Kwok Yan Lam

Several classes of binary sequences with three-level autocorrelation

In this correspondence we describe several classes of binary sequences with three-level autocorrelation. Those classes of binary sequences are based on cyclic almost difference sets. Some classes of binary sequences have optimum autocorrelation.

A New Construction of Algebraic Geometry Codes

Abstract. We present a new construction of linear codes based on algebraic geometry. An important feature of this construction is that we can use places of arbitrary degree and not just rational places as in Goppas construction. Examples show that this leads to various improvements on Goppas construction.

Constructions of authentication codes from algebraic curves over finite fields

We present a new application of algebraic curves over finite fields to the constructions of universal hash families and unconditionally secure codes. We show that the constructions derived from the Garcia-Stichtenoth curves yield new classes of authentication codes and universal hash families which are substantially better than those previously known.

An optimized protocol for mobile network authentication and security

Recent years have seen an explosive growth of interest in mobile networks that support the mobility. The mobility of users, the transmission of signals through open air and the requirement of low power consumption by a mobile user bring to a mobile network a large number of new security issues. In this paper, we propose an optimized protocol for mobile network authentication and security. The particular features of the new proposal are: (1) only a public parameter (a large prime p) and the public key of the certification authority (yca) is required knowledge for all network participants; (2) only a block cipher is used as both the secret-key encryption algorithm and the underlying cipher of the hash function.

Loyalty Program Scheme for Anonymous Payment System

Loyalty program is a marketing effort by the merchant to keep customers loyal to their stores. It tries to keep track of the purchasing-behavior of a customer by recording customers purchase information, including his credit card number, as a key identifier to the customer. While it may benefit the customer, the drawback is that the privacy of the customer is intruded. If the customer is using an anonymous payment system such as electronic cash / digital coins, his privacy is protected, but he will not get any benefit from the loyalty program which tries to record his payment information. This paper suggests several solutions to solve merchants need to gather statistical data from customers purchasing behavior versus customers need for privacy. Among the solutions, we present the idea of blindly signed pseudo digital certificates, which satisfies our requirement for a loyalty program scheme with an anonymous payment system.

On identification secret sharing schemes

Let P be a set of participants sharing a secret from a set of secrets. A secret sharing scheme is a protocol such that any qualified subset of P can determine the secret by pooling their shares, the messages which they receive, without error, whereas non-qualified subsets of P cannot obtain any knowledge about the secret when they pool what they receive. In (optimal) schemes, the sizes of shared secrets depend on the sizes of shares given to the participants. Namely the former grow up exponentially as the latter increase exponentially. In this paper, instead of determining the secret, we require the qualified subsets of participants to identify the secret. This change would certainly make no difference from determining secret if no error for identification were allowed. So here we relax the requirement to identification such that an error may occur with a vanishing probability as the sizes of the secrets grow up. Under relaxed condition this changing allows us to share a set of secrets with double exponential size as the sizes of shares received by the participants exponentially grow. Thus much longer secret can be shared. On the other hand, by the continuity of Shannon entropy we have that the relaxation makes no difference for (ordinary) secret sharing schemes. We obtain the characterizations of relations of sizes of secrets and sizes of the shares for identification secret sharing schemes without and with public message. Our idea originates from Ahlswede-Duecks awarded work in 1989, where the identification codes via channels were introduced.

A Secure Pay-per View Scheme for Web-Based Video Service

With the development of high speed computer networks, video service on the Web has huge market potential in that the video service can be provided to subscribers with greater time and schedule flexibility compared to the current cable TV system. Under the pay-perview (PPV) scheme, subscribers only need to pay for the programs that they have watched. A critical issue on PPV service is the capability of settling disputes over PPV service charges. This is especially important in the case that the Internet communication could be interrupted (by accident or deliberately) in the middle of a viewing session. This paper proposes a fair PPV billing protocol for web-based video service. With this protocol, a video service will be divided into small units, and a subscriber needs to submit cryptographic evidence which enables fair billing based on the number of units being provided in a viewing session. In addition, by the establishment of a one-way sequential link, the validity of evidence is maintained efficiently without any involvement of trusted third parties. Our scheme is light-weighted in terms of the storage requirement and computation overheads on subscribers, thus subscribers can request PPV service securely with their own smart cards regardless of their physical location.

Construction and Enumeration of All Binary Duadic Codes of Length p m

In this paper we present a binary-tree approach to the construction of all binary duadic codes of length n = p m. We also calculate the number of binary duadic codes of length n = p m, where p ≡ +1 (mod 8) is a prime.

A Class of Explicit Perfect Multi-sequences

In [7], perfect multi-sequences are introduced and a construction based on function fields over finite fields is given. In this paper, we explore the construction in [7] by considering rational function fields. Consequently a class of perfect multi-sequences are obtained.

Weak Invertibility of Finite Automata and Cryptanalysis on FAPKC

FAPKC [17, 18, 19, 20, 22] is a public key cryptosystem based weakly invertible finite automata. Weak invertibility of FAs is the key to understand and analyze this scheme. In this paper a set of algebraic terminologies describing FAs is developed, and the theory of weak invertibility of FAs is studied. Based on this, a cryptanalysis on FAPKC is made. It is shown that the keys proposed in [17, 18, 19, 20, 21] for FAPKCs are insecure both in encrypting and in signing.