Privacy

As mentioned earlier, privacy is the right of each individual to determine the degree to which they will interact and exchange information with their environment. As such, privacy is strongly associated with data confidentiality, which mandates that data should not be accessible by unauthorized individuals.

Popular privacy concepts in the context of payment systems consist of transaction anonymity and transaction unlinkability. Assuming a set of user identities that make use of a payment system, transaction anonymity requires that one cannot link a particular transaction to a specific identity more than to any other identity that is part of the system. On the other hand, transaction unlinkability requires that two transactions of the same individual cannot be linked as such. Depending on the system, privacy of clients committing to transactions can be considered from the perspective of the banks, and/or users’ transaction partners.

Given that the transactions of a particular individual contain sensitive information about consumers, privacy has been the subject of investigation in payment systems for a considerable amount of time. As we shall see later, cryptographic primitives, such as anonymous credentials and anonymous electronic cash, are means that were proposed almost a decade ago to protect the fundamental rights of individuals.