Publication Date


Date of Final Oral Examination (Defense)


Type of Culminating Activity


Degree Title

Master of Science in Computer Science


Computer Science

Major Advisor

Jyh-haw Yeh, Ph.D.


Gaby Dagher, Ph.D.


Dianxiang Xu, Ph.D.


Over the years, email has evolved and grown to one of the most widely used form of communication between individuals and organizations. Nonetheless, the current information technology standards do not value the significance of email security in today's technologically advanced world. Not until recently, email services such as Yahoo and Google started to encrypt emails for privacy protection. Despite that, the encrypted emails will be decrypted and stored in the email service provider's servers as backup. If the server is hacked or compromised, it can lead to leakage and modification of one's email. Therefore, there is a strong need for point-to-point (P2P) email encryption to protect email user's privacy. P2P email encryption schemes strongly rely on the underlying Public Key Cryptosystems (PKC). The evolution of the public key cryptography from the traditional PKC to the Identity-based PKC (ID-PKC) and then to the Certificateless PKC (CL-PKC) provides a better and more suitable cryptosystem to implement P2P email encryption. Many current public-key based cryptographic protocols either suffer from the expensive public-key certificate infrastructure (in traditional PKC) or the key escrow problem (in ID-PKC). CL-PKC is a relatively new cryptosystem that was designed to overcome both problems. In this thesis, we present a CL-PKC group key agreement protocol, which is, as the author's knowledge, the first one with all the following features in one protocol: (1) certificateless and thus there is no key escrow problem and no public key certificate infrastructure is required. (2) one-way group key agreement and thus no back-and-forth message exchange is required; (3) n-party group key agreement (not just 2- or 3-party); and (4) no secret channel is required for key distribution. With the above features, P2P email encryption can be implemented securely and efficiently. This thesis provides a security proof for the proposed protocol using ``proof by simulation''. Efficiency analysis of the protocol is also presented in this thesis. In addition, we have implemented the prototypes (email encryption systems) in two different scenarios in this thesis.