A hash chain H for a hash function hash(·) is a sequence of hash values ⟨ xn, xn-1,..., x0 ⟩, where x0 is a secret value, xi is generated by xi = hash(xi-1) for 1 ≤ i ≤ n, and xn is a public value. Hash values of H are disclosed gradually from xn-1 to x0. The correctness of a disclosed hash value xi can be verified by checking the equation xn =? hashn-i(xi). To speed up the verification, Fischlin introduced a check-bit scheme at CT-RSA 2004. The basic idea of the check-bit scheme is to output some extra information cb, called a check-bit vector, in addition to the public value xn, which allows each verifier to perform only a fraction of the original work according to his or her own security level. We revisit the Fischlin's check-bit scheme and show that the length of the check-bit vector cb can be reduced nearly by half. The reduced length of cb is close to the theoretic lower bound.

A distance bounding protocol provides an upper bound on the distance between communicating parties by measuring the round-trip time between challenges and responses. It is an effective countermeasure against mafia fraud attacks (a.k.a. relay attacks). The adversary success probability of previous distance bounding protocols without a final confirmation message such as digital signature or message authentication code is at least . We propose a unilateral distance bounding protocol without a final confirmation message, which reduces the adversary success probability to .

With the increased deployment of wireless sensor networks (WSNs) in location-based services, the need for accurate localization of sensor nodes is gaining importance. Sensor nodes in a WSN localize themselves with the help of anchors that know their own positions. Some anchors may be malicious and provide incorrect information to the sensor nodes. In this case, accurate localization of a sensor node may be severely affected. In this study, we propose a secure and lightweight localization method. In the proposed method, uncertainties in the estimated distance between the anchors and a sensor node are taken into account to improve localization accuracy. That is, we minimize the weighted summation of the residual squares. Simulation results show that our method is very effective for accurate localization of sensor nodes. The proposed method can accurately localize a sensor node in the presence of malicious anchors and it is computationally efficient.

Traditional authentication protocols are based on cryptographic techniques to achieve identity verification. Distance bounding protocols are an enhanced type of authentication protocol built upon both signal traversal time measurement and cryptographic techniques to accomplish distance verification as well as identity verification. A distance bounding protocol is usually designed to defend against the relay attack and the distance fraud attack. As there are applications to which the distance fraud attack is not a serious threat, we propose a streamlined distance bounding protocol that focuses on the relay attack. The proposed protocol is more efficient than previous protocols and has a low false acceptance rate under the relay attack.

As deployment of wireless ad hoc networks for location-based services increases, accurate localization of mobile nodes is becoming more important. Localization of a mobile node is achieved by estimating its distances from a group of anchor nodes. If some anchors are malicious and colluding, localization accuracy cannot be guaranteed. In this article, we present the security conditions for exact localization in the presence of colluding malicious anchors. We first derive the minimum number of truthful anchors that are required for exact localization in 2-D Euclidean space where some anchors may be collinear. Second, we extend our security condition to 3-D localization where some anchors may be coplanar.