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Java Card 101 - Black Hat USA 2003 Bruce Potter [email protected] Senior Security Consultant Cigital, Inc. Who Am I and Why Care About this Talk? 3 years of Java Card security experience Other security foo Senior Security Consultant at Cigital Founder of The Shmoo Group

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Java Card 101 - Black Hat USA 2003

Bruce Potter

[email protected]

Senior Security Consultant

Cigital, Inc.


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Who Am I and Why Care About this Talk?

  • 3 years of Java Card security experience

  • Other security foo

  • Senior Security Consultant at Cigital

  • Founder of The Shmoo Group

  • Smart cards gaining traction… finally.

    • Post 9/11 security concerns

    • US Gov’t deploying 11k smart cards a day

    • Java card puts smart card tech within reach

  • Last talk before heavy drinking

    • Hopefully a good segue

    • Broad coverage of Smart Cards security and Java Card Technology


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What is a Smart Card

  • Originally, there were mag stripes cards

    • Predefined card shape, strength, etc

    • Information encoded on a magnetic stripe on card

      • You’ve seen a credit card, right?

    • Easily copied

    • Data is static

  • Physical and electronic characteristics defined by ISO7816

    • Same form factor as mag stripe

    • Now, “punch outs” for phone like applications

  • Many other specifications.. EMV talks about financial trans

  • Integrated Circuit Card (embedded microprocessor)

    • Not a memory card!


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What is a Smart Card

  • Receives clock and power from external source

    • Never trust your environment

  • Contact and contact-less

  • Three types of memory

    • ROM (64KB-ish)

    • EEPROM (32KB-ish)

    • RAM (8KB-ish)

  • Used to be much less memory

    • But we’ll never need more than 640KB


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Talking to a Smart Card - Entities

  • Terminal

    • Contains off-card application

    • Card is useless without something to interact with it

  • Reader

    • Physically interface with card

    • “smart” and “dumb” readers

    • Sometimes contained within the terminal

  • Card

    • Surprise!

  • Application Creator

  • Card Issuer


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Uses of Smart Cards

  • Stored Value

    • It’s money in there, ma…

  • Wallet Applet

    • Cuz carrying your regular wallet is hard

  • Loyalty Applications

    • Keeping track of your airline miles

  • Identity

  • Access Control

  • Secure storage

  • All of the above?


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Talking to a Smart Card - Conversation

  • Command - Response based

    • I ask, you tell… no independent thought

  • Application Protocol Data Unit (APDU)

    • Basic building block of a conversation

    • ISO 7816-4

    • There’s lower level (encoding) specs too…

      • T=0 - byte oriented (real simple)

      • T=1 - block oriented (no so simple)

  • Answer to Reset (ATR)

    • On power-on, card tells about protocol and other low-level comms parameters


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Command APDU

  • CLA - Class of the APDU

  • INS - Particular instruction within the class

  • P1, P2 - Parameters (case 1 ends here)

  • Lc - # of bytes of data (case 3 and case 4)

  • Data - as you would expect

  • Le - # of byes expected (case 2 and 4)


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Response APDU

  • Data - Sent if Le was set in command APDU

  • SW - Status word. Like an exit code, but with more info (2 bytes)


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Attacks Against Smart Cards

  • First off… just because you use smart cards doesn’t make you secure

    • Just like using SSL, etc…

  • Glitching

    • Pulling power at appropriate times

    • Under/over clocking

    • Under/over volting

  • Differential power analysis

    • Kocher et al - http://www.cryptography.com/

    • Watching the power draw over repeated cryptographic operations

    • Performing differential cryptanalysis


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Attacks Against Smart Cards

  • Ross Andersen’s work - http://www.cl.cam.ac.uk/users/rja14/

    • Low budget but sophisticated attacks

    • Inducing errors with a lightbulb!

    • Using laser cutters and microprobes to change data within card

  • Shaving the ICC

    • Yes Virginia, there are physical changes to registers

    • Able to see 1’s and 0’s in memory

  • Vendor Response?

