On the Security of RFID

1. On the Security of RFID Hung-Min Sun (孫宏民) Information Security Lab. Department of Computer Science National Tsing Hua University

2. What is RFID? • Radio-Frequency Identification Tag Reference http://glossary.ippaper.com

3. Roles of RFID applications Secure channel Tags Reader Server(Database)

4. Barcode v.s. RFID Barcode RFID • can be read at much greater distances • unique object id • more expensive • require a direct line of sight to the printed barcode • have no read/write capability • cheap Reference www.cs.utexas.edu/~shmat/

5. Where Are RFID Used? • Physical-access cards • Inventory control • Gillette Mach3 razor blades, ear tags on cows, kid bracelets in waterparks, pet tracking • Logistics and supply-chain management • Track a product from manufacturing through shipping to the retail shelf • Gas station and highway toll payment • Mobile SpeedPass Reference www.cs.utexas.edu/~shmat/

6. Commercial Applications of RFID • RFID cost is dropping dramatically, making it possible to tag even low-value objects • Around 5c per tag, $100 for a reader • Logistics and supply-chain management is the killer application for RFID • Shipping, inventory tracking, shelf stocking, anti-counterfeiting, anti-shoplifting • Massive deployment of RFID is in the works • Wal-Mart pushing suppliers to use RFID at pallet level, Gillette has ordered 500,000,000 RFID tags Reference www.cs.utexas.edu/~shmat/

7. Future Applications of RFID • Location Awareness • Health Care • Apparel • Smart Shelf Reference http://www.rfidjournal.com/

8. RFID Tag Power Sources • Passive (this is what mostly used now) • Tags are inactive until the reader’s interrogation signal “wakes” them up • Cheap, but short range only • Semi-passive • On-board battery, but cannot initiate communication • Can serve as sensors, collect information from environment: for example, “smart dust” for military applications • More expensive, longer range • Active • On-board battery, can initiate communication Reference www.cs.utexas.edu/~shmat/

9. Security Problems of RFID • Eavesdropping • Hot-listing • Attacker has special interests in certain items • Replay attack • Cloning • Tracing • Data forging • Denial of Service Fundamental problem: Lack of mutual authentication

10. Cryptography and Authentication

11. Cryptographic System

12. Four Basic Services of Cryptography: • Confidentiality (Secrecy): The intruder cannot read the encrypted message from the ciphertext. • Authentication: It should be possible for the receiver of a message to ascertain its origin; an intruder should not be able to masquerade as someone else. • Integrity: It should be possible for the receiver of a message to verify that it has not been modified in transit; an intruder cannot substitute a false message for a legitimate one. • Nonrepudiation: A sender should not be able to falsely deny later that he sent a message.

13. Cryptographic System • Symmetric Cryptosystem: The encryption & decryption keys are the same. (EK(M)= C & DK(C)= M). • Asymmetric Cryptosystem: Encryption & decryption keys are different. (EK1(M)=C & DK2(C)=M) The encryption key is public, while the decryption key can not be calculated from the public key.

14. Symmetric Cryptosystem • DES (1977) • IDEA (1992) • RC5 (1994) • AES (2001)

15. Asymmetric Cryptosystem • RSA (1978) • El-Gamal (1984) • McEliece (1978) • Knapsack (1978)

16. RSA (Encryption & Decryption) • Public key: n = pq, p and q are large primes(512 bit), e ( gcd (e, (p-1)(q-1)) =1) • Private key: d, where ed = 1 mod (p-1)( q-1) • Encryption: C=M e mod n • Decryption: M= C d mod n p=47, q=71, => n=3337 e=79, => d = 1019 M=688 Encryption: C=M e mod n = 68879 mod 3337 = 1570 Decryption: M= C d mod n =15701019 mod 3337 = 688

17. One-way hash function • A hash (also known as a message digest) is a one-way function. It is considered a one-way because it’s not practical to figure out what input corresponds to a given output. • We will use the term hash and message digest interchangeably. The NIST message digest function is called SHA-1, which stands for secure hash algorithm,whereas the MD in the MD2,MD4,MD5 algorithm stands for message digest.

18. One-way hash function • Input: X (unlimited length) • Output: Y=H(X) (fixed length, e.g., 160 bit) • Given X, it is easy to compute Y. • Given Y, and H( ), it is computational infeasible to compute X. • Given X and Y, it is computational infeasible to find X’ such that Y=H(X’).

19. One-way hash function • There certainly will be many message that yield the same message digest, because a message can be of arbitrary length and the message digest will be fixed length, for instance 128bits. • By trying lots of messages, one would eventually find two that mapped to the same message digest. • The problem is that “lots” is so many that it is essentially impossible.

20. The significant difference between a secret key algorithm and a message digest algorithm is that a secret key algorithm is designed to be reversible and a message digest algorithm is designed to be impossible to reverse. • In this section we’ll use MD as a “generic” message digest algorithm.

