Broadcast encryption ( BE ) allows a sender to encrypt a message to an arbitrary target set of legitimate users and to prevent non-legitimate users from recovering the broadcast information. BE has numerous practical applications such as satellite geolocation systems, file sharing systems, pay-TV systems, e-Health, social networks, cloud storage systems, etc. This paper presents two new decentralized BE schemes. Decentralization means that there is no single authority responsible for generating secret cryptographic keys for system users. Therefore, the scheme eliminates the concern of having a single point of failure as the central authority could be attacked, become malicious, or become unavailable. Recent attacks have shown that the centralized approach could lead to system malfunctioning or to leaking sensitive information. Another achievement of the proposed BE schemes is their performance characteristics that make them suitable for environments with light-weight clients, such as in Internet-of-Things (IoT) applications. The proposed approach improves the performance over existing decentralized BE schemes by simultaneously achieving constant size ciphertext, constant size secret key and fast decryption.
We investigate the open problem to characterize whether the infinite power of a given language is generated by an ω-code. In case the given language is a code (i.e. zero-relation language), the problem was solved. In this work, we solve the problem for the class of one-relation languages.
In a proxy re-signature ( PRS) scheme, a semi-trusted proxy is able to transform a signature signed by a user to a new signature of the same message signed by another user, it however cannot sign on any other message on behalf of those users. PRS thus has found many practical applications such as distributed storage, distributed rights management or cloud infrastructure. To our knowledge, all of the PRS schemes without using random oracle (RO for short) need to use the Waters' hash function, which leads to PRS schemes with large key size and inefficient computing time. In this paper, we propose a new bidirectional PRS scheme without using RO and without using the Waters' hash function. Our scheme is therefore the best PRS scheme without using RO to date in term of efficiency.
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