    • Make ICC’s more complicated

    • Multi-dimensional tangle of circuits

    • Still, with time and tools, ICC can be mapped

    • Difficult to interact with ICC


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Attacks Against Smart Cards Systems

  • The card may not be the weak point

  • Reverse-engineering *gasp* really lame protocols

    • Watch yourself…. DMCA is being used as a hammer

  • By-passing smart card system

    • Some systems use mag-stripes as backups

    • Much easier to dupilicate


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Java Card

  • So, you still want to deploy them?

  • Back in the day, cards were made from a mask that contained the program

    • Cards were single vendor and fixed applications

    • Application mistake in the mask meant reissuance

  • More advanced operating systems now allow for applications to be added post-fabrication

    • Lots can be done with multi-application, dynamic cards

  • Sounds like a good place for Java, eh?

  • A really, really, really stripped down version of Java

    • Applets need to be compiled to a few KB of bytecode

    • Smaller than J2ME


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New uses for Smart Cards Thanks to JC

  • Smaller, custom deployments for Access Control and Identification

  • Cheaper, large scale deployments

    • Buy a vendors Java Card implementation

    • All you need to do is write some card code, terminal code, and backend code

  • Spoofing for other Smart Card systems

    • If you know the APDU’s and transaction structure for another system (say stored value), write an applet to subvert terminal

    • Nice hacking too, eh?


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Java Card API

  • Java.lang - a subset of the java language

    • Objects

      • No double, long, chars

    • Exceptions

  • Javacard.framework - classes for the core functionality of an applet

    • APDU

    • PIN

    • JCSystem

  • Javacard.security - Security Classes

    • Keys

    • Random Data

  • Javacardx.crypto - mad crypto foo


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Java Card Virtual Machine

  • Actually split into two parts

    • Off card Converter (yes.. Part of the VM is off card)

      • Performs security checks

      • Creates optimized bytecode

      • Initializes static variables

      • Creates class datastructures

      • Final Result: CAP file… like a shrunken JAR file

    • On card installer

    • On card interpreter

      • For execution, bytecode is interpreted by on-card VM

      • Handles memory allocation and very limited garbage collection



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Java Card Runtime Environment

  • Think of it as “the OS”

  • Lifetime of JCRE is lifetime of card

    • A bit non-intuitive… unlike Java on a PC

    • Instantiation of an applet usually only happens once

    • Applet and Runtime remain between card resets

  • Subset of the JRE

    • Focused on things that matter to card in hostile environment

    • Protects applets from each other and the world


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Java Card Runtime Environment

  • Command Processing

    • APDU dispatch to the applet’s process() method

  • Handling of Transient objects

    • Allows objects to be created and used in RAM for security and performance

  • Transactions and atomicity

    • Any single field write is made atomic by JCRE

    • Futher, JCRE provides for safety within transactions boundaries

    • Interrupting a transaction can be profitable if not properly handled


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Java Card Runtime Environment

  • Applet isolation via applet firewall

    • Unlike standard java, applets cannot invoke other applet’s methods

    • Each applet in a package (basically a CAP file in JC case) runs in its own context

    • Applet firewall forces applets to explicitly share interfaces to allow external access

  • Exception Handling

    • Key for a safe and secure application, card, and system


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Java Card Security Architecture

  • Type-safety

  • Most important verification done off-card

    • Byte code verified during compile

    • Checks for language violation

      • No bad datatypes, no threatds

  • Once code on the card, most of the checks are runtime issues

    • During the interim period, code (and ergo the cards, ultimately) are vulnerable

  • Malicious bytecode a real problem

    • Needs extra juice

  • Applet firewall prevents silliness

    • If properly implemented, remarkably effective


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Controlling Code

  • So… it’s good that anyone can load an applet, right?

    • Situation: Credit Card Vendor gives you a smart card which allows post-issuance applet loading

      • Wallet applet

      • Loyalty program

    • Attack: Malicious applet loaded on card to attack other applets

    • Attack: Malicious terminal terminates wallet applet

    • Attack: Legit terminal tries to load code on card… code changed in transit

  • Need a higher level controls to limit post-issuance code loading

  • Also, due to off card validation, need some code signing mechanism to verify that code can be trusted


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Controlling Code

  • Enter Global Platform (from Visa originally)

    • APDU MAC’ing

    • Cryptographically signed CAP file

    • Authentication process for loading and installing code

    • If multi-application, multi-vendor smart cards ever take off in the consumer financial industry.. They’ll use GP


