Ripping Coins For a Fair Exchange

A fair exchange of payments for goods and services is a barter where one of the parties cannot obtain the item desired without handing over the item he ooered. We introduce the concept of ripping digital coins to solve fairness problems in payment transactions. We demonstrate how to implement coin ripping for a recently proposed payment scheme 9, 8], giving a practical and transparent coin ripping scheme. We then give a general solution that can be used in any payment scheme with a challenge. We also indicate how fairness can be obtained by building a contract into the coin.