[HN Gopher] AI unmasks anonymous chess players, posing privacy r...
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       AI unmasks anonymous chess players, posing privacy risks
        
       Author : O__________O
       Score  : 148 points
       Date   : 2022-12-11 12:09 UTC (10 hours ago)
        
 (HTM) web link (www.science.org)
 (TXT) w3m dump (www.science.org)
        
       | Havoc wrote:
       | This seems incredibly ominous when transferred to social media.
       | Large parts of the internet rely on the pseudo anonymity of it
       | quite heavily - see reddit etc.
        
         | dewey wrote:
         | Basic opsec principles always say that if you want to stay
         | anonymous you have to switch the way you are writing (by
         | adopting a differnet personality, running it through
         | translation apps etc.).
         | 
         | If someone would want to stay anonymous the unmasking % would
         | probably be lower. The threat-model of the chess players
         | doesn't include that they have to stay anonymous and need to
         | switch up their way of playing.
        
           | Havoc wrote:
           | >>switch the way you are writing
           | 
           | I'd be very surprised if that actually works. Stuff like
           | vocabulary can't exactly be turned off at will
        
           | greggarious wrote:
           | I'm fond of occasionally throwing in some ou s and references
           | to cities other than Ontario to throw folks off, but it's
           | hard to pull off long term
        
         | wussboy wrote:
         | I'm not convinced that, for 99.9% of use cases, anonymity is a
         | feature. I think it's far more likely that the easy anonymity
         | that has been the default for much of the existence of the
         | Internet has harmed society.
         | 
         | I get downvoted whenever I say this, but anonymous speech is
         | only allowed by recent technology and has never been a part of
         | our ancestral environment.
        
           | potatototoo99 wrote:
           | Freedom of speech is also a recent invention.
        
           | hairofadog wrote:
           | I'm not downvoting, but I think the concept of anonymous
           | speech goes way way back to the origins of writing, doesn't
           | it? The change in recent years is that it's extra hard to
           | stay anonymous, what with the surveillance economy?
        
             | wussboy wrote:
             | Perhaps. But if you consider:
             | 
             | 1. The cost of printing/transcribing something 2. Literacy
             | rates 3. Constraints tied to physical distribution
             | 
             | ...the reach of that potentially "anonymous speech" was the
             | tiniest fraction of what we experience today. And even then
             | it wasn't necessarily anonymous, unless you just left books
             | lying around?
        
               | hairofadog wrote:
               | I think it was pretty doable: https://en.wikipedia.org/wi
               | ki/List_of_anonymously_published_...
        
               | wussboy wrote:
               | I won't argue that it wasn't possible. But that link
               | shows 20-40 books, and covers 3000 years of human
               | culture. That's about one anonymous book per century. I
               | think we need more anonymity than that. But I think the
               | amount of anonymity we have now is disastrous to civil
               | society.
               | 
               | Appreciate the link though. Thanks for engaging.
        
         | kypro wrote:
         | Seems quite easy to solve this though. An AI could easily
         | anonymise your text by rephasing sentences.
        
         | s3000 wrote:
         | For those you haven't seen it, from 2 weeks ago:
         | 
         | Show HN: Using stylometry to find HN users with alternate
         | accounts [1]
         | 
         | [1] https://news.ycombinator.com/item?id=33755016
        
           | [deleted]
        
         | makeworld wrote:
         | Perhaps anonymous social media (like 4chan, with its lack of
         | usernames) will become more popular.
        
           | [deleted]
        
           | LarryMullins wrote:
           | Or less popular, because there is now a greater risk of your
           | 4chan comments being associated with your other online
           | identities.
           | 
           | There may be some additional safety in conforming to the
           | local "memespeak" dialect, and not using that dialect
           | elsewhere.
        
       | password4321 wrote:
       | In case you missed this two weeks ago, "find by example" is
       | possible in many datasets even without AI:
       | 
       |  _Show HN: Using stylometry to find HN users with alternate
       | accounts_
       | 
       | https://news.ycombinator.com/item?id=33755016
        
         | r3trohack3r wrote:
         | This is one of the use cases I see AI helping with. You can
         | already ask ChatGPT to reword content for you - breaking
         | analysis like this.
         | 
         | A (humorous) example: https://vc.blankenship.io
         | 
         | If you want to remain anonymous, use an AI filter for your
         | written content.
        
           | jacooper wrote:
           | Thats definitely not private, which is the point of defeating
           | stylometry
           | 
           | If only there was some kind of re wording AI that can be run
           | locally.
        
