Publicly Verifiable Nominations Committee (NomCom) Random Selection

Internet-Draft	Verifiable Random Selection	June 2024
Eastlake	Expires 30 December 2024	[Page]

Abstract

This document describes a method for making random selections in such a way as to promote public confidence in the unbiased nature of the choice. This method is referred to in this document as "verifiable selection". It focuses on the selection of the voting members of the IETF Nominations Committee (NomCom) from the pool of eligible volunteers; however, similar techniques could be and have been applied to other selections. It provdes an optional extension for multiple rounds of such selection that can be induced by earlier selectees without compromising the unpredictable nature of the selections. This document obsoletes RFC 3797.¶

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 cannot 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.¶

3.1. Sources of Randomness

The random sources MUST NOT include anything that a reasonable person would believe to be under the control or influence of the selection administrator. In the case of the IETF NomCom, that includes anything under the control or influence of the IETF or its components, such as IETF meeting attendance statistics, numbers of documents issued, or the like.¶

Examples of good information to use are winning lottery numbers for specified runnings of specified public lotteries. Particularly for major government run lotteries, great care is taken to see that they occur on time (or with minimal delay) and produce random quantities. Even in the very unlikely case one was 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 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 example code given below will not handle integers that are too large.) Sporting events can also be used. Experience has indicated that individual stock prices and/or volumes are a poor source of unambiguous data due to trading suspensions, company mergers, delistings, splits, multiple markets, etc. In all cases, great care MUST be taken to specify exactly what quantities are being used for randomness and what will be done if their issuance is cancelled, delayed, or advanced.¶

It is desireable 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 RECOMMENDED that the last source be an especially strong and unbiased source of a large amount of randomness such as a major 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 an unanticipated situation. 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 in what, for the IETF NomCom, needs to be a time bounded process. Three or four would be a good number of randomness sources. More than five is too many and is NOT RECOMMEDED.¶

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 [RFC4086] will extract the available entropy and produce a hash value whose bits and whose remainder modulo a small divisor, only deviate from a uniform distribution 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)!

To do this in a completely random fashion requires as many random bits as the logarithm base 2 of that quantity. Some example approximate calculated number of random bits for the completely random selection of 10 items, such as IETF NomCom members, or 1 item, from various pool sizes are given below:¶

Table 1
Completely Random Selection of One or Ten Items From A Pool
Pool size	60	80	100	125	150	175	200	250
Bits needed to select 1	5.9	6.3	6.6	7.0	7.2	7.4	7.6	8.0
Bits needed to select 10	36	41	44	47	50	52	54	58

Using a smaller number of bits means that not all of the possible selections would be available, for example not all sets of 10 if 10 things are being selected. For a substantially smaller amount of entropy, if multiple things are being selected, there could be a correlation between the selection of two different members of the pool. However, as a practical matter, for pool sizes likely to be encountered in IETF NomCom membership selection, 42 bits of entropy should provide a sufficiently random selection of 10 items as further discussed in Appendix B.¶

The current USA Power Ball and Mega Millions lottery drawings have about 24 bits of entropy each in the five selected regular numbers and about 6 bits of entropy each in the Power Ball / Mega Ball. A four-digit daily numbers game drawing that selects four decimal digits has a little over 13 bits of entropy.¶

The source code in Section 10 uses the HMAC-SHA-256 [RFC6234] hash function which has 256 bits of output and therefore can preserve no more than that number of bits of entropy. However, this is very much more than what is likely to be needed for IETF NomCom membership selection and it is a strong mixing function that will defeat skew in the randomness input (see Section 3.2).¶

Table 2
Input	Canonicalized
0	0.
0.0	0.
42	42
7.0	7.
013.	13.
.420	0.42
12.34	12.34
1.2340	1.234

6. Extended NomCom Selection

There may be reasons why one or more of the selected members of the pool need to be eliminated and further selections made. This is particularly true for the IETF NomCom given the strong recommendation above that, in case of doubt or not-yet-resolved eligibility dispute, possible pool members should be left in the pool with the understanding that, in the event they are selected, they can be eliminated should it be decided they are not eligible. For the IETF NomCom, there are two types of reasons for elimination as follows:¶

The reasons for elimination are divided into two categories, A and B, below. Only eliminations for category B reasons could benefit from the Extension mechanisms of this section.¶

A.

Elimination due to direct rule enforcement by the administrator. Examples would be someone that did not meet the eligibility requirements or whose inclusion would violate the rule (or similar future rules) limiting the number of NomCom voting members with the same sponsor or all but one occurrence of someone included multiple times due to a name change or similar confusion. When there are such eliminations in the initial selectees, the administrator simply goes further down the ordered list produced with the initial randomness sources until there are the desired number of selectees who are not eliminated by such decisions. The administrator SHOULD announce who has been eliminated and the reason for the administrator's decision to eliminate them.¶

B.

