Security and Privacy Threats

In this section, we describe some of the security and privacy threats related to the deployment of RFID technology.

3.1.4.1 Security Threats

RFID technology faces various security threats such as denial of service, relay attacks, and cloning.

• Denial of service: Such an attack can be performed by creating a signal in the same frequency band as legitimate readers, and causing therefore electromagnetic jamming that prevents legitimate tags from communicating with legitimate readers.

• Relay attacks: These attacks are implemented by placing an adversarial device be-tween a legitimate RFID tag and a legitimate reader. This device relays information exchanged between the two legitimate parties which are fooled into thinking that they are physically close to each other.

• Cloning: This attack can be executed by eavesdropping on tags’ communication with readers to retrieve the tags’ unique identifiers, then writing these identifiers into new rewritable and reprogrammable tags. Cloning attacks could be for instance used to re-place the content of tags attached to expensive objects with the content of tags attached to cheaper ones at a retail store.

To safeguard RFID systems against the above attacks, Karygiannis et al. (95) suggested some security countermeasures that can be taken. For example, cloning can be mitigated by

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3.1 RFID Fundamentals using challenge-response authentication protocols. However, the scarcity of computational resources in RFID tags makes the design of secure protocols withstanding attacks by powerful adversaries very challenging. Moreover, RFID distance bounding protocols (8, 27, 77, 99) have been proposed to protect against relay attacks. The idea behind distance bounding protocols is to estimate the physical distance separating readers and tags during tag-reader communication, detecting thus relay attacks.

Finally, jamming attacks can be tackled by increasing physical security near RFID readers through guards, fences, cameras, and shielding walls to block external electromagnetic signals to limit both accidental and malicious radio interferences (95).

3.1.4.2 Privacy Threats

As RFID tags respond to any reader without the consent of their owners or holders, the pro-liferation of RFID also brings up new exposures that can lead to potential privacy violations such as industrial espionage, consumer profiling and tracking of individuals.

• Industrial espionage: By eavesdropping on tagged objects traveling along the supply chain, a company can gather confidential and sensitive information about the internal business processes of an industrial competitor. Such information could be used to infer production and distribution schedules, daily rate of production, availability or shortage of stock, and the identity of suppliers and partners.

• Consumer profiling: A person carrying objects tagged with RFID is prone to surrep-titious inventorying. By reading tags attached to products that a person carries when entering a shop, the shop owner can learn what type of products interest that person, and he may then adjust his offers based on the information he just has gathered.

• Tracking: As most RFID tags transmit static unique identifiers, they can be used to track the position and trace the activity of individuals holding RFID tagged objects.

In the following, we list some of the proposed approaches to mitigate the privacy threats related to RFID technology.

• Tag deactivation: RFID tags can be deactivated by using a “KILL” command sent by readers. When a tag receives the KILL command from a reader, it becomes permanently out of service. Now, to prevent denial of service attacks through tags’ deactivation, the KILL command is protected with a secret PIN that only authorized readers know. Even though killing tags is a very effective measure to protect the privacy of individuals, this technique precludes the potential post-purchase applications of RFID technology.

• Proxying: This approach aims at protecting tag privacy by using privacy enforcing devices that act as RFID firewalls (94,136). These devices relay reader requests while implementing sophisticated privacy policies. A reader’s request is forwarded to a tag only when it meets the privacy policies specified by the tag holder.

3. RFID SECURITY AND PRIVACY

• Tag blocking: This approach protects tag privacy by relying on physical measures.

For instance, a Faraday cage can be used to protect tags from unauthorized reading by blocking external radio signals. It is also possible to prevent an unauthorized tag reading by using a blocker tag (93). A blocker tag exploits the properties of the anti-collision protocols that readers use to communicate with tags to disrupt tag singulation.

When a reader starts a tag singulation protocol, the blocker tag simulates all tags in the universe in order to cause continuous collisions, and to eventually stall the interrogating reader.

• Pseudonyms: Instead of having a unique permanent identifier, Inoue and Yasuura (82) proposed using tag pseudonyms that change over time to prevent tracking. A reader is required to periodically rewrite the pseudonym (identifier) of tags that it is reading while keeping a record of tags’ old pseudonyms.

• Re-encryption: While encrypting tags’ identifiers may protect identifier confidentiality, it cannot prevent the tracking of tags. When the identifier of a tag is encrypted, the tag sends the encryption of its identifier when queried, instead of sending its identifier in cleartext. However, this encryption can serve as a “new identifier” to trace and track the tag. To tackle this limitation, Ateniese et al. (3), Golle et al. (73), Juels and Pappu (90) suggest using re-encryption techniques. A tag in this approach stores an IND-CPA encryption (cf. Definition2.17) of its identifier. When a reader reads the encryption c stored into a given tag T, it re-encrypts the ciphertext c to obtain a new ciphertext c^′ and then it writes c^′ intoT. Consequently, an adversary cannot track tags over a long period of time.

• Privacy preserving authentication: This approach allows tags to authenticate them-selves to legitimate readers in a privacy preserving manner. That is, after tag authenti-cation, adversaries only learn whether the tag authentication was successful, while only legitimate readers can identify tags.

Most of previous work on RFID security and privacy has focused on

• Privacy preserving authentication protocols that suit the resource constraints of RFID tags. These protocols range from lightweight authentication protocols that rely on bitwise operations (18,66,91), to symmetric authentication protocols (48,50,58,122, 153), to finally public key authentication protocols (103,113,126).

• Formal security and privacy models that provide a comprehensive description of the adversary’s capabilities and goals (5,92,129,159).

We present the prominent formal RFID security and privacy definitions in Section3.2, then in Section3.3, we discuss in more details some of the state of the art of RFID authentication.

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