             | r3trohack3r wrote:
             | Given current trends, I guess I'd say give it 6months?
        
               | Siira wrote:
               | There is OPT and BLOOM, which need lots of expensive GPUs
               | to run. Not as good as GPT3, IMO. I doubt there will be
               | any good local alternatives in a year. StableDiffusion
               | needed light compute, not at all comparable to these
               | beasts.
        
               | JadeNB wrote:
               | > Given current trends, I guess I'd say give it 6months?
               | 
               | I'm happy to give it 6 months until the technology is
               | there to do it, if it's not already--but, as long as
               | there's an owner of the technology (that is, as long as
               | the technology is pre- the point where I can easily roll
               | my own), I'm skeptical of any owner in today's privacy
               | climate intentionally forgoing the opportunity to suck up
               | personal data whenever and however they can.
        
         | kristopolous wrote:
         | This is nice. I consider my stuff fairly easy for me to
         | recognize so when I read the other users I found a bit of
         | myself in them.
         | 
         | I thought "well this person seems a bit cynical" - you know,
         | it's not a bad way to go outside yourself
        
       | alkonaut wrote:
       | Pseudonymous. Just like anyone who is willing to do the work can
       | identify my real identity from my HN writing, a pseudonymous
       | chess handle gives a lot of information. A chess player who wants
       | to be anonymous should not re-use a handle for two games. There
       | is no anonymity anywhere if you provide enough entropy which you
       | do if you use a persistent pseudonym.
        
         | nextlevelwizard wrote:
         | If you want to play against good players you need some games to
         | gain rating
        
           | alkonaut wrote:
           | Yes. That's fine so long as you never play in person as well,
           | thereby tying a real identity to your pseudonym.
           | 
           | Otherwise you can remain pseudonymous (not anonymous) for as
           | long as you want.
           | 
           | But there is no way to do a mix of in-person and pseudonymous
           | writing/chess/art/anything with a personal "style".
        
           | random_kris wrote:
           | Mmmm this could be solved using Zero-Knowledge proofs.
           | 
           | When registering pick an elo. Provide a proof that you own
           | the account in that Elo range and then you can create another
           | account that will start in that Elo range.
        
         | cute_boi wrote:
         | So, to solve such issue we can add noise? So, lets say I play 1
         | game, i let another people/bot to play another game using same
         | account?
        
         | sureglymop wrote:
         | What if the playing style of one game is already enough to hint
         | at who might be playing?
        
           | alkonaut wrote:
           | Then you are never entirely anonymous. I doubt that's the
           | case though.
        
             | YetAnotherNick wrote:
             | They aren't comparing two sets of games. They are comparing
             | a single game with all player's known set of game. Any FIDE
             | rated player will have a set of games that is known to
             | everyone.
        
       | matsemann wrote:
       | To not get unmasked by things like this I throw in some blunders
       | here and there. Unfortunately my other moves are often also
       | blunders..
        
         | djexjms wrote:
         | Maybe the strategy here is to just not make any blunders.
        
           | dtgriscom wrote:
           | Oh, right. Like it sounds so easy when YOU say it.
        
       | neaden wrote:
       | There was recently a player who shot up the Chess.com blitz
       | leaderboard under the name Sinister Magnus. They were eventually
       | removed from the leaderboard, presumably for being an alt of an
       | existing GM, but I don't think anyone has figured it out for sure
       | who they are, it would be interesting test to see if they are
       | able to figure the player out using this.
        
         | rollcat wrote:
         | Interesting! Why is it not allowed to have alt accounts? And
         | why was such severe action taken, without enough evidence? Why
         | do people want using alts in the first place, in a game with
         | perfect information?
         | 
         | In StarCraft II, having alts is tolerated (well, depending on
         | your manners - nobody likes smurfing), but we have
         | sc2revealed.com which takes crowd-sourced reports to try to
         | unmask "barcode" (llllllllllll) players. Many pros try to
         | practice anonymously on the ladder, because SC2 a game of
         | imperfect information, and in a best-of-3 series (like in a
         | tournament), you 1. don't want to use the same opening every
         | match, and 2. don't want your opponent to immediately recognize
         | what you're doing, or work on preparing a counter ahead of
         | time.
        
           | neaden wrote:
           | You can have an alt account, and Sinister Magnus is still
           | around, you just can't be on the leaderboard more then once.
           | So SM is presumably the alt of someone who is already on the
           | leaderboard. Similar to StarCraft a GM might want to prep
           | openings without revealing that's what they are doing, so
           | there are reasons for having alts but that applies more for
           | longer time controls rather then blitz. Generally GMs do
           | their prep with a small and usually secret team before a big
           | tournament.
        