Eliminations due to inability by the administrator to obtain confirmation of agreement from the selectee to serve before an established deadline. For example, either the selectee declines to serve or, despite reasonable efforts, a response cannot be obtained from the selectee as to whether they are willing to serve.¶

(The elimination of someone due to non-contactability may be viewed by the indiviual involved as working a hardship for them if it was due to no fault of their own and they wanted to serve. But there is no reasonable alternative if a NomCom voting membership of volunteers with a confirmed agreement to serve is to be finalized in a timely manner. Since someone so eliminated will, as provided below, be replaced by another randomly selected and fully qualified pool member, there is no problem from the point of view of NomCom composition.)¶

It will frequently be the case that, after the initial selection from the pool and the handling of any Type A eliminations as above, there will be a small number of Type B eliminations. If no further actions were taken, there will be an insufficient number of people selected and not eliminated. If additional selectees were found in such a case by just going further down the ordered list, as with Type A eliminations, this would give initially selected persons the ability to, by declining to serve, in effect, transfer their voting NomCom membership to a known different person since the entire initial ordered list is, at that point, publicly known. Some believe this is a problem and some do not. If the administrator decides to do so and announces it in advance, this is resolved by the administrator iteratively using what is essentially a miniature version of the initial selection to re-randomize the remaining pool members as described below.¶

6.1. Preparing for Possible Extension

Before the announcement of the public randomness sources, the administrator determines a secret random seed R possibly using the techniques given in Section 4 using secret sources of randomness which MUST be different from those publicly announced for the initial selection. For example, multiple rolls of a 20-sided die with numbered sides. The administrator MUST record this secret random seed and SHOULD record its randomness source(s) although these need not be publicly verifiable.¶

The administrator then secretly calculates and records a hash chain using the SHA-256 [RFC6234] hash function, denoted as H, as follows: denote H(R) as H[1](R), H(H(R)) = H(H[1](R)) as H[2](R), H(H(H(R))) = H(H[2](R)) as H[3](R), ... H(H[N-1](R))) as H[N](R), where N is a number chosen by the administrator as somewhat larger the maximum plausible number of times it might be necessary to extend selection due to Type B eliminations. It would always be safe to set N to the size of the pool minus the number of people to be selected but, as a practical matter for IETF NomCom selection, an N of 20 or so should be a generous allowance.¶

If the adminsitrator has decided to provide for possible extensions, the last hash chain value, H[N](R), is publicly announced at the same time as the publicly verifiable randomness sourced and algorithm and is used as specified in Step 5.B in Section 4.¶

6.2. Extension Procedure

The new pool consists of the initial pool in the same order without any selectees who have agreed to serve and without any pool members eliminated by any earlier Type A or B eliminations.¶
The new randomness is the next earlier value in the hash chain, that is H[N - 1](R). This randomness is used as part of the message being hashed by HMAC-SHA-256 as specified in Step 5.B in Section 4. The key remains the same. (See worked example and the example code below.)¶
The administrator publicly announces the selectees who were not eliminated, how many additional selections are needed, and H[N - 1](R). Since H[N(R) was previously made public, anyone can check that the administrator has correctly announced H[N - 1](R) by calculating H(H[N - 1](R)) and comparing it with H[N](R). The administrator announces the extended selections and any further selectees from the extended selection due to category A eliminations.¶
The administrator still needs to check for category B eliminations among the new Extended Selection selectees. At this point in the process, the time constraints are likely to be very tight so contacting extensions selectees to be sure they are still willing to serve MUST be done urgently and with a very tight firm deadline. Since there may be further category B eliminations among the extended selectees, more than one cycle of Extended Selection may be needed. If so, steps 2 through 5 are repeated with minor modifications as follows: For Step 2, those in the pool before the next extension are all those from the pool who have not been selected or been subject to category A or B elimination so far. In particular, note that because they have been previous eliminated and to avoid various complex disputes and timing race conditions, someone who was uncontactable or declined to serve in an earlier round does NOT become eligible for later rounds even if they later become contactable or change their mind about declining. For Step 3, the next earlier hash in the hash chain is used as the additional randomness in the message hashed. In Step 4 the hash chain value announced is H[N-E](R) where this is the Eth Selection Extension.¶

The use of a hash chain, as in step 1 above, is a well known technique that first appeared in [Lamport] and is used in [RFC1760]. Because the hash function H is assumed to be non-invertible, the public announcement of H[N](R) or any other value in the chain does not reveal any earlier values in the hash chain. While the administrator could try various values of R and could thus influence the value of H[N](R) or other H[*](R), this does not provide any control over the selections because the hash chain value is combined with the output of the pre-specified public randomness sources using HMAC-SHA-256.¶

Multiple extension cycles may be required so the selection administration should allow enough time for at least 5 of them. For example, in the selection of the 2022/2023 NomCom, 3 extensions would have been required: The pool was, by historical standards, huge, with 267 members, the largest up till then. In the initial selection, one of the 10 potential selectees was category B eliminated because confirmation of their willingness to serve could not be obtained in a timely fashion. In the 1st Extended Selection, the 11th potential selectee was category B eliminated because they declined to serve and the 12th was category A eliminated because there were already two selectees with the same sponsor. In the 2nd Extended Selection, the 13th potential selected also declined to serve. In the 3rd Extended Selection, the 14th potential selectee became the final voting member of the Nomcom when they confirmed their willingness to serve.¶

