When Mobile Code and Smart Cards Meet: Java Card Security Gary McGraw, Ph.D. Vice President, Corporate Technology Cigital .

When Mobile Code and Smart Cards Meet: Java Card Security

Gary McGraw, Ph.D.Vice President, Corporate Technology

Cigitalhttp://www.cigital.com

This lecture made possible by...

This lecture made possible by...

• Software Risk Management authority: – safety, security, reliability– services and technology for making software

behave

• Clients include: – Visa, Agile, Microstrategy, Ericsson, Motorola,

Microsoft, NSF, DARPA, NIST’s Advanced Technology Program

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Why use mobile code?Why use mobile code?

• Offload processing from servers– CGI bottlenecks– look and feel

problems– cross-platform

solution desirable

• Mobile devices– Phones– Smart cards– PDAs

• Managing highly interconnected distributed systems– the famed Internet

toaster– IP numbers for

everything!– we’ve only

scratched the surface

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Mobile code is smartMobile code is smart

• Code that traverses the network during its lifetime and executes at the destination machine– send around data that automatically executes– the more platforms, the better– embedded, mobile devices need this!

• Many forms– Java, ActiveX, Postscript, TCL/tk, Word

macros, JavaScript, VBScript, ...

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Mobile code is dumbMobile code is dumb

• Running somebody else’s code is risky

• What might it do?• What if it is hostile?• How can we protect

against possible attack?

Not a new problem!

IEEE IC, 2(6), Nov/Dec 1998

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A brief history A brief history

• 1980s– downloading arbitrary

binaries and executing them is a BAD IDEA

– Archie and ftp– risks include:

• Trojan Horses• viruses

– checksumming to the rescue?

• 1992– the Web arrives– Archie dies

• 1995– Java and Javascript

introduce widespread mobile code

– the concept virus appears

• 1999– Melissa

• 2000– The Love Bug

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Mobile code and securityMobile code and security

• JavaScript– invasion of privacy– denial of service– Web spoofing

• Macro problems– the concept virus– the Melissa virus– the Love Bug

• ActiveX– system

modification attacks

– stealing money

• Java security– more power equals

more risk– attack applets in

the lab

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The classic security tradeoffThe classic security tradeoff

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Java’s answerJava’s answer

• Add as much functionality as is prudent while managing security risks

• JDK 1.0.2 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

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A question of trustA question of trust

Untrusted code is restrictedUntrusted 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– http://www.rstcorp.com/javasecurity/hotlist.html

Type safetyType 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 proneNote: type safety is NOT security

The original sandboxThe 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 classesFour 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

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A chronology of attack applets

A chronology of attack applets• February 96: DNS flaw in

JDK 1.0.1• 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 1.1JDK 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 2Java 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 inspectionStack 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

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What is a smart card?What is a smart card?

• A simple processor embedded in a plastic card– Same size as a credit

card

• New technology allows multiple applications on the same card

• Useful for hundreds of applications– Debit, credit, cash– Identity, cryptography

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How Java and smart cards mix

How Java and smart cards mix• Java Card is a stripped down version of

Java for smart cards– up to version 2.1 (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

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How can Java fit on a card?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

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Multi-application cardsMulti-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

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Java Card security != Java security

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

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Security risks in Java Card 2.1

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

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Multi-application issuesMulti-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?!

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Physical attacks still applyPhysical 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

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The terminal problemThe 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

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Protocol interaction risksProtocol 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

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Security is harder than it sounds

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

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What to do?What to do?

• Assume the platform is secure– it really is getting better

• Applets must be carefully designed and implemented

• Testing applets for security is essential

• Java Card Security = platform + applets

• Did I say security testing?

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ConclusionConclusion

• 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

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Where to learn moreWhere to learn more

Cigital provides expert advice onsmart card and mobile systemsoftware security issues.• Contact Pat Higgens ([email protected])

• http://www.securingjava.com– Chapter 8: Java Card Security

http://[email protected]