Internet DRAFT - draft-eastlake-rfc3797bis
draft-eastlake-rfc3797bis
Network Working Group D. Eastlake
Internet-Draft Futurewei Technologies
Obsoletes: 3797 (if approved) 31 December 2023
Intended status: Best Current Practice
Expires: 3 July 2024
Publicly Verifiable Nominations Committee (NomCom) Random Selection
draft-eastlake-rfc3797bis-05
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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 3 July 2024.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
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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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. General Flow of a Publicly Verifiable Process . . . . . . . . 4
2.1. Determination of the Pool . . . . . . . . . . . . . . . . 4
2.2. Publication of the Algorithm . . . . . . . . . . . . . . 4
2.3. The Selection . . . . . . . . . . . . . . . . . . . . . . 5
3. Randomness . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Sources of Randomness . . . . . . . . . . . . . . . . . . 5
3.2. Skew . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Entropy Needed . . . . . . . . . . . . . . . . . . . . . 6
4. A Specific Algorithm for Initial Selection . . . . . . . . . 8
5. Handling Real World Problems . . . . . . . . . . . . . . . . 10
5.1. Uncertainty as to the Nomcom Pool . . . . . . . . . . . . 10
5.2. Randomness Ambiguities . . . . . . . . . . . . . . . . . 11
6. Extended NomCom Selection . . . . . . . . . . . . . . . . . . 11
6.1. Preparing for Possible Extension . . . . . . . . . . . . 13
6.2. Extension Procedure . . . . . . . . . . . . . . . . . . . 13
7. Fully Worked Examples . . . . . . . . . . . . . . . . . . . . 15
8. Security Considerations . . . . . . . . . . . . . . . . . . . 17
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
10. Source Code . . . . . . . . . . . . . . . . . . . . . . . . . 17
11. Normative References . . . . . . . . . . . . . . . . . . . . 35
12. Informative References . . . . . . . . . . . . . . . . . . . 36
Appendix A. History of NomCom Voting Member Selection . . . . . 37
Appendix B. More Equations and Numbers . . . . . . . . . . . . . 39
Appendix C. Changes from RFC 3797 . . . . . . . . . . . . . . . 40
Appendix D. Versions Change History . . . . . . . . . . . . . . 41
D.1. -00 to -01 . . . . . . . . . . . . . . . . . . . . . . . 41
D.2. -01 to -02 . . . . . . . . . . . . . . . . . . . . . . . 41
D.3. -02 to -03 . . . . . . . . . . . . . . . . . . . . . . . 41
D.4. -03 to -04 . . . . . . . . . . . . . . . . . . . . . . . 42
D.5. -04 to -05 . . . . . . . . . . . . . . . . . . . . . . . 42
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 42
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 42
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1. Introduction
This document describes a method for making random selections in such
a way that 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 methods could be and have been
applied to other cases such as the following:
* This method as documented in [RFC2777] was used by IANA in
February 2003 to determine the ACE prefix for Internationalized
Domain Names ("xn--") [RFC5890] so as to make claim jumping more
difficult.
* This method as documented in [RFC3797] was sometimes used to
determine the agenda order for the presentation of submissions to
the effort which produced IEEE Std 802.11aq-2018 in order to
assure a fair ordering.
This document provdes an optional extension for multiple rounds of
selection that can be induced after earlier rounds without
compromising the unpredictable nature of the selection. It obsoletes
[RFC3797]. The primary changes to that RFC are listed in Appendix C.
Under the IETF rules, each year from among eligible volunteers as
specified in [RFC9389] a set of people are randomly selected to be
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 over 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
NomCom Chair) from suspicion of bias as it is for the protection of
the IETF.
A method meets this criterion if public information will enable any
person to reproduce the selection process and have reasonable
confidence that it is unbiased. This document specifies such a
method.
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1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"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.
2. General Flow of a Publicly Verifiable Process
A publicly verifiable selection could follow the three steps given in
the subsections below: Determination of the Pool from which selection
is made, Publication of the Algorithm, and Publication of the
Resulting Selection. These steps are further detailed below.
Section 3 then goes into greater depth on the required randomness.
The full selection of the IETF Nomcom is more complex in that, after
the initial selection, a subsequent selection extension or extensions
may be required. This is covered in Section 6 and touched on in
earlier sections including this section.
2.1. Determination of the Pool
First, determine the pool of items from which the selection is to be
made.
For the IETF NomCom, this is as provided in [RFC9389] or its
successor. Their names are checked for eligibility and ineligible
volunteers are dropped. The full list of eligible Nomcom volunteers
MUST be made public early enough that a reasonable amount of time can
be given for review so as to receive and hopefully 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, the initial selection of someone included in the list who
should not have been included can be easily handled as described
below.
