563.11.1 Java Card Programming: Overview

1. 563.11.1 Java Card Programming: Overview Presented by: Raman Sharykin University of Illinois Spring 2006

2. Overview • Java Cards • Java Card/Terminal System • Features of Java for Java Cards compared to Java • Java Card Applets: Developing Cycle • Structure of Applets and Messages • On approach to overcome the issue of restricted resources on card • Game of Battleship: Using terminal’s memory

3. Java Card Features • Receives clock and power from terminal • Three types of memory: • Random Access Memory (RAM) • Read-Only Memory (ROM) • Erasable Read-Only Memory (EEPROM) • Restricted Resources • Slow and simple microprocessor (8-bit) • RAM ~1Kb • ROM ~64Kb • EEPROM ~16-64Kb • Restricted Version of Java

4. The use of Java Cards • SIM cards in cell phones • Identity cards (government, health-care) • Financial cards supporting online and offline transactions • Smart tickets for mass transit

5. Java Card/Terminal System APDU = Application Protocol Data Unit An introduction to Java Card Technology

6. Small primitive data types: boolean, byte, short. One dimensional arrays. Object oriented features: inheritance, virtual methods, dynamic object creation, overloading, scope. Large primitive data types: long, double, float. Characters, strings. Multidimensional arrays. Dynamic class loading. Garbage collection. Threads. Object Cloning. Java for Java Cards Features Supported Not Supported

7. Developing a Java Card Applet • Write the Java source • Compile your source • Convert the class files into a Converted Applet (CAP) file (binary representation of classes and interfaces) • Verify that the CAP is valid (structure, valid bytecode subset, inter-package dependencies) • Install the CAP file

8. Message-Passing Model An introduction to Java Card Technology

9. APDU Structure • CLA, INS define the command • P1, P2 – parameters • Lc – data field lentgh • Le – maximum response length • SW1, SW2 – response status An introduction to Java Card Technology

10. Applet Structure • import javacard.framework.* • ... • public class MyApplet extends Applet { • // Definitions of APDU-related instruction codes • ... • MyApplet() {...} // Constructor • // Life-cycle methods • install() {...} • select() {...} • deselect() {...} • process() {...} • // Private methods ... • }

11. Important Methods: Install • install() called when a new applet is being installed public static void install ( byte[] bArray, short bOffset, byte bLength) { new myApplet(null); } • Must call register() to let JCRE know that a new applet has been installed.

12. Important Methods: Select/Deselect • select() • when we want to use an applet • is called when SELECT APDU is received • deselect() • is called when another SELECT APDU is received

13. Important Methods: Use • process() • when an APDU is received and applet is selected its method process is called to process the APDU • the selected applet parses the APDU and perform whatever it needs to perform • normally the body of process() method is a big switch with code for each INS value defined

14. A Challenge in Java Card Programming • Java Cards have very restricted resources • Limited Memory • Limited Computing Power • Can we use terminal’s resources to overcome the restriction provided that the terminal is potentially untrusted? • At Penn we used terminal’s memory to overcome the first restriction

15. Game of Battleship • Playing Field is n by n • Ships are vertical or horizontal and of a fixed length • Players shoot in turns • The winner is the player who has eliminated the ships of the opponent first

16. How to Prevent Cheating? • Before starting the game players assign random numbers to each cell, compute the hash of the resulting pair and exchange the tables of hashes • When a player shoots, the opponent provides not only the contain of the requested cell, but also the random number assigned to it and the hash • This way the other player can compute the hash of the delivered data and check if it coincides with the value stored in the beginning.

17. Terminal Services Card • If we want to play the game on 10 by 10 field we need 10*10*16*2 = 3200 bytes when only ~600 is available • We used terminal’s memory to store the tables of random numbers and hashes • To request a services from the terminal we have two types of respond APDU’s • The result • A request from the card to perform an operation (store or retrieve data)

18. Terminal’s Structure Terminal Application request respond Service Layer service repond1 service repond2 request service request1 service request2 respond Java Card

19. Data Flow and the Structure of an Applet Terminal Java Card process(apdu) { ..... switch (message){ .... case Request: ..... send ServiceRequest1; break; ..... case ServiceResponde1: ..... send ServiceRequest2; break; ..... case ServiceResponde2: ..... send Respond; } Request Service Request 1 Service Respond 1 Service Request 2 Service Respond 2 Respond

20. Future Work • The implementation stores its data on terminal without making sure that the server does not alternate the stored data (also it can just look at it!) • The structure of the code on card is complicated when we need Service Requests • inside a function call • inside a loop • It would be interesting to know if we can use the computational power of the terminal as well