Abstract
Fueled by the exponential growth in the number of people with access to the Internet, electronic-commerce (e-commerce) transactions via the Internet have become a major part of our economy. For a wider range of e-commerce applications to take
advantage of the untapped business potential of the Internet, some challenging and interesting security problems need to be solved. In this thesis, we study two such problems, and provide efficient solutions for both.
In the foreseeable future, some e-commerce vendors will generate revenue by providing digital streaming applications such as information broadcasts (e.g., stock quotes). For the first issue, we investigate the problem of authenticating packet
streams in multicast or broadcast networks. Our approach is to encode the hash values and digital signatures with Rabin's Information Dispersal Algorithm (IDA) to construct an authentication scheme that amortizes a single signature operation over
multiple packets. This strategy is especially efficient in terms of space overhead because just the essential elements needed for authentication (i.e., one hash per packet and one signature per group of packets) are used in conjunction with an erasure
code that is space optimal. We evaluate the performance of our scheme using both analytical and empirical results.
Applications such as e-commerce payment protocols using electronic money require that fair exchange be assured. For the second issue, we investigate the problem of constructing fair-exchange protocols. Our approach uses a novel signature
paradigm-the gradational signature scheme-to construct protocols that are efficient and scalable. Unlike previous approaches, our scheme does not employ any costly zero-knowledge proof systems in the exchange protocol. Use of zero-knowledge
proofs is needed only in the protocol setup phase-this is a one-time cost. The resulting exchange protocol is more e
