Re: discussion of publicly verifiable random selection procedure in internet-drafts that led up to RFC 2777
Subject: nomcom algorithm: the last input to be made public matters most
Date: Wed, 14 Oct 98 00:25:42 IDT
From: Neal McBurnett <nealmcb@lucent.com>
To: poised@tis.com
Reply-to: Neal McBurnett <nealmcb@bell-labs.com>
The selection procedure before us and the draft it is based on seem most highly focussed on demonstrating that Don did not manage to cleverly pick an algorithm which allows him to influence the winners ahead-of-time. I see no reason to challenge that assertion. But the more important question, I think, is whether *anyone else* can improperly influence the selection result. After all, we are likely to be picking nomcom chairs who have ethical reputations. But many people who are not picked to be part of the process at all may want to affect the outcome. Imagine an adversary "Mallet" who simply wants to see that a particular person is picked for the committee. In this case, with an average selection probability of about 1 in 4 (10 out of 41), Mallet simply needs to move the result into one of 4 equally large result sets. All Mallet has to do is observe the various inputs as they are made public and then influence the *last* source of input. In this case it appears that the last source is the Massachusetts Numbers Game draw time: 19:55 US/Eastern on the 16th. <http://www.masslottery.com/>> If Mallet could manipulate even just the last digit of that number, he could probably manage to pick one or two members of the committee. even if there is ample entropy in the whole set of inputs, if the last input can be swayed, an adversary can have their way. Suppose that instead the stock prices were the last inputs to be publicly available. Moving the price of Cybercash stock for one day (volume of 165,200 shares today at a price of 7 1/8) would not be too hard to do. Little money would be at risk if the original stock position was brought back to its previous level in the next few days. Selecting the closing price to target would be done by estimating the closing prices of the other stocks as the day ended, and running the algorithm with those prices and all the other inputs plugged in to see which Cybercash prices would result in the best algorithm outcome. [What are the criteria for making information on individual stock trades public? How much shows up on the ticker tapes? Who will be watching Cybercash on Friday? :-] Even if Mallet can't affect the last input, it may be possible to influence other inputs in such a way that the overall outcome is biased. I suggest that it would be preferable to select several inputs that all are announced at the same time by different jurisdictions. Stocks, stock trading volumes, and even stock indexes are probably a poor choice as inputs from this standpoint. Lotteries seem useful in this context, and it is nice to be able to use the lottery infrastructure for something more enlightened than their raison d' etre. Cheers, Neal McBurnett <nealmcb@bell-labs.com>> 303-538-4852 Denver Bell Labs / Lucent Technologies http://bcn.boulder.co.us/~neal/ (with PGP key)