Network Working Group                                        D. Eastlake
INTERNET-DRAFT                                    Futurewei Technologies
Obsoletes: 3797
Intended Status: Best Current Practice
Expires: March 14, 2023                               September 15, 2022

  Publicly Verifiable Nominations Committee (NomCom) Random Selection


   This document describes a method for making random selections in such
   a way that the unbiased nature of the choice is publicly verifiable.
   It focuses on the selection of the voting members of the IETF
   Nominations Committee (NomCom) from the pool of eligible volunteers;
   however, similar or, in some cases, identical techniques could be and
   have been applied to other cases.

Status of This Memo

   Distribution of this document is unlimited. Comments should be sent
   to the authors.

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Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents

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   ( in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document. Code Components extracted from this document must
   include Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

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Table of Contents

      1. Introduction............................................4
      1.1 Requirements Language..................................4

      2. General Flow of a Publicly Verifiable Process...........5
      2.1 Determination of the Pool..............................5
      2.2 Publication of the Algorithm...........................5
      2.3 The Selection..........................................5

      3. Randomness..............................................7
      3.1 Sources of Randomness..................................7
      3.2 Skew...................................................8
      3.3 Entropy Needed.........................................8

      4. A Specific Algorithm for Initial Selection.............10

      5. Extended Selection.....................................12

      6. Handling Real World Problems...........................15
      6.1 Uncertainty as to the Pool............................15
      6.2 Randomness Ambiguities................................15

      7. Fully Worked Example...................................17

      8. Security Considerations................................19
      9. IANA Considerations....................................19

      10.  Reference Code.......................................20

      Normative References......................................26
      Informative References....................................26

      Appendix A: History of NomCom Member Selection............27
      Appendix B: Changes from RFC 3797.........................28


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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), the Internet Architecture
   Board (IAB), and other bodies as described in [RFC8713].  The number
   of eligible volunteers in the early years of the use of the NomCom
   mechanism was around 50 but in recent years has been around 200.

   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 specifies such a method.

   This method, in the form it appeared in RFC 2777, was also used by
   IANA in February 2003 to determine the ACE prefix for
   Internationalized Domain Names ("xn--", [RFC5890]) so as to avoid
   claim jumping.

1.1 Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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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 in the
   subsections below: Determination of the Pool, Publication of the
   Algorithm, and Publication of the Selection.

2.1 Determination of the Pool

   First, determine the pool from which the selection is to be made as
   provided in [RFC8713] or its successor.

   Currently, volunteers are solicited by the selection administrator.
   Their names are then checked for eligibility.  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 before a deadline at which the pool is frozen. Although no one
   can be added after this deadline, someone included in the list who
   should not have been can be easily handled as described later in this

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 hash function [RFC4086]
   of these future sources of randomness.

2.3 The 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 SHOULD 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 is available. Under
   some circumstances, additional rounds of extended selection may be
   useful as specified in Section 5.

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   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.

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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 cannot be known to the person
   executing 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 any reasonable
   person would believe to be under the control or influence of the
   selection administrator or the IETF or its components, such as IETF
   meeting attendance statistics, numbers of documents issued, or the

   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 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 reference 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 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 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

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   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.  Three would be a good number of randomness sources.  More
   than six is way 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
   [RFC4086] will extract the available entropy and produce a hash value
   whose bits and whose remainder modulo a small divisor, 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:

                               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 completely
   random selection of 10 items (e.g., NomCom members) from various pool
   sizes are given below:

                  Random Selection of Ten Items From Pool

      Pool size     40   60   80   100   125   150   175   200
      Bits needed   30   36   41    44    47    50    52    54

   Using a smaller number of bits means that not all of the possible
   sets of ten selected items would be available.  For a substantially
   smaller 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 be more than adequate.  Even if 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

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   correlation between the selection of any pair of pool members, or the

   The current US Power Ball lottery drawing has 23.5 bits of entropy in
   the five selected regular numbers and about 6 bits of entropy in the
   Power Ball. A four-digit daily numbers game drawing that selects four
   decimal digits has a bit over 13 bits of entropy.

