Balancing privacy and accountability in digital payment methods using zk-SNARKs.

The bank card has overtaken cash as the most used payment method. This increased use has also given our banks larger amounts of information. In a world where the value of information has increased this puts clients in a weak position with respect to their banks. Legislation also requires banks to use this information to ensure that their clients do not use bank accounts for malicious activities. At the same time many people start to value their privacy more and more, leading to a conflict of interest. We present a digital permissioned decentralised anonymous payment scheme. Our scheme provides anonymity for its users, whilst also allowing banks to adhere to current regulations without decreasing anonymity. zk-SNARKs form the basis for our anonymity and implement possibilities for banks to enforce certain regulations. Finally, we introduce an additional group of actors in our anonymous payment scheme called judges. These judges have the ability to view encrypted transaction details of any transaction that does not adhere to the limits imposed by the scheme. The details can be viewed at any later point in time, as correctness of the values is guaranteed by the verifiable encryption scheme.