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Smart grid allows fine-grained smart metering data collection which can improve the efficiency and reliability of the grid. Unfortunately, this vast collection of data also impose risks to users' privacy. In this paper, we propose a novel protocol that allows suppliers and grid operators to collect users' aggregate metering data in a secure and privacy-preserving manner. We use secure multiparty computation to ensure privacy protection. In addition, we propose three different data aggregation algorithms that offer different balances between privacy-protection and performance. Our protocol is designed for a realistic scenario in which the data need to be sent to different parties, such as grid operators and suppliers. Furthermore, it facilitates an accurate calculation of transmission, distribution and grid balancing fees in a privacy-preserving manner. We also present a security analysis and a performance evaluation of our protocol based on existing multiparty computation algorithms.

Abstract-This paper proposes a local electricity trading market and provides a comprehensive security analysis of this market. It first presents a market for electricity trading among individual users, and describes the different entities and the interactions among them. Based on this market model and the interactions, the paper analyses security problems and potential privacy threats imposed on users, which leads to the specification of a set of security and privacy requirements. These requirements can be used to guide the future design of secure local electricity trading markets or to perform a risk assessment of such markets.

Digital signatures are one of the most important cryptographic primitives. In this work we construct an information-theoretically secure signature scheme which, unlike prior schemes, enjoys a number of advantageous properties such as short signature length and high generation efficiency, to name two. In particular, we extend symmetric-key message authentication codes (MACs) based on universal hashing to make them transferable, a property absent from traditional MAC schemes. Our main results are summarised as follows.-We construct an unconditionally secure signature scheme which, unlike prior schemes, does not rely on a trusted third party or anonymous channels.-We prove information-theoretic security of our scheme against forging, repudiation, and non-transferability.-We compare our scheme with existing both "classical" (not employing quantum mechanics) and quantum unconditionally secure signature schemes. The comparison shows that our new scheme, despite requiring fewer resources, is much more efficient than all previous schemes.-Finally, although our scheme does not rely on trusted third parties, we discuss this, showing that having a trusted third party makes our scheme even more attractive.

In this paper, we study the security of two recently proposed privacy-preserving biometric authentication protocols that employ packed somewhat homomorphic encryption schemes based on ideal lattices and ring-LWE, respectively. These two schemes have the same structure and have distributed architecture consisting of three entities: a client server, a computation server, and an authentication server. We present a simple attack algorithm that enables a malicious computation server to learn the biometric templates in at most 2N´τ queries, where N is the bit-length of a biometric template and τ the authentication threshold. The main enabler of the attack is that a malicious computation server can send an encryption of the inner product of the target biometric template with a bitstring of his own choice, instead of the securely computed Hamming distance between the fresh and stored biometric templates. We also discuss possible countermeasures to mitigate the attack using private information retrieval and signatures of correct computation.

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We demonstrate how adversaries with large computing resources can break Quantum Key Distribution (QKD) protocols which employ a particular message authentication code suggested previously. This authentication code, featuring low key consumption, is not Information-Theoretically Secure (ITS) since for each message the eavesdropper has intercepted she is able to send a different message from a set of messages that she can calculate by finding collisions of a cryptographic hash function. However, when this authentication code was introduced it was shown to prevent straightforward Man-In-TheMiddle (MITM) attacks against QKD protocols.In this paper, we prove that the set of messages that collide with any given message under this authentication code contains with high probability a message that has small Hamming distance to any other given message. Based on this fact we present extended MITM attacks against different versions of BB84 QKD protocols using the addressed authentication code; for three protocols we describe every single action taken by the adversary. For all protocols the adversary can obtain complete knowledge of the key, and for most protocols her success probability in doing so approaches unity. Since the attacks work against all authentication methods which allow to calculate colliding messages, the underlying building blocks of the presented attacks expose the potential pitfalls arising as a consequence of non-ITS authenti- cation in QKD-postprocessing. We propose countermeasures, increasing the eavesdroppers demand for computational power, and also prove necessary and sufficient conditions for upgrading the discussed authentication code to the ITS level.

Biometric authentication is becoming increasingly popular as a convenient authentication method. However, the privacy and security issues associated with biometric authentication are very serious. Privacy-preserving biometric authentication addresses privacy concerns associated with the use of biometrics and offers a secure solution for user authentication. Given the tremendous expansion of wireless communications a new distributed architecture in biometric authentication is evolving. In this distributed setting, a resource constrained client may outsource part of the computations during the biometric authentication process to a more powerful device (cloud server). In this work, we consider one such distributed setting consisting of clients, a cloud server, and a service provider and make a case for the need for verifiable computation to achieve security against malicious, as opposed to an honest-but-curious, cloud server. In particular, we propose to use verifiable computation on top of an homomorphic encryption scheme to verify that the cloud server correctly performs the computations outsourced to it. A proof of security of a generic protocol in the presence of a malicious cloud server is also provided. Finally, we discuss how an XOR-linear message authentication code can be used to verify the correctness of the computation.