Java Card Programming: Overview Presented by: Raman Sharykin PISCES Group: Soumyadeb Mitra, Sruthi Bandhakavi, Ragib Hasan, Raman Sharikyn 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 terminals 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 Java for Java Cards Features 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. SupportedNot Supported

7 Developing a Java Card Applet 1.Write the Java source 2.Compile your source 3.Convert the class files into a Converted Applet (CAP) file (binary representation of classes and interfaces) 4.Verify that the CAP is valid (structure, valid bytecode subset, inter-package dependencies) 5.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 terminals resources to overcome the restriction provided that the terminal is potentially untrusted? At Penn we used terminals 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 terminals memory to store the tables of random numbers and hashes To request a services from the terminal we have two types of respond APDUs –The result –A request from the card to perform an operation (store or retrieve data)

18 Terminals Structure Java Card Service Layer Application Terminal request service request1 service repond1 service request2 service repond2 respond

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

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