Table 3
index	Base64 value of SHA-256	div	selected
1	fgSNUcziqvUcd1j46xGZdpLQmgyW+OZzGfJAx2/EyS0=	31	> 4 <
2	kMd2sgTSiCF1o11lM6Rs8yeQeRMLPnZo5k0wSFPMjHw=	30	> 30 <
3	pwrk69jq8cUF5KrD0vg31SQMOvtf5117Y6Ox5cm38f0=	29	> 19 <
4	KRXZEdXGiprKvqQ2aSnzYQpzaE0YwlfyDTBBI+R8kv8=	28	> 13 <
5	K2qq2NImq28ESPaVB9uCVrI0tPT/NOYAtryUcjGpzt8=	27	> 7 <
6	8PQ4tm652Kr8yV2D2OBKAYrKxWtkddxqtiMvIuknhgU=	26	> 22 <
7	fJQRVYErqgAmJAs7a01/SoACdnCBNcqzrGbUsFticjM=	25	> 12 <
8	wlfiQaw6S/bxcbT2u+7oshpAFxrsy6wIZyFD+uWle80=	24	> 28 <
9	ekEoRHYTkT6p5m2fP3mn354kQSI1pz/B1RKC+Fa8YXA=	23	> 15 <
10	ggmvds6SzOGPwr8vUwSPNHtk7WIsQLYiO2tl0V3yzZQ=	22	> 11 <
11	ntjVm6AGBtydG6l9aiTSSojdcp6UcYhk55Rg71y0Z+s=	21	> 5 <
12	CE14MeW+JUzb+D/gQ82dJF62NBapfROt7Ff2ngkT/XE=	20	> 27 <
13	ZRYzTo0OZ0ASx5keWlh3YH1Di4o9p5jefz+MCWmWjFk=	19	> 23 <
14	lvA2rjCw7sT0+SVNOZB29HZOVvIAiS3yA85wqE9ugPk=	18	> 6 <
15	aQy+Eof9q4MbDZam/D+Sxc5yLixLYdArJ6kr1KmrbKA=	17	> 14 <

Table 4
1. G. Huston (4)	6. M. Richardson (22)
2. R. Salz (30)	7. D. McPherson (12)
3. S. Krishnan (19)	8. B. Stark (28)
4. R. Droms (13)	9. L. Dondet (15)
5. A. Doria (7)	10. R. Draves (11)

10. Source Code

The C source code below makes use of the SHA-256 reference code from [RFC6234]. The original code in [RFC2777] was written by Donald Eastlake except for the code dealing with multiple floating point number input which was written by Matt Crawford. The [RFC2777] code could only handle pools of up to 255 members and was extended to 2**16-1 by Erik Nordmark for the code in [RFC3797]. Both of these earlier versions used MD-5 [RFC1321] rather than SHA-256.¶

Python code by Rich Salz to implement the method in [RFC3797] is available at https://github.com/richsalz/ietf-rfc3797¶

The code below uses HMAC-SHA-256 [RFC6234] and has provisions for extended selections (see Section 6). It has been compiled, and tested. While no flaws were found, it is possible that when used with some compiler on some system under some circumstances some flaw will manifest itself.¶

<CODE BEGINS>

//*****************************************************************
/*  Example code for
 *      "Publicly Verifiable Random Selection"
 *          Donald E. Eastlake 3rd
 *              Original February 2004
 *              Updated August 2022 and June/July 2023
 *
 * Redistribution and use in source and binary forms, with or
 * without modification, is permitted pursuant to, and subject
 * to the license terms contained in, the Revised BSD License
 * set forth in Section 4.c of the IETF Trust's Legal Provisions
 * Relating to IETF Documents
 * (http://trustee.ietf.org/license-info).                       */
//*****************************************************************

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <ctype.h>


//  SHA-256, HMAC, RFC 6234
//  Note: If you build this with the RFC 6234 sources then, because
//        of the way that HMAC dispatches on the SHA type, you have
//        to include in your build not just sha224-256.c and
//        sha-private.h but also sha1.c and sha384-512.c.

#include "sha.h"


// CONSTANTS

#define MAXLINE 256           /* maximum input line */
#define MAXGENERATIONS 99     /* maximu hash chain length */


//  Local prototypes in alphabetic order
//*****************************************************************
void     b64parse ( char *input, uint8_t *output );
void     b64print ( uint8_t *p, int length );
void     b64toHex ( void );
int      b64v ( char );
void     CheckSum ( int gen, uint8_t *data,
                    int datalength, uint8_t *result );
int      getChain ( int *gen, uint8_t *hash64 );
long int getInteger ( char *prompt );
int      getNP ( void );
int      getSeed ( char *key );
void     hashChain ( void );
void     hashSHA256 ( int errreturn, int errloc );
void     hexprint ( uint8_t *p, int length );
void     hexToB64 ( void );
int      longremainder ( unsigned int divisor,
                         uint8_t hash[SHA256HashSize] );
double   NPentropy ( void );
void     pick ( void );    // RFC 3797 but with HMAC-SHA-256
void     selectExt ( void );  // [this document]
void     testCrypto ( void );


//  Global Variables
//*****************************************************************
char           tin[MAXLINE+2];  // type in buffer
int            keysize;
char           key[800];  // where key string is accumulated
unsigned int   N; // Number of items to be selected
unsigned int   P; // Size of pool
char           b64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                       "abcdefghijklmnopqrstuvwxyz0123456789+/";
int            debug = 0;/* debug level, = 1 print some extra stuff
                           > 1 print even more extra stuff */


//  Main driver/dispatch routine
//*****************************************************************
int main ( int argc, const char * argv[] ) {
 char       *cherr;
 int         i;
 char        ch;

