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Smartcards & RFID

Erik PollDigital Security

Radboud University Nijmegen

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1900's technology

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2000's technology

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Overview

• What are smartcards & RFID ?• Why use them?• Possibilities and limitations

– hardware, software, communication protocols

• Attacks on security

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What is a smartcard?

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What is a smartcard?

• Tamper-resistant computer, embedded in piece of plastic, with limited resources

• capable of securely– storing information– processing information (This is what makes a smartcard smart; stupid cards

can store but not process data)

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Smartcard form factors

• traditional credit-card sized plastic card– ISO 7816

• mobile phone SIM– cut-down in size

• contactless cards– aka proximity card

or RFID transponder/tag

– also possible: dual interface

• iButton

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Smartcard example uses

• banking cards– bank or credit card, electronic purse

• telephone card for use in public phone booths• GSM SIM• pay TV• public transport – eg London Oyster card • health cards • passports and other e-id cards• access cards

– to control access to buildings, computer networks, laptops,...

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Magnetic stripe cards

• Older mag-stripe card can only store information, without read/write protection, and cannot process it.

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Anything suspicious?

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Skimming

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Skimming

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Skimming

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Skimming

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Smartcard vs mag-stripe cards

• Smartcard cannot easily be copied or altered, unlike a mag-stripe card

• Skimming is big criminal business– copying (aka cloning) mag-stripe cards and

observing PIN codes is easy...

• Still, credit card companies in US are sticking to mag-stripe, and in Europe they are only slowly moving to smartcards– apparently, it is secure enough for them to make a

profit

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smartcard essentials

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Smartcard contacts

External power supply and external clockOn a SIM card the clock can be stopped to safe power

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Smartcard contacts

Vpp is higher voltage than Vcc needed for writing EEPROM• no longer used because of security problem

– painting over this contact prevents changes to EEPROM

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Smart vs stupid smartcards

Big range in capabilities of smartcards. Rough division:• Memory cards (stupid)

– provide a file system– possibly with some access control, or, simpler still, destructive (irreversible) writes as in old payphone-

cards – functionality hardwired in ROM

• Microprocessor cards (very smart)– contain CPU

• possibly also crypto co-processor– programmable

• program burnt into ROM, or stored in EEPROM

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Smartcard hardware

• CPU – 8 to 32 bits

• memory

– RAM – ROM (for some program code)

– EEPROM/Flash/... (“hard disk”, for code and data)

Modern cards may have 1K RAM, 16K ROM, 64K EEPROM • limited I/O: just a serial port

• possibly: crypto co-processor, random number generator

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Communication (ISO 7816)

• All subsequent communication via APDUs– Application Protocol Data Units

which are just byte sequences in particular format

• Master-Slave mode, with terminal master:1. Terminal sends command APDU2. Card replies with response APDUetc, etc ....

– Smartcard cannot initiate any actions:– on phones the phone polls the SIM periodically

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Command & response APDU

• CLA class byte• INS instruction byte• P1,P2 parameters• Lc length of data block • Data Lc bytes of data

• Response Lc bytes of data

• SW1, SW2 2 byte status word

CLA INS P1 P2 Lc ...Data .... Le

Response ...

SW1 SW2

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Smartcard software

• (Microprocessor) smartcard contains very simple operating system, capable of executing programs

• Programs can be written in– proprietary machine code language, or– higher level language, notably Java Card

Most new SIMs are now Java Cards.

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old vs new smartcards

• one program (applet)

• written in machine

code, specific to chip

• burnt into ROM or

uploaded once to

EEPROM

• applet written in high-level language (eg Java Card)• compiled into bytecode• stored in EEPROM• interpreted on card

• multi-application: several applets on one card

• post-issuance: adding or deleting applets after it's issued

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Multi-application cards

• multi-application vision: everyone carrying just one card, with all their smartcard applications

• This is not going to happen. Problems include:– trust: bank won't allow untrusted applet

code on their cards, despite any VM+ firewall security guarantees

– marketing: who gets to put their logo on the plastic?