       | version_five wrote:
       | Reminds me of this - predating AI
       | 
       | https://axbom.com/keystroke-dynamics/                 As early as
       | 1860, experienced telegraph operators realized they could
       | actually recognize each individual by everyone's unique tapping
       | rhythm. To the trained ear, the soft tip-tap of every operator
       | could be as recognizable as the spoken voice of a family member.
        
         | myself248 wrote:
         | Oh yeah, every ham knows you can recognize the sending fist. If
         | they're actually using a real key, anyway.
        
           | Victerius wrote:
           | I don't understand your sentence.
        
             | wbl wrote:
             | Hey's saying if you are using a straight key instead of an
             | iambic keyer (different morse sending tech) then you can
             | recognize the operator from their patterns (the first)
        
             | dd82 wrote:
             | https://en.wikipedia.org/wiki/Telegraph_key#Operators'_%22f
             | i...
             | 
             | > With straight keys, side-swipers, and, to an extent,
             | bugs, each and every telegrapher has their own unique style
             | or rhythm pattern when transmitting a message. An
             | operator's style is known as their "fist".
             | 
             | > Since every fist is unique, other telegraphers can
             | usually identify the individual telegrapher transmitting a
             | particular message. This had a huge significance during the
             | first and second World Wars, since the on-board
             | telegrapher's "fist" could be used to track individual
             | ships and submarines, and for traffic analysis.
        
             | Tempest1981 wrote:
             | Identifiable ... by the way they tap out Morse code with
             | their hand/fist.
             | 
             | Ham = amateur radio operator:
             | https://en.wikipedia.org/wiki/Amateur_radio
        
           | flak48 wrote:
           | This made my Google the etymology of 'ham-fisted' and I was
           | disappointed that it had nothing to do with ham operators
           | with carpal tunnel syndrome.
        
             | mzi wrote:
             | It's the opposite, really. The radio term was a pejorative,
             | as the professionals saw the amateurs as ham-fisted.
        
         | mattr47 wrote:
         | My Dad was a morse intercept operator for the US Army, mid 60s,
         | stationed in Northern Japan. He has stories of them naming all
         | the Soviet morse operators by the way the tapped.
        
           | Rodeoclash wrote:
           | Cryptonomicon mentions this as well. Each operator having a
           | particular "fist" that was unique to them.
        
         | nextlevelwizard wrote:
         | I remember playing FPS game called Enemy Territory as teenager
         | and after awhile whenever I was in 1v1 shoot out with one of my
         | "clan" members I knew who it was based on their movement.
        
           | sitkack wrote:
           | I was walking down the street a couple years ago, in my
           | peripheral vision I noticed the gait of someone walking
           | across the street traveling the other direction, instant
           | recall of that former coworkers name from 10 years previous.
           | It would have taken longer to recognize them visually if they
           | were standing still. Still amazes me, years later.
        
             | jacquesm wrote:
             | Gait?
        
               | sitkack wrote:
               | Fixed, thanks!
        
               | [deleted]
        
           | erk__ wrote:
           | Off topic, but if it was Wolfenstein ET I will just add that
           | there still is a community for it and a Foss version of it
           | that runs on modern operating systems
           | 
           | https://www.etlegacy.com/
        
             | smarri wrote:
             | Thanks, I spent many hours and late nights into early
             | mornings playing this game.
        
       | iLoveOncall wrote:
       | I doubt those players are really anonymous anyway, as either
       | lichess or chess.com can easily identify them.
       | 
       | I don't see this changing anything, especially when we already
       | know that chess.com is not impartial in its treatment of players.
        
       | croes wrote:
       | Could it be used to find cheaters?
       | 
       | If you don't play like yourself you're likely cheating.
        
         | recursive wrote:
         | I really don't like this. Sometimes I want try a different
         | style. It sounds like a presumption of guilt. "Machine doesn't
         | know what' he's doing? Probably cheating"
        
           | WJW wrote:
           | For most normal humans, if they merely try a different style
           | than what they are used to their performance would probably
           | go down rather than up. After all, you'd have seen many
           | common positions before and know most of the usual ideas for
           | your chosen openings etc.
           | 
           | If someone suddenly plays a different style and also their
           | move quality goes up significantly, that might be an
           | additional indicator of cheating. All cheat detection works
           | in a probabilistic fashion, since it is not allowed (and
           | would be way worse) to actually observe players 24/7 in their
           | home to verify whether they're cheating or not.
        
