Proxy signature scheme is an extension of digital signature scheme first introduced by Mambo et al. in 1996, which allows a signer to delegate the signing capability to a designated person, called a proxy signer. There are three types of delegation, namely, full delegation, partial delegation, and delegation by warrant. In early proxy signature schemes, the identity of the proxy signer can be revealed by any trusted authority if needed. How- ever, a secured proxy signature scheme must satisfy various properties, such as, verifiability, strong un-forgeability, nonrepudiation, privacy, and strong identifiability. In this thesis, we propose a strong proxy signature scheme based on two computationally hard assumptions, namely, Discrete Logarithmic Problem (DLP) and Computational Die-Helmann (CDH) problem, which satisfies all the security properties of a standard proxy signature scheme. The property `strong' refers to the fact that only a designated person can only verify the authenticity of the proxy signature