   An MD5 [RFC1321] hash has 128 bits of output and therefore can
   preserve no more than that number of bits of entropy.  However, this
   is much more than what is likely to be needed for IETF NomCom
   membership selection. There have also been defects noted in MD5 for
   cryptographic usage [RFC6151] but these are not significant here. The
   hash function is just being used to, effectively, compress, deskew,
   and extract selections from the random input. For example, it would
   not hurt this process if a hash function was used for which it was
   easy to compute a pre-image.

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4. A Specific Algorithm for Initial Selection

   It is important that a precise algorithm be given for mixing the
   random sources being used 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 65 or the like, a sporting event could produce the
   scores of two teams, etc.).  A precise algorithm is as follows:

      1. For each source producing one or more numeric values, each
         value is canonicalized by representing each value 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 on the part after the period. Some
         examples follow:

               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

      2. If a source produced multiple values, order those values from
         smallest to the largest.  (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 have no inherent order.)

      3. If a source produced multiple values, concatenate them and
         suffix the result with a "/".  If a source produced a single
         number, simply represent it as above with a suffix "/".

      4. At this point you have a string for each source, say s1/, s2/,
         ... for source 1, source 2, ... Concatenate these strings in a
         pre-specified order, the order in which the sources were listed
         when they were announced if no other order is specified, and
         represent each character as its ASCII code [RFC20] producing
         "s1/s2/.../" as the random seed from which selection is

      5. Produce a sequence of random values derived from a mixing of
         these sources by calculating the MD5 hash [RFC1321] of the seed

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         specified in step 4 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.

      6. Finally impose a total pseudo-random ordering on the pool of
         listed items (e.g., NomCom 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.  And so on.

   Any ambiguity in the above procedure is resolved by consulting the
   reference code below.

   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 the administrator of
   the selection process chooses 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 single number above and suffixed with a "./".  The
   administrator MUST NOT use even more complex and harder to
   canonicalize quantities such as complex numbers or UNICODE
   internationalized text.

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5. Extended 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 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 initially selected, they can be later eliminated.
   For the IETF NomCom, there are two types of reasons for elimination
   as follows:

      A. Elimination due to simple rule enforcement by the
         administrator.  Examples would be someone that did not meet the
         eligibility requirements or whose inclusion would violate the
         rule limiting the number of voters 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 administration
         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 a selectee, that is, agreement from the
         selectee to serve cannot be obtained by the administrator
         before a deadline established by the administrator. For
         example, either the selectee declines to serve or, despite all
         reasonable efforts, the selectee is not adequately contactable.

         (The elimination of someone due to non-contactability may work
         a hardship for that individual 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 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, 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 selection were extended in this case by just going
   further down the ordered list, as with Type A eliminations, this
   would give initially selected persons the ability to, 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 perceive this as a problem, so it is resolved by the
   administrator iteratively using what is essentially a miniature

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   version of the initial selection as follows:

      1. The new pool consists of the initial pool without any selectees
         who have agreed to serve and without any pool members
         eliminated by any earlier Type A or B eliminations.

      2. The new randomness is created using a specific instance of a
         public daily source announced at the same time as the initial
         sources. Since an extended selection is normally of a much
         lower number of selectees (typically 1 or 2) from a smaller
         pool, much less entropy is needed. For example, a 4 or 5 digit
         daily number announced by a government lottery would be
         adequate. This random source is treated as an additional source
         added to the initially announced list of random sources and
         processed as specified resulting in it being suffixed to the
         key produced by the initial randomness sources. (See worked
         example and reference code below.)

      3. The administrator announces how many additional selections are
         needed and the specific future daily random source that will be
         used. At least a few hours should be allowed between this
         announcement and the public availability of the extension
         random source. As soon as the random source is available, the
         administrator announces the extended selections and any further
         extension of the extended selections due to Type A eliminations
         as above.

      4. The administrator still needs to check for Type B eliminations
         among the new selectees. Unfortunately, at this point, the time
         constraints are likely to be quite tight so contacting an
         extensions selectees to be sure they are still willing to serve
         must be done urgently and with a tight deadline.  Since there
         may be further Type B eliminations among the extended
         selectees, more than one cycle of extension may be needed. If
         so, these steps 1 through 4 are repeated with minor
         modifications as follows: For Step 1, those in the pool before
         the next extension are all those from the initial pool who have
         not, in the initial selection or any previous extensions, been
         selected or been subject to Type A or Type B elimination. In
         particular, someone who was uncontactable in an earlier round
         does NOT become eligible for later rounds even if they have
         become contactable. For Step 2, a different future version of
         the daily randomness source is used as the additional
         randomness; when multiple selection extensions have to be run,
         the additional randomness does not pile up making the random
         key longer and longer but rather each extension's additional
         randomness is used with the initial random sources. Step 3 and
         4 are unaltered.

