Date Added: Dec 2011
In the standard definition of a commitment scheme, the sender commits to a message and immediately sends the commitment to the recipient interested in it. However, the sender may not always know at the time of commitment who will become interested in verifying it. Further, when the interested party does emerge, it could be critical to establish when the commitment was made. Employing a proof of work protocol at commitment time will later allow anyone to "Carbon date" when the commitment was made, approximately, without trusting any external parties. The authors present CommitCoin, an instantiation of this approach that harnesses the existing processing power of the Bitcoin peer-to-peer network; a network used to mint and trade digital cash.