Java Security: SSL Data Exchange Analysis and Language Safety Features

1. Lecture 18: Java™ Decaffeinated David Evans http://www.cs.virginia.edu/~evans CS551: Security and Privacy University of Virginia Computer Science

2. Menu • SSL Challenge Question • Java • Voting University of Virginia CS 551

3. SSL Challenge Question Are there skeletons in VeriSign’s closet? University of Virginia CS 551

4. grab a snickers 141 Sextillion years; Secure Socket Layer (SSL) Not going any where for awhile;

5. SSL Background • Two Kinds of SSL • Low Encryption (40-bit; 1.1x1012 possible keys) • High Encryption (128-bit; 3.8x1038 possible keys) • SSL is a transport level technology for authentication and data encryption between a web server and a Web server (example). • Applied at the socket interface from the application to the network software. Internet Header Application Header Data Link Header Transport Header Data being sent Plaintext Cipher Text

6. SSL Handshake Server Client • Tell me who you are; • Here are the protocols I support. • Here is my Digital ID to provewho I am; • Here is the protocols I have decided we should use. • For your ID, I know who you are and have your public key; • Here is a secret key I createdwith your protocols encrypted with your key • Here is a copy of everything we’ve said encrypted with oursecret key. • Here is a copy of everything we’vesaid encrypted with our secret key. SSL Data Exchange

7. Years Key length (bits) 1995 2000 2005 40 68 hours 8.6 minutes 1.07 minutes 56 7.4 weeks 6.5 days 19 hours 64 36.7 years 4.6 years 6.9 months 128 6.7x1017 millennia 8.4x1016 millennia 1.1x1016 millennia Time to Break Specific Keys [Erkomaa, 1998]

8. Brute Force Attacks University of Virginia CS 551

9. VeriSign’s Claim

10. Moore’s Law 18 months

12. Not to scale CS-551 Class (1.25 hours) Actual 128- bit Time to Crack Two Universe Lifetimes Total Human Lifetime VeriSign’s Claim Universe Lifetime General Timeline 0 1010 1020 1019 1023 Quintillion years Sextillion years

13. VeriSign’s Assumptions • Hackers or key breakers have computers that are extremely slow. • We are using the processing speed of computers that were built in the 1980’s era. • Distributed networks and special hardware are not authorized for key breaking schemes. • We are not increasing our processing power every 18-24 months (based on Moore’s Law). University of Virginia CS 551

14. Java SecurityReal or Decaf? University of Virginia CS 551

15. Java • Island in Indonesia • A Programming Language (Java) • A Portable Low-Level Language (JVML) • A Platform (JavaVM) • A successful marketing strategy • JavaScript is not related to Java or Java • So you can have more time to work on your projects • All of the above University of Virginia CS 551

16. Java : Programming Language “A simple, object-oriented, distributed, interpreted, robust, secure, architecture neutral, portable, high-performance, multithreaded, and dynamic language.” [Sun95] University of Virginia CS 551

17. What is a secure language? • Language is designed so it cannot express certain computations considered insecure. • Language is designed so that (accidental) program bugs are likely to be caught by the compiler or run-time environment instead of leading to security vulnerabilities. A few attempts to do this: PLAN, packet filters University of Virginia CS 551

18. Safe Programming Languages • Type Safety • Compiler and run-time environment ensure that bits are treated as the type they represent • Memory Safety • Compiler and run-time environment ensure that program cannot access memory outside defined storage • Control Flow Safety • Can’t jump to arbitrary addresses Which of these does C++ have? Not a new idea: LISP had these in 1960! University of Virginia CS 551

19. Java Safety • Type Safety • Most types checked statically • Coercions, array assignments type checked at run time • Memory Safety • No direct memory access (e.g., pointers) • Primitive array type with mandatory run-time bounds checking • Control Flow Safety • Structured control flow, no arbitrary jumps University of Virginia CS 551

20. Malicious Code Can a safe programming language protect you from malcode? • Code your servers in it to protect from buffer overflow bugs • Only allow programs from untrustworthy origins to run if the are programmed in the safe language University of Virginia CS 551

21. Safe Languages? • But how can you tell program was written in the safe language? • Get the source code and compile it (most vendors, and all malicious attackers refuse to provide source code) • Special compilation service signs object files generated from the safe language (SPIN, [Bershad96]) • Verify object files preserve safety properties of source language (Java) University of Virginia CS 551

22. Joe User JVML malcode.java Java Source Code malcode.class JVML Object Code javac Compiler JavaVM Joe wants to know JVML code satisfies Java’s safety properties. University of Virginia CS 551

23. No! This code violates Java’s type rules. Does JVML satisfy Java’s safety properties? iconst_2 push integer constant 2 on stack istore_0 store top of stack in variable 0 as int aload_0 load object reference from variable 0 arraylength replace array on top of stack with its length University of Virginia CS 551

24. Trusted Computing Base Joe User Bytecode Verifier malcode.class JVML Object Code Java Bytecode Verifier Invalid “Okay” STOP JavaVM University of Virginia CS 551

25. Bytecode Verifier • Checks JVML code satisfies Java’s safety properties • Type safe – stack and variable slots must store and load as same type • Memory safe (guaranteed by instruction set) • Control flow safe: jumps must be within function, or call/return University of Virginia CS 551

