In most current financial transactions, the record of each transaction is stored in three places: with the seller, with the buyer, and with the bank. This currently used scheme is not always reliable. It is therefore desirable to introduce duplication to increase the reliability of financial records. A known absolutely reliable scheme is blockchain -- originally invented to deal with bitcoin transactions -- in which the record of each financial transaction is stored at every single node of the network. The problem with this scheme is that, due to the enormous duplication level, if we extend this scheme to all financial transactions, it would require too much computation time. So, instead of sticking to the current scheme or switching to the blockchain-based full duplication, it is desirable to come up with the optimal duplication scheme. Such a scheme is provided in this paper.