longremainder ( unsigned short divisor,
                      unsigned char dividend[16] );
  long int getinteger ( char *string );
  double NPentropy ( int N, int P );
  /* limited to up to 16 inputs of up to sixteen integers each */
  /* pool limit of 2**8-1 extended to 2**16-1 by Erik Nordmark */
  /****************************************************************/
  main ()
  {
  int         i, j,  k, k2, err, keysize, selection, usel;

Eastlake 3rd Informational [Page 10] RFC 3797 Verifiable Random Selection June 2004

  unsigned short   remaining, *selected;
  long int    pool, temp, array[16];
  MD5_CTX     ctx;
  char        buffer[257], key [800], sarray[16][256];
  unsigned char    uc16[16], unch1, unch2;
  pool = getinteger ( "Type size of pool:\n" );
  if ( pool > 65535 )
      {
      printf ( "Pool too big.\n" );
      exit ( 1 );
      }
  selected = (unsigned short *) malloc ( (size_t)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" );
  else
      {
      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 );

Eastlake 3rd Informational [Page 11] RFC 3797 Verifiable Random Selection June 2004

      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
              {   /* 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] )

Eastlake 3rd Informational [Page 12] RFC 3797 Verifiable Random Selection June 2004

                      {
                      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], "/" );
          }
      }   /* 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] = (unsigned short)(i + 1);
  printf ( "index        hex value of MD5        div  selected\n" );
  for (   usel = 0, remaining = (unsigned short)pool;
          usel < selection;
          ++usel, --remaining )
      {
      unch1 = (unsigned char)usel;
      unch2 = (unsigned char)(usel>>8);
      /* prefix/suffix extended to 2 bytes by Donald Eastlake */
      MD5Init ( &ctx );
      MD5Update ( &ctx, &unch2, 1 );
      MD5Update ( &ctx, &unch1, 1 );
      MD5Update ( &ctx, (unsigned char *)key, keysize );
      MD5Update ( &ctx, &unch2, 1 );
      MD5Update ( &ctx, &unch1, 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",
  usel+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;

Eastlake 3rd Informational [Page 13] RFC 3797 Verifiable Random Selection June 2004

                  break;
                  }
      }
   printf ( "\nDone, type any character to exit.\n" );
   getchar ();
   return 0;
   }
   /* prompt for a positive non-zero integer input */
   /****************************************************************/
   long int getinteger ( char *string )
   {
   long int     i;
   int          j;
   char    tin[257];
   while ( 1 )
   {
   printf ( string );
   printf ( "(or 'exit' to exit) " );
   gets ( tin );
   j = sscanf ( tin, "%ld", &i );
   if (    ( j == EOF )
       ||  ( !j && ( ( tin[0] == 'e' ) || ( tin[0] == 'E' ) ) )
           )
       exit ( j );
   if ( ( j == 1 ) &&
        ( i > 0 ) )
       return i;
   }   /* end while */
   }
   /* get remainder of dividing a 16 byte unsigned int
      by a small positive number */
   /****************************************************************/
   int longremainder ( unsigned short 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;

Eastlake 3rd Informational [Page 14] RFC 3797 Verifiable Random Selection June 2004

       }
   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 0.0;     /* degenerate case */
  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 */

Eastlake 3rd Informational [Page 15] RFC 3797 Verifiable Random Selection June 2004

Appendix A: 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   RFC 2777
      1999/2000  Avri Doria            RFC 2777
      2000/2001  Bernard Aboba         RFC 2777
      2001/2002  Theodore Ts'o         RFC 2777
      2002/2003  Phil Roberts          RFC 2777
      2003/2004  Rich Draves           RFC 2777
 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 similar concepts to those
 documented in RFC 2777 and herein.
 RFC 2777 = Algorithmic selection using the algorithm and reference
 code provided in RFC 2777 (but not the fake example sources of
 randomness).

Appendix B: Changes from RFC 2777

 This document differs from [RFC 2777], the previous version, in three
 primary ways as follows:
 (1) Section 5, on problems actually encountered with using these
     recommendations for selecting an IETF NomCom and on how to handle
     them, has been added.
 (2) The selection algorithm code has been modified to handle pools of
     up to 2**16-1 elements and the counter based prefix and suffix
     concatenated with the key string before hashing has been extended
     to two bytes.
 (3) Mention has been added that the algorithm documented herein was
     used by IANA to select the Internationalized Domain Name ACE
     prefix and some minor wording changes made.

Eastlake 3rd Informational [Page 16] RFC 3797 Verifiable Random Selection June 2004

 (4) References have been divided into Informative and Normative.
 (5) The list in Appendix A has been brought up to date.

Acknowledgements

 Matt Crawford and Erik Nordmark made major contributions to this
 document.  Comments by Bernard Aboba, Theodore Ts'o, Jim Galvin,
 Steve Bellovin, and others have been incorporated.

References

Normative References

 [ASCII]    "USA Standard Code for Information Interchange", X3.4,
            American National Standards Institute: New York, 1968.
 [RFC 1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
            April 1992.
 [RFC 1750] Eastlake, 3rd, D., Crocker, S. and J. Schiller,
            "Randomness Recommendations for Security", RFC 1750,
            December 1994.
 [RFC 3174] Eastlake, 3rd, D. and P. Jones, "US Secure Hash Algorithm
            1 (SHA1)", RFC 3174, September 2001.

Informative References

 [RFC 3777] Galvin, J., "IAB and IESG Selection, Confirmation, and
            Recall Process: Operation of the Nominating and Recall
            Committees", BCP 10, RFC 3777, April 2004.
 [RFC 2777] Eastlake, 3rd, D., "Publicly Verifiable Nomcom Random
            Selection", RFC 2777, February 2000.
 [RFC 3490] Falstrom, P., Hoffman, P. and A. Costello,
            "Internationalizing Domain Names in Applications (IDNA)",
            RFC 3490, March 2003.

Eastlake 3rd Informational [Page 17] RFC 3797 Verifiable Random Selection June 2004

Author's Address

 Donald E. Eastlake, 3rd
 Motorola Laboratories
 155 Beaver Street
 Milford, MA 01757 USA
 Phone: +1-508-786-7554(w)
        +1-508-634-2066(h)
 EMail: Donald.Eastlake@motorola.com

Eastlake 3rd Informational [Page 18] RFC 3797 Verifiable Random Selection June 2004

Full Copyright Statement

 Copyright (C) The Internet Society (2004).  This document is subject
 to the rights, licenses and restrictions contained in BCP 78, and
 except as set forth therein, the authors retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM 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.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
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 this standard.  Please address the information to the IETF at ietf-
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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Eastlake 3rd Informational [Page 19]

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