RFID Privacy Models & A Minimal Condition Robert H. Deng Singapore Management University 2018/11/21

Radio Frequency IDentification (RFID) Radio signal (contactless) Range: from 3-5 inches to 3 yards Database Match tag IDs to physical objects Tags (transponders) Attached to objects, “call out” identifying data on a special radio frequency Reader (transceivers) Read data off tags without direct contact Range can be 100 meters Perfect working conditions for attackers! 2018/11/21

RFID Applications Most important usage: identifying valid users or entities eTicket Credit Cards Access Control Cheap Expensive Supply Chain ePass High computational and storage resources No computational and very low storage resources 2018/11/21

RFID Security Issues Tag Authentication: Only valid tags are accepted by a valid reader Reader Authentication: Only valid readers are accepted by valid tags Not always required but mandatory in some applications (e.g., e-tickets) Prevents unauthorized access to /or tampering with tag data Availability: Infeasible to manipulate honest tags such that honest readers do not accept them 2018/11/21

RFID Privacy Issues Unauthorized tracking © RSA Laboratories Unauthorized tracking Disclosure of the tag identity Linkability of the transactions of a tag  Allows creation & misuse of user profiles 2018/11/21

Physical Privacy-Enhancing Methods (from Sadeghi et. al MINES2009) “Kill”-command [EPC05] Tag-specific password programmed at manufacturing that permanently deactivates the tag to prevent readout Used for electronic product labels (e.g., EPC-Tags) that are disabled when the labeled product is given to end user Passive jamming [DIFR09] Faraday cage (e.g., embedded into wallets) prevents readout of RFID tag User must manually authorize readout by removing Faraday cage Active jamming [LCTR06] Jamming device disturbs radio signals of tags and readers in the vicinity User must manually authorize readout by deactivating jammer  Inefficient: Tags permanently disabled or user interaction required [EPC05] EPCglobal Inc.: Specification for RFID air interface—EPC radio-frequency protocols, Class-1 Generation-2 UHF RFID, protocol for communications at 860 MHz–960 MHz, version 1.1.0 (December 2005) [DIFR09] DIFRwear: Web site of difrwear. http://www.difrwear.com/products.shtml (January 2009) [LCTR06] Peris-Lopez, P., Hernandez-Castro, J.C., Estevez-Tapiador, J.M., Ribagorda, A.: RFID systems: A survey on security threats and proposed solutions. In Cuenca, P., Orozco-Barbosa, L., eds.: IFIP TC6 11th International Conference, PWC 2006, Albacete, Spain, September 20–22, 2006, Proceedings. Volume 4217 of LNCS., Springer Verlag (2006) 159–170 New Directions in RFID Security and Privacy 6 2018/11/21 6

Cryptographic Protocols for RFID Privacy Numerous lightweight RFID protocols for low-cost tags have been proposed They use simple operations (XOR, bit inner product, CRC, etc) Many have been broken (T. van Deursen and S. Radomirovic: Attacks on RFID Protocols, ePrint Archive: Report 2008/310) 2018/11/21

Outline Existing RFID Privacy Models A New Model A Minimal Condition Conclusion 2018/11/21

RFID System Model T = {T1,…,Tn} - a fixed, polynomial-size tag set Read / Update T = {T1,…,Tn} - a fixed, polynomial-size tag set R/D - and a reader/database as the elements for an RFID system. The adversary A has complete control over communications between R and T, while the communications between R and D are over a secure channel. 2018/11/21

A Canonical RFID Protocol  Tag T Reader R c  C r  R f  F (optional) Shorthand notation: (c, r, f) ← (R, T) 2018/11/21

Query Types Available to Adversary Launch(): return a session id sid and the 1st message c. SendTag(sid, c, T): return r, the response of tag T. SendReader(sid, r): return f, the response of Reader. Corrupt(T): return the secret information of tag T. Let O1, O2, O3, O4 denote, Launch, SendTag, SendReader, Corrupt oracles, respectively. 2018/11/21

JW06 (Jules & Weis, ePrint 2006, PerCom 2007) Ind-privacy: indistinguishability of two tags. Experiment: {Ti, Tj} ← A1O1,O2,O3,O4(R, T); b∈{0, 1}; If b = 0 then Tc = Ti, else Tc= Tj; T’ = T - {Ti, Tj}; b’ ←A2O1,O2,O3,O4(R, T’, Tc). A1 not allowed to query O4 on Ti and Tj A2 not allowed to query O4 on Tc Adversary A wins the game if b’ = b The advantage of adversary A = |Pr[b'=b]-1/2| Drawback: Not easy to work with 2018/11/21

HMZH08 (Ha, Moon, Zhou & Ha, ESORICS 2008) Unp-privacy: unpredictability of protocol Experiment: Tc← A1O1,O2,O3,O4(R, T); b∈ {0, 1}; If b = 0 then (c, r, f) ← (R, Tc), else (c, r, f) ← random; b’ ← A2 (c, r, f). A1 not allowed to query O4 on Tc The advantage of adversary A = |Pr[b'=b]-1/2| Drawback – Incomplete: A2 is not allowed to query O2 (SendTag) oracle on Tc   protocols meeting Unp-privacy but with known weakness in privacy (Deursen & Radomirovic, ePrint Archive: Report 2008/477) 2018/11/21