       | swayvil wrote:
       | To state the obvious : of course we are using this exact same
       | technology to identify people by writing style. All of us. Right
       | now.
        
       | quotemstr wrote:
       | Just wait until quantum computing breaks all non-PFS encrypted
       | internet traffic from the past 20 years. It's going to be _wild_.
       | David Brin is going to get to live out his vision of a
       | transparent society.
        
         | [deleted]
        
       | philippejara wrote:
       | I'm not sure why they ham up the risk of privacy loss regarding
       | unmasking anon players, the only "risk" I can think of would be
       | someone developing and testing new strategies but then I'd assume
       | the fingerprinting would be far less accurate, testing if you can
       | effectively hide your own quirks while deviating from them would
       | be far more interesting. As it stands this is nothing new and the
       | concerns seem weirdly pointed, everyone(?) already knows the
       | risks of fingerprinting and pattern recognition in more general
       | applications. It was a fun paper to read, shame half the article
       | promoting it was cautioning.
        
         | lobe wrote:
         | Often the new strategies top level players test on anonymised
         | accounts are subtle tweaks in lines deep into / slightly beyond
         | opening theory. Often these lines are slightly inferior to
         | mainline but come with an edge due to the "surprise factor"
         | making it harder for opponents to prepare. Each of these subtle
         | tweaks will only arise in a small proportion of games (as only
         | some of the time your opponent will play the line you want to
         | test), so I imagine fingerprinting based on play style will
         | still work relatively well.
        
       | forrestthewoods wrote:
       | Super cool and fascinating.
       | 
       | I don't know why, but I don't like that the headline frames it as
       | a "privacy risk". Are we really concerned about privacy when
       | playing chess?
       | 
       | I think the world probably needs to accept there's no such thing
       | as "anonymous behavior". Behavior itself is individualized.
       | Therefore if behavior can be observed the probability that it is
       | anonymous rapidly approaches zero with time and observations. The
       | only way to be verifiably anonymous is to not be observed.
       | 
       | This means if you are a person at risk of harm if your identity
       | is unmasked that you can't rely on supposedly anonymous behavior.
       | Bummer.
        
         | JadeNB wrote:
         | > I don't know why, but I don't like that the headline frames
         | it as a "privacy risk". Are we really concerned about privacy
         | when playing chess?
         | 
         | To the extent that headlines matter, I'd way rather that people
         | worry about the privacy risks of de-anonymizing technology long
         | before it's at the point where it's a practical issue. If we
         | only worry about it when it becomes an actual issue already
         | being, or about to be, applied to unambiguously privacy-
         | invading matters, then, well, that's the way we've already done
         | it and it's too late now--why didn't you bring it up earlier?
         | 
         | I'd also prefer to avoid the "what do you have to hide?" issue.
         | Maybe someone, for whatever reason, _does_ have something to
         | hide; if they intentionally play chess anonymously, presumably
         | they intend to do so. It shouldn 't be up to me to decide
         | whether or not their need, or even just desire, for privacy is
         | legitimate.
         | 
         | (Of course, it's already too late--and has been since, at the
         | very latest, the AOL incident--to worry about the onset of such
         | de-anonymization, but it's always (or only almost always?)
         | better to face inevitable future problems now, rather than
         | waiting for that future.)
        
       | rvba wrote:
       | Why did meta hire someome to study poker bots? Arent they afraid
       | that after spending a lot of money on some developer that peraon
       | will just quit facebook and write own poker bots?
       | 
       | How does this research help facebook?
       | 
       | Im very, very far away from Musk and his antics, but really some
       | of those big companies seem to have lots of people who do passion
       | projects.
       | 
       | Meanwhile an actual user has low if no chance to get decent
       | support (probably for the cost of that of programmer they could
       | get multiple people).
       | 
       | And yes I am aware that I sound anti illectual here and research
       | the sake of reseaech can lead to nice things. I just think that
       | the person will quit facebook to write poker bots and ruin the
       | game for those who play it by detecting their weaknesses ( btw. I
       | dont even play poker).
        
         | Jerrrry wrote:
         | Studying poker and humans style of play of the game translate
         | directly to improving generalized agents that can play other
         | games.
         | 
         | For all we know, the guy who was kinda good at poker made the
         | small break-thru that led Google's Alpha/Omega chess or Go
         | achievement.
         | 
         | It's actually difficult to tell what piece of such complex
         | systems are responsible for which - but in general, applying
         | incremental piecemeal improvements have been monumental for the
         | magnitude jump in progress in recent years.
        
