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1、MOBILE CHIP ELECTRONIC COMMERCE: ENABLING CREDIT CARD PAYMENT FOR MOBILE DEVICES Marko Schuba and Konrad WronaEricsson Research, GermanyABSTRACTThis paper describes the Mobile Chip Electronic Commerce system architecture, an adaptation of the Chip Electronic Commerce specification for credit card pa

2、yments to mobile phones. The new architecture splits the functionality required at the payment client into two separate units. The main parts of the protocol, i.e. all tasks which are computational intensive but not sensitive with respect to security, are performed on a server in the fixed part of t

3、he communication network. The mobile phone or to be more specific a smart card, in-serted into the phone or a phone accessory, serves as security device, which signs the transaction data and thus not only confirms the correctness of the payment transaction data but also ensures that the credit card

4、has actually been present in the transaction.INTRODUCTIONThe deployment of new technologies like WAP (Wireless Application Protocol 1 and i-mode will lead to a large number of users accessing the Internet with their mobile phones. A key issue when looking at the Internet as a marketplace for these u

5、sers is to enable secure payment from mo-bile phones to Internet merchants. Since such merchants can be located anywhere in the world, a widely accepted payment mechanism, e.g. based on credit cards, is required.Although credit cards have been in use for PC-based Internet payments for a long time, t

6、he secu-rity mechanisms, especially with respect to authentication, are either very weak or too compli-cated to be handled by typical users. In order to overcome these problems, a new specification called Chip Electronic Commerce has been re-leased in the end of 1999. The goal of this specifi-cation

7、 is to combine the benefits of smart cards (as authentication token with the SET1 (Secure Elec-tronic Transactions standard for credit card pay-ment in the Internet. However, Chip Electronic Commerce has been developed for powerful com-puters connected to Internet via fixed lines. Imple-menting the

8、same client functionality directly in mobile devices is not feasible today, because of the power and bandwidth constraints of mobiles.In order to overcome the limitations of mobile de-vices with respect to bandwidth, processing and1SET is a trademark owned by SET Secure Electronic Transaction LCC ba

9、ttery power, an adaptation of the Chip Electronic Commerce standard is necessary. The so-called Mobile Chip Electronic Commerce approach cho-sen in the present paper splits the client part of the original specification into a mobile device and a server part. While the server, which is located in the

10、 fixed part of the network, performs time and re-source consuming protocol tasks, only the critical functions from a security perspective are executed in the mobile terminal. Thus, the processing load as well as the bandwidth requirements for the mo-bile are reduced, while preserving end-to-end se-c

11、urity between the mobile terminal and the trans-action processing system in the fixed network. STANDARDS FOR CREDIT CARD PAYMENT Internet Credit Card PaymentsToday, there are two main protocols, which are used to secure online purchases with credit cards: the Secure Sockets Layer (SSL protocol, and

12、the Secure Electronic Transaction (SET protocol. A drawback of the both SSL and SET protocols is that they require the use of cryptographic algo-rithms that place a significant load on the computer systems involved in the commercial transactions. SSL has a lower impact on the e-commerce serv-ice, bu

13、t provides fewer features to eliminate secu-rity risks.Secure Electronic Transaction ProtocolAfter the separate development of Secure Trans-action Technology (STT by VISA and SecureElectronic Payment Protocol (SEPP by Master-Card, the companies joined forces and announced in 1996 the joint developme

14、nt of one standard protocol, SET, to secure payment card transac-tions over open networks. SET has been published as open specification for the industry 2.The current version of SET was designed for common desktop PCs as the typical user terminal, and with the Internet as the transport network.SET p

15、rovides an electronic commerce infrastruc-ture that delivers:Confidentiality of informationIntegrity of data InteroperabilityCertificate based authenticationSET uses both primary encryption methods: se-cret-key (symmetric cryptography and public-key (asymmetric cryptography. A secret-key cryptog-rap

16、hy algorithm used by SET is the Data Encryp-tion Standard (DES, and the public-key cryptogra-phy algorithm is RSA with 1024-bit keys.In Figure 1 the processing flows for purchase re-quest and payment authorization are shown.1. After browsing and selecting an item from themerchant, the cardholder sen

17、ds a purchase initialization request to the merchant, request-ing a copy of the certificates belonging to the merchant and payment gateway (INITI-ATE_REQUEST.2. After receiving the purchase initialization re-quest, the merchant sends a purchase initiali-zation response (digitally signed with the mer

18、-chants private signature key along with the merchants and payment gateways certificates to the cardholder (INITIATE_RESPONSE.3. The cardholder software verifies the certifi-cates and the merchants signature included in the purchase initialization response. The card-holder software creates an order

