The Outer Limits of RFID Security

All slides © 2006 RSA Laboratories

RFID (Radio-Frequency IDentication)

takes many forms…

“RFID” really denotes a spectrum of devices

Automobile ignition key Mobile phone

Toll paymentplaque

Basic“smart label”

passive passivesemi-passive

no crypto no crypto some crypto

few cm tofew meters

range

several metersrange

several cmrange

“Smart labels”:EPC (Electronic Product Code) tags

Barcode EPC tag

Line-of-sight Radio contact

Specifies object type Uniquely specifies object

Fast, automated scanning

Provides pointerto database entryfor every object, i.e., unique, detailed history

• 30 April: RFID-tagged cow “Bessie” produces milk• 30 April: Milk transferred to RFID-tagged tank

– Cow identity and milking time recorded in tank-tag database

• 1 May: RFID portal on truck records loading of refrigeration tanks– Truck also has active RFID (+GPS) to track geographical location and RFID transponder to pay tolls

• 2 May: Chemical-treatment record written to database record for milk barrel– Bessie’s herd recorded to have consumed mustard grass; compensatory sugars added to milk

• 3 May: Milk packaged in RFID-tagged carton; milk pedigree recorded in database associated with carton tag

• 4 May: RFID portal at supermarket loading dock records arrival of carton• 5 May: “Smart” shelf records arrival of carton in customer area• 5 May 0930h: “Smart” shelf records removal of milk• 5 May 0953h: Point-of-sale terminal records sale of milk (to Alice)

2030: Week in the life of a milk carton

• 6 May 0953h: Supermarket transfers carton tag ownership to Alice’s smart home

• 6 May 1103h: Alice’s refrigerator records arrival of milk• 6 May 1405h: Alice’s refrigerator records removal of milk; refrigerator looks up database-recorded pedigree and displays:

“Woodstock, Vermont, Grade A, light pasturization, artisanal, USDA organic, breed: Jersey, genetic design #81726”

• 6 May 1807h: Alice’s “smart” home warns domestic robot that milk has been left out of refrigerator for more than four hours• 6 May 1809h: Alice’s refrigerator records replacement of milk

• 7 May 0530h: Domestic robot uses RFID tag to locate milk in refrigerator; refills baby bottle

2030: Week in the life of a milk carton

• 6 May 0953h: Supermarket transfers carton tag ownership to Alice’s smart home

• 6 May 1103h: Alice’s refrigerator records arrival of milk• 6 May 1405h: Alice’s refrigerator records removal of milk; refrigerator looks up database-recorded pedigree and displays:

“Woodstock, Vermont, Grade A, light pasturization, artisanal, USDA organic, breed: Jersey, genetic design #81726”

• 6 May 1807h: Alice’s “smart” home warns domestic robot that milk has been left out of refrigerator for more than four hours• 6 May 1809h: Alice’s refrigerator records replacement of milk

• 7 May 0530h: Domestic robot uses RFID tag to locate milk in refrigerator; refills baby bottle

• 7 May 2357h: Recycling center scans RFID tag on carton; directs carton to paper-brick recycling substation

• 7 May 0531h: Robot discards carton; “Smart” refrigerator notes absence of milk; transfers order to Alice’s PDA/phone/portable server grocery list

2030: Week in the life of a milk carton

Proximity cards

RFID Today: IN Your POcket

Note: Often just emit static identifiers, i.e., they are just smart labels!

Automobile ignition keys

f

RFID helps secure hundreds of millions of automobiles•Cryptographic challenge-response•Philips claims more than 90% reduction in car theft thanks to RFID!•Note: some devices, e.g., Texas Instruments DST, are weak…

in your pocket

Payment devices

•ExxonMobil SpeedpassTM

in your pocket

•RFID now offered in all major credit cards in U.S.…

“Not Really Mad”• Cattle

• Housepets

The cat came back, the very next day…

50 million+

in ANIMALs

• Schools• Amusement parks• Hospitals• In the same vein: mobile phones with GPS…

on People

• Dozens of countries issuing or soon to issue RFID-enabled passports

• Other identity documents, e.g., drivers’ licenses, to follow

In PAssports

NFC (Near-Field Consortium)

Showtimes:16.00, 19.00

• Also, ticket purchases, payments, comparison shopping Phone can act as reader or tag

• NFC is a general-purpose protocol• Already available in some models

In Mobile phones

• Talk in 2003-4 of planting RFID tags in 10,000 Yen banknotes and Euro banknotes

• Talk has dissipated• Main interest: anti-counterfeiting

In Currency?

