RFID Systems and Security and Privacy Implications

1. RFID Systems and Security and Privacy Implications Auto-ID Center Massachusetts Institute of Technology www.autoidcenter.org Sanjay E. Sarma Stephen A. Weis Daniel W. Engels

2. 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

3. Overview • Radio Frequency Identification (RFID) • EPC System • Security Benefits and Threats • Future

4. 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

5. 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

6. 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! 

7. 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

8. RFID System Components • RFID Tag • Transponder • Located on the object • RFID Reader • Transceiver • Can read and write data to Tag • Data Processing Subsystem

9. 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

10. 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

11. 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

12. 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

13. RFID • Transceivers are strategically placed for given application • Access Control has readers near entrance • Sporting events have readers at the start and finish lines

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. Coding • Level Codes • Non-Return-to-Zero • Return-to-Zero • Transition Codes • Manchester • Miller

23. 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

24. Coding for Readers and Tags • Reader to Tag uses PPM or PWM (lower bandwidth) • Tag to Reader uses Manchester or NRZ (higher bandwidth)

25. 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

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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

39. 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

40. 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

41. 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

42. 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

43. 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

44. 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

45. 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

46. 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

47. 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

48. 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

49. 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