21. Computing a MAC with a Hash • The obvious thought is that MD(m) is a MAC for message m. But it isn’t. anyone can compute MD(m). • We concatenate a shared secret KAB with the message m, and use MD(KAB|m) as the MAC. • Some proposals with no known weaknesses are: • Put the secret at the end of the message instead of at the beginning. • Use only half the bits of the message digest as the MAC

22. Concatenate the secret to both the front and the back of the message. • We call any hash combining the secret key and the data a keyed hash.

23. HMAC • HMAC result from an effect to find a MAC algorithm that could be proven to be secure if the underlying message digest’s compression function was secure. • They defined secure as having two properties: • Collision resistance • An attacker doesn’t know the key K cannot compute the proper digest(K,x) for data x, even if the attacker can see the value of digest(K,y) , for arbitrary numbers of inputs y, with y no equal to x.

24. How to achieve “Mutual Authentication” between two parties?

25. Authentication functions • By … Message encryption • The ciphertext of the entire message serves as its authenticator • By … Message authentication code (MAC) • A public function of the message and a secret key that produces a fixed-length value that serves as the authenticator • By … Hash function • A public function that maps a message of any length into a fixed-length hash value, which serves as the authenticator

26. C = EK(M) Authentication (a) • Symmetric encryption Stores Key K Stores Key K RFID tag is authenticated If M == DK(C) • Confidentiality and authentication

27. Epublic_key(M) Authentication (b) • Public-key encryption Uses Reader’s private key Uses Reader’s public key RFID tag is authenticated If M == Dprivate_key(C) • Only Confidentiality

28. Eprivate_key(M) Authentication (c) • Public-key encryption Uses tag’s public key Uses tag’s private key RFID tag is authenticated If M == Dpublic_key(C) • Authentication and signature

29. C=EK(M||Hash(M)) Authentication (d) • Hash function Stores key K Stores key K RFID tag is authenticated If DK(C)==Hash(M) • Confidentiality and authentication

30. Authentication (e) Authentication (e) • 30

31. However, RFID tag … • No or very limited power • Little memory • Static 64- or 128-bit identifier in current 5-cent tags • Little computational power • A few thousand gates at most • Static keys for read/write access control • Not enough resources to support public- or symmetric-key cryptography • Cannot support modular arithmetic (RSA, DSS), elliptic curves, DES, AES; hash functions are barely feasible • Is resettable • Passive tag resets when power off

32. Physical Solutions for RFID

33. Physical Solutions • Kill tag after purchase • Faraday cage • Active jamming • Disables all RFID, including legitimate applications • Guardian • Blocker Tag

34. Killing approach • Special command permanently de-activates tag after the product is purchased • Disables many futuristic applications Reference www.rsa.com/rsalabs/staff/bios/ajuels/

35. Faraday Cage • Container made of foil or metal mesh, impenetrable by radio signals of certain frequencies • Shoplifters are already known to use foil-lined bags • Maybe works for a wallet, but huge hassle in general Reference www.rsa.com/rsalabs/staff/bios/ajuels/

36. Active Jamming (Guardian) • A mobile battery-powered device that offers personal RFID security and privacy management. Reference http:// www.rfidguardian.org

37. Blocker Tag (The RXA Pharmacy) Reference http:// www.rfidjournal.com

38. Blocker Tag : How Does the Reader Read a Tag? • When the reader sends a signal, more than one RFID tag may respond: this is a collision • Reader cannot accurately read information from more than one tag at a time • Example: every tagged item in a supermarket cart responds to the cashier’s RFID reader • Reader must engage in a special singulation protocol to talk to each tag separately • Tree-walking is a common singulation method • Used by 915 Mhz tags, expected to be the most common type in the U.S. Reference www.cs.utexas.edu/~shmat/

39. Reference www.cs.utexas.edu/~shmat/ Blocker Tag : Tree Walking prefix=0 prefix=1 Reader broadcasts current prefix Each tag with this prefix responds with its next bit prefix=00 prefix=01 prefix=10 prefix=11 If responses don’t collide, reader adds 1 bit to current prefix, otherwise tries both possibilities 000 001 010 011 100 101 110 111 Every tag has a k-bit identifier This takes O(k  number of tags)

40. Collision! No collision No collision No collision Collision! 3. ID=001 3a. ID=110 Talk to tag 001 Talk to tag 110 3b. ID=111 Talk to tag 111 Next=1 Next=1 Next=1 Next=1 Next=0 Next=1 Next=1 Next=0 Next=0 Reference www.cs.utexas.edu/~shmat/ Blocker Tag : Example 1. Prefix=“empty” prefix=0 prefix=1 1a. Prefix=0 1b. Prefix=1 2. Prefix=00 2. Prefix=11 prefix=00 prefix=01 prefix=10 prefix=11 000 001 010 011 100 101 110 111