26. Are Java Bytecode Verifiers Complicated? • ~700 rules to enforce, JVML specification is (not all clearly specified) • Emin Gün Sirer found > 100 bugs in commercial bytecode verifiers (using automatic test generation) • At least 15 of them were security vulnerabilities • JVML includes jsr instruction (jump to subroutine), can be called with different types in variables and on stack University of Virginia CS 551

27. Joe User Java javac Compiler malcode.java malcode.class JVML Trusted Computing Base Java Bytecode Verifier Invalid “Okay” STOP JavaVM University of Virginia CS 551

28. JavaVM • Virtual machine – interpreter for JVML programs • Has complete access to host machine • Bytecode verifier ensures some safety properties, JavaVM must ensure rest: • Type safety of run-time casts, array assignments • Memory safety: array bounds checking • Resource use policy University of Virginia CS 551

29. JavaVM Policy Enforcment [JDK 1.0 – JDK 1.1] From java.io.File: public boolean delete() { SecurityManager security = System.getSecurityManager(); if (security != null) { security.checkDelete(path); } if (isDirectory()) return rmdir0(); else return delete0(); } University of Virginia CS 551

30. java.lang.SecurityManager /** Throws a SecurityException if the calling thread is not allowed to delete the specified file. This method is invoked for the current security manager by the delete method of class File. */ (Some other comments deleted.) public void checkDelete(String file) { throw new SecurityException(); } University of Virginia CS 551

31. Security Manager • Reference monitor • How well does it satisfy the requirements? • Complete mediation • Can stop execution/prevent action • Limited effect on execution until policy violation • User/host application creates a subclass of SecurityManager to define a policy University of Virginia CS 551

32. HotJava’s Policy (JDK 1.1.7) public class AppletSecurity extends SecurityManager { ... public synchronized void checkDelete(String file) { checkWrite(file); } ... } University of Virginia CS 551

33. Note: no checking if not inApplet! Very important this does the right thing. AppletSecurity.checkWrite(some exception handling code removed) public synchronized void checkWrite(String file) { if (inApplet()) { if (!initACL) initializeACLs(); String realPath = (new File(file)).getCanonicalPath(); for (int i = writeACL.length ; i-- > 0 ;) { if (realPath.startsWith(writeACL[i])) return; } throw new AppletSecurityException ("checkwrite", file, realPath); } } University of Virginia CS 551

34. inApplet boolean inApplet() { return inClassLoader(); } Inherited from java.lang.SecurityManager: protected boolean inClassLoader() { return currentClassLoader() != null; } University of Virginia CS 551

35. currentClassLoader /** Returns an object describing the most recent class loader executing on the stack. Returns the class loader of the most recent occurrence on the stack of a method from a class defined using a class loader; returns null if there is no occurrence on the stack of a method from a class defined using a class loader. */ protected native ClassLoader currentClassLoader(); University of Virginia CS 551

36. Recap • java.io.File.delete calls SecurityManager.checkDelete before deleting • HotJava overrides SecurityManager with AppletSecurity to set policy • AppletSecurity.checkDelete calls AppletSecurity.checkWrite • AppletSecurity.checkWrite checks if any method on stack has a ClassLoader • If not no checks; if it does, checks ACL list University of Virginia CS 551

37. JDK 1.0 Trust Model • When JavaVM loads a class from the CLASSPATH, it has no associated ClassLoader (can do anything) • When JavaVM loads a class from elsewhere (e.g., the web), it has an associated ClassLoader University of Virginia CS 551

38. JDK Evolution • JDK 1.1: Signed classes from elsewhere and have no associated ClassLoader • JDK 1.2: • Different classes can have different policies based on ClassLoader • Explict enable/disable/check privileges • SecurityManager is now AccessController University of Virginia CS 551

39. What can go wrong? • Java API doesn’t call right SecurityManager checks (63 calls in java.*) • Font loading bug, synchronization • ClassLoader is tricked into loading external class as internal • Bug in Bytecode Verifier can be exploited to circumvent SecurityManager • Policy is too weak and allows damaging behavior University of Virginia CS 551

40. Hostile Applets • See http://java.sun.com/sfaq/chronology.html (about 1 new vulnerability/month) • Easy to write “annoying” applets (policy is too imprecise; no way to constrain many resource operations) • http://www.cigital.com/hostile-applets/index.html University of Virginia CS 551

41. Voting University of Virginia CS 551

42. VA Absentee Voting: Ballot • Print out form from state web site • Fill in name and address, sign by voter and a witness • Mail to local election official • Local election official mails ballot to voter’s address (presumably: checks voter is registered, verifies address, marks on election rolls) University of Virginia CS 551

43. VA Absentee Voting • Open Envelope A in presence of witness (do not open without witness present) • Borrow No. 2 pencil and mark ballot. • Place ballot in Envelope B and seal. Do not put anything else in that envelope. • Fill in identification and sign Envelope B. Witness signs Envelope B. • Place Envelope B in return envelope pre-addressed to Secretary of the Electoral Board. Mail or hand deliver in person. University of Virginia CS 551

44. Voting Challenges • (50 points) Explain why VA absentee ballot protocol uses Envelope A and requires voter to open it in presence of a witness • (50 points) Devise a good absentee voting protocol (better than my baseline) • (200 points) Exploit vulnerabilities in electoral protocols so Harry Browne or Ralph Nader wins election • Remember getting me arrested is -10000 points! University of Virginia CS 551

45. Charge • Tomorrow: Vote • Pay attention to security protocols: who are you trusting? • Don’t get arrested, but think about how a malicious person might defeat the system • Next time • Guest Lecture: Chenxi Wang University of Virginia CS 551