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Post-issuance download

• Downloading additional applets protected by digital signatures

• Switched of on many cards for security reasons

• Enabled on SIMs it allows telco to install new software on the SIM

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Java Card

• dialect of Java for programming smartcards:– superset of a subset of normal Java

• subset of Java (due to hardware constraints)– no threads, doubles, strings, garbage

collection, and very restricted API• with some extras (due to hardware peculiarities)

– communication via APDUs or RMI– persistent & transient data in EEPROM &RAM– transaction mechanism

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Java Card platformJava Card platformJava Card platformJava Card platform

Java Card architecture

smartcard hardwaresmartcard hardware

app

let

app

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tapp

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Java CardVirtual Machine

Java Card API(mini OS)

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app

let

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Java Card I/O with APDUs

Java Card platformJava Card platformap

ple

tapp

let

ap

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tapp

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smartcard hardwaresmartcard hardware

command APDU,incl. applet ID

OS selects applet

and invokes itsprocess method

Applet sendsresponse APDU

appletexecutesa

pp

let

app

let

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Pros of JavaCard

• vendor-independance• easy to program

– higher-level language => smaller programs with fewer bugs

– standard functionality (eg for PINs) provided once by the API

• open standard– no reliance on security-by-obscurity– specs can be studied and criticised

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Cons of JavaCard

• overhead of VM makes cards slow and requires lots of memory => expensive

• ease of programming may be deceptive: non-experts programming cards may make silly mistakes– every idiot can program a JavaCard, not every idiot should

• trust: how secure is the whole JavaCard infrastructure– complicated platform, and complexity <-> security

• blank programmable JavaCard easy for attacker to experiment with– security by obscurity may have its merits...

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Java Card vs Java

Java Card applets are executed in a sandbox• like applets in a web browserBut important differences:• no bytecode verifier on most cards

– due to space required

• downloading applets controlled by digital signatures instead– plus bytecode verification, if card supports it

• sandbox more restrictive, and includes runtime firewall between applets

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Java Card Runtime Environment (JCRE = VM+API)

Java Card Runtime Environment (JCRE = VM+API)

Java Card firewall

smartcard hardwaresmartcard hardware

app

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ap

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app

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ap

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ap

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tap

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t eg prevents accessto public fields ofother appletsor references to objects belongingto other appletsor JCRE

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Java Card 3.0

• Releases up to Java Card 2.2.2 use traditional smartcard communication model – small byte array (APDU) sent back and forth to

applet on the card (using ISO 7816 standard)• Java Card 3.0 (March 2008) introduces new

communication model:– smartcard becomes a webserver with IP-stack etc

– applets become servletsSo you can talk http(s) to the smartcard

• Proclaimed goal:easier development of SIM services

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Why use smartcards?What are the possibilities and limitations

of smartcards?

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Why use smartcard?

SIM responsible for authentication to network•telco doesn't trust phone, but trusts SIM

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CIA and smartcards

• Confidentiality– of data (crypto keys) on card

• Integrity– of data and program code

• Authentication– because (data on) card cannot be copied

• Non-repudiation– because (data on) card cannot be copied – also logging on the smartcard (and integrity

of this log)

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crypto key K CPU

challenge c

response fK(c)

Typical use of smartcard

• key K never leaves the card

• Card issuer does not have to trust the network, the terminal, or card holder

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Example: logging on over a network

• Send password unencrypted over net (eg. rlogin) Trust network, terminal, user• Send password encrypted over net (eg. slogin) Trust terminal, user• Idem, but user, not terminal, does encryption

Trust user• Using smartcard Trust no-one, except the smartcard (NB smartcard is controlled by card issuer, not card

holder!)

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NB the problem with cryptography

Any use of crypto introduces problems:1. key distribution

• how do we generate & distribute keys?

2. key storage• where can we safely store keys?

3. en/decryption• who do we trust to perform en/decryption?

Smartcards can offer a solution

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TCB and smartcards

• Smartcard typically part of the TCB (Trusted Computing Base), ie. the trusted part of the system

• NB “trusted” is a negative quality: it means “you have to trust it” not “you can trust it”

– If any part of the TCB fails, security is broken– TCB should be as small and reliable as

possible

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RFID

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RFID tags

• RFID = Radio-Frequency IDentification • RFID devices are called tags or transponders• More powerful RFID tags can be called

(contactless) smartcards

• Inductive coupling is used for– energy transfer to card– transmission of clock signal– data transfer

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Types of RFID: different capabilities & ranges

animal identification

product identification (like bar codes)

contactless smartcards(possibly dual interface)

NFC mobile phones

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contactless smartcard inside

antennachip

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Different capabilities of RFID tags

• Simplest tags just broadcast fixed data (serial number) when activated– ie only communication from tag to reader

• Some tags provide basic file system, with simple access control

– ie reading & writing, and communication both ways• More advanced tags can do cryptographic

operations to protect data & encrypt communication

• Most advanced tags are programmable • Range can be a few mm, a few cm, a few feet

or several meters, depending on the type

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Pros & cons wireless

• Advantage– convenience– faster– contacts not subject to wear and tear

• Disadvantage– eavesdropping– virtual pickpocketing

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NFC

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Near Field Communication (NFC)

• Latest Nokia phones have NFC

• These can act as RFID tag

and as RFID reader

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NFC

• Advantage of NFC phone over smartcard:– (trusted?) display and keyboard

• Envisaged use– payment applications– RFID tags providing info to phone

• eg in information signs & billboards

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Attacks on smartcards & RFID tags

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Smartcard are not 100% secure

• Growing range of attacks (and associated countermeasures)

• Crucial question: is the risk acceptable?– are the costs of an attack larger than the

potential financial gain for the attacker?