         | LarryMullins wrote:
         | > _Arent they afraid that after spending a lot of money on some
         | developer that peraon will just quit facebook and write own
         | poker bots?_
         | 
         | That's a risk when you pay workers to research or learn nearly
         | anything new. If you run a pizzeria, you teach your workers how
         | to make pizzas; they could turn around and make pizzas for
         | another business instead. Maybe even open their own pizza shop
         | and compete with you, using your own recipe.
         | 
         | I think accepting this kind of risk is simply table stakes for
         | running a business.
        
       | [deleted]
        
       | Fricken wrote:
       | In the early to mid-2010s AI hype peaked, radical Kurzweillean
       | ideas became sales pitches from founders, and a great wave of
       | discussion and speculation passed through the media public
       | consciousness.
       | 
       | For a time r/futurology was an interesting place for discussion,
       | and there were really great comments to be found amidst the
       | internet chaff .
       | 
       | One of the things I speculated about then was that ai doesn't
       | need be sentient to ruin everything. Powerful tools in the hands
       | of malicious actors could wreak havoc on the internet.
       | 
       | The internet could become compromised in so many ways via privacy
       | invasions and data theft, aggressive spam, misinformation,
       | propaganda and malicious code that nobody can reliably depend on
       | it for much of anything any longer. One could receive a phone
       | call from someone who sounds like their own mother, an ai that
       | says things only a mother would know. That voice could be very
       | persuasive.
       | 
       | that was the kind of stuff we talked about years ago. There were
       | no instantaneous results, of course, and it became boring and
       | uncool to keep going on about such things.
       | 
       | Nonetheless, it seems now that the tools and incentives needed to
       | create a dystopia such as what I described are really starting to
       | come into focus.
        
         | trompetenaccoun wrote:
         | The better the tech, the better it can be used for good as well
         | as evil purposes such as deception/scams, disinformation, mass
         | surveillance, election manipulation, etc.
         | 
         | It's not the tech that's wrong, it's the populace in democratic
         | states losing more and more power, to the point where most of
         | these systems can only be described as hybrid regimes anymore.
         | The actual power does not lie with the voters but corporations,
         | the mega wealthy, their various lobby groups and corrupt
         | politicians. There is no monopoly of power exercised by elected
         | officials and law enforcement respecting the constitutions,
         | it's different groups and fractions fighting each other for
         | supremacy. AI is just another tool at their disposal, of course
         | they're making use of it.
         | 
         | Guns can be used for protection as well as oppression. The
         | internet can be about free information or about censorship and
         | spying on users. We can live in digital Maoism or digital
         | liberalism. It's up to the common people and for them to
         | realize this before it's too late.
        
       | [deleted]
        
       | O__________O wrote:
       | Related paper:
       | 
       | https://proceedings.neurips.cc/paper/2021/hash/ccf8111910291...
        
       | greggarious wrote:
        
         | danuker wrote:
         | Should downloading/looking at people's chess games not be
         | socially acceptable, in spite of it being a good way to learn?
        
           | greggarious wrote:
           | I think the issue is if you go beyond "who am I playing" to
           | connecting that to the rest of their online life, if that
           | makes sense.
           | 
           | It's fine to want to tailor strategy but not say, out their
           | dissident writings.
        
       | dmurray wrote:
       | > They gave the system 100 games from each of about 3000 known
       | players, and 100 fresh games from a mystery player. To make the
       | task harder, they hid the first 15 moves of each game. The system
       | looked for the best match and identified the mystery player 86%
       | of the time...A non-AI method was only 28% accurate.
       | 
       | This sounds incredible, to pick the right player out of 3000
       | candidates 86% of the time.
       | 
       | I am not sure that pruning the first 15 moves is enough to
       | eliminate the information you get from choice of opening (which
       | is presumably the intention of the restriction). For example, if
       | a player religiously plays the Najdorf Sicilian as Black, you can
       | immediately rule out many(most? ) positions that started with a
       | French or a Ruy Lopez.
       | 
       | I'd like to see what the best results are from a model that just
       | looks at the position after move 15, and use that as a baseline.
        
         | oneoff786 wrote:
         | Does anyone good religiously play the same opening as black?
         | 
         | I don't know chess but that sounds like a bad idea
        
         | bee_rider wrote:
         | It seems really impressive.
         | 
         | I wonder how a chess GM would do at this test (although we'd
         | have to restrict it to other top GMs that are active at the
         | same time as them).
        
