A cryptographic study of tokenization systems

Payments through cards have become very popular in today’s world. All businesses now have options to receive payments through this instrument; moreover, most organizations store card information of its customers in some way to enable easy payments in future. Credit card data are a very sensitive information, and theft of this data is a serious threat to any company. Any organization that stores credit card data needs to achieve payment card industry (PCI) compliance, which is an intricate process where the organization needs to demonstrate that the data it stores are safe. Recently, there has been a paradigm shift in treatment of the problem of storage of payment card information. In this new paradigm instead of the real credit card data a token is stored, this process is called “tokenization.” The token “looks like” the credit/debit card number, but ideally has no relation with the credit card number that it represents. This solution relieves the merchant from the burden of PCI compliance in several ways. Though tokenization systems are heavily in use, to our knowledge, a formal cryptographic study of this problem has not yet been done. In this paper, we initiate a study in this direction. We formally define the syntax of a tokenization system and several notions of security for such systems. Finally, we provide some constructions of tokenizers and analyze their security in light of our definitions.