Improving Security and Privacy in Large-Scale RFID Systems

Radio Frequency Identification (RFID) technologies lay in the very heart of Internet of Things (IoT), in which every physical objects are tagged and identified in an internet-like structure. High performance and privacy-preserving interrogations of individual tags, generally called private tag authentication, is crucial for effective monitoring and management of a large number of objects with RFID tags. An RFID system consists of RF readers and RF tags. RF tags are attached to objects, and used as a unique identifier of the objects. RFID technologies enable a number of business and personal applications, and smooth the way for physical transactions in the real world, such as supply chain management, transportation payment, animal identification, warehouse operations, and more. Though bringing great productivity gains, RFID systems may cause new security and privacy threats to individuals or organizations, which have become a major obstacle for their wide adaptions. Therefore, it is important to address the security and privacy issues in RFID systems. In this dissertation, we investigate two important security and privacy issues for large-scale RFID systems. First, we discuss the private tag authentication problems. In a singulation process, an RF reader first sends a query and energizes an RF tag, and then the tag replies its ID or data to the reader. As the tag\u27s ID itself is sensitive information, the reply from tags must be protected against various threats, such as eavesdropping and compromise attacks, where tags are physically tampered and the keys associated with compromised tags are disclosed to adversaries. Fast and secure object identification, generally called private tag authentication, is critical to efficiently monitor and manage a large number of objects with Radio Frequency Identification (RFID) technologies. In a singulation process, an RF reader queries an RF tag, and then the tag replies its ID or data to the reader. Since the tags ID itself is private information, the reply must be protected against various threats, such as eavesdropping and com-promised attacks, where tags are physically tampered and the keys associated with compromised tags are disclosed to adversaries. Hence a large amount of efforts have been made to protect tags replies with low-cost operations, e.g., the XOR operation and 16-bit pseudo random functions (PRFs). In the primitive solution, a tag sends a hashed ID, instead of its real ID, to a reader, and then, the reader searches the corresponding entry in the back-end server. While this approach defends tags replies against various attacks, the authentication speed is of 0(N), where N is the number of tags in the system. Hence, such a straightforward approach is not practical for large-scale RFID systems. In order to efficiently and securely read tags content, private authentication protocols with structured key management have been proposed. In these schemes, each tag has its unique key and a set of groups keys. Groups keys are shared by several tags and used to confine the search space of a unique key. With efficient data structures, the tag authentication completes within 0(log k N). How-ever, private authentication protocols with structured key management unfortunately reduce the degree of privacy, should some tags in the system be compromised. This is because group keys are shared by several tags, and physical tampering of some tags makes the other tags less anonymous. How to remedy this issue is equivalent to reducing the probability that two tags share common group keys (hence after we refer to it as the correlation probability). The introduction of random walking over a data structure, e.g., randomized tree-walking and randomized skip-lists, significantly reduces the correlation probability. Nevertheless, two tags are still correlated should they have same groups keys at all the levels of in a balanced tree or skip lists. In our study, we design a private tag authentication protocol, namely Randomized Skip Graphs-Based Authentication (RSGA), in which unique and group keys are maintained with a skip graph. The RSGA achieves lower correlation probability than the existing scheme while maintaining the same authentication speed as the tree structure. Second, we discuss the fast and secure grouping problems. In the large-scale RFID systems, categorization and grouping of individual items with RF tags are critical for efficient object monitoring and management. For example, when tags belonging to the same group share a common group ID, the reader can transmit the same data simultaneously to the group ID, and it is possible to save considerably the communication overhead as compared with the conventional unicast transmission. To this end, Liu et al. recently propose a set of tag grouping protocols, which enables multicast-like communications for simultaneous data access and distribution to the tags in the same group. In the reality, not only the performance issue, but also security and privacy-preserving mechanisms in RFID protocols are important for protecting the assets of individuals and organizations. Although a number of works have been done for protecting tag\u27s privacy, to the best of our knowledge, the problem of private tag grouping is yet to be addressed. To address the problem of private tag grouping in a large-scale RFID system, we first formulate the problem of private tag grouping and define the privacy model based on the random oracle model. As a baseline protocol, we design a private traditional polling grouping (PrivTPG) protocol based on traditional tag polling protocol. Since PrivTPG is a straightforward approach, it can take a long time. Hence, based on the idea of broadcasting group IDs, we propose a private enhanced polling grouping (PrivEPG) protocol. To further improve the efficiency of tag grouping, we propose a private Bloom filter-based grouping (PrivBFG) protocol. These protocols broadcast unencrypted group IDs. Therefore, we propose a private Cuckoo filter-based polling grouping (PrivCFG) protocol, which is a more secure protocol using a data structure called a cuckoo filter. Then, the protocol-level tag\u27s privacy of the proposed PrivTPG, PrivEPG, PrivBFG, and PrivCFG is proven by random oracles. In addition, computer simulations are conducted to evaluate the efficiency of the proposed protocols with different configurations.首都大学東京, 2018-03-25, 修士（工学）首都大学東