Cryptographic coin flipping, now in Keybase
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Re: Cryptographic coin flipping, now in Keybase
#2this is brilliant AND super useful.
also love the details like “flip again”
Re: Cryptographic coin flipping, now in Keybase
#3this is brilliant AND super useful. also love the details like “flip again”
Author here, thank you for the comment. "flip again" was added at the last minute, after a night at a bar...where some beta testers were making real-world decisions using the app.
I didn't cover some details I find fascinating but which might have been overkill outside of HackerNews. For example, some assume the "one-way"ness of a hash function makes this protocol work. But that's not enough: we can't have Alice generating 2 different secrets with the same hash, even if Barb can't reverse the hash. What we also need is _collision resistance_, so Alice doesn't get to pick and choose what to expose in the final stage.
https://en.wikipedia.org/wiki/Collision_resistance
Lately, we've made much bigger, but less blogworthy, improvements to Keybase. It's faster, team on-boarding is getting better, and we'll be launching a very improved UX in the next month or so. I rarely get to stop and write about Keybase, so this was fun.
And for anyone looking to test, I'm `chris` on keybase. You can start a chat with me and do a `/flip cards 5 chris,yourname` and we'll see who gets a better poker hand. If you can deal yourself a flush or better on your first try I'll give a prize or something? Who knows. Anyway, we're having fun with it.
Re: Cryptographic coin flipping, now in Keybase
#4I got lost on the line "If the final answer is odd, the flip is TAILS." For example: Alice flips 1 for tails. Barb/Charlie/Danika flip 0. Why is the answer tails when most of the people flipped 0 for heads? Why use XOR instead of just taking the most common answer?
Re: Cryptographic coin flipping, now in Keybase
#5I got lost on the line "If the final answer is odd, the flip is TAILS." For example: Alice flips 1 for tails. Barb/Charlie/Danika flip 0. Why is the answer tails when most of the people flipped 0 for heads? Why use XOR instead of just taking the most common answer?
So you only have to trust one person to play fair. If you used most common vote, then if 10 people play, 6 could conspire to always achieve tails.
But when using XOR even if 9 people conspire they can not know if the 10th votes 1 or 0.
Re: Cryptographic coin flipping, now in Keybase
#6This may not be the intended use of your application, but I organize a local bdsm group (if unfamiliar, do not Google this at work), and we appreciate the security offered very much.
We can even think of a few "fun" uses of this new feature.
Re: Cryptographic coin flipping, now in Keybase
#7I got lost on the line "If the final answer is odd, the flip is TAILS." For example: Alice flips 1 for tails. Barb/Charlie/Danika flip 0. Why is the answer tails when most of the people flipped 0 for heads? Why use XOR instead of just taking the most common answer?
Perhaps an even simpler analogy is a light switch. Each person decides randomly either to flip the light switch or leave it where it is. This is basically what random XOR'ing is.
If you're one of 10 people doing this to the light switch, then as long as you choose randomly, it doesn't matter what the other 9 people do. It has a 50% chance of ending up on and a 50% chance of ending up off. Even if the other 9 people are cheating together.
Of course this has the problem that whoever goes last wins, which is why the commitment ceremony is necessary.
Re: Cryptographic coin flipping, now in Keybase
#8There's a slight variation on this that I had pondered for designing a distributed election algorithm. I'm sure the idea is not novel, but it would be nice to know what work has been done on it.
The goal is to fairly select some candidate from a set of candidates. Each candidate `Ci` generates a UUID `Ui`. The hash of their UUID `hash(Ui)` is published by each candidate. Once all hashes have been collected, each candidate reveals the verifiable original UUID to all the others.
Each candidate then concatenates these UUIDs together (after normalizing the sequence in some way - e.g. sorting), and produce a selector code: `H = hash(U1 ++ U2 ++ ... ++ Uk)`. Finally, the selected candidate is simply the one whose UUID is the closest to `H` under some distance metric.
I tinkered a bit with adapting it for situations where the candidate set could shrink during the selection process (i.e. a candidate drops out), but didn't really pursue it much.
Re: Cryptographic coin flipping, now in Keybase
#9I got lost on the line "If the final answer is odd, the flip is TAILS." For example: Alice flips 1 for tails. Barb/Charlie/Danika flip 0. Why is the answer tails when most of the people flipped 0 for heads? Why use XOR instead of just taking the most common answer?
Think of it this way. If everyone is cheating and fixes their answers to be tails one fair coin flip will still randomly determine the outcome because their fair flip will swap between heads and tails for the whole group.
Re: Cryptographic coin flipping, now in Keybase
#10Has Keybase lost it's way? I thought they were onto something cool and maybe could explore an enterprise play with private chats, filesharing and git for teams or something like that. Basically make money by selling to teams. But Keybase seems to have stagnated, existing apps are still quite buggy, not enough new developments recently. The facepalm moment for me was when they announced they were supported by the Stellar foundation. I lost all hope then and there. I get that you guys are buddies with the Stellar folk, you think Stellar is cool etc but an objective analysis leads to only one answer : don't do it you'll regret. Maybe add it as a feature (stellar integration) but don't go all in. Speaking of Stellar, still no integration after 1 year?? Focus on what you have and start making money. So, what went wrong malgorithms?
(Sorry if this sounds harsh or rude, there's no point in sugar coating the truth. Hopefully the keybase teams reads this criticism and does a little soul searching.)