19、information for the merchant and completes payment in-structions for the payment gateway and gener-ates a dual signature for both messages. In the end, the order information and the encrypted payment instructions are sent back to the mer-chant along with the cardholders certificate (PURCHASE_REQUEST

20、.4. The merchant software verifies the card-holders certificate and the dual signature. The merchant software creates an authorization request for the payment gateway and digitallysigns it. The merchant software sends the authorization request and the encrypted pay-ment instructions along with the c

21、ardholders and merchants certificates to the payment gateway (AUTHORISATION_REQUEST.5. The payment gateway verifies the certificates,the authorization request and the payment in-structions. Then it sends an authorization re-quest through the financial network to the cardholders financial institution

22、 (i.e. issuer, where the payment instructions are to be cleared. The payment gateway generates an encrypted authorization response and gener-ates then a capture token. The authorization response and the capture token are then transmitted to the merchant along with the gateways certificate (AUTHORISA

23、-TION_RESPONSE.6. The merchant software verifies the gatewayscertificate and decrypts the authorization re-sponse. The capture token is stored for later capture processing. The merchant software creates a purchase response, digitally signs it and sends it back to the cardholder (PUR-CHASE_RESPONSE.

24、If the transaction was authorized, the merchant fulfils the order, e.g.by delivering the purchased goods.7. In order to obtain the money from the purchase(after fulfilling the cardholders order, the mer-chant starts a payment capture process with the payment gateway using the stored capture token. F

25、igure 1: Processing flows for purchase request and authorization in SETEMV96 and EMV2000 a Smart Credit Card Europay, MasterCard and Visa (EMV jointly de-veloped specifications that define a set of require-ments to ensure interoperability between chip cards and terminals on a global basis, regardles

26、s of manufacturer, financial institution, or location of card usage.EMV offers both asymmetric (public-key and symmetric (shared-key security mechanisms. Asymmetric security mechanisms authenticate the card as a valid card to the terminal. Symmetric se-curity mechanisms generate and verify transacti

27、on cryptograms (essentially Message Authentication Codes, MACs based on a key shared between card and issuer.Chip Electronic CommerceChip Electronic Commerce is a part of the EMV 2000 specification 3. It defines the use of an inte-grated chip card (smart card application to con-duct a credit or debi

28、t transaction in an electronic commerce environment using SET 1.0 compliant software.Chip Electronic Commerce leverages the EMV functions with the Secure Electronic Transaction specification to provide a protocol for secure smart card based transactions over the Internet.Chip Electronic Commerce tak

29、es advantage of two enhancements to the SET protocol: SET Common Chip Extension: Extends the SET protocol to support the transport of smart card re-lated data. Online PIN extension: Extends the SET protocol to support the online transport of a cardholders PIN.In addition, Chip Electronic Commerce ex

30、tends the SET specification by supporting two key features native to EMV smart card applications: Online card authentication, through the use of a cryptogram. Cardholder verification, through the use of an op-tional cardholder PIN.Chip Electronic Commerce does not require any modification to EMVcomp

31、liant smart cards. RESTRICTIONS OF MOBILE SYSTEMS Electronic commerce in a wireless environment faces a number of constraints. Firstly, the bearer service in wireless networks is rather limited when compared to fixed networks, i.e. less bandwidth, longer latencies and more errors. Secondly, cheap mo

32、bile devices produced for the mass market have several restrictions, e.g. concerning the input and output of data (small keyboard and display, processing power, and memory. Thus, services suitable for desktop computers in fixed networks cannot be deployed in wireless systems without modification.To

33、illustrate this problem in connection with electronic commerce let us take a closer look at one of the main applications for mobile electronic commerce: shopping. As in real shops shopping with a mobile device consists of several phases. After the selection of goods to be purchased (phase 1, the mer

34、chant transmits a contract containing a list of the goods and the amount of money to be paid to the mobile device (phase 2. If the customer agrees on the contract the money is transferred (phase 3 and the goods are delivered (phase 4. Depending on the type of good this delivery can be either physica

35、lly or electronically. The main problems for the wireless environment arise from phase 1 and 3, i.e. selection and payment. In a fixed network customers usually select goods by browsing on an Internet merchants web page. Providing a similar service on a mobile device is rather difficult, because mer

36、chant web pages usually contain a lot of information and pictures, resulting in a high data rate and the need for a large display. But even if these problems are solved, the problems with respect to the payment phase still remain. The required cryptographic algorithms, which are usually based on pub

37、lic key infrastructures, need a lot of computational power (i.e. battery power as well as memory. Due to the resource limitations of the mobile device specific solutions for mobile electronic commerce have to be found. Typically, such solutions consist of a thin client, which is supported by a serve

