path: root/doc/rfc/rfc3797.txt

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]
^L
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]
^L
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]
^L
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]
^L
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]
^L
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]
^L
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]
^L
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]
^L
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]
^L
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]
^L
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]
^L
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]
^L
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]
^L
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]
^L
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]
^L
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]
^L
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]
^L
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]
^L
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
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at ietf-
   ipr@ietf.org.

Acknowledgement

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









Eastlake 3rd                 Informational                     [Page 19]
^L