   Unfortunately, multiple extension cycles may be required so the

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   selection administration should allow enough time for 5 or so of
   them. For example, in the selection of the 2022/2023 NomCom, 3
   extensions would have been required: The pool had 267 members,
   probably the largest ever. In the initial selection, one of the 10
   selectees was Type B eliminated because confirmation of their
   willingness to serve could not be obtained in a timely fashion. In
   the 1st extended selection, the 11th selectee declined to serve and
   the 12th was Type A eliminated because there were already two
   selectees with the same sponsor. In the 2nd extended selection, the
   13th person selected also decline to serve. In the 3rd extended
   selection, the 14th person selected became the final voting member of
   the Nomcom when they confirmed their willingness to serve.

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6. Handling Real World Problems

   In the real world, problems can arise in following the steps and flow
   outlined in Sections 2 through 5 above.  Some problems that have
   actually arisen are described below with recommendations for handling

6.1 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, or the like,
   there may still be 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 one or more people in the pool are later
   selected by the algorithm and random input but it has been determined
   they are ineligible, they can be skipped and subsequently selected
   persons used.  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 unbiased 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.

6.2 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

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   randomness, the real world has thrown a curve ball and it isn't quite
   clear what data to use.  Problems have particularly arisen in
   connection with individual 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
   financial volumes or prices avoided.

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7. Fully Worked Example

   <<Example needs to also cover the Section 5 Extension provisions.>>

   Assume the eligible volunteers published in advance of selection are
   the numbered list of 30 past NomCom Chairs appearing below in
   Appendix A.

   Assume the following (fake example) ordered list of randomness

   1. The Kingdom of Alphaland State Lottery daily number for 1 November
      2022 treated as a single four-digit integer.
   2. The People's Democratic Republic of Betastani State Lottery six
      winning numbers for 1 November 2022 and then the seventh "extra
      number" for that day as if it was a separate random source.

   Hypothetical randomness publicly produced:
    Source 1:  9319
    Source 2a:  9, 61, 26, 34, 42, 41
    Source 2b:  55

   Resulting key string:


   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  5A0EE2F8849A8C8DFC93BE36FE2D674A  30  -> 15 <-
    2  E390DA3449C586B6BBD9F56B23B86E25  29  -> 11 <-
    3  D053FC140209EADB8340C185B8EC58FD  28  -> 10 <-
    4  0C9DC84909A82D2203959EE54A8B1867  27  ->  6 <-
    5  BD92A498AEF2E60E7867E5B7B434892F  26  -> 30 <-
    6  28E9021C3788F54BF0FD6835BCD1E3C2  25  -> 27 <-
    7  FF6C6197802654B3B1B341DD754A4BE0  24  ->  1 <-
    8  991135A2767FB80D4CEBB736CD7E3BAE  23  ->  9 <-
    9  4E18F325603FF603FC24F43459C2CFAC  22  -> 25 <-
   10  4A0AA0F72441B6345E69FCDD4C378558  21  -> 18 <-
   11  4E9EBC623E2930D4DD61B0FDEC3B2875  20  -> 16 <-
   12  8780D26F8C724EB09CDD155C3B66AF17  19  -> 24 <-
   13  FFF90A6A23BE02D07BA2FA18E6275791  18  ->  5 <-
   14  39FBCDC0CC4F0147CDEABC31D28D36A9  17  -> 28 <-
   15  6F6C2DC3A682E11CF3BC90C682C9104C  16  -> 22 <-

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   Resulting first ten selected, in order selected:

       1.  L. Dondeti (15)     6.  V. Kuarsingh (27)
       2.  R. Draves (11)      7.  J. Case (1)
       3.  P. Roberts (10)     8.  T. Ts'o (9)
       4.  D. Eastlake (6)     9.  P. Yee (25)
       5.  R. Salz (30)       10.  T. Walsh (18)

   Should one of the above turn out to be ineligible or uncontactable or
   decline to serve, the next would be J. Halpern, number 16.

