Dr Nazatul Sultan

This paper proposes a secure inter-cloud authorization scheme using ciphertext-policy attribute-based encryption (CP-ABE). The proposed scheme enables data owners to access files which are stored in cloud storage servers, managed by a service provider, using web applications which may be registered with another service provider. To access the stored files using a web application, the data owner can issue one time access tokens. For issuing the access tokens, the data owner does not need collaboration with any other entities in the cloud environments. In addition, single access token can be used to access several files, which reduces the number of required access tokens. Moreover, ciphertext re-encryption is performed to prevent unauthorized access. The re-encryption is delegated to a cloud storage service provider to reduce overhead on the data owner side. The security analysis of the proposed scheme has been done under the Decisional Bilinear Diffie¿Hellman assumption and it is proven to be secure against Chosen Plaintext Attack. Moreover, performance analysis of the proposed scheme shows that it incurs low overhead in terms of communication and storage and it takes minimum delay and computation costs while providing better functionality.

Cloud storage service allows its users to store and share data in a cloud environment. To secure the data from unauthorized entities while sharing, cryptographic mechanisms are used. Ciphertext-Policy Attribute-Based Encryption (CP-ABE) is one such mechanism, which has been widely used to achieve fine-grained access control over encrypted data. However, user revocation and key-escrow, in CP-ABE, are still remaining as challenging problems. In this paper, we propose a key-escrow resistant CP-ABE based access control scheme to provide efficient user revocation. The security analysis of the scheme has been done using Information Theory Tools. The security analysis establishes that it is unconditionally secure and provides any-wise revocation capability. Moreover, comparison with the other notable works in the area shows that it outperforms them in terms of computational and communication overheads.

With the increase in popularity of electronic voting, it has become necessary to have secure online voting mechanism. This paper presents a novel online voting scheme by using combination of biometric and password based security. The scheme uses Fuzzy Extractor to provide biometric based authentication, while secret password is used to provide password based protection of the voter. In addition, Pairing-Based Cryptography is used to provide the necessary security requirements of an online voting system. A prototype of the proposed scheme is implemented and its performance and security analysis shows that the proposed scheme is cost-effective and at the same time satisfies the security requirements of an online voting system.

To share encrypted data in cloud storage, data owner provides decryption keys to authorised users. When such a user is revoked, the encrypted data related to revoked user is re-encrypted and new decryption keys are re-distributed among the non-revoked users. In this paper, an efficient and secure re-encryption scheme has been proposed for data sharing in unreliable cloud environment. The scheme is built on top of Ciphertext-Policy based Attribute-Based Encryption (CP-ABE), which will provide fine-grained access control to share data. The scheme can achieve user revocation without whole ciphertexts re-encryption and key re-distributions. In addition, re-encryption is not performed until a user requests for that data, which reduces overheads. Further, it does not need any clock synchronization. Moreover, the scheme is proven to be secured under Computational Bilinear Diffie-Hellman (CBDH) assumption. A comparison with the other notable work in this area shows that the performance is better in terms of functionality, computational and communication overheads.

In wireless networks, secure authentication protocol should enable a legitimate roaming user to get roaming services from foreign server when he/she is away from home domain. However, a basic authentication protocol requires participation of home server, foreign server and roaming user during the authentication between roaming user and foreign server. Recently, two-party based anonymous authentication protocols have been proposed, which does not require home server's participation, to protect identity, location and route information of the roaming users. But, the available anonymous authentication protocols are not efficient due to the shortcomings in security and high computational cost. This paper addresses those problems and proposes a novel two-party based anonymous authentication protocol for the roaming users, named PAPAR. PAPAR uses pairing-based cryptography to secure and to provide computationally efficient authentication. Further, PAPAR uses pseudo identities to ensure user anonymity. Moreover, PAPAR efficiently mitigates the effect of DoS (Denial of Service) attack by using light computational operations, such as Message Authentication Code. Comparison and experimental results show that PAPAR outperforms the existing works in terms of security and computational cost.