Abstract Broadcast encryption is a key‐distribution technique for sending encrypted messages to arbitrary groups of users in public channels. When applied to large systems (e.g., pay‐TV), the existing symmetric‐key‐setting schemes usually exhibit high transmission costs; thus, numerous efforts have been made to enhance the transmission performance. However, tremendous additional computation cost or storage size requirements are often necessary. In this paper, a symmetric‐key‐setting scheme, called balanced double subset difference, and its variant, BDSDλ, are proposed. By enlarging the subset collection of the subset difference scheme with special subsets, calledbalanced subsets, the proposed schemes retain the excellent computational performance of subset difference and offer the capability of reducing transmission costs with a reasonable storage requirement. Copyright © 2014 John Wiley & Sons, Ltd.

The conditional access system (CAS) is an essential part of digital pay-TV systems for controlling access to the program services. Conventionally, due to the restrictions of bandwidth and computational capability, a CAS only supports period subscription services that are charged on a monthly basis. In this paper, based on the concept of hierarchical key assignment, we propose three key distribution schemes for the access control of pay-TV systems. With these schemes, a CAS can support more charging strategies for service providers, such as adopting a smaller charging unit and allowing a subscription of any subset of channels with little communication and computational overhead. In addition, the piracy management problem can also be dealt with easily.

Conventional hierarchical key assignment schemes have not been concerned with a practical situation: Users might be assigned to a class for only a period of time. When a user leaves a class, the keys of that class and all the descendent classes must be renewed. For applications where the privileges of users change frequently or where there are many users, the communication load for key redistributions is very large. Recently, Tzeng (2002) proposed a time-bound hierarchical key assignment scheme to address this issue. However, Tzeng's scheme was very complex and suffered from a collusion attack. In this paper, we propose an efficient time-bound scheme based on a technique called merging. The idea behind merging is to consider primitive keys instead of hierarchies. It is conceptually like the compression used in source coding. Through this technique, it is feasible to combine multiple keys into an aggregate key. Thus, communication and storage requirements are greatly reduced. This technique can also be used for an alternative implementation of Akl-Taylor's scheme. Moreover, it can be used to construct a systematic approach for adjusting hierarchies in Akl-Taylor's scheme as well. Through the insights gained from these exercises, we may see that some problems that are usually addressed by the conventional key assignment schemes can be solved directly via merging, with better performance. Furthermore, if other suitable merging functions are found in the future, new secure hierarchical key assignment schemes and time-bound schemes is obtained accordingly.

This multiplexer is assumed to have wideband (WB) and narrowband (NB) customers, where the arrival process for the former is modeled as a single birth-death Markovian chain and that of the latter is modeled as an independent Poisson. Each NB customer needs a single server for service while each WB customer needs more than one server; both of their service times are the same and constant. Higher access priority is given to WB customers. To protect the NB service quality, a cutoff parameter which denotes the maximum number of WB customers simultaneously served in one slot, is provided. Performance measures including queue length distribution, blocking probability, and mean waiting time are obtained.>