The 26 papers and six items of correspondence in this special issue focus on information theoretic security. The papers and items of correspondence are summarized here.

Testing of database applications is of great importance. A significant issue in database application testing consists in the availability of representative data. In this paper, we investigate the problem of generating a synthetic database based on a-priori knowledge about a production database. Our approach is to fit general location model using various characteristics (e.g., constraints, statistics, rules) extracted from the production database and then generate the synthetic data using model learnt. The generated data is valid and similar to real data in terms of statistical distribution, hence it can be used for functional and performance testing. As characteristics extracted may contain information which may be used by attacker to derive some confidential information about individuals, we present our disclosure analysis method which applies cell suppression technique for identity disclosure analysis and perturbation for value disclosure.

For decades, video surveillance systems have been crucial in protecting critical infrastructures. Currently the systems are adopting the emerging internetworking digital technology, changing from the traditional isolated analog technology. While there are several advantages of IP-based video surveillance systems, the systems are also exposed to additional new security threats. Security is a critical factor to make the IP-based video surveillance systems practical and usable. In this paper, we address the security threats to the data communications in IP-based video surveillance systems. We first analyze the current approaches, mainly naive and selective methods, to secure real-time video data, and identify their limitations to IP-based video surveillance systems. Then we propose a system design of secure internetworking video surveillance systems. Our proposed approach adopts a randomly adjustable encryption method to provide confidentiality to the data. Our implementation and performance study demonstrate that our approach achieves a good balance of cost-efficiency and security.

In this paper, we construct a new threshold cryptosystem from the Gap Diffie-Hellman (GDH) group. The proposed scheme enjoys all the most important properties that a robust and practical threshold cryptosystem should possess, that is, it is noninteractive, computationally efficient and provably secure against adaptive chosen ciphertext attacks. In addition, thanks to the elegant structure of the GDH group, the proposed threshold cryptosystem has shorter decryption shares as well as ciphertexts when compared with other schemes proposed in the literature.

Traditional network security technologies such as firewalls and intrusion detection systems usually work according to a static ruleset only. We believe that a better approach to network security can be achieved if we use quantified levels of risk as an input. In this paper, we describe a dynamic access control architecture which uses risk to determine whether to allow or deny access by a source connection into the network. A simulation of our architecture shows favorable and promising results.

Efficient ID-based key sharing schemes are desired worldwide for secure communications on Internet and other networks. The Key Predistribution Systems (KPSs) are a large class of such key sharing schemes. The remarkable property of KPSs is that in order to share the key, a participant should only input its partner's identifier to its secret KPS algorithm. Although it has many advantages in terms of efficiency, on the other hand it is vulnerable to certain collusion attacks. While conventional KPSs establish communication links between any pair of entities in a communication system, in many practical communication systems, such as broadcasting, not all links are required. In this paper, we propose a new version of KPS which is called the Hierarchical KPS. In the Hierarchical KPS, simply by removing unnecessary communication links, we can significantly increase the collusion threshold. As an example, for a typical security parameter setting, the collusion threshold of the Hierarchical KPS is 16 times higher than that of the conventional KPS while using the same amount of memory at the KPS center. The memory required by the user is even reduced by a factor $1/16$ in comparison with the conventional linear scheme. Hence, Hierarchical KPS provides a more efficient method for secure communication.

The focus of this article is on nonlinear characteristics of cryptographic Boolean functions. First, we introduce the notion of plateaued functions that have many cryptographically desirable properties. Second, we establish a sequence of strengthened inequalities on some of the most important nonlinearity criteria, including nonlinearity, avalanche, and correlation immunity, and prove that critical cases of the inequalities coincide with characterizations of plateaued functions. We then proceed to prove that plateaued functions include as a proper subset all partially bent functions that were introduced earlier by Claude Carlet (1993). This solves an interesting problem that arises naturally from previously known results on partially bent functions. In addition, we construct plateaued, but not partially bent, functions that have many properties useful in cryptography.

Authenticated session key establishment is a central issue in network security. This paper addresses the question of whether we can design a compact, efficient and authenticated key establishment protocol that has the following two properties: (1) each message exchanged between two participants can be transferred in a short packet such as an ATM cell whose payload has only 384 bits, and (2) messages that carry key materials are unforgeable and nonrepudiatable without the involvement of a trusted key distribution center. We discuss why the answer to this question is negative if one follows the currently standard approach to key establishment, namely employing secret/public key encryption and, possibly, digital signature. We then present a number of protocols that represent a positive answer to the question. Our protocols are all based on a cryptographic primitive called "signcryption" that fulfils both the functions of digital signature and public key encryption with a cost far smaller than that required by "digital signature followed by encryption".

This correspondence studies resilient functions which have applications in fault-tolerant distributed computing, quantum cryptographic key distribution, and random sequence generation for stream ciphers. We present a number of new methods for synthesizing resilient functions. An interesting aspect of these methods is that they are applicable both to linear and nonlinear resilient functions. Our second major contribution is to show that every linear resilient function can be transformed into a large number of nonlinear resilient functions with the same parameters. As a result, we obtain resilient functions that are highly nonlinear and have a high algebraic degree.

A (t, w) threshold scheme is a method for sharing a secret among w shareholders so that the collaboration of at least t shareholders is required in order to reconstruct the shared secret. This paper is concerned with the re-use of shares possessed by shareholders in threshold schemes. We propose a simple (t, w) threshold scheme based on the use of cryptographically strong pseudo-random functions and universal hash functions. A remarkable advantage of the scheme is that a shareholder can use a single string in the share of many different secrets; in particular, a shareholder need not be given a new share each time a new secret is to be shared.

Substitution boxes (S-boxes) are a crucial component of DES-like block ciphers. This research addresses problems with previous approaches towards constructing S-boxes, and proposes a new definition for the robustness of S-boxes to differential cryptanalysis, which is the most powerful cryptanalytic attack known to date. A novel method based on group Hadamard matrices is developed to systematically generate S-boxes that satisfy a number of critical cryptographic properties. Among the properties are the high nonlinearity, the strict avalanche characteristics, the balancedness, the robustness against differential cryptanalysis, and the immunity to linear cryptanalysis. An example is provided to illustrate the S-box generating method.

Three methods for strengthening public key cryptosystems in such a way that they become secure against adaptively chosen ciphertext attacks are presented. In an adaptively chosen ciphertext attack, an attacker can query the deciphering algorithm with any ciphertext except for the exact object ciphertext to be cryptanalyzed. The first strengthening method is based on the use of one-way hash functions, the second on the use of universal hash functions, and the third on the use of digital signature schemes. Each method is illustrated by an example of a public key cryptosystem based on the intractability of computing discrete logarithms in finite fields. Security of the three example cryptosystems is formally proved. Two other issues, namely, applications of the methods to public key cryptosystems based on other intractable problems and enhancement of information authentication capability to the cryptosystems, are also discussed.>