MLDL09 (Ma, Li, Deng & Li, CCS 2009) Unp’-privacy: unpredictability of protocol Experiment: {Tc, c}← A1O1,O2,O3,O4(R, T); b∈ {0, 1}; If b = 0 then (c, r, f) ← (R, Tc), else (c, r, f) ← random; T’ = T – {Tc} b’ ← A2O1,O2,O3,O4(R, T’, r, f). A1 not allowed to query O4 on Tc The advantage of adversary A = |Pr[b'=b]-1/2| Drawback: (c,r,f)←(R, Tc)??? A2 is not allowed to query O2 (SendTag) oracle on Tc 2018/11/21

Vau07, PV08 (Vaudenay AsiaCrypt07, Paise & Vaudenay AsiaCCS08) Adversary’s capabilities modeled by oracles Adversary A Tag Initialization Tag Communication Tag Corruption Reader Initialization Reader Communication Side channel Information (whether authentication was successful) 2018/11/21

Vau07 (Vaudenay AsiaCrypt07) b R {0,1} Adversary A1 Querying Phase Privacy Challenger Reader Initialization /Tag Initialization / Tag Corruption Blinder B simulates Tag Communication / Reader Communication / Side channel Information b = 1 Tag Communication / Reader Communication / Side channel Information b = 0 Adversary A2 Analysis Phase A wins privacy experiment if b’=b RFID system is private if every A has negligible advantage to detect blinder B: AdvA = |Pr[ b’=1 | b=0 ] - Pr[ b’=1 | b=1 ]| b’ 2018/11/21

PV Model (Paise & Vaudenay AsiaCCS08) Privacy and Security Framework for RFID Based on model of [Vau07] Additionally captures reader authentication Problem Privacy definition contradicts reader authentication for any privacy notion that allows tag corruption (except the weak privacy notions which do not alllow tag corruption)  PV model cannot be used for evaluation of practical protocols where adversary can corrupt tags 2018/11/21

Outline Existing RFID Privacy Models A New Model A Minimal Condition Conclusion 2018/11/21

New Model – Definition Experiment: Unp’’-privacy: indistinguishability of a real tag and a virtual tag Experiment: Tc ← A1O1,O2,O3,O4(R, T); b∈ {0, 1}; When A2 makes queries to O1, O2, O3 on Tc If b = 0, return oracles’ responses Else (b = 1) return c R C if query O1 return r R R if query O2 Return f R F if query O3 b’ ← A3 A1 and A2 are not allowed to query O4 on Tc The advantage of adversary A = |Pr[b'=b]-1/2| 2018/11/21

Summary of the Privacy Models Ind-privacy model No flaws being found but not easy to work with Unp-privacy and Unp’-privacy models Incomplete PV model Contraction between reader authentication and their notions of privacy that allow tag corruption Unp”-privacy model Does not suffer from the above problems Relationship between Ind-privacy and Unp”-model? 2018/11/21

Relation Between Ind-privacy & Unp”-privacy Assume that (c, r, f) (R, T) is of Ind-privacy. Let (c, r|r, f)  ’(R,T). ’(R,T) is of Ind-privacy, but it is not of Unp”-privacy. 2018/11/21

New Model –Relations (2) Ind-privacy  Unp”-privacy. Ind-privacy Adversary A Unp”-privacy adversary B Unp”-privacy protocol 2018/11/21

Outline Existing RFID Privacy Models A New Model A Minimal Condition Conclusion 2018/11/21

Minimal Condition – Results Minimal requirement for RFID systems to achieve RFID system privacy Unp”-privacy PRF Theoretical foundation to explain why so many lightweight RFID protocols suffer from privacy vulnerabilities without implementing necessary cryptographic primitives 2018/11/21

Minimal Condition – Unp”-privacy ⇒ PRF Given a RFID system with Unp”-privacy, each tag’s computation function Fki,sti can be used to construct a PRF family, ki is tag’s secret key, and sti is tag’s internal state. Reader Tag c r f 2018/11/21

Minimal Condition – PRF ⇒ Unp”-privacy An efficient construction using PRF Reader {(I, k, ctr, ID)} Tag (k, ctr) c I = Fk(ctr|pad1) r1 = Fk(c|I)(ctr|pad2) ctr = ctr + 1 I | r1 Search: {If find (I, k, ctr, ID) then If ctr|pad2 = r1Fk(c|I) then Update & accept; Else reject Else if  (*, k, *, *) s. t. ctr|pad2 = r1Fk(c|I) & I = Fk(ctr|pad1) then Update & accept; Else reject } Update: {ctr = ctr + 1 & I = Fk(ctr|pad1) } 2018/11/21

Outline Existing RFID Privacy Models A New Model Relations Between Two Models & A Minimal Condition Conclusion 2018/11/21

Conclusion Existing privacy models Ind-privacy, unp-privacy, unp’-privacy, Vau07 & PV08 A new model: Unp”-privacy Relations Unp”-privacy Ind-privacy PRF 2018/11/21

Acknowledgement Junzuo LAI1, 2 Tieyan LI3 Yingjiu LI1 Changshe MA1 Singapore Management University Shanghai Jiaotong University Institute for Infocomm Research, Singapore 2018/11/21

Thank You! 2018/11/21