nextcommand:
 printf ( "How may I serve you? " );
 cherr = fgets( tin, MAXLINE, stdin );   // get commeand
 if ( cherr == NULL )
     exit ( 102 );
 for ( i = 0; i < MAXLINE; ++i ){
     ch = tin[i];
     if ( debug > 0 )
         printf ( "%s%X%s",
             "Command character 0X", ch, "\n");
     switch ( ch ) {
         case '?': // help
             printf ( " ? -> Help\n"
                     " d -> set debug level\n"
                     " e -> entropy needed\n"
                     " h -> hash chain\n"
                     " p -> pick from pool\n"
                     " q -> quit\n"
                     " s -> select with extensions\n" );
             if ( debug )
                 printf ( " t -> test Crypto\n"
                         " 8 -> hex to base64\n"
                         " 9 -> base64 to hex\n" );
             // falls through
         case 0: case '\n': // "gets" string is zero terminated
             goto nextcommand;
         case ' ': case 127: case '\t': // skip white space
         case'\v': case '\r': case '\f': case '\b':
             continue;  // try next character
         case 'd': case 'D': // set debug level
             debug = (int)getInteger ( "Set debug level" );
             if ( debug > 1 ) {
             printf ( "argc: %i\n", argc );
             if ( argc > 0 )
                 printf ( "%s\n", argv[0] );
             }
             goto nextcommand;
         case 'e': case 'E':  // calculate entropy needed
             if ( !getNP ( ) )
                 NPentropy ( );
             goto nextcommand;
         case 'h': case 'H': // calculate hash chain
             if ( !getSeed ( key ) )
                 hashChain ( );
             goto nextcommand;
         case 'p': case 'P':  // pick from pool
             if ( !getNP ( ) && !getSeed ( key ) )
                 pick ( );
             goto nextcommand;
         case 'q': case 'Q': case '\a':  // quit
             exit ( 0 );
         case 's': case 'S':  // select with extensions
             if ( !getNP ( ) && !getSeed ( key ) )
                 selectExt ( );  // [this document]
             goto nextcommand;
         case 't': case 'T':
             testCrypto ( );
             goto nextcommand;
         case '8':
             hexToB64 ( );
             goto nextcommand;
         case '9':
             b64toHex ( );
             goto nextcommand;
         default:
             printf ( "%s%s%s", "Undefined command: ",
                      tin, "\n");
             goto nextcommand;
         }  // end switch
 }  // end "for i"
}  // end main


//  parse some base64
//  assumes input already cleaned to just Base64 characters
//    excluding '=' and is a legal length, zero terminated.
//*****************************************************************
void b64parse ( char *input, uint8_t *output ) {
 int     i, k;

 for ( i = 0, k = 0; i < MAXLINE; i += 4, k += 3 ) {
     output[k] = ( b64v ( input[i] ) << 2 ) |
                ( ( b64v ( input[i+1] ) >> 4 ) & 0xF );
     if ( !input[i+2] ) {
         output[k+1] = ( b64v ( input[i+1] ) << 4 ) |
                       ( ( b64v ( input[i+2] ) >> 2 ) &0xF );
         if ( !input[i+3] ) {
             output[k+2] = ( b64v ( input[i+2] ) << 6 ) |
                            b64v ( input[i+3] );
             }
         }
     if ( !input[i+4] )
         break;
 }  // end for i
}  // end b64parse


//  print binary as base64
//*****************************************************************
void b64print ( uint8_t *p, int length ) {
 uint8_t   nib;

 while ( length > 0 ) {
     nib = p[0] >> 2;
     printf ( "%c", b64[nib] ); // print 1st 6 bits
     nib = ( p[0] & 0x3 ) << 4; // get bottom 2 bits of 1st byte
     if ( --length ) {
         nib += ( p[1] >> 4 ); // get top 4 bits of 2nd byte
         printf ( "%c", b64[nib] ); //print 2nd 6 bits
         nib = ( p[1] & 0xF ) << 2; //get bottom 4 bits of 2nd byte
         if ( --length ) {
             nib += ( p[2] >> 6 ); // get top 2 bits of 3rd byte
             printf ( "%c%c", b64[nib], b64[ p[2] & 0x3F ] );
       }
       else  // length was 2, print rest of 2nd byte
           printf ( "%c=", b64[nib] );
     }
     else  // length was 1, print rest of 1st byte
         printf ( "%c==", b64[nib] );
     p += 3;
     --length;
 } // while
} // end b64print


//  read base64, print as hex // xxx
//*****************************************************************
void b64toHex ( void ) {
 char       clean[MAXLINE];
 uint8_t    val64[((MAXLINE*3)/4)+2];
 int        i, j, k, v;
 int        equalsigns = 0;
 char      *cherr;

 printf ( "Type some Base64: " );
 cherr = fgets ( tin, MAXLINE, stdin );
 if ( cherr == NULL )
     exit ( 902 );
 for ( i = 0, j = 0; i < MAXLINE; ++i ) {
     if ( ( tin[i] == '\n' ) || ( tin[i] == 0 ) )
         break;  // end of the line
     if ( isspace ( tin[i] ) )
         continue;  // skip white space
     if ( isalnum ( tin[i] ) ||
          ( tin[i] == '+' ) || ( tin[i] == '/') ) {
         if ( equalsigns ) {
             printf ( "Stuff after an equal sign.\n" );
             return;
             }
         clean[j] = tin[i];
         ++j;
         continue;
         }
     if ( tin[i] == '=' ) {
         switch ( equalsigns ) {
             case 0:
                 v = j % 4;
                 if ( ( v != 2 ) && ( v != 3 ) )
                     printf ( "Wrong length before '='.\n" );
                 // fall through
             case 1:
                 ++equalsigns;
                 break; // out of switch equalsigns
             case 2:
                 printf ( "Too many equal signs.\n" );
                 return;
             } // switch equalsigns
         } // if equal sign
 } // for i
 clean[j] = 0;
 if ( debug ) {
     hexprint ( (uint8_t *)clean, j+1 );
     printf ( " " );
     }
 v = j % 4;
 if ( v == 1 )
     printf ( "Wrong Base64 length.\n" );
 b64parse ( clean, val64 );
 hexprint ( val64, ( (j*3)/4 ) );
 printf ( "\n" );
} // end b64toHex


