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  • commitment.coffee

  • ¶

    Commitments are a cryptographic method of allowing somebody to “commit” to a value without revealing what that value is (confidential). Later in time, they admit the value that they committed to and a “decommitment” so third parties can verify that they have not tried to change the value they committed to initially.

    http://en.wikipedia.org/wiki/Commitment_scheme#Coin_flipping

    ursa = require 'ursa'
key = require './key'
  • ¶

    Makes a commitment. Returns the pair (commitment, decommitment). As above indicates, the commitment should be published immediately. The decommitment should be published along with the commited item later in time.

    1. info is the value to be commited to. (I choose heads.) (Buffer)
    exports.make = (info) ->
    privKey = key.createPrivate()
    sig = privKey.hashAndSign 'sha512', info
    
    [sig, privKey.toPublicPem()]
  • ¶

    Verifies a commitment. Returns true or false.

    1. cand is the candidate value admitted by the committer. (He says he chose heads.) (Buffer)
    2. commitment is the commitment they published. (Buffer)
    3. decommitment is the value published with the candidate as proof of commitment.
    exports.verify = (candidate, commitment, decommitment) ->
    pubKey = ursa.createPublicKey decommitment
    pubKey.hashAndVerify 'sha512', candidate, commitment