• Medical compliance: Greater independence (and privacy!), particularly for elderly

• Anti-counterfeiting: Better supply-chain visibility means less fraud– U.S. govt. urging RFID to combat counterfeiting of drugs

In pharmaceuticals

1500 Eurosin wallet

Serial numbers:597387,389473

…

Wigmodel #4456

(cheap polyester)

30 items of lingerie

Das Kapital and Communist-

party handbook

Replacement hipmedical part #459382

The consumer privacy problem

Here’sMr. Jonesin 2020…

Wig serial #A817TS8

…and the tracking problem

• Mr. Jones pays with a credit card; his RFID tags now linked to his identity; determines level of customer service– Think of car dealerships using drivers’ licenses to run credit checks…

• Mr. Jones attends a political rally; law enforcement scans his RFID tags

• Mr. Jones wins Turing Award; physically tracked by paparazzi via RFID

Suica

Image courtesy of Kevin Fu

Suica

Images courtesy of Kevin Fu

What data are vulnerable?

CURRENT BALANCE

Travel history: visited stations and dates

Details ofmerchandisepurchase

Image courtesy of Kevin Fu

RFID privacy

Only definitive way to achieve privacy is:– Emit an identifier only – Change identifier across reads

Wig serial #A817TS8u

RFID privacy

Only definitive way to achieve privacy is:– Emit only an identifier– Change identifier across reads

#A817TS8u

RFID privacy

Only definitive way to achieve privacy is:– Emit only an identifier– Change identifier across reads

#Z87d68aK

1500 Eurosin wallet

Serial numbers:597387,389473

…

Replacement hipmedical part #459382

The authentication problem

Mad-cowhamburgerlunch Counterfeit!

Counterfeit!

Good readers, bad tags

Mr. Jones’s car is stolen!

Mr. Jones in 2020

Won’t crypto solve our problems?We can do:• Challenge-response for

authentication• Mutual authentication

and/or encryption for privacy

AES

Side-channel countermeasures

But:

1. Moore’s Law vs. pricing pressure

2. Beyond simple “terrestrial” problems, basic cryptography may not be enough…

This is the theme of our talk!

Simple authentication:Possession is the law

• How does Alice’s refrigerator get read/write privileges for the history for the milk carton bearing tag T?

• The straightforward approach:– A central registry R shares symmetric key k with the tag T– Alice’s refrigerator acts as authentication proxy between R and T– Tag T authenticates via challenge-response

c

r = fk(c) k

Registry R

k

c

r = fk(c)

Simple authentication:Possession is the law

• But what if the tag is on Alice’s wristwatch? – Should any nearby reader be able to read tag

history?– Should any nearby reader be able to modify

tag history?

• What if registry R is unavailable? – Will the tag carry information on board? – If so, who can access it? – Does Alice’s baby get its milk?

???

The VeriChipTM

+ =Human-implantable RFID

The VeriChipTM

+ =Human-implantable RFID

• Proposed for medical-patient identification• Also proposed and used as an authenticator for

physical access control, a “prosthetic biometric”– E.g., Mexican attorney general purportedly used for

access to secure facility

• What kind of cryptography does it have?– None: It can be easily cloned

• So shouldn’t we add a challenge-response protocol?

• Cloning may actually be a good thing

The VeriChipTM

• Physical coercion and attack– In 2005, a man in Malaysia had his fingertip cut off by

thieves stealing his biometric-enabled Mercedes– What would happen if the VeriChip were used to

access ATM machines and secure facilities?• Perhaps it is better then if tags can be cloned

and are not used for authentication—only for identification

• But if a tag is cloneable, and used for identification, does that mean that privacy is impossible? – I.e., does cloneability imply an ability to track?

Private identification• A very simple scheme allows for

simultaneous cloneability and privacy

• El Gamal public-key cryptosystem:– Randomized scheme: C = EPK,r [m]

– Semantic security: Cannot distinguish between ciphertexts C and C’ on known plaintexts without knowledge of SK

• Adversary cannot distinguish between C = EPK,r [Alice] and C’ = EPK,r’ [Bob]

Private identificationOur simple scheme:

“Who are you?”

C = EPK,r [Alice]

SK

“Proceed to authenticateOfficer Alice”

Officer Alice

Private identificationTake two:

“Who are you?”

C’ = EPK,r’ [Alice]

SKOfficer Alice

“Proceed to authenticateOfficer Alice”

Private identification

• Semantic security → An attacker who intercepts C and C’ cannot tell if they come from the same chip– Attacker cannot identify or track Alice

• But attacker can still clone Alice’s chip!• El Gamal re-encryption (homomorphism):

– Let U = EPK,r [1] have uniformly random r

– Then given C = EPK,r’ [m], the distribution CxU is uniform over ciphertexts on m

• Clone chip selects U and outputs CxU • Clone chip is indistinguishable from Alice’s!

