Java Security Meets Smart Cards Gary McGraw, Ph.D. Vice President, Corporate Technology Cigital

This lecture made possible by... Software Risk Management authority: –safety, security, reliability –services and technology for making software behave Clients include: –Visa, MasterCard, Agile, Microstrategy, Ericsson, Motorola, Microsoft, NSF, DARPA, NIST’s Advanced Technology Program

3 The classic security tradeoff

4 Java’s answer Add as much functionality as is prudent while managing security risks JDK Sandbox JDK 1.1 Code signing Java 2 Shades of gray JVMs for mobility Java Virtual Machine A language-based approach to mobile code security is complex Java is by far the best approach available Java has had real security problems

5 A question of trust

Untrusted code is restricted The Virtual Machine mediates access Some code cannot make direct system calls Code can be forbidden to: –access the filesystem –open sockets (except back home) –interfere with other applets –spy on the local environment See Frank Yellin’s paper or Java Security –Java Security Hotlist –

Type safety Each piece of memory has a type Type system must work for security to work –type safety is the cornerstone of Java security –guarantee that a program can’t treat pointers as integers and vice versa Java uses static type checking to ensure this Because the type system is complicated, it is error prone Note: type safety is NOT security

The original sandbox The Byte Code Verifier Verify Java byte code before running it The Class Loader System Load local and network classes separately The Security Manager Keep tabs on “dangerous” methods

Four attack classes System modification Invasion of privacy Denial of service Antagonism There is some overlap among these classes, but they make the risks easier to understand

10 A chronology of attack applets February 96: DNS flaw in JDK March 96: Path name bug March 96: Princeton Class Loader bug May 96: type casting attack June 96: Array type implementation error July 96: More type casting problems August 96:Flaw in Microsoft’s Java VM February 97: Invasion of Privacy attack applets March 97: JVM hole April 97: Code signing flaw May 97: Verifier problems discovered in many VMs July 97: Vacuum bug August 97: redirect bug July 98: ClassLoader bug March 99: Verifier hole August 99: Race condition October 99: Verifier hole 2 August 2000: Brown Orifice October 2000: ActiveX/Java All of these bugs have been fixed.

JDK 1.1 Classes for developers of secure systems –Crypto API started SHA, MD5, digital signatures –More crypto in U.S. DES possibly RSA Signed applets –JDK 1.1 signing makes classes “local” (system) –trust models introduced

Java 2 Fine-grained access control –no longer requires hacking ClassLoader and SecurityManager Configurable security policy –this is very hard to do correctly –managing policy Extensible access control structure –typed permissions and automatic handling Trust little stance –built-in code will no longer be trusted –signed local classes –no more hacking the zip archive!

Stack inspection Security decisions in Java 2 are made by searching the runtime call stack –this is an implementation dependent strategy –seemingly ad hoc –restricts compiler optimization All three vendors use variation of stack inspection Very little prior art –LISP dynamic binding –effective UID in unix Formalized by the Princeton team

Mobile code on smart cards Java Virtual Machines get small

15 How Java and smart cards mix Java Card is a stripped down version of Java for smart cards –up to version (and security is improving) –one major vendor behind Java Card is Visa Java Card makes multi-application cards based on a common platform possible –open up smart card development –use a real language

16 How can Java fit on a card? Supported Java Features packages dynamic object creation virtual methods interfaces exceptions Unsupported Java Features dynamic class loading security manager threading object cloning garbage collection large data types

17 Multi-application cards Multi-application cards are an important goal –getting more developers on board is essential Multiple applets can execute on a card –credit, debit, e-cash, loyalty programs Explicit and covert channels between applets must be eliminated –software risk management –“applet firewall” is minimal at best

18 Java Card security != Java security Good no dynamic class loading –type safety issues only one active applet no threading objects include rudimentary access control Bad applets added post issuance (ARGH) no sandbox –trusted code required native method calls no garbage collection object sharing complexity out of band verification

19 Security risks in Java Card 2.1 protocol interactions –sharing secrets between protocols introduces new problems security is hard –linking, export, CAP files –native methods –verification –object sharing multi-application risks –applets MUST behave the usual suspects apply –physical attacks –side-channel monitoring (DPA) –the terminal problem

20 Multi-application issues Secure Features no dynamic class loading –reduces threat of malicious applets no multi-threading –non-interference applet firewalls –prevents referencing another applet’s objects Risks and Assumptions trust-based applet model –assume applets are non-malicious –security testing JCRE must be perfect –prevents collusion more developers?!

21 Physical attacks still apply Physical attacks attempt to reverse engineer card or monitor a running card to obtain card secrets –Differential power analysis (Kocher) –No card is tamper proof (Anderson & Kuhn) Cards often include secrets from owner Some secrets could be used to add functionality and/or add value –Cost of hacking the card must be greater than return on investment

22 The terminal problem No trusted interface for interacting with users A common solution is to use PCs –but PCs are easily hacked –windows 95/98 are inherently insecure Some suggestions –palm pilot? (Felten’s Usenix 99 paper) –simple dedicated devices

23 Protocol interaction risks Unintended protocol interactions pose risks: –secure protocols do not necessarily compose –different protocols share same key material –observation of protocol P can be used against Q Shared key material is motivated by: –digital certificates for multi-applications –small memory for public/private key pairs –crypto APIs

24 Security is harder than it sounds Java Card is not truly “cross platform” –byte code  CAP –export files linking problems –no strings, thus tables code verification? –before conversion exception handling native methods BAD INT? (32 bits) applet testing and debugging issues sharing methods among applets (difficult) ISO 7816 APDU problems hostile applets –denial of service

25 What to do? Assume the platform is secure –it really is getting better –Cigital has extensive security tests for Globlal Platform Applets must be carefully designed and implemented Testing applets for security is essential Java Card Security = platform + applets Did I say security testing?

26 Conclusion Java Card and other flavors of Java will open new markets New technologies pose significant risks when deployed in security-critical applications –Java Card mitigates some risks associated with Java such as dynamic class loading –Existence of multiple applets (mobile code) is a significant risk that must be mitigated by solid software risk management

27 Where to learn more Cigital provides expert advice on smart card and mobile system software security issues. Contact Ed McComas –Chapter 8: Java Card Security