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Network Working Group                                    D. Eastlake 3rdRequest for Comments: 2777                                      MotorolaCategory: Informational                                    February 2000Publicly Verifiable Nomcom Random SelectionStatus 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 Contents1. Introduction............................................22. General Flow of a Publicly Verifiable Process...........22.1 Determination of the Pool..............................22.2 Publication of the Algorithm...........................22.3 Publication of Selection...............................33. Randomness..............................................33.1 Sources of Randomness..................................33.2 Skew...................................................43.3 Entropy Needed.........................................44. A Suggested Precise Algorithm...........................55. Fully Worked Example....................................66. Security Considerations.................................77.  Reference Code.........................................8   Appendix: History of NomCom Member Selection..............14   References................................................15   Author's Address..........................................15   Full Copyright Statement..................................16Eastlake                     Informational                      [Page 1]

RFC 2777              Verifiable Random Selection          February 20001. 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 runEastlake                     Informational                      [Page 2]

RFC 2777              Verifiable Random Selection          February 2000   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, andEastlake                     Informational                      [Page 3]

RFC 2777              Verifiable Random Selection          February 2000   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 IETFEastlake                     Informational                      [Page 4]

RFC 2777              Verifiable Random Selection          February 2000   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.Eastlake                     Informational                      [Page 5]

RFC 2777              Verifiable Random Selection          February 2000   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/Eastlake                     Informational                      [Page 6]

RFC 2777              Verifiable Random Selection          February 2000   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.Eastlake                     Informational                      [Page 7]

RFC 2777              Verifiable Random Selection          February 20007.  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 );       }Eastlake                     Informational                      [Page 8]

RFC 2777              Verifiable Random Selection          February 2000   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;           elseEastlake                     Informational                      [Page 9]

RFC 2777              Verifiable Random Selection          February 2000               {   /* 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], "/" );           }Eastlake                     Informational                     [Page 10]

RFC 2777              Verifiable Random Selection          February 2000       }   /* 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 );Eastlake                     Informational                     [Page 11]

RFC 2777              Verifiable Random Selection          February 2000   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 */Eastlake                     Informational                     [Page 12]

RFC 2777              Verifiable Random Selection          February 2000   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                     Informational                     [Page 13]

RFC 2777              Verifiable Random Selection          February 2000Appendix: 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.Eastlake                     Informational                     [Page 14]

RFC 2777              Verifiable Random Selection          February 2000ReferencesRFC 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.comEastlake                     Informational                     [Page 15]

RFC 2777              Verifiable Random Selection          February 2000Full Copyright Statement   Copyright (C) The Internet Society (2000).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Eastlake                     Informational                     [Page 16]