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Prashant Lamba

CMSC 838 Y Class Paper Presentation. Prashant Lamba. Mechanisms for Secure Modular Programming in JAVA. Lujo Bauer Andrew W Appel Edward W Felten. Theme of the Paper. To provide a new module system for java which improves deficiencies of the java package system.

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Prashant Lamba

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  1. CMSC 838 YClass Paper Presentation Prashant Lamba

  2. Mechanisms for Secure Modular Programming in JAVA Lujo Bauer Andrew W Appel Edward W Felten

  3. Theme of the Paper • To provide a new module system for java which improves deficiencies of the java package system. • To emphasize the need of modular systems rather than Object oriented software system.

  4. Deficiencies in JAVA Package System • Limited ability for the control access to their member class. • No explicit interfaces • Don’t support multiple view of modules • Problems with dynamic linking

  5. Solution to the problem • ML-style hierarchical module system • provides Explicit interface • Multiple views of Module • More control over external modules with which the code is linked

  6. Module System Source FilesModule description file Export Membership Import Interface List Statement

  7. Abstract class Codgen{ Frame frame; Abstract Assem.InstrList Codgen(Tree.Stm stm) } Export Interface Membership List Import Interface Access AccessList Codegen Frame Proc Access.Java AccessList.Java Codgen.Java Frame.Java Proc.Java Tree…/Tree/ Temp../Temp/ Assem../Assem/ Util../Util Codegen.Java

  8. Fixing Java Packages • Export Interfaces • Explicit export interfaces • Java package system lacks this feature • Membership List • Deficiency of java package makes malicious code to be part of trusted application like application.

  9. Fixing Java Packages Attack Scenario in Java Package System: Package Class1.Java Class2.java Class3.java Class4.java Malicious Code class.Java Malicious Code class.Java

  10. Fixing Java Packages • Hierarchical Scalability and Multiple Interface • Multiple view of an module is possible. • Example • Module M can have V1 and V2 view with class access A,B,C and A,D respectively

  11. Module MO Exporting A,B,C,and D Multiple View of Module M0 Module M1 Importing M0.A,M0.B,M0.C Module M2 Importing M0.A,M0.D

  12. Fixing Java Packages Name-Space management • Java packages are named it merely lifts the problem to package level. Example: We can have clash between the two classes called Util.Parser

  13. Solution: Module system assigns the names via import statements.

  14. Secure Linking • Java uses Type checking mechanism for the secure dynamic linking • Problem: Type checking guarantees that programs and libraries at least agree on the types they are using. • Java uses code signature when a system must trust the behavior of a particular executable. • Problem: In this scheme also we don’t know about the properties of the code

  15. Solution: • We allow the programmer to require certain properties of the modules on which his code depends. • The properties our system supports are keywords about the behavior of his code. • It will cryptographically hash the < byte code, module description, property name>

  16. Class Loader Module Description File Trf 3 Trf 2 JVM Trf 1 Java Complier Java Source Byte Code Trf = Transform Implementation

  17. Execution in Virtual Machine • Dynamic linking in JVM is managed by Class Loader. • A request to load a class is may be allowed by the digital signature of the class. • The Class loader of the system described uses module description file to set appropriate environment.

  18. Class Loader manipulation leads to security problems and Type system can be broken • New JVM have stricter namespace management policies. • Machine verifies the encoded name of the class(returned by load Class request) with which load class is invoked.

  19. Problem: In our Module system identifiers for class names has very little resemblance with the actual package names they refer. Solution: Rewriting the byte code replacing the symbolic name with actual name.

  20. Future Work • Support for the Refection API • Dynamic linking is an area that deserves more study.

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