More and more companies start offering digital payment systems. Smartphones evolve to a digital wallet such that it seems like we are about to enter the era of digital finance. In fact we are already inside an digital economy. The market of e-x (x = "finance", "money", "book", you name it . . ....

Blockchains are the most well-known example of a distributed ledger technology (DLT). Unlike classic databases, the ledger is not maintained by any central authority. The integrity of the ledger is maintained automatically by an algorithmic consensus process whereby nodes vote and agree upon the...