Time Stamped Proxy Blind Signature Scheme With Proxy Revocation Based on Discrete Logarithm Problem

Proxy blind signature combines both the properties of blind signature and proxy signature. In a proxy blind signature scheme, the proxy signer is allowed to generate a blind signature on behalf of the original signer. It is a protocol played by three parties in which a user obtains a proxy signer’s signature for a desired message and the proxy signer learns nothing about the message. During the verification of a proxy blind signature scheme, the verifier cannot get whether signing is within the delegation period or after delegation period. In this thesis a time stamped proxy blind signature scheme with proxy revocation is proposed which records the time stamp during the proxy signing phase and satisfies all the security properties of proxy blind signature i.e distinguishability, nonrepudiation, unforgeability, verifiability, identifiability, unlinkability, prevention of misuse. In a proxy revocation scheme, the original signer can terminate the delegation power of a proxy signer before the completion of delegation period. Proxy blind signature has wide applications in real life scenarios, such as, e-cash, e-voting and e-commerece applications

Secure access privilege delegation using attribute-based encryption

Attribute-based encryption (ABE) is widely used for a secure and efficient data sharing. The predetermined access policy of ABE shares the data with intended data users. However, ABE is not preferable in many applications that require collaboration among data users. In such applications, an authorized data user may be interested to collaborate with another data user who does not adhere to the access policy. Fixed access policy of ABE does not allow an authorized data user (who satisfies the access policy) to collaborate or share the data with any unauthorized data user (who fails to satisfy the access policy). Thus, due to the static and predefined access policy, data collaboration in ABE is significantly challenging. In this work, we attempt to address this important issue of ABE through proxy re-encryption mechanism. We have formally proved the security of our proposed system. Moreover, we have demonstrated that the proposed system permits revocation of delegation rights