38、r in the fixed part of the network. Several methods for adapting the original SET protocol to wireless systems have been proposed in 4. The following Mobile Chip Electronic Commerce approach, i.e. the mobile adaptation of the Chip Electronic Commerce specification, is based on a similar architecture

39、. MOBILE CHIP ELECTRONIC COMMERCEThe concept of Mobile Chip Electronic Commerce has to take the following considerations into ac-count:1 Mobile Chip Electronic Commerce must fit intorestrictions of mobile systems.2 Mobile Chip Electronic Commerce softwaremust conform to both SET and EMV specifica-ti

40、ons.3 Mobile Chip Electronic Commerce should offerthe same security level as standard Chip Elec-tronic Commerce.4 Mobile Chip Electronic Commerce should worktransparently for the merchants as well as forother SET entities as specified in the specifi-cations.In order to adapt the Chip Electronic Comm

41、erce specification to the mobile environment, the card-holder part of the architecture is divided into a Mo-bile Chip Electronic Commerce Client and a Mobile Chip Electronic Commerce Server. While the server performs the main part of the protocol, i.e. it compiles and exchanges messages with the mer

42、-chant, checks certificates etc., the clients task is limited to important security related tasks like authentication of the user or authorization of the payment transaction (achieved by an EMV crypto-gram calculated on the smart card. Note that the splitting of functionality between client and serv

43、er not only substantially limits the processing load put on the mobile device, but also reduces the traffic on the wireless link.The Mobile Chip Electronic Commerce Payment Transaction FlowA number of messages have to be transmitted between the different parties during a payment transaction. Figure

44、2 shows the overall message flow in the Mobile Chip Electronic Commerce ar-chitecture. A more detailed description of the mes-sage exchange between server, client and EMV smart card is given in Figure 3. Figure 2: Mobile Chip Electronic Commerce overall message flow Figure 3: Mobile Chip Electronic

45、Commerce message flow between server, client, and EMV smart cardPhases of a Mobile Chip Electronic Commerce PaymentFrom the Mobile Chip Electronic Commerce Servers perspective, a payment can be divided into three phases:1. Initialization2. Purchase Request/Response3. Completion1. Initialization Phas

46、eDuring this phase the Mobile Chip Electronic Commerce Server obtains the information that it needs to start the typical SET purchase re-quest/response dialog with the Merchant Server. It consists of:SET Initiation Message: The Merchant Server in-vokes the Mobile Chip Electronic Commerce Client and

47、informs it about accepted payment brands.Card Selection: The cardholder presents to the Mobile Chip Electronic Commerce Client the pay-ment card to be used for the purchase.Application Selection: The Mobile Chip Electronic Commerce Client selects an application from the card, with input from the car

48、dholder if necessary.Application Initiation: The Mobile Chip Electronic Commerce Client initiates the card application to determine whether it and the card agree about how the transaction should be processed.Read Application: The Mobile Chip Electronic Commerce Client reads the application data. Pay

49、ment Request: The Mobile Chip Electronic Commerce Client invokes the Mobile Chip Elec-tronic Commerce Server by sending the order in-formation, the merchants address and other data objects obtained during the initialization phase. The sources of these data objects and elements are either the SET Ini

50、tiation Message or the EMV card application. Once converted, these data ob-jects serve as inputs to the SET Purchase Initiali-zation Request (PInitReq message as shown in Table 1.SET PInitReq Data Input CorrespondingCard Data ObjectSourceLanguage Language Pref-erence Application SelectionBrandID Sel

51、ected Appli-cation ID Application SelectionBank Ident. Number (BINPersonal AccountNumber (PANReadApplicationDataCardExpiry Application Expi-ration Date Read Applica-tion DataPayment Amount SET Initiation MessageOrder De-scription SET Initiation MessageTransaction Currency Code SET Initiation Message

52、Merchant Ad-dress SET Initiation MessageTable 1: Input for the SET PinitReq message Mobile Chip Electronic Commerce Clients may provide an option to use a cardholderselected language rather than the EMV cards language. Alternatively, language settings may be stored in the user profile at the Mobile

53、Chip Electronic Commerce Server.Some data objects used in the Chip Electronic Commerce messages (e.g. Amount Other, or Transaction Type are constant values and do not need to be send to the Mobile Chip Electronic Commerce Server.2. Purchase Request/Response PhaseIn this phase the Mobile Chip Electro

54、nic Com-merce Server requests the actual purchase from the merchant and gets a positive or negative re-sponse back. The phase is the longest one and is quite similar to a normal SET transaction, except that it uses a cryptogram instead of a SET dual signature for authorization. It consists of: Purchase Initialization Request: The Mobile Chip Electronic Commerce Server initializes the pur-chase by informing the Merchant Server how the cardholder intends to pay.Purchase Init