//  convert a base64 char to int
//*****************************************************************
int b64v ( char ch ) {
 int     i;

 for ( i = 0; i < 64; ++i )
     if ( ch == b64[i] )
         return i;
 exit ( 1 );
} // end b64v


// calculate and store back a 24 bit checksum of the low order
// byte of an int and a block of bytes
// This is an FNV-32 xor folded to 24 bits
//****************************************************************
void CheckSum ( int gen, uint8_t *hash,
                int hashlength, uint8_t *result ) {
 uint32_t    temp = 0x811C9DC5; // FNV32basis
 int         i;

 temp ^= gen & 0xFF;
 temp *= 0x01000193;
 for ( i = 0; i < hashlength; ++i ) {
     temp ^= hash[i];
     temp *= 0x01000193; // FNV32prime
 } // for i
 result[2] = ( temp & 0xFF ) ^ ( temp >> 24 );
 temp >>= 8;
 result[1] = temp & 0xFF;
 result[0] = temp >> 8;
}  // end CheckSum


//  get a hash chain entry
//  return zero for success, non-zero for error/quit
//*****************************************************************
int getChain ( int *gen, uint8_t *hash ) {
 char       *cherr;
 int         j;
 char        hash64[44];
 uint8_t     hashBin[SHA256HashSize];
 uint8_t     checkIn[5];  // checksum read in
 uint8_t     checkCalc[5];  // checksum calculated

 printf ( "Format is gen-hash=check where gen is the\n"
           " decimal generation number, hash= is the\n"
           " Base64 hash, and check the Base64\n checksum.\n"
           "Input hash chain value (or 'quit'): " );
 cherr = fgets ( tin, MAXLINE, stdin );
 if ( cherr == NULL )
     exit ( 1 );
 j = sscanf ( tin, "%2d-%43s=%4s", gen, hash64, (char *)checkIn );
 if ( j != 3 ) {
     if ( ( tin[0] == 'q' ) || ( tin[0] == 'Q' ) )
         return 1;  // quit
     printf ( "Bad hash chain entry foramt.\n" );
     return 1;
     }
 hash64[43] = 0;
 if ( ( *gen > MAXGENERATIONS ) || ( *gen <= 0 ) ) {
         printf ( "Bad hash chain generation.\n" );
         return 1;
     }
 b64parse ( hash64, hashBin );
 CheckSum ( *gen, hashBin, SHA256HashSize, checkCalc );
 if ( memcmp ( checkIn, checkCalc, 3 ) ) {
   printf ( "Checksum fails.\n" );
   return 1; // not equal
   }
 return 0;  // Check Sunm checks
} // end getChain


//  prompt for and get an integer input
//*****************************************************************
long int getInteger ( char *prompt ) {
 long int    i;
 char        *cherr;
 int         j;

 while ( 1 ) {
    printf ( "%s (or 'quit' to exit) ", prompt );
    cherr = fgets ( tin, MAXLINE, stdin  );
    if ( cherr == NULL )
        exit ( 1 );
    j = sscanf ( tin, "%ld", &i );
    if ( j == 1 )
        return i;
    if ( ( tin[0] == 'q' ) ||
         ( tin[0] == 'Q' ) )
        exit ( j );
 }
} // end getInteger


//  get pool size and number of items to pick
//  returns zero for success, non-zero for failure
//****************************************************************
int getNP ( void ) {

 P = (unsigned int)getInteger ( "Type size of pool:" );
 if ( ( P > 65535 ) ||
      ( P <= 0 ) ) {
     printf ( "Pool zero, negative, or too big.\n" );
     return 1;
     }
 N = (unsigned int)getInteger (
     "Type number of items to be selected:" );
 if ( N > P ){
     printf ( "Pool too small.\n" );
     return 1;
     }
 if ( N <= 0 ) {
     printf ( "Selecting zero or negative things?\n" );
     return 1;
     }
 return 0;  // got possibly reasonable values
} // end getNP


//  get the "random" inputs. echo back to user so the user may
//  be able to tell if truncation or other glitches occur.
//
//  Up to 16 inputs each of which can be either up to 16 integers
//      or up to 16 floating point numbers
//
//  output 1 for failure, 0 for success
//****************************************************************
int getSeed ( char *key ) {
 long int    temp, array[16];
 int         i, j, k, k2;
 char        sarray[16][256];
 char        *cherr;

 for ( i = 0, keysize = 0; i < 16; ++i ) {
     if ( keysize > 511 ) {
         printf ( "Too much input.\n" );
         return 1;
         }
 nexttry:
     printf (
 "Type #%d randomness, 'end', or 'quit' followed by new line.\n",
         i+1 );
     if ( i == 0 )
         printf (
         "Up to 16 integers or the word 'float' followed by up\n"
         "to 16 x.y format reals.\n" );
     cherr = fgets ( tin, MAXLINE, stdin );
     if ( cherr == NULL )
         exit ( 403 );
     j = sscanf ( tin,  // try to parse as "long int"s
                "%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 )  // empty input
         goto nexttry;
     if ( !j ) {
         if ( ( tin[0] == 'q' ) || ( tin[0] == 'Q' ) ) // "q"uit
             return 1;
         if ( ( tin[0] == 'e' ) || ( tin[0] == 'E' ) ) // "e"nd
             break; // break out of "for i"
         else {   // floating point code by Matt Crawford
             j = sscanf ( tin,
                 "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." );
                 return 1;
             }
             else {
                 for ( k = 0, j /= 2; k < j; k++ )
                 /* strip trailing zeros */
                     for ( k2 = (int)strlen(sarray[k]);
                         sarray[k][--k2]=='0'; )
                             sarray[k][k2] = '\0';
                     printf ( "%ld.%s\n", array[k], sarray[k] );
                     keysize += sprintf ( &key[keysize], "%ld.%s",
                                          array[k], sarray[k] );
                 }
                 keysize += sprintf ( &key[keysize], "/" );
             }
         }  // end "if ( !j )"
         else
         { // sort integer 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
                 printf ( "%ld ", array[k] );
                 keysize += sprintf ( &key[keysize], "%ld.",
                                      array[k] );
             }  // end "for k"
             printf ( "\n" );
             keysize += sprintf ( &key[keysize], "/" );
         }  // end "if ( !j )" else
 }  // end "for i"
 if ( i == 0 ) {
     printf ( "No key input.\n" );
     return 1;
     }
 printf ( "Key is:\n %s\n", key );
 return 0;
}  // end getSeed