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8. Security Considerations

   Careful choice 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.

   Publication of the results and a one-week window for the community of
   interest to duplicate the calculations should give a reasonable
   assurance against implementation tampering.

9. IANA Considerations

   This document requires no IANA actions.

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10.  Reference Code

   This code makes use of the MD5 reference code from [RFC1321] ("The
   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 under some circumstances some flaw will
   manifest itself.



    *  Reference code for
    *      "Publicly Verifiable Random Selection"
    *          Donald E. Eastlake 3rd
    *              Original February 2004, Updated September 2022
    * 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
    * (

   #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 */

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   int main ()
   int         i, j,  k, k2, err, keysize, usel;
   unsigned short   remaining, *selected;
   long int    pool, selection, temp, array[16];
   MD5_CTX     ctx;
   char        buffer[257], key [800], sarray[16][256];
   unsigned char    uc16[16], unch1, unch2;

   /* get basic parameters */
   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" );
       err = printf ( "Approximately %.1f bits of entropy needed.\n",
                       NPentropy ( selection, pool ) + 0.05 );
       if ( err <= 0 )
           exit ( 1 );

   /* get the "random" inputs. echo back to user so the user may
      be able to tell if truncation or other glitches occur.  */
   for ( i = 0, keysize = 0; i < 16; ++i )
        if ( keysize > 500 )
            printf ( "Too much input.\n" );
            exit ( 1 );
        err = printf (

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            "\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,
            &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' )  /* "e"nd */
                break;     /* break out of "for i" */
            {   /* floating point code by Matt Crawford */
                 j = sscanf ( buffer,
                     "float %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] = ' ';
                      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], "/" );
            {   /* sort values, not a very efficient algorithm */

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            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], "/" );
       }    /* end "for i" */
   if ( i == 0 )
       printf ( "No key input.\n" );
       exit (1);

   /* 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] )

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               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[14],uc16[15], remaining, selected[j] );
                   selected[j] = 0;

   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 ( "%s", 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;

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   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 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 */


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Normative References

   [RFC20]   Cerf, V., "ASCII format for network interchange", STD 80,
             RFC 20, DOI 10.17487/RFC0020, October 1969,

   [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
             DOI 10.17487/RFC1321, April 1992, <https://www.rfc-

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, DOI
             10.17487/RFC2119, March 1997, <https://www.rfc-

   [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, "Randomness
             Requirements for Security", BCP 106, RFC 4086, DOI
             10.17487/RFC4086, June 2005, <https://www.rfc-

   [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119
             Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May
             2017, <>.

Informative References

   [RFC3797] Eastlake 3rd, D., "Publicly Verifiable Nominations
             Committee (NomCom) Random Selection", RFC 3797, DOI
             10.17487/RFC3797, June 2004, <https://www.rfc-

   [RFC5890] Klensin, J., "Internationalized Domain Names for
             Applications (IDNA): Definitions and Document Framework",
             RFC 5890, DOI 10.17487/RFC5890, August 2010,

   [RFC6151] Turner, S. and L. Chen, "Updated Security Considerations
             for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
             RFC 6151, DOI 10.17487/RFC6151, March 2011,

   [RFC8713] Kucherawy, M., Ed., Hinden, R., Ed., and J. Livingood, Ed.,
             "IAB, IESG, IETF Trust, and IETF LLC Selection,
             Confirmation, and Recall Process: Operation of the IETF
             Nominating and Recall Committees", BCP 10, RFC 8713, DOI
             10.17487/RFC8713, February 2020, <https://www.rfc-

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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:

      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 2797

   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

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   RFC 3797 = Algorithmic selection using the algorithm and reference
   code provided in RFC 3797 (but not the fake example sources of

Appendix B: Changes from RFC 3797

   This document differs from [RFC3797], the previous version, in the
   following primary ways:

      1. Many editorial changes. Add IANA Considerations section.

      2. Use [RFC20] as the reference for ASCII.

      3. Update Appendix A.

      4. Add Section 5: Extended Selection.

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   Acknowledgements for this document: TBD

   Acknowledgements for RFC 3797: 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

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Authors' Address

      Donald E. Eastlake 3rd
      Futurewei Technologies
      2386 Panoramic Circle
      Apopka, FL 32703

      Phone: +1-508-333-2270

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