Address Privacy of Bluetooth Low Energy
1.1. Previous Work on Bluetooth Privacy
- Privacy of advertisement and device address. Some literature [13,14] focused on implementing the addresses privacy mechanisms for the LE devices. Some literature [15,16,17,18,19,20] showed that the advertising procedure possibly leaks the identity information of the LE devices and therefore enhances the privacy of the advertising procedure. Ludant et al.  reported that LE advertisements could link to Bluetooth classic frames and the device’s globally unique identifier (i.e., BDADDR) due to the bad design of Bluetooth chips. They also developed several mitigations for the Bluetooth stack. Very recently, regarding Bluetooth LE, Zhang and Lin  showed that the address randomization scheme using the message authentication code (MAC) is vulnerable to replay attacks and further suggested timestamps-based randomized MAC addresses.
- Privacy of secure connection. Secure connection is the basis for LE devices to achieve authentication, integrity, confidentiality and other security services. The task of secure connection is to establish the link key between devices. In , we demonstrated the privacy vulnerability of the secure connection due to the reuse of the Diffie–Hellman key, and enhanced the privacy of the secure connection. Zhang et al.  showed downgrade attacks on secure connections only (SCO) and built a prototype for the SCO mode on Android 8 atop Android open-source project (AOSP). Tschirschnitz et al.  described a design flaw in the pairing mechanism of Bluetooth called method confusion and proposed changes to the Bluetooth specification that immunize it against method confusion.
1.2. Bluetooth Address and Its Privacy
1.3. Our Contributions
- Although both attacks exploit replaying the sniffed RPA values to probe whether a device will respond or not, Zhang and Lin’s attack focuses on the linkage relations among the obsolete RPA values, tracking the targeted device using a real-time tunnel, and tracking the absent device. Our attack aims to recognize the targeted device that currently runs the RPA mechanism.
- Zhang and Lin proposed a timestamp-based RPA mechanism and discussed possibility of the synchronized sequence number-based RPA mechanism and storage-based RPA mechanism. Our improvement only employs the counter to prevent the existing attacks. Note that the counter is not a sequence number because it does not require strict synchronization. We argue that the trust timestamp is not easily available in the IoT environments.
- We propose a formal model to evaluate the privacy of the RPA mechanisms and further prove that our improvement is private under the proposed privacy model. However, Zhang and Lin’s work does not evaluate their timestamp-based RPA mechanism using the provable security approach. In fact, it is impossible due to the timestamp.
2. RPA Mechanism
2.1. Flow of RPA Mechanism
2.1.1. Initial Connection Procedure
2.1.2. Reconnection Procedure
2.2. Generation and Resolution of RPA
3. Privacy Weakness in RPA Mechanism
4. Improved RPA Mechanism
4.1. Improved Initial Connection Procedure
4.2. Improved Reconnection Procedure
4.3. Processing RPA/Local RPA Counter/Peer RPA Counter
4.4. Perforamce Evaluation of Our Improvement
5. Privacy Evaluation of Improved RPA Mechanism
5.1. Model Definition
- sid: the unique identifier of Πi, j;
- IRKi and IRKj: i’s local IRK and i’s peer IRK with j;
- IAj: j’s IA;
- LCi and PCi: i’s local RPA counter and i’s peer RPA counter with j;
- tran: a transcript of i’s current run of Πi, j so far, i.e., the ordered set of packets transmitted and received by i so far;
- δ: a Boolean variable set to true or false denoting whether accepts or rejects at the end of the run of Πi, j.
|Pr[Pri-ExpΠ, E(k) = 1|b = 0]Pr[b = 0] + Pr[Pri-ExpΠ, E(k) = 1|b = 1]Pr[b = 1] −
Pr[Pri-ExpΠ, E(k) = 0|b = 0]Pr[b = 0] − Pr[Pri-ExpΠ, E(k) = 0|b = 1]Pr[b = 1]| ≤
|1/2 + (1 − ν)/2 − 0/2 − ν/2| = 1 − v.
5.2. Privacy Result of Improved RPA Mechanism and Its Proof
|Pr[D(1k, F(k, )) = 1] − Pr[D(1k, R()) = 1]| ≤ ε(k).
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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Sun, D.; Tian, Y. Address Privacy of Bluetooth Low Energy. Mathematics 2022, 10, 4346. https://doi.org/10.3390/math10224346
Sun D, Tian Y. Address Privacy of Bluetooth Low Energy. Mathematics. 2022; 10(22):4346. https://doi.org/10.3390/math10224346Chicago/Turabian Style
Sun, Dazhi, and Yangguang Tian. 2022. "Address Privacy of Bluetooth Low Energy" Mathematics 10, no. 22: 4346. https://doi.org/10.3390/math10224346