2.2. Publication of the Algorithm
The exact algorithm to be used, including the future public 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 method is specified whereby
eligible volunteers are selected based on a hash function [RFC4086]
based on these future sources of randomness, such as the method in
this document.
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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 and its results SHOULD be announced so that anyone can
verify that the correct randomness source values were used and the
algorithm properly executed.
For the IETF NomCom, 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 6.
A cut off time for any complaint that the algorithm was run with the
wrong inputs or not faithfully executed MUST be specified for the
initial selection and any extensions under Section 6 to finalize the
output and provide a stable selection.
3. Randomness
The crux of the unbiased nature of the selection is that it is based
in an exact, predetermined fashion on random information which will
be revealed in the future and 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
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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)!
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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:
+==============================================================+
| Completely Random Selection of One or Ten Items From A Pool |
+==============+=====+=====+=====+=====+=====+=====+=====+=====+
| Pool size | 60 | 80 | 100 | 125 | 150 | 175 | 200 | 250 |
+--------------+-----+-----+-----+-----+-----+-----+-----+-----+
| Bits needed | 5.9 | 6.3 | 6.6 | 7.0 | 7.2 | 7.4 | 7.6 | 8.0 |
| to select 1 | | | | | | | | |
+--------------+-----+-----+-----+-----+-----+-----+-----+-----+
| Bits needed | 36 | 41 | 44 | 47 | 50 | 52 | 54 | 58 |
| to select 10 | | | | | | | | |
+--------------+-----+-----+-----+-----+-----+-----+-----+-----+
Table 1
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).
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4. A Specific Algorithm for Initial Selection
It is important that a precise algorithm be given for canonicalizing
and 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 75 or the like, a sporting event
could produce the scores of two teams, etc.). A suggested precise
algorithm is as follows:
1. For each source producing one or more numeric values, each value
is canonicalized by representing the 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 fractional 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 |
+--------+---------------+
Table 2
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2. If a source produced multiple values, order those values from
smallest to the largest in magnitude. 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. The selection results would not
be reproducible if different persons executing the algorithm
could use different orderings.
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 an added "/" 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 [RFC0020] producing
"s1/s2/.../" as the random key from which selection is derived.
5. Produce a sequence of random values derived from applying the
HMAC-SHA-256 function [RFC6234] using the key specified in step 4
to a 64-byte "messaage" composed as in 5.A or 5.B. Treat each of
these "random" HMAC-SHA-256 output values as a positive 256-bit
multiprecision big endian integer.
5.A If one or more items are being selected without need for
extensions as described in Section 6, the messsage consists of
32 copies of the all zeros two-byte sequence for the first
value, the 32 copies of 0x0001 for the second value, etc.,
treating the replicated two bytes as a big-endian counter.
5.B For selections of the IETF Nomcom that may require
extension(s) the initial 32 bytes (256 bits) of the messages
are a hash chain value as specified in Section 6.1. The
remaining 32 bytes are 16 copies of the two byte sequences as
specified in 5.A above.
6. Finally, do a pseudo-random series of selections from the pool of
listed items (e.g., NomCom volunteers) as follows: If there are P
pool members, select the first by dividing the first derived
random value, treated as an unsigned integer, 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.
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Any ambiguity in the above procedure is resolved by consulting the
example code below.
Use of alphanumeric random sources is NOT RECOMMENDED 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 alphanumeric 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 international text.
5. Handling Real World Problems
In the real world, problems can arise in following the steps and flow
outlined above. Some problems that have actually arisen are
described below with recommendations for handling them.
5.1. Uncertainty as to the Nomcom Pool
Every reasonable effort should be made to see that the published
NomCom 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/or 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.
This is handled by maintaining the announced schedule, including in
the published pool those whose eligibility is uncertain and keeping
the published pool list numbering IMMUTABLE after it is frozen. 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. (This is
referred to in Section 6 as Type A elimination.) 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.
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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 scrambles who is selected. Even if done before the
random numbers are known, such fiddling with the list after its
publication looks bad. To avoid schedule slips, there MUST be clear
fixed firm public deadlines and someone who challenges their absence
from the pool after the published deadline MUST have their challenge
automatically denied for tardiness even if their delay is not the
fault of the challenger.
5.2. Randomness Ambiguities
The best good faith efforts have been made to specify precise and
unambiguous sources of randomness. These sources have been made
public in advance and there has not been objection to them. However,
it has happened that when the time comes to actually get and use this
randomness, the real world has thrown a curve ball and it isn't quite
clear what data to use. Problems have particularly arisen in
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 might 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 as well as causing
substantial delay. 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.
