RFID Systems and Security and Privacy Implications

Sanjay E. Sarma

Stephen A. Weis

Daniel W. Engels

Auto-ID Center

Massachusetts Institute of Technology

www.autoidcenter.org

Auto-ID Center

• International industry-sponsored research center

• MIT, Cambridge University, and University of Adelaide

• Design, develop, and deploy large-scale field trials including RFID projects

Overview

• Radio Frequency Identification (RFID)

• EPC System

• Security Benefits and Threats

• Future

Uses of Automatic-ID Systems

• Access control and security

• Tracking of products in Supply Chain

• Id of products at Point of Sale

Most widely used is the Bar Code System

Potential Application of RFID

• Consider supply chain and EAN-UCC bar codes

• 5 billion bar codes scanned daily

• Each scanned once only at checkout

• Use RFID to combine supply chain management applications

Benefits of Supply Chain Management

• Automated real-time inventory monitoring

• Automated Quality Control

• Automated Check-out

Picture your refrigerator telling you that you’re out of milk!

Why not yet implemented

• Cost too high. Needs to be <$0.10

• Lack of standards and protocols

• Security concerns – similar in smart cards and wireless

• Privacy issues – Big Brother

RFID System Components

• RFID Tag– Transponder– Located on the object

• RFID Reader– Transceiver– Can read and write data to Tag

• Data Processing Subsystem

Transponder

• Consist of microchip that stores data and antenna

• Active transponders have on-tag battery

• Passive transponders obtain all power from the interrogation signal of reader

• Active and passive only communicate when interrogate by transceiver

Transceiver

• Consist of a RF module, a control unit, and a coupling element to interrogate tags via RF communication

• Also have secondary interface to communicate with backend systems

• Reads tags located in hostile environment and are obscured from view

Data Processing Subsystem

• Backend System

• Connected via high-speed network

• Computers for business logic

• Database storage

Also as simple as a reader attached to a cash register

RFID

• Basic components of RFID system combine in the same manner

• All objects are physically tagged with transponders

• Type of tag used varies from application to application

• Passive tags are most promising

RFID

• Transceivers are strategically placed for given application

• Access Control has readers near entrance

• Sporting events have readers at the start and finish lines

Transceiver-Transponder Coupling and Communication

• Passive tags obtain power from energy in EM field generated by reader

• Limited resource require it to both get energy and communicate within narrow frequency band – regulatory agencies

Inductive Coupling

• Uses magnetic field to induce current in coupling element

• Current charges the on-tag capacitor that provides operating voltage

• This works only in the near-field of signal – up to c/(2πf) meters

Inductive Coupling

• Operating voltage at distance d is proportional to flux density at d

• Magnetic field decreases in power proportional to 1/d3 in near field

• Flux density is max when R ≈ d√2, where R is radius of reader’s antenna coil

Far Field energy harvesting

• Uses reader’s far field signal to power tag

• Far field begins where near field ends

• Signal incident upon the tag induces voltage at input terminals of the tag, which is detected by RF front-end circuitry and is used to charge capacitor

Passive tag power

• Reader uses same signal to communicate with and power tag

• Any modulation of signal causes power reduction

• Modulating information spreads the signal – referred to as “side band.”

• Side band and max power is regulated

Transponder Communication

• RFID systems generally use the Industrial-Scientific-Medical bands

• In near field, communication is achieved via load modulation

• In far field, backscatter is used. Backscatter is achieved by modulating the radar-cross section of tag antenna

Limitations of Passive Tag communication

• Very little power available to digital portion of the IC, limited functionality

• Length of transactions is limited – Length of power on– Duration within communication range

• US regulations for 915 MHz limit transaction time to 400 ms

• Limit of state information

Data Coding and Modulation

• Determines bandwidth, integrity, and tag power consumption

• Limited by the power modulation / demodulation capabilities of the tag

• Readers are generally low bandwidth, due to government regulations

• Passive tags can use high bandwidth

Coding

• Level Codes– Non-Return-to-Zero– Return-to-Zero

• Transition Codes– Manchester– Miller

Coding Considerations

• Code must maintain power to tag as much as possible

• Code must not consume too much bandwidth

• Code must permit the detection of collisions

Coding for Readers and Tags

• Reader to Tag uses PPM or PWM (lower bandwidth)

• Tag to Reader uses Manchester or NRZ (higher bandwidth)

Modulation

• RF communications typically modulate high frequency carrier signal to transmit baseband code

• Three classes of digital modulation are ASK, FSK, and PSK.

