Java Mobile Code Security by Bytecode Analysis ABSTRACT

Since mobile code can migrate from a remote site to a host and can interact with the resources and facilities of the host, security becomes the key to the success of mobile code computation. Existing mobile code security mechanisms such as access control are not able to fully address the import security properties of the host including confidentiality and integrity. And these practices tend to protect the host from potential attacks by confining the mobile code, thus will impair the function of mobile code. Information-flow policy is a technique that can ensure confidentiality, however the analysis of the information flow is practically difficult. This paper describes an innovative approach to provide Java mobile code system security by bytecode analysis. The key technique of the approach is the dependence analysis adapted to information flow analysis. A security model for mobile code system is also proposed in this paper. By this approach, two major properties of the host security – integrity and confidentiality can be protected while the additional restriction on mobile code can be greatly avoided. A prototype has been implemented, which can be applied to analyze Java class file, applet and mobile agent

Damage in Creep Aging Process of an Al-Zn-Mg-Cu Alloy: Experiments and Modeling

In creep age forming (CAF), large integral panel components of high-strength aluminum alloy can be shaped and strengthened under external elastic loading at an elevated temperature through creep deformation and age hardening, simultaneously. However, the high ribbed structure on panel may induce stress concentration, inhomogeneous plastic deformation and even damage evolution on the bending rib, leading to the difficulty in controlling forming precision and material properties. Therefore, the generation and evolution of damage are necessary to be considered in the design of CAF. Taking 7050 aluminum alloy as the case material, the continuous and interrupted creep aging tests at 165 °C and three stress levels (300, 325, and 350 MPa) were conducted, and the corresponding material properties, precipitate, and damage microstructures were studied by mechanical properties tests, transmission electron microscope (TEM) and scanning electron microscope (SEM) characterizations. With the increase of stress level, the creep deformation occurs easier, the precipitates grow up faster, the creep damage occurs earlier, the growth rate and the size of microvoids increase, the mechanical properties decrease more rapidly, and the dominant mechanism of creep fracture changes from shear to microvoid coalescence. To simulate creep aging behavior with damage, a continuum damage mechanics (CDM) based model is calibrated and numerically implemented into ABAQUS solver via CREEP subroutine. The CAF of 7050 aluminum alloy panels with different height ribs were conducted by experiment and FE simulation. The forming process presents a typical stress relaxation phenomenon. The creep damage mainly occurs on the bending rib due to the severe stress concentration. With the increase of rib height, the creep strain and damage degree increase, but the springback decreases