With the advance of the Internet and development of information technologies, many conventional off-line services such as banking, mailing and governmental affairs are migrating to on-line ones. Currently, building information-oriented company comes to be not only scientific technology but also business strategy to acquire competitive power. Ecommerce, which treats commercial activities by on-line, is the most prominent example and intimately associated with our real life.
However, people are still hesitant about using such convenient tools. This is originated from uncertainties on safety of their information. Inherent weaknesses of the Internet and trade-offs between performance and security increases users’ distrust. Large number of communications which contains user``s confidential message are confronted with malicious behaviors. Thus it is obvious that we should devote ourselves to designing secure E-commerce applications but not compromising efficiency.
Through this thesis, we propose two secure and efficient E-commerce protocols: mobile payment system and on-line sealed-bid auction. Two protocols are based on number-theoretic hard problems like DLP and use cryptographic hash function and digital signature as major primitives.
In case of mobile payment, it computes only two modular multiplications, one modular inversion and two hashes by the customer to pay using two public key pairs and keyed hash function. These low computation makes the protocol loaded and run in mobile devices. Nevertheless, it satisfies general electronic payment requirements; unforgeability and double spending prevention.
Two strong sealed-bid auction protocols are presented, which are-based on RSA problem and Discrete Logarithm Problem, respectively. Main characteristics of the protocols are non-repudiation of winner(s) but keeping anonymity during the bidding process. And the computational complexity to decide winner(s) is reduced to $\omicron(n log_2P)$, where n is the num...