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Issuing Smart Cards

  • Pre-issuance - card assumed physically secure

  • Post-issuance - Wild Wild West

    • Card needs to protect itself

    • No native methods may be declared

      • Direct interaction with ICC would compromise all Java card security - no verification mechanism


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Important Methods

  • Skipping a complete sample applet…

  • install()

    • Called when card installer wants to install a new Applet

    • Instantiates applet (basically like regular Java)

      public static void install ( byte[] bArray, short bOffset, byte bLength) {

      new myApplet(null);

      }

      Note: myApplet must call register() so the JCRE knows the new applet has been instantiated


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Important Methods

  • select()

    • When an off card entity wants to use an applet, it must be selected first

    • Upon reception of SELECT APDU, JCRE calls applets select() method

    • Applet verifies it is selectable and gets ready to receive more commands

  • deselect()

    • When another applet is selected, previous JCRE calls deselect() on previous applet first

    • JCRE will not allow previous applet to block and stop deselection

      • No DoS for you!


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Important Methods

  • process()

    • The real meat of the thing

    • When an APDU is received and the applet is selected, its process method is called by the JCRE and the passes it an APDU object.

    • Now you can parse the APDU, do what you need to do with it and then respond.


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Example Execution

# power on card and select AID 1 2 3 4 5 6 7 8

poweron: card turned on; connection establish

sendraw: transmitting (raw) (13): 0x80 0x50 0x00 0x00 0x08 0x01

0x02 0x03 0x04 0x05 0x06 0x07 0x08

sendraw: receiving: (2): 0x61 0x1c

# there are 27 bytes of data to get. Get them.

sendraw: transmitting (raw) (5): 0x00 0xc0 0x00 0x00 0x1c

sendraw: receiving: (30): 0x00 0x00 0x02 0x80 0x00 0x00 0x29 0x31 0x00 0xa7 0x0d 0x01 0x59 0x11 0xfe 0x51 0x49 0x45 0x4e 0x09 0x19 0x35 0xec 0x2c 0x5a 0x8e 0xe0 0xb4 0x90 0x00


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Secure Coding Guidelines

  • A bad applet can destroy the system

  • Use some manner of code signing… home brewed or otherwise

    • Barring that, verify chain of custody of code before installing

  • Velocity Checking

    • Note: Not like typical Velocity checking

      • On a smart card, time has no meaning

    • Any sensitive activity should only be allowed a reasonable number of times… then lock/terminate

      • Don’t forget harvesting “random” data

  • Only share what you need to

    • Watch out for transitivity issues with Shared Interface Objects


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Secure Coding Guidelines

  • Proper exception handling

    • Hacking a smart card may rely on making bad things happen

    • Detect, throw, protect

  • Use transient data where needed. Use transactions where needed

    • When updating sensitive information, wrap in a transaction boundary

    • Check commit capacity first

    • JCSystem.beginTransaction();

    • JCSystem.endTransaction();

    • Don’t forget to abortTransaction() if things go wrong


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Secure Coding Guidelines

  • Remember things are smaller on smart cards

    • Int may not be supported

    • Keep your code tight

  • When designing your protocol… think like an attacker

    • Both terminal and card can be forged

      • How does a fake terminal effect the card

      • Vice-versa

    • A simple Command-ACK protocol will likely be subverted

    • Cryptographically sign sensitive operations

    • Lots of prior art here

      • See resent Blackboard ID hack

      • http://features.slashdot.org/article.pl?sid=03/04/14/1846250


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Extra bits

  • MUSCLE Project

    • Movement for Use of Smart Cards in Linux Environments

    • www.linuxnet.com

    • PC/SC Daemon

    • Lots of reader drivers

  • Sun’s stuff

    • http://java.sun.com/products/javacard/

    • “Java Card Technology for Smart Cards” - Zhiqun Chen


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Card Vendors

  • Oberthur - http://www.oberthurcs.com/

  • Gemplus - http://www.gemplus.com/

    • Low priced development kits with reader/cards

  • Schlumberger - http://www.smartcards.net

    • $50 readers / $12 a card

    • Cards with USB logic imbedded in card


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Questions?

  • Buy some books!


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