Abstract machine modelling is a technique used frequently in developing the retargetable compilers. By translating the abstract machine operations into target machine instructions, we can construct retargetable compilers. However, such a technique will cause two problems. First, the code produced by the compilers is inefficient. Next, in order to emit the efficient code, the compilation time is too long. In view of these two disadvantages, we apply PO (peephole optimizer) in our retargetable compilers to do code optimization. Peephole optimizer searches for the adjacent instruction candidates in the intermediate code, and then replaces them with equivalent instructions of less cost. Furthermore, the peephole description table consists of simple tree-rewriting rules which are easily retargeted into different machines. At the same time, we have proposed a simple peephole pattern matching algorithm to reduce the peephole pattern matching time. The experiment indicates that the machine code generated by our compiler runs faster than that by GNU c compiler (gcc).

A modified cryptographic key assignment scheme for the dynamic access control in a group-oriented user hierarchy is presented. In the partially ordered set (poset, for short) user hierarchy (GjGi) embedded in a group-oriented (t, n) threshold cryptosystem, the source group Gi has higher security clearance to access the information items held in the target group Gj. If a target group Gj has multipe paths reachable from a source group Gi, we must choose the least cost path to rapidly resolve the dynamic access control problem Furthermore, multiple threshold values are also considered in order to meet the different security requirements.

A novel cryptographic key assignment scheme for dynamic access control in a user hierarchy is presented. Based on Rabin's public key system and Chinese remainder theorem, each security class SCi is assigned a secret key Ki and some public parameters. In our scheme, a secret key is generated in a bottom-up manner so as to reduce the computation time for key generation and the storage size for public parameters. We also show that our proposed scheme is not only secure but also efficient.

According to the grey data generating techniques in grey system theory, we propose a novel cryptosystem, whose applications can develop a new direction in the field of information security. In this paper, we present the concepts of sum-lock, difference-lock, sum-ladder, and difference-ladder. By using these concepts, we can obtain a cryptosystem with lock generation and sum-difference replacement ladder. In addition, we provide the encryption and decryption algorithms of our cryptosystem and adopt an illustrative example to verify it.

This study employs secret codes and secret keys based on the elliptic curve to construct an elliptic curve cryptosystem with a dynamic access control system. Consequently, the storage space needed for the secret key generated by an elliptic curve dynamic access control system is smaller than that needed for the secret key generated by exponential operation built on the secure filter (SF) dynamic access control system. Using the elliptic curve to encrypt/decrypt on the secure filter improves the efficiency and security of using exponential operation on the secure filter in the dynamic access control system. With the proposed dynamic elliptic curve access control system, the trusted central authority (CA) can add/delete classes and relationships and change the secret keys at any time to achieve an efficient control and management. Furthermore, different possible attacks are used to analyze the security risks. Since attackers can only obtain the general equations for the elliptic curve dynamic access control system, they are unable to effectively perform an elliptic curve polynomial (ECP) conversion, or to solve the elliptic curve discrete logarithm problem (ECDLP). Thus, the proposed elliptic curve dynamic access control system is secure.