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Does a method exist where a secret is generated so that is is unknown until 3 or more people (predetermined) reach consensus that it should be revealed?

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    $\begingroup$ Yes, you even managed to find the tag for it. $\endgroup$ – otus Oct 9 '15 at 6:52
  • $\begingroup$ A simple XOR is the most trivial example of such method. Anyway, wiki is your friend. en.wikipedia.org/wiki/Secret_sharing#Efficient_secret_sharing $\endgroup$ – Leśny Rumcajs Oct 9 '15 at 9:22
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    $\begingroup$ Shamir's only solves part of the problem. At some point one of the participants will know both the full secret and also all the shares. This might be more about distribution of a secret, rather than crypto in itself? $\endgroup$ – c0dem4gnetic Oct 9 '15 at 15:44
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If I understand the question right, what you are looking for is a fair secret sharing protocol. Most secret sharing protocols are unfair. For example, in 3-out-of-4 secret sharing with 2 dishonest parties, once one honest party broadcasts their share, the two dishonest parties can privately collude to reconstruct the secret. Then if they refuse to participate, the 2 honest parties cannot reconstruct the secret.

Fairness is described as "if there is a player getting the secret in the recovery phase, then each player participating to the reconstruction process does too" [1]. That reference proposes such a protocol and you can find a number of others by looking at the references in that paper.

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