The ESPRIT Project CAFE - High Security Digital Payment Systems

CAFE (“Conditional Access for Europe”) is an ongoing project in the European Community's ESPRIT program. The goal of CAFE is to develop innovative systems for conditional access, and in particular, digital payment systems. An important aspect of CAFE is high security of all parties concerned, with the least possible requirements that they are forced to trust other parties (so-called multi-party security). This should give legal certainty to everybody at all times. Moreover, both the electronic money issuer and the individual users are less dependent on the tamper-resistance of devices than in usual digital payment systems. Since CAFE aims at the market of small everyday payments that is currently dominated by cash, payments are offline, and privacy is an important issue. The basic devices used in CAFE are so-called electronic wallets, whose outlook is quite similar to pocket calculators or PDAs (Personal Digital Assistant). Particular advantages of the electronic wallets are that PINs can be entered directly, so that fake-terminal attacks are prevented. Other features are: • Loss tolerance: If a user loses an electronic wallet, or the wallet breaks or is stolen, the user can be given the money back, although it is a prepaid payment system. • Different currencies. • Open architecture and system. The aim is to demonstrate a set of the systems developed in one or more field trials at the end of the project. Note that these will be real hardware systems, suitable for mass production. This paper concentrates on the basic techniques used in the CAFE protocols.