41. Reference www.cs.utexas.edu/~shmat/ Blocker Tag [Rivest, Juels, Szydlo] • A form of jamming: broadcast both “0” and “1” in response to any request from an RFID reader • Guarantees collision no matter what tags are present • To talk to a tag, reader must traverse every tree path • With 128-bit IDs, reader must try 2128 values – infeasible! • To prevent illegitimate blocking, make blocker tag selective (block only certain ID ranges) • E.g., blocker tag blocks all IDs with first bit=1 • Items on supermarket shelves have first bit=0 • Can’t block tags on unpurchased items (anti-shoplifting) • After purchase, flip first bit on the tag from 0 to 1

42. Query RN16 (16-bit random number) Tag ID ACK (RN16) EPCglobal Class 1 Generation 2 • Most popular in long-range RFID applications • Frequency: 860-960 MHz • Reading range:10-20 Feet • ISO 18000-6C Reader RFID tag Memory Read/Write & Other commands • slide 42

43. Query RN16 (16-bit random number) Tag ID ACK (RN16) Problems in EPCglobal C1G2 • Long reading range • A naïve protection: • Use of 16-bit random number • Tag ID is transmitted in plaintext • Lack of “reader-to-tag” authentication Malicious Reader RFID tag Memory Read/Write & Other commands • slide 43

44. Secure Protocols for RFID

45. Secure RFID Protocols Hash-based Approaches • [1] S. Weis, “Security and Privacy in Radio-Frequency Identification Devices,” master’s thesis, Massachusetts Inst. of Technology (MIT), Massachusetts, USA, May 2003. • [8] M. Ohkubo, K. Suzuki, and S. Kinoshita, “Cryptographic Approach to “Privacy-Friendly” Tags,” RFID Privacy Workshop, MIT, Massachusetts, USA, Nov. 2003. • [9] T. Dimitriou, “A Lightweight RFID Protocol to protect against Traceability and Cloning Attacks,” Proc. 1st IEEE Conf. Security and Privacy for Emerging Areas in Comm. Networks (SecureComm ’05), Sep. 2005. • [12] G. Tsudik, “YA-TRAP: Yet Another Trivial RFID Authentication Protocol,” Proc. 4th IEEE Int’l Conf. Pervasive Computing and Comm. (PerCom’06), Mar. 2006. • [13] G. Avoine and P. Oechslin, “A Scalable and Provably Secure Hash Based RFID Protocol,” Proc. 3rd IEEE Int’l Workshop Pervasive Computing and Comm. Security (PERCOMW ’05), Mar. 2005. • [14] D. Henrici and P. M¨ uller, “Hash-Based Enhancement of Location Privacy for Radio-Frequency Identification Devices Using Varying Identifiers,” Proc. First IEEE Int’l Workshop Pervasive Computing • and Comm. Security (PerSec ’04), Mar. 2004. • [36] Ohkubo, M., Suzuki, K., and Kinoshita, "RFID privacy issues and technical challenges," Commun. ACM 48, 9 (Sep. 2005).

46. Secure RFID Protocols Lightweight Approaches • [23] A. Juels, “Strengthening EPC Tags Against Cloning,” Manuscript, RSA Laboratories, Mar. 2005. • [24] Y.C. Chen, W.L. Wang, and M.S. Hwang, “RFID Authentication Protocol for Anti-Counterfeiting and Privacy Protection,” Proc. 9th IEEE Int’l Conf. Advanced Comm. Technology (ICACT ’07), Feb. 2007. • [25] A. Juels, “Minimalist Cryptography for Low-Cost RFID Tags,” Proc. 4th Int’l Conf. on Security in Comm. Networks (SCN ’04), Sep. 2004. • [26] Y.Z. Li et al., “Security and Privacy on Authentication Protocol for Low-cost RFID,” Proc. Int’l Conf. Computational Intelligence and Security (CIS ’06), Nov. 2006. • [27] P. Peris-Lopez et al., “M2AP: A Minimalist Mutual-Authentication Protocol for Low-Cost RFID Tags,” Proc. 3rd Int’l Conf. Ubiquitous Intelligence and Computing (UIC-06), Sep. 2006. • [29] H.Y. Chien, “SASI: A New Ultralightweight RFID Authentication Protocol Providing Strong Authentication and Strong Integrity,” IEEE T. Dependable Secure Comput., vol. 4, no. 4, pp. 337–340, 2007. • [32] D.N. Duc et al., “Enhancing Security of EPCglobal Gen2 RFID Tag against Traceability and Cloning,” • Proc. 3rd Conf. Symp. Cryptography and Inf. Security (SCIS’06), Jan. 2006. • [35] A. Juels and S. Weis, “Authenticating Pervasive Devices with Human Protocols.” Crypto, Aug. 2005.

47. Security Analysis of RFID Protocols

48. So…How to design a secure protocol for low-end RFID Tag?

49. Hung-Min Sun and Wei-Chih Ting , “A Gen2-based RFID Authentication Protocol for Security and Privacy,” accepted by IEEE Transactions on Mobile Computing, Dec. 2008.

50. Gen2+ • Setup at manufacturer • After sold Write Tag keypool Write Tag keypool M M Tag keypool U End users or companies