Electronic Cash with Blind Deposits: How to Have No Spare Change

Unknown author (2003-10-14)

Electronic cash schemes in which the bank authenticates many coins at once suffer from the problem that coins that are authenticated together can be linked to one another. Unfortunately, unless a user spends coins in a closely prescribed manner, different batches of coins ("wallets") will be linked together in these schemes. This is illustrated by the problem of what a customer does with the "spare change" - an unusable small amount of money left in a wallet. We propose a new protocol to be used in e-cash schemes: blind deposits. In a blind deposit, a customer returns a coin to the bank without revealing the coin. We present a secure and efficient e-cash scheme with this added feature based on that of Liskov-Micali [LM01].