Common Electronic Purse Specifications (CEPS)
In the mid-1990s, many electronic purse systems based on smart cards were developed independently of each other in many European countries. Some typical examples are Quick in Austria, Geldkarte in Germany and Proton in Belgium and the Netherlands. All of these purse systems have similar functionality, but they are all mutually incompatible. The need to make these purse systems compatible with each has become increasing compelling, in part due to the introduction of a common European currency in 2002. Since all electronic purse cards are generally only valid for a period of three years, it is in principle possible to make gradual modifications to the purse systems over the course of several years using a migration path that is yet to be defined. The fundamental prerequisite for achieving mutual compatibility among several electronic purse systems is a document specifying the features that the systems must have for compatibility. This document bears the name ‘Common Electronic Purse Specifications’ (CEPS), and the first version was published in 1999 by CEPSCO [CEPSCO]. In an earlier specification stage, the focus of CEPS was on an internationally interoperable electronic purse system, rather than one limited to European interests. CEPS includes the standard functions for modern electronic purse systems, such as offline payment, online loading and online currency conversion. It is based on the European standard for electronic purses, EN 1546,10 but it contains several extensions and modifications with respect to this standard. For instance, in contrast to EN 1546, RSQ-based certificates are used for authentication of terminals and smart cards. Triple DES is recommended as the cryptographic algorithm. CEPS, like many electronic purse systems, is optimized for simple smart card microcontrollers. A typical implementation of CEPS in assembler or C requires 8 kB of ROM, 4 kB of EEPROM, 1 kB of RAM and a numeric coprocessor for the asymmetric cryptographic algorithm. In the future, most European electronic purse systems will be compatible with CEPS, so in the medium term it should be possible to make payments in various European countries using a single purse card.

Proton
Proton is an internationally used electronic purse system, which up to now has been developed almost exclusively by Bull, starting as early as 1995. It originates from Belgium and the Netherlands (where it is known under the brand name ‘Chipknip’), which is also where it is most widely used and presently has the status of a national electronic purse system. There are also relatively large purse systems based on Proton in Switzerland and Sweden (under the ‘Cash’ brand name). As of the spring of 2002, there were approximately 40 million cards issued internationally and around 360,000 terminals. This electronic purse system was originally called CC 60, which is a name that originates from Bull. The current version is designated R3, and the next generation, which is already available in initial versions and has been strongly extended, is designated R4. R3 is a purse system that is optimized for inexpensive smart card microcontrollers, and it can be readily implemented in chips having 16 kB of ROM, 6 kB of EEPROM and 256 bytes of RAM. R4 is an extended version of R3 and is compatible with CEPS. Besides the actual purse system, the specifications for R4 define an operating system for multiapplication smart cards that includes debit and credit capabilities in accordance with the EMV specification,12 as well as a digital signature application and Java functionality. There is also a contactless version of Proton, which is primarily intended to be used in the local public transportation sector. The publisher of the specification, which is confidential, is ProtonWorld [Proton]. The electronic purse system includes the usual functions, such as loading, individual payment, incremental payment (‘sliced payment’) and refunding a payment. The main use for incremental payment is public card phones, which require small amounts to be repeatedly debited from the purse balance at short intervals during a session. Transactions are stored in record-oriented log files. The purse parameters are also stored in files. In order to allow the system to be implemented using inexpensive microcontrollers, which have relatively little memory, it is allowed to place the files directly below the MF without a DF. Both DES and triple DES are used as cryptographic algorithms in R3. Many of the smart card commands used in the system are based on or compatible with the ISO/IEC 7816-4 and EN 1546 standards. They are supplemented by several application-specific commands. The actual purse function is related to the standard EN 154613 procedures in many aspects. However, it is readily apparent that Proton is several years older than EN 1546.

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