//  print out a hash Chain based on key
//*****************************************************************
void hashChain ( void ) {
 int            i;
 long int       j;
 SHA256Context  context;
 uint8_t        hash[SHA256HashSize];
 uint8_t        check[3];

 j = getInteger ( "Length of chain to print:" );
 if ( j > MAXGENERATIONS ) {
     j = MAXGENERATIONS;
     printf ( "Chain length clipped at %d.\n", MAXGENERATIONS );
     }
 testCrypto ( );
 hashSHA256 ( SHA256Reset ( &context ), 511 );
 hashSHA256 ( SHA256Input ( &context,
                            (uint8_t *)key,
                            (int)strlen ( key ) ), 512 );
 hashSHA256 ( SHA256Result ( &context, hash ), 513 );
 if ( debug ) {
     printf ( "Hex of SHA-256 of Key:\n" );
     hexprint ( hash, SHA256HashSize );
     printf ( "\n" );
     }
 printf ( "Generation- HashValue= Checksum\n00-" );
 b64print ( hash, SHA256HashSize );
 CheckSum ( 0, hash, SHA256HashSize,check );
 b64print ( check, 3 );
 printf ( "\n" );
 for ( i = 1; i <= j; ++i ) {
     hashSHA256 ( SHA256Reset ( &context ), 521 );
     hashSHA256 ( SHA256Input ( &context, hash, SHA256HashSize ),
                  522 );
     hashSHA256 ( SHA256Result ( &context, hash ), 523 );
     printf ( "%02d-", i );
     b64print ( hash, SHA256HashSize );
     CheckSum ( i, hash, SHA256HashSize, check );
     b64print ( check, 3 );
     printf ( "\n" );
 } // for i
} // end hashChain


//  check SHA256/HMAC return code
//*****************************************************************
void hashSHA256 ( int errreturn, int errloc ) {

 if ( !errreturn )  // zero -> success
     return;
 else
     printf ( "SHA returns error %i at %i.\n",
              errreturn, errloc );
 exit ( 1 );
}  // end hashSHA256


// print out a SHA-256 hash in hex
//****************************************************************
void hexprint ( uint8_t *p, int length ) {
 int    i;

 for ( i = 0; i < length; ++i ) {
     printf ( "%02X", p[i] );
 } // for i
} // end hexprint


//  read hex, print as base64
//*****************************************************************
void hexToB64 ( void ) {
 uint8_t   hexval[(MAXLINE/2)+2];
 char      clean[MAXLINE];
 char     *cherr;
 int       i, j, v;

 printf ( "Type some bytes in hex: " );
 cherr = fgets ( tin, MAXLINE, stdin );
 if ( cherr == NULL )
     exit ( 1102 );
 for ( i = 0, j = 0; i < MAXLINE; ++i ) {
     if ( ( tin[i] == '\n' ) || ( tin[i] == 0 ) )
         break;  // end of the line
     if ( isspace ( tin[i] ) )
         continue;  // skip white space
     if ( isxdigit ( tin[i] ) ) {
         clean[j] = tolower ( tin[i] );
         ++j;
         continue; // for
         }
     printf ( "Non-hex digit encountered: %02X\n", tin[i] );
     exit ( 1 );
     return;
}  // for i
 clean[j] = 0;
 if ( j & 1 ) {
     printf ( "Odd number of hex digits? %i\n", j );
     return;
 }
 for ( i = 0; i < j; ++i ) { // from clean to hexval
     if ( clean[i] >= 'a' && clean[i] <= 'f' )
         v = clean[i] - 'a' + 10;
     else
         v = clean[i] - '0';
     if ( i & 1 )
         hexval[i/2] += v;
     else
         hexval[i/2] = v << 4;
 }  // for i
 if ( debug ) {
     hexprint ( hexval, j/2 );
     printf ( "\n" );
     }
 b64print ( hexval, j/2 );
 printf ( "\n" );
}  // end hexToB64


// get remainder of dividing a SHA-256 hash
//   by a small positive number
//****************************************************************
int longremainder ( unsigned int divisor,
                    uint8_t hash[SHA256HashSize] ) {
 long int     kruft;
 int          i;

 if ( divisor <= 0 )
     exit ( 1 );
 for ( i = 0, kruft = 0; i < SHA256HashSize; ++i )
     {
     kruft = ( kruft << 8 ) + hash[i];
     kruft %= divisor;
     }
 return (int)kruft;
}  // end longremainder