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:
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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.)
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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
1. 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.
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2. 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.)
3. 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.
4. 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.
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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.
7. Fully Worked Examples
>> EXAMPLE NEEDS TO ALSO COVER THE SECTION 5 EXTENSION PROVISIONS. <<
1. Assume the eligible volunteers published in advance of selection
are the numbered list of 31 past NomCom Chairs appearing below in
Appendix A.
2. Assume the following (fake example) ordered list of randomness
sources:
2.1 The Kingdom of Alphaland State Lottery daily number for 1
November 2025 treated as a single five-digit integer.
2.2 (a) The People's Democratic Republic of Betastani State
Lottery six winning numbers for 1 November 2025 and then (b) the
seventh "extra number" for that day as if it was a separate
random source.
Hypothetical randomness publicly produced:
Source 1: 29319
Source 2a: 9, 61, 26, 34, 42, 41
Source 2b: 55
Resulting seed string:
29319./9.26.34.41.42.61./55./
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The table below gives the hex of the MD-5 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| 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 3
Resulting first ten selected, in order selected:
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+-----------------------+-------------------------+
| 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) |
+-----------------------+-------------------------+
Table 4
Should one of the above turn out to be ineligible or otherwise be
eliminaged by a Type A reason, the next would be M. St.Johns, number
5.
8. Security Considerations
Careful choice should be made of randomness inputs so that there is
no reasonable likelihood that they are under the control of the
administrator. Guidelines given above to use a reasonably 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 random inputs and results, including the hash
chain seed R (Section 6), and something like a one-week window for
the community of interest to duplicate the calculations and protest
if there is any discrepancy should give a reasonable assurance of
faithful implementation and execution.
9. IANA Considerations
This document requires no IANA actions.
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.
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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
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//*****************************************************************
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 );
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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 ) )
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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;
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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];
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++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
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//****************************************************************
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;
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}
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" );
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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;
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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.",
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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 ),
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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 ) {
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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 )
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{
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;
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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
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// 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,
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(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 };
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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>
11. Normative References
[RFC0020] Cerf, V., "ASCII format for network interchange", STD 80,
RFC 20, DOI 10.17487/RFC0020, October 1969,
<https://www.rfc-editor.org/info/rfc20>.
[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-editor.org/info/rfc2119>.
[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-editor.org/info/rfc4086>.
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[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/info/rfc6234>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
12. Informative References
[Lamport] Lamport, L., "Password Authentication with Insecure
Communication", Communications of the ACM 24.11,
pages 770-772, November 1981.
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
DOI 10.17487/RFC1321, April 1992,
<https://www.rfc-editor.org/info/rfc1321>.
[RFC1760] Haller, N., "The S/KEY One-Time Password System",
RFC 1760, DOI 10.17487/RFC1760, February 1995,
<https://www.rfc-editor.org/info/rfc1760>.
[RFC2777] Eastlake 3rd, D., "Publicly Verifiable Nomcom Random
Selection", RFC 2777, DOI 10.17487/RFC2777, February 2000,
<https://www.rfc-editor.org/info/rfc2777>.
[RFC3797] Eastlake 3rd, D., "Publicly Verifiable Nominations
Committee (NomCom) Random Selection", RFC 3797,
DOI 10.17487/RFC3797, June 2004,
<https://www.rfc-editor.org/info/rfc3797>.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, DOI 10.17487/RFC5890, August 2010,
<https://www.rfc-editor.org/info/rfc5890>.
[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-editor.org/info/rfc8713>.
[RFC9389] Duke, M., "Nominating Committee Eligibility", BCP 10,
RFC 9389, DOI 10.17487/RFC9389, April 2023,
<https://www.rfc-editor.org/info/rfc9389>.
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Appendix A. History of NomCom Voting 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 |
+-----+-----------+---------------------+------------------+
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| 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 |
+-----+-----------+---------------------+------------------+
Table 5
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 [RFC2777] and [RFC3797].
RFC 2777 = Algorithmic selection using the algorithm and reference
code provided in [RFC2777] (but not the fake example sources of
randomness).
RFC 3797 = Algorithmic selection using the algorithm and reference
code provided in [RFC3797] (but not the fake example sources of
randomness).
RFC 3797 + hash chain extensions = As with [RFC3797] but using a hash
chain for Extended Selection as generally specified in Section 6.
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Appendix B. More Equations and Numbers
You can skip this informational appendix unless you want to dig a
little bit further into the statistical arguments.