• Threats depend on application – eg. cloning more interesting for PayTV than

GSM SIMs

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Logical & protocol attacks

Find & exploit bug in software or security protocol

• Possible weaknesses– silly programming error in card or terminal– hidden commands (eg for initialisation)– buffer overflows, eg to read past end of file– badly configured file access privileges– weaknesses in crypto-protocol

• eg replay attacks• Little equipment needed, but change of success low

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Logical & protocol attacks

Equipment• card reader• PC• maybe also a

programmable JavaCard

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Eavesdropping on card-terminal communication

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Eavesdropping on contactless card

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replay attack

• eavesdrop on communication

communication

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replay attack

• eavesdrop on communication

and make an emulator that mimics this

communication

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replay attack works on disposable Dutch public transport card!

gate cannot distinguishreal card and emulator

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challenge-response

• Better cards use challenge-response mechanism to prevent replays

n

encryptKEY{n}

random challenge n

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Mifare Classic

• > 1 billion sold– eg London metro Oyster card, Dutch public transport card,

Radboud university access cards,....

• uses proprietary crypto algorithm CRYPTO1– with 42 bit keys

• very weak crypto broked by Digital Security group– key to retrieved in seconds– Details http://www.ru.nl/ds/research/rfid/– or google YouTube for MIFARE

• Kerckhoffs principle: security of system should be based on secrecy of the key only, not on secrecy of the crypto algorithm!

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More specialised hardware attacks

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Countermeasures

• Used well-researched crypto & security protocols

• Write qualitity software– Testing– Formal verification – Perform code reviews to spot software problems– Improve OS, APIs, programming languages to make

software bugs less likely– Open research area !!

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Side-channel attacks

• Side-channel = any other channel than the normal I/O channel that may be observed

• Possible side-channels:– power consumption– timing– electro magnetic radiation– ....

• A side-channel might leak information

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Power consumption of a smartcard

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This is probably a DES encryption!

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Differential Power Analysis (DPA)

Deduce information from power consumption Simple power analysis (SPA) or Differential Power

Analysis (DPA)

Countermeasuresin software

– careful coding of crypto-algorithms– redundancy in data representation

• in hardware– add clock jitter or other noise– dual rail logic

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Power glitching

• precisely timed dip in power supply to induce fault, eg– prevent an EEPROM write

• eg to PIN counter

– read all memory cells as containing zero• eg of crypto-key

– attack crypto-algorithms attacks may leak info about keys

(DFA-Differential Fault Analysis)

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Active side-channel attacks

• Other side channels:– clock frequency – temparature/heat– light or X-rays– EM radiation

• Countermeasures:– hardware: sensors to detect changes in

voltage, etc.– software: double-checking results of

computations

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Physical (or invasive) attacks

• reverse engineer and tamper with the physical chip

• first step: getting access to chip’s surface– remove chip from the smartcard– use chemical to remove expoxy resin and

the top metal/silicon layers of the chip

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Removing chip from smartcard

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Etched smartcard with chip exposed

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Tools for physical attacks

• Microscope– optical or scanning electron microscope

(SEM)

• Focused Ion Beam (FIB)– not only observe, but also make changes:

removing or adding wires, insulators,...

• Probe station – to probe wires on the chip

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Probing

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Probing

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Probing

• Observe data on the chip in operation• Typically: tap data on bus

– by putting needle on bus wires

• Probing can be done using– physical needles (>0.35 micron) or – electron beam

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Using Focused Ion Beam in probing

Fibbing can be used to• add probe pads for

lines too thin or fragile for needles

• surface buried lines

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Multiple layers on chip

The same gate before and after etching to remove top layer

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Using Focused Ion Beam (fibbing)

• all chips contain circuitry to check chip after production

• after testing, test logic is disabled by blowing a fuse

• FIB can restore test logic

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ROM memory content extraction

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RAM voltage contrast SEM

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Smartcards attacks - future

• Ongoing arms race between smartcard manufacturers and attackers

• Physical attacks becoming harder, due to improved countermeasures and smaller circuitry

• But increasing complexity of software on smartcard may introduce new logical attacks

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Smartcard attacks - conclusions

• Smartcards is not tamper-proof, as witnessed by – logical attacks– side-channel attacks: DPA, glitching– physical attacks

• Smartcards are tamper-resistant and tamper-evident, to a degree