Attacker’s perspective

“Who are you?”

C

Alice’schip

Attacker’s perspective

“Who are you?”

C x U

“Proceed to authenticateOfficer Alice”

Attacker can simulate Alice’s chip, but…•He cannot track Alice•He may not even know whose chip he’s cloned!

The covert-channel problemSuppose there is a secret sensor…

“Who are you?”

C

SKOfficer Alice

“Officer Alicehas low bloodpressure andhigh blood-alcohol”

The covert-channel problemSuppose there is a secret sensor…

“Who are you?”

C

SKOfficer Alice

“Officer Alicerecently passed near the RFID reader of a casino”

The covert-channel problemSuppose there is a secret sensor…

“Who are you?”

C

SKOfficer Alice

“Mercury switchindicates that OfficerAlice took a nap this afternoon.”

How can we ensure no covert channels?

• Must make outputs deterministic

• Can also, e.g., give PRNG keys to Alice

• But can we:– Allow Alice to verify covert-freeness without

exposing secret keys to her?– Enable a third party to verify covert-freeness?

• It turns out that privacy and such verifiable covert-freeness are contradictory!

Covert-freeness detector

A

A’

“No covertchannel”

“Yes, covertchannelsuspected”

Here’s a covert channel!

1. Create identifier for Bob• Bob need not actually own a chip

2. Alice’s chip does following:• If no nap, output ciphertexts A, A’, A’’,

etc. with Alice’s identity• If Alice has taken a nap, output

ciphertexts B,B’,B’’, etc. with Bob’s identity

Suppose we detect the covert channel…

“No covertchannel”

A

A’

Suppose we detect the covert channel…

“Yes, covertchannel

suspected”

A

B

Then we can distinguish between Alice and Bob: Privacy is broken!

“Yes, covertchannel

suspected”

A

B

Then we can distinguish between Alice and Bob: Privacy is broken!

“A and B represent different

people”

A

B

• Let’s change (relax) the definition of privacy!• If non-sequential tag outputs are checked, detector learns nothing…

READ EVENTS

“?????”

Covert-freeness and privacy?

Covert-freeness and privacy?• Detector can do pairwise check only…

READ EVENTS

“Covert-free pair”

• Achievable “efficiently” with pairings-based cryptography (ECC)

Covert-freeness and privacy?• Privacy is largely preserved because of locality• Covert-freeness checkable probabilistically, i.e., with spot checks

READ EVENTS

“Covert-free pair”

Returning to basic issue of privacy:Kill codes

• EPC tags have a “kill” function• On receiving password, tag self-destructs• Tag is permanently inoperative

• Developed for EPC to protect consumers after point of sale

• “Dead tags tell no tales”• Privacy is preserved

• Simple and categorical, but not a wholly satisfying solution…

Problem 1: Post-consumer uses of tags

k

Dead tags perhaps not harmful, but certainly not beneficial…

Problem 2: RF signatures• Y. Oren and A. Shamir attacked EPC kill passwords via over-the-

air power analysis• Found that dead tags are detectable!

– Backscatter from antennas• Hypothesize manufacturer type may be learnable

•3 type A tags (merchandise)•2 type B tags (medication)•10 type C tags (500-Euro banknotes)

• Probably of limited significance, but still bears on privacy• Do tags possess uniquely detectable RF fingerprints?

– Device signatures a staple of electronic warfare

• Cryptography would not help here!

So what might solve our problems?

• The fact that privacy is not RFID specific

• Laws and policy

• RFID security as a database problem– Reduces problem to access control, but:– Accept tracking of identifiers– Create further dependence on network

connectivity

So what might solve our problems?

• Higher-powered intermediaries like mobile phones– RFID “Guardian” and RFID REP

Please show reader certificate and privileges

So what might solve our problems?

• Cryptography!– Urgent need for cheaper hardware for primitives and better side-

channel defenses

• Some of talk really in outer limits, but basic caveats are important:– Pressure to build a smaller, cheaper tags without cryptography– RFID tags are close and personal, giving privacy a special

dimension– RFID tags change ownership frequently– Key management will be a major problem

• Think for a moment after this talk about distribution of kill passwords…

• Are there good hardware approaches to key distribution, e.g., proximity as measure of trust

To learn more

• Largely collaborative work within RFID CUSP– www.rfid-cusp.org– Papers available on publications page

• Papers:– “RFID security and privacy: a research survey”– “The security implications of VeriChipTM

cloning,” • Joint work with J. Halamka, A. Stubblefield, and J. Westhues

– “Covert channels in privacy-preserving identification systems”• Forthcoming joint work with Dan Bailey

– “Power analysis of RFID tags” (on Internet; not RFID-CUSP)• Y. Oren and A. Shamir