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In this correspondence, we propose a new model for threshold schemes with disenrollment capability (TSDC), to address the scenarios in which the ability of a coalition to construct future shared secrets is prohibited. Compared to existing TSDC models, our model provides forward secrecy by adding a constraint that the broadcast from the dealer is required to activate the reconstruction of any secret. We also present a TSDC model in which the dealer has the enhanced capability of disenrolling any subset of participants, to prevent the otherwise unnecessary rekey of the entire group when a large number of participants are compromised. We establish the lower bounds on the entropy of broadcast messages in both proposed models, as guidelines on constructing broadcast efficient schemes, and present bound achieving schemes. [ABSTRACT FROM AUTHOR]

In this paper, we explore a new direction towards solving the identity authentication problem in RFID systems. We break the RFID authentication process into two main problems: message authentication and random number generation. For parties equipped with a good source of randomness and a secure cryptographic primitive to authenticate messages, the literature of cryptography is rich with well-studied solutions for secure identity authentication. However, the two operations, random number generation and message authentication, can be expensive for low-cost RFID tags. In this paper, we lay down the foundations of a new direction towards solving these problems in RFID systems. We propose an unconditionally secure direction for authenticating RFID systems. We use the fact that RFID readers are computationally powerful devices to design a protocol that allows RFID readers to deliver random numbers to RFID tags in an unconditionally secure manner. Then, by taking advantage of the information-theoretic security of the transmitted messages, we develop a novel unconditionally secure message authentication code that is computed with a single multiplication operation. The goal of this work is to bring more research to the design of such unconditionally secure protocols, as opposed to the computationally secure protocols that have been proposed extensively, for the purpose of suiting the stringent computational capabilities of low-cost devices. [ABSTRACT FROM AUTHOR]

Message authentication codes (MACs) based on universal hash-function families are becoming increasingly popular due to their fast implementation. In this paper, we investigate a family of universal hash functions that has been appeared repeatedly in the literature and provide a detailed algebraic analysis for the security of authentication codes based on this universal hash family. In particular, the universal hash family under analysis, as appeared in the literature, uses operation in the finite field ℤℤ p. No previous work has studied the extension of such universal hash family when computations are performed modulo a non-prime integer n. In this work, we provide the first such analysis. We investigate the security of authentication when computations are performed over arbitrary finite integer rings ℤℤ n and derive an explicit relation between the prime factorization of n and the bound on the probability of successful forgery. More specifically, we show that the probability of successful forgery against authentication codes based on such a universal hash-function family is bounded by the reciprocal of the smallest prime factor of the modulus n. [ABSTRACT FROM AUTHOR]