To illustrate the relatively minor effect in practice of less entropy
than needed for complete randomization, assume you select N items
from a pool of P things and that you do this T times where N << P <<
T. Obviously, the expected value of the number of times each thing
would be selected is
N * T
Expected Value = ---------
P
Although NomCom selection is done without replacement (since it makes
no sense to select the same person more than once), given that N << P
we can approximate selection statistics assuming selection with
replacement. Making the further approximation of the binomial
distribution for the Gaussian distribution, the standard deviation of
the number of times a thing would be selected is
___________________
2 / N N
Standard Deviation of Value = / T * --- * (1 - ---)
V P P
Assuming the specific case of selecting 10 items from a pool of 200,
typical of an IETF NomCom selection near the date of the document.
The following table shows, for various powers of 2 number of item set
selections, the expected number of times each item would be selected
and the standard deviation in the expected number.
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+=============+============+===========+==============+==========+
| Times a Set | Base 2 | Expected | Standard | SD as a |
| of 10 is | Log(Times) | Times | Deviation of | % of |
| Selected | | Each Item | Times Item | Expected |
| | | Selected | Selected | |
+=============+============+===========+==============+==========+
| 1,024 | 10 | 51.2 | 22.1 | 43.2% |
+-------------+------------+-----------+--------------+----------+
| 1,048,576 | 20 | 52,429 | 706 | 1.35% |
+-------------+------------+-----------+--------------+----------+
| 1,073,741, | 30 | 53,687, | 22,584 | 0.0421% |
| 824 | | 091 | | |
+-------------+------------+-----------+--------------+----------+
| 1,099,511, | 40 | 54,975, | 722,681 | 0.00131% |
| 627,776 | | 581,389 | | |
+-------------+------------+-----------+--------------+----------+
Table 6
Thus, 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 correlation between the selection of any
pair of pool members, and the like for a small number of pool
members.
Appendix C. Changes from RFC 3797
The primary differences between this documenet and [RFC3797], the
previous version, are the following:
* Add Section 5: Extended Selection, using hash chain.
* Many editorial changes. Add IANA Considerations section.
* Use [RFC0020] as the reference for ASCII.
* Update Appendix A.
* Define "publicly verifiable" as "promotes public confidence" to
avoid technical meanings of "verify".
* Change text and code to use HMAC-SHA-256 instead of MD-5.
* Change "Fully Worked Example". Update code to generally improve
it. Use new code for examples.
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* Add Appendix B which argues that an amount of entropy less than
that required for perfect randomization is OK.
Appendix D. Versions Change History
RFC EDITOR NOTE: Please remove this Appendix before publication
D.1. -00 to -01
* Add Extended NomCom Selection, Section 5, incrementing following
section numbers.
* Add text emphasizing that no entries can be added after the
volunteer list is frozen.
* Editorial improvements.
D.2. -01 to -02
* Covert nroff source to IETF xml2rfc v3.
* Change pool formation reference to [RFC9389].
* Increased use of all caps requirements language.
* Editorial improvements.
D.3. -02 to -03
* Change over extension under Section 6 to use a hash chain as per
https://mailarchive.ietf.org/arch/msg/eligibility-discuss/
D0CQ9p6-RiPD3x77dna7IXkwcLQ/
* Define "verifiable" as "promoting confidence" to avoid technical
meansings of "verify".
* Add Martin Thomson to Appendix A.
* Add Acknowledgements Section.
* Add Appendix B on More Equations and Numbers.
* Add pointer to Rich Salz's implementation of the [RFC3797] method.
* Add this changes history Appendix.
* Change text and code to use SHA-256 instead of MD-5.
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* Change "Fully Worked Example" and update code to generally improve
it. Use new code for example.
* Change Table 1 on randomness required to cover a 250 person pool
and to cover the case of selecting 1 item.
* Add "More Equations and Numbers" appendix.
D.4. -03 to -04
* Change to using HMAC-SHA-256 with "key" derived as before and
specify how "message" is derived.
* Editorial improvements.
D.5. -04 to -05
* Make inclusion/use of the Extensions mechanism more optional for
the Administrator.
* Minor editorial changes.
Acknowledgements
The suggestions and comments on this document from the following
persons are gratefully acknowledged: Paul Hoffman and Martin Thomson.
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
incorporated.
Author's Address
Donald E. Eastlake 3rd
Futurewei Technologies
2386 Panoramic Circle
Apopka, Florida 32703
United States of America
Phone: +1-508-333-2270
Email: d3e3e3@gmail.com, donald.eastlake@futurewei.com
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