Transcript Smartcards

Smartcards & RFID
Erik Poll
Digital Security
Radboud University Nijmegen
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1900's technology
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2000's technology
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Overview
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•
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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 clock
On 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
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(ISO 7816)
All subsequent communication via APDUs
– Application Protocol Data Units
which are just byte sequences in particular format
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Master-Slave mode, with terminal master:
1. Terminal sends command APDU
2. Card replies with response APDU
etc, etc ....
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Smartcard cannot initiate any actions:
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on phones the phone polls the SIM periodically
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Command & response APDU
CLA INS P1 P2 Lc
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•
•
•
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...Data ....
Le
CLA class byte
INS instruction byte
P1,P2 parameters
Lc length of data block
Data Lc bytes of data
Response ... SW1
• Response
SW2
Lc bytes of data
• SW1, SW2 2 byte status word
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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
• applet written in high-level
language (eg Java Card)
• compiled into bytecode
• stored in EEPROM
• interpreted on card
uploaded once to
EEPROM
• 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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applet
applet
applet
Java Card architecture
Java Card
Java Card API
Java
Card
platform
Virtual Machine
(mini OS)
smartcard hardware
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applet
applet
applet
Java Card I/O with APDUs
Java Card platform
OS selects
applet
command
APDU,
Applet
sends
appletits
and incl.
invokes
applet
ID
response
APDU
executes
process
method
smartcard hardware
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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 browser
But 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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applet
applet
applet
Java Card firewall
Java Card Runtime Environment
(JCRE = VM+API)
eg prevents access
to public fields of
other applets
or references to
objects belonging
to other applets
or JCRE
smartcard hardware
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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 servlets
So 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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Typical use of smartcard
crypto
key K
CPU
challenge c
response fK(c)
• 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
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how do we generate & distribute keys?
2. key storage
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where can we safely store keys?
3. en/decryption
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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
chip
antenna
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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
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–
–
–
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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
communication
and make an emulator that mimics this
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replay attack works on disposable
Dutch public transport card!
gate cannot distinguish
real card and emulator
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challenge-response
• Better cards use challenge-response
mechanism to prevent replays
random challenge n
n
encryptKEY{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
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–
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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)
Countermeasures
in 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:
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–
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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
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