The Blocker Tag: Selective Blocking of RFID Tags for

Consumer PrivacyA. Juels, R. L. Rivest, and M. Szydlo

8th ACM Conference on Computer and Communications Security,

pp. 103-111. ACM Press. 2003.

Presented by: Sean Mondesire

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Contributionso Blocker Tags:

oProtects consumer privacyoRelatively inexpensiveoProves the RFID Bill of

Rights and practical tags can coexist

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Agendao RFID Tagso Security Issueso Previous Worko Blocker Tags

• Privacy Protection• Malicious Blocker Tags

o Critique

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RFID Tagso Simple Radio-

Frequency Identification Tags• Passive: Battery-less• Contain an assigned

serial number• Can be modified

o Replacement for the barcode• Cost about 5 cents• No more laser scanning• Consumers can use the

benefits

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Security Issueso Eavesdroppers

• Gather what items are in your possession

• Privacy Violation Exampleso Dress sizeo Medicationo Amount of money in wallets

o Petty Thieves• Modify serial numbers in

store• Deactivate tags before

purchase

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Previous Worko “Kill Tag” o Faraday Cage o Active Jammingo “Smart” RFID Tags

• Hash-Locks• Re-encryption

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Tree-Walking Singulationo Singulation

• Reader processes one tag at a timeo Tree-Walking Singulation Algorithm

• Recursively signal tags with next prefix• Tag with prefix respond with next prefix

0 1

00 01 10 11

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Blocker Tagso Goal:

o Protect the privacy of consumers affordably

o Motivation:o Guaranteed privacy will push

the use of RFID tagso How They Work

o Universal Blocker: For every signal send 0 and 1

o Selective Blocker: Block a subset of tags

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Privacy Protection Toolo Selective Blocker:

• Forces readers to signal nonexistent and existent tags

• Readers cannot guarantee tags are in the vicinity

• Hides tags with false signalso Supermarket Example:

• Shelved items start with 0• Purchased items tags set to 1• Sticker of a blocker tag placed

on item’s tag (blocks 1’s)

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Malicious Blocker Tagso Blocker tags that do not

respect the privacy zones• Blocker signaling 0’s in previous

exampleo Universal blockers are

maliciouso DOS attacks on readers

• Universal blockers: Readers signal all possible serial numbers

• Selective blockers: Simulate actual tags that should not be scanned at that time

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Strengthso Inexpensive

• RFID to reply to signals• Less than 10 cents to

manufactureo Satisfies the RFID Bill of

Rightso Simple to implement

• Create tag that returns 0 or 1 when ever signaled

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Weaknesseso Can force DOS on reader

• Encourages nonsense broadcastso Requires additional RFID tags

• Forces consumers to have blocker tags to guarantee privacy

o Many unanswered questions:• What if malicious blocker tags

were left throughout a store?• Thieves can swap tags easier

than barcodes

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Areas of Improvemento Improve inefficiencies

placed on the Reader• Universal Blocker impractical• Limit blocking capabilities

o Incorporate blockers within each tag• Cost for addition registers

should be comparable to having separate blockers

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Related Worko RSA Laboratories

• Inventors of RSA public-key cryptosystem

• Focus on RFID privacy and security

o Soft Blockingo Encryption in RFID

o RFID chips can carry a virus• Amsterdam’s Free University• RFIDs can return data to

infect a reader’s DB• Can spread to other tags

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Contributionso Protects consumer privacy

• Readers can’t pinpoint existing tags

o Relatively inexpensive• About 5 cents for one antennae• At most 10 cents per blocker

o Proves the RFID Bill of Rights and practical tags can coexist• No sacrifices on consumer rights

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Referenceso Juels, A., Rivest, R. L., and M. Szydlo, “The

Blocker Tag: Selective Blocking of RFID Tags for Consumer Privacy,” 8th ACM Conference on Computer and Communications Security, pp. 103-111. ACM Press. 2003.

o Reuters, “Scientists: RFID Chips Can Carry a Virus”, http://www.cnn.com/2006/TECH/ptech/03/15/rfid.virus.reut/index.html, CNN.com, March 15, 2006

o RSA Laboratories, http://www.rsasecurity.com/, March 28, 2006.