//  calculate how many bits of entropy it takes to select N from P
//      withour replacement. Print and return it.
//****************************************************************
/*               P!
    log  ( ----------------- )
       2    N! * ( P - N )!
*/
double NPentropy ( void )
{
 long int    i;
 double      result = 0.0;

 if (    ( N < 1 )   // not selecting anything?
    ||   ( N >= P )  // selecting all of pool or more?
    )
    result = 0.0;    // degenerate case
 else {
     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 /= log ( 2 );
 }
 printf ( "Approximately %.1f bits of entropy needed.\n",
                     result );
 return result;
} // end NPentropy


//  Pick N items from the pool of P items using the probe method
//****************************************************************
void pick ( void ) {
 unsigned short     *selected;
 HMACContext        context;
 uint8_t            hash[SHA256HashSize];
 uint8_t            message[64];
 unsigned int       i, remaining, divisor;
 int                j, k;

 selected =
     (unsigned short *)malloc ( P * sizeof ( unsigned short ) );
 if ( !selected ) {
     printf ( "Out of memory.\n" );
     exit ( 1 );
 }
 for ( i = 0; i < P; ++i )
     selected [i] = (unsigned short)(i + 1);
 printf ( " No extensions.\n "
"index       base64 value of HMAC-SHA-256        div selected\n"
         );
 remaining = N;
 divisor = P;
 testCrypto ( );
 for ( i = 0; i < N; ++i, --remaining, --divisor ) {
     hashSHA256 (
         hmacReset ( &context, SHA256,
                     (uint8_t *)key,
                     (int)strlen ( key ) ),
         201 );
     for ( j = 0; j < 64; ++j ) {
         if ( j & 1 )
             message[j] = i & 0xFF;
         else
             message[j] = i >> 8;
     }
     if ( debug > 1 ) {
       printf ( "message:" );
       hexprint ( message, 64 );
       printf ( "\n" );
     }
     hashSHA256 ( hmacInput ( &context, message, 64 ), 202 );
     hashSHA256 ( hmacResult ( &context, hash ), 203 );
     k = longremainder ( divisor, hash );
     for ( j = 0; j < P; ++j) {
       if ( selected[j] )
             if ( --k < 0 ) {
                 printf ( "%3d ", i + 1 );
                 b64print ( hash, SHA256HashSize );
                 printf ( " %3d  >%3d<\n", divisor,
                                           selected[j] );
                 selected[j] = 0;
                 break;  // for j
             }
     } // for j
 } // for i
 free ( (void *)selected );
} // end pick


//  Select items from a pool with possible extensions
//  You must already have a hashChain() you have saved
//****************************************************************
void selectExt ( void ) {
 unsigned short     *selected;
 HMACContext        context;
 uint8_t            hash[SHA256HashSize];
 uint8_t            chainhash[SHA256HashSize];
 uint8_t            message[64];
 unsigned int       remaining, divisor, cumulative = 0;
 int                i, j, k;
 int                stepIn;
 int                stepPrev = 0;
 int                extension = 0;

 selected =
     (unsigned short *)malloc ( P * sizeof ( unsigned short ) );
 if ( !selected ) {
     printf ( "Out of memory.\n" );
     exit ( 1 );
 }
 for ( i = 0; i < P; ++i )
     selected [i] = (unsigned short)(i + 1);
 printf ( "Input final hash chain string.\n" );
 remaining = N;
 divisor = P;

extendloop:
 if ( getChain ( &stepIn, chainhash ) )
     return;
 if ( stepPrev && ( stepIn != (stepPrev - 1) ) ) {
   printf ( "Wrong generation hash chain string. "
            "Should have been %i.\n", stepPrev - 1 );
   goto extendloop;
   }
 // set first half of message from hash chain
 for ( i = 0; i < 32; ++i )
   message[i] = chainhash[i];
 stepPrev = stepIn;
 if ( extension )
     printf ( " Extension #%i.\n", extension );
 else
     printf ( " Initial selection.\n" );
 printf (
 "index       base64 value of HMAC-SHA-256        div selected\n"
         );
 for ( i = 0; i < N; ++i, --remaining, --divisor ) {
     hmacReset ( &context, SHA256,
                (uint8_t *)key, (int)strlen ( key ) );
     for ( j = 32; j < 64; ++j ) {
       if ( j & 1 )  // set second half of message
             message[j] = i & 0xFF;
         else
             message[j] = i >> 8;
     }
     if ( debug > 1 ) {
       printf ( "message:" );
       hexprint ( message, 64 );
       printf ( "\n" );
     }
     hmacInput ( &context, message, 64 );
     hmacResult ( &context, hash );
     k = longremainder ( divisor, hash );
     for ( j = 0; j < P; ++j) {
       if ( selected[j] )
             if ( --k < 0 ) {
                 printf ( "%3d ", cumulative + i + 1 );
                 b64print ( hash, SHA256HashSize );
                 printf ( " %3d  >%3d<\n", divisor, selected[j] );
                 selected[j] = 0;
                 break;  // for j
             }
     } // for j
 } // for i
 extension += 1;
 cumulative += N;
 N = (unsigned int)getInteger (
     "Number of picks in next extension, 0 to end: " );
 if ( N > 0 )
     goto extendloop;
 free ( (void *)selected );
}