         | dmurray wrote:
         | > I'd like to see what the best results are from a model that
         | just looks at the position after move 15, and use that as a
         | baseline.
         | 
         | Reading the paper, they have an "opening baseline" which
         | consists of frequency analysis on a player's first 5 moves.
         | That model has 93% accuracy!
         | 
         | The mapping of first-five-move sequences to the positions
         | obtained after them is almost a bijection (there are some
         | transposition, but a small effect) so that's similar to my
         | proposal.
         | 
         | I can't tell whether the 15-move cutoff is 15 half-moves, so
         | 7-8 moves per player, or 15 moves each which is how every chess
         | player would read the sentence.
         | 
         | Either way, I haven't completely read the paper yet, but I
         | don't think it addresses the rebuttal of "I will just change my
         | openings and the machine won't detect me".
        
         | abecedarius wrote:
         | Yeah, that means it extracts roughly 12 bits of information
         | from observing a game after move 15. It takes 33 bits to pick
         | out one human from everyone alive. You get at least 3 bits just
         | knowing someone plays chess, so you're halfway there?
         | 
         | Good point about baseline.
        
           | dmurray wrote:
           | From observing 100 games after move 15, I think you mean.
        
             | abecedarius wrote:
             | Oh, I thought the 100 applied only to training. But the
             | article agrees with you -- thanks.
        
           | kirse wrote:
           | Where can one learn more about this technique of equating
           | bits to pieces of information? I get that it's used in
           | various contexts like cryptography, randomness, compression,
           | games of Guess Who, etc. but basically just nod in fake
           | agreement when someone formally describes a system this way.
           | Like what first principles did you use to make this
           | statement:
           | 
           |  _It takes 33 bits to pick out one human from everyone alive_
           | 
           | Is it basically just 2^33 > ~8 billion humans, therefore
           | that's the minimum information context to identify a single
           | individual? But then what counts as an information bit - any
           | valid Yes/No question? And how do you calculate the bit value
           | of a piece of info (i.e. 3 bits for the knowledge of playing
           | chess)?
        
             | tijsvd wrote:
             | It's the field of information theory.
             | 
             | https://en.m.wikipedia.org/wiki/Information_theory
        
             | notafraudster wrote:
             | It's any valid question at all, it needn't be yes or no.
             | Humans have, at minimum, red, black, brown, blonde, dyed,
             | grey, white, and no hair. Learning what colour hair a
             | person has eliminates the other categories.
             | 
             | The way to think about the information content of a problem
             | or of something you learn is exactly what you're
             | suggesting. If you numbered every living person on earth,
             | it'd take more than 32 bits and not quite fill the 33rd
             | bit.
             | 
             | If you then learn a person's gender, you can eliminate all
             | the people with the incorrect gender, which is going to
             | leave you either 31.x bits (assuming binary gender) or
             | 25-27 bits of remaining entropy (assuming some non-binary
             | gender and, say, a 1-3% incidence rate).
             | 
             | When the parent you're responding to says you get 3 bits
             | for knowing someone plays chess, they're guessing that
             | 1/(2^3) = 1/8 of people, in an undifferentiated sense, play
             | chess. Of course if we knew someone's age or gender or
             | country of origin, the conditional information value in
             | knowing they play chess could be greater or lesser. And
             | realistically no one is ever trying to identify a human
             | among all humans (partially because it seems highly
             | unlikely that there are many questions that could equally
             | implicate the president of the United States and a six year
             | old on the Marshall Islands in their answer). Each bit of
             | information represents a halving of the entropy of the
             | target surface.
             | 
             | I think you got to within 1 bit of the answer from first
             | principles ;)
        
             | InitialLastName wrote:
             | It's a rough estimation technique. If every choice/factor
             | divides the number of candidates in half (on average), you
             | can choose between 2^N candidates with N yes/no questions
             | (on average).
             | 
             | I'd assume that they are estimate that 1/8 of the human
             | population plays chess, which feels like an over-estimate
             | to me (but not absurdly, depending on your threshold of
             | "plays"; by a similar process I'd estimate that at least
             | 1/8 of humans alive are under 10 years old).
        
               | abecedarius wrote:
               | > feels like an over-estimate
               | 
               | That's why I said at _least_ 3 bits. If chess players are
               | rarer, then knowing someone is a chess player is a
               | stronger filter. (By the same token, knowing that they
               | 're not is a weaker one; but that's not the case we're
               | discussing.)
        
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