• ASK most common in 13.56 MHz load modulation

• PSK most common in 915 MHz backscatter modulation

Tag Anti-Collision

• Limited power consumption

• State information may be unreliable

• Collisions may be difficult to detect due to varying signal strengths

• Cannot be assumed to hear one another

Algorithm Classification

• Probabilistic– Tags respond in randomly generate times– Slotted Aloha scheme

• Deterministic– Reader sorts through tags based on tag-ID– Binary tree-walking scheme

Algorithm Performance Trade-offs

• Speed at which tags can be read

• Outgoing bandwidth of reader signal

• Bandwidth of return signal

• Amount of state that can be reliable stored on tag

• Tolerance of the algorithm to noise

Algorithm Performance Trade-offs

• Cost of tag

• Cost of reader

• Ability to tolerate tags with enter and leave during interrogation period

• Desire to count tags exactly as opposed to sampling

• Range at which tags can be read

Regulations Effect

• US regulations on 13.56 MHz bandwidth offer significantly less bandwidth, so Aloha is more common

• 915 MHz bandwidth allows higher bandwidth, so deterministic algorithms are generally used

13.56 MHz Advantages

• Frequency band available worldwide as an ISM frequency

• Up to 1 meter reading distance in proximity / vicinity read

• Robust reader-to-tag communication

• Excellent immunity to environmental noise and electrical interference

13.56 MHz Benefits

• Well-defined transponder interrogation zones

• Minimal shielding effects from adjacent objects and the human body

• Damping effects of water relatively small, field penetrates dense materials

915 MHz Benefits

• Long range (from a few to several meters, depending on regulatory jurisdiction)

• High data rates

• Fast anti-collision and tags per second read rate capabilities

The EPC System

• System that enables all objects to be connected to the Internet by adding an RFID tag to the object

• EPC

• ONS

• SAVANT

• Transponders

The EPC

• Electronic Product Code

• ID scheme designed to enable unique id of all physical objects

• Only data stored on tag, since information about object is stored on network

• EPC acts like a pointer

The ONS

• Object Name Service

• Directory service that maps EPS to IP

• Based entirely on DNS

• At the IP address, data is stored in XML and can be accessed via HTTP and SOAP

The ONS

• Reduces power and memory requirements on tag

• Transfer data communication to backend network, saving wireless bandwidth

• Makes system more robust

• Reduces size of microchip on tag

Savant

• System based on hierarchical control and data management

• Provides automated control functionality

• Manages large volumes of data

• Acts as a gateway for the reader network to the next higher level

Savant

• Transfers computationally intensive functionality from tag to powered system

• Any single point of failure has only local effect

• Enables entire system to be scalable since reader sub-systems are added seamlessly

RFID Transponder

• Most numerous parts of system

• Most cost-sensitive part

• Protocols designed for 13.56 MHz and 915 MHz frequencies

• Implement a password-protected Self Destruct command

RFID Security Benefits and Threats

• Airline passenger and baggage tracking made practical and less intrusive

• Authentication systems already in use (key-less car entry)

• Non-contact and non-line-of-sight

• Promiscuity of tags

Previous Work

• Contact-less and constrained computational resource similar to smart cards

• Analysis of smart card security concerns similar to RFID

• RFID especially susceptible to fault induction and power analysis attacks

Security Goals

• Tags cannot compromise privacy of holders

• Information should not be leaked to unauthorized readers

• Should not be possible to build long-term tracking associations

• Holders should be able to detect and disable tags they carry

Security Goals

• Publicly available tag output should be randomized

• Private tag contents should be protected by access control and encryption

• Spoofing tags or readers should be difficult

Low-cost RFID Issues

• Inexpensive read-only tags are promiscuous and allow automated monitoring – privacy concern

• Neither tags nor readers are authenticated – security concern

• Full implementation of privacy and security is costly – cost concern

Possible solutions

• Erase unique serial numbers at point of sale – tracking still possible by associating “constellations” of tags

• Public key cryptography – too expensive

• Shared key – if one tag is compromised, entire batch is effected

Approach to RFID Protection

• Use one-way hash function on tag – “meta-ID”

• When reader knows meta-ID, tag is ‘unlocked’ and readable

• After reader is finished, tag is locked

• Tag has self-destruct mechanism to use if under attack

Future Research

• Development of low cost crypto primitives – hash functions, random number generators, etc.

• Low cost hardware implementation w/o computational loss

• Adaptation of symmetric encryption and public key algorithms from active tags into passive tags

Future Research

• Developing protocols that make tags resilient to power interruption and fault induction.

• Power loss graceful recovery of tags

• Research on smart cards and other embedded systems