//  Test that SHA-256 and HMAC code seems to be working
//****************************************************************
void testCrypto ( void ) {
 SHA256Context  contexts;
 HMACContext    contexth;
 char           test1[] = "abc";  // SHA-256
 char           test2k[] = "Jefe";  // HMAC key
 char           test2d[] = "what do ya want for nothing?";
 uint8_t        corrects[] = { 0xBA, 0x78, 0x16, 0xBF, 0x8F, 0x01,
     0xCF, 0xEA, 0x41, 0x41, 0x40, 0xDE, 0x5D, 0xAE, 0x22, 0x23,
     0xB0, 0x03, 0x61, 0xA3, 0x96, 0x17, 0x7A, 0x9C, 0xB4, 0x10,
     0xFF, 0x61, 0xF2, 0x00, 0x15, 0xAD };
 uint8_t        correcth[] = { 0x5B, 0xDC, 0xC1, 0x46, 0xBF, 0x60,
     0x75, 0x4E, 0x6A, 0x04, 0x24, 0x26, 0x08, 0x95, 0x75, 0xC7,
     0x5A, 0x00, 0x3F, 0x08, 0x9D, 0x27, 0x39, 0x83, 0x9D, 0xEC,
     0x58, 0xB9, 0x64, 0xEC, 0x38, 0x43 };
 uint8_t        hash[SHA256HashSize];

 hashSHA256 ( SHA256Reset ( &contexts ), 1201 );
 hashSHA256 ( SHA256Input ( &contexts, (uint8_t *)test1, 3 ),
              1202 );
 hashSHA256 ( SHA256Result ( &contexts, hash ), 1203 );
 if ( memcmp ( hash, corrects, SHA256HashSize ) ) {
     printf ( "SHA256 not working.\n" );
     exit ( 1 );
     }
 if ( debug )
     printf ( "SHA256 OK.\n" );
 hashSHA256 ( hmacReset ( &contexth, SHA256,
                          (uint8_t *)test2k,
                          (int)strlen ( test2k ) ),
              1203 );
 hashSHA256 ( hmacInput ( &contexth, (uint8_t *)test2d,
                          (int)strlen ( test2d ) ),
              1204 );
 hashSHA256 ( hmacResult ( &contexth, hash ), 1205 );
 if ( memcmp ( hash, correcth, SHA256HashSize ) ) {
     printf ( "HMAC not working.\n" );
     exit ( 1 );
     }
 if ( debug )
     printf ( "HMAC OK.\n" );
} // end testCrypto


<CODE ENDS>

Num	YEAR	CHAIR	SELECTION METHOD
1	1993/1994	Jeff Case	Clergy
2	1994/1995	Fred Baker	Clergy
3	1995/1996	Guy Almes	Clergy
4	1996/1997	Geoff Huston	Spouse
5	1997/1998	Mike St.Johns	Algorithm
6	1998/1999	Donald Eastlake 3rd	RFC 2777
7	1999/2000	Avri Doria	RFC 2777
8	2000/2001	Bernard Aboba	RFC 2777
9	2001/2002	Theodore Ts'o	RFC 2777
10	2002/2003	Phil Roberts	RFC 2777
11	2003/2004	Rich Draves	RFC 2777
12	2004/2005	Danny McPherson	RFC 3797
13	2005/2006	Ralph Droms	RFC 3797
14	2006/2007	Andrew Lange	RFC 3797
15	2007/2008	Lakshminath Dondeti	RFC 3797
16	2008/2009	Joel M. Halpern	RFC 3797
17	2009/2010	Mary Barnes	RFC 3797
18	2010/2011	Tom Walsh	RFC 3797
19	2011/2012	Suresh Krishnan	RFC 3797
20	2012/2013	Matt Lepinski	RFC 3797
21	2013/2014	Allison Mankin	RFC 3797
22	2014/2015	Michael Richardson	RFC 3797
23	2015/2016	Harald Alvestrand	RFC 3797
24	2016/2017	Lucy Lynch	RFC 3797
25	2017/2018	Peter Yee	RFC 3797
26	2018/2019	Scott Mansfield	RFC 3797
27	2019/2020	Victor Kuarsingh	RFC 3797
28	2020/2021	Barbara Stark	RFC 3797
29	2021/2022	Gabriel Montenegro	RFC 3797
30	2022/2023	Rich Salz	RFC 3797
31	2023/2024	Martin Thomson	RFC 3797 + hash chain extensions

Times a Set of 10 is Selected	Base 2 Log(Times)	Expected Times Each Item Selected	Standard Deviation of Times Item Selected	SD as a % of Expected
1,024	10	51.2	22.1	43.2%
1,048,576	20	52,429	706	1.35%
1,073,741,824	30	53,687,091	22,584	0.0421%
1,099,511,627,776	40	54,975,581,389	722,681	0.00131%

Publicly Verifiable Nominations Committee (NomCom) Random Selection

Abstract

Status of This Memo

Copyright Notice

Table of Contents

1. Introduction

1.1. Requirements Language

2. General Flow of a Publicly Verifiable Process

2.1. Determination of the Pool

2.2. Publication of the Algorithm

2.3. The Selection

3. Randomness

3.1. Sources of Randomness

3.2. Skew

3.3. Entropy Needed

4. A Specific Algorithm for Initial Selection

5. Handling Real World Problems

5.1. Uncertainty as to the Nomcom Pool

5.2. Randomness Ambiguities

6. Extended NomCom Selection

6.1. Preparing for Possible Extension

6.2. Extension Procedure

7. Fully Worked Examples

8. Security Considerations

9. IANA Considerations

10. Source Code

11. Normative References

12. Informative References

Appendix A. History of NomCom Voting Member Selection

Appendix B. More Equations and Numbers

Appendix C. Changes from RFC 3797

Appendix D. Versions Change History

D.1. -00 to -01

D.2. -01 to -02

D.3. -02 to -03

D.4. -03 to -04

D.5. -04 to -05 to -06

Acknowledgements

Author's Address