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Public Key Cryptosystem (PKC) completely relies under the assumption that user's private key is absolutely secure. Exposure of private key may lead to disastrous situations in the communication network. To diminish the damage of private key exposure in PKC, key-insulation mechanism was introduced. In key-insulated cryptosystems, a user can update his private key with the help of a physically secure device from time to time. Identity-based cryptosystem alleviates the heavy certificate management problems in traditional PKC. Recently, many Identity-based key insulated signature schemes have been proposed in literature; however, most of the Identity-based schemes are designed based on the expensive bilinear pairing operation over elliptic curves. Due to the heavy computational cost of a pairing, the pairing based schemes are less efficient in practice. In order to improve the computational and communicational efficiency and to resist the problem of private key exposure in Identity-based signature schemes, we present a pairing-free key insulated signature scheme in identity based setting. We show that this scheme is unforgeable and achieves strong key insulation property with secure key updates, under the hardness of the Elliptic Curve Discrete Logarithm Problem (ECDLP). The performance analysis shows that our scheme is more efficient than the existing schemes. [ABSTRACT FROM AUTHOR]

The most important contribution of modern cryptography is the invention of digital signatures. To deal with specific application scenarios, digital signature schemes have been evolved with different variants. One of such variants is the aggregate signature scheme, which allows aggregation of different signatures by different users on different messages, to achieve computational and communication efficiency. Such schemes are useful in the design of Wireless Sensor Networks, Mobile Ad-hoc Networks, and Vehicular Ad-hoc Networks, where storage, bandwidth, and computational complexity are major constraints. In order to improve the computational and communicational efficiency along with security, in this paper, we propose a novel Certificateless Aggregate Signature (CLAS) scheme and extended it to achieve full aggregation. The proposed CLAS scheme uses bilinear pairings over elliptic curves and is proven secure in the Random Oracle Model under the assumption that Computational Diffie–Hellman Problem is hard. The security of the proposed CLAS scheme is proven without using forking lemma to achieve tight security. We compared our scheme with well-known existing schemes. Efficiency analysis shows that our scheme is much efficient than existing schemes in terms of communication and computational costs. [ABSTRACT FROM AUTHOR]