Integrity protection for code-on-demand mobile agents in e-commerce

The mobile agent paradigm has been proposed as a promising solution to facilitate distributed computing over open and heterogeneous networks. Mobility, autonomy, and intelligence are identified as key features of mobile agent systems and enabling characteristics for the next-generation smart electronic commerce on the Internet. However, security-related issues, especially integrity protection in mobile agent technology, still hinder the widespread use of software agents: from the agent’s perspective, mobile agent integrity should be protected against attacks from malicious hosts and other agents. In this paper, we present Code-on-Demand(CoD) mobile agents and a corresponding agent integrity protection scheme. Compared to the traditional assumption that mobile agents consist of invariant code parts, we propose the use of dynamically upgradeable agent code, in which new agent function modules can be added and redundant ones can be deleted at runtime. This approach will reduce the weight of agent programs, equip mobile agents with more flexibility, enhance code privacy and help the recoverability of agents after attack. In order to meet the security challenges for agent integrity protection, we propose agent code change authorization protocols and a double integrity verification scheme. Finally, we discuss the Java implementation of CoD mobile agents and integrity protection

Electron transport through a mesoscopic hybrid multiterminal resonant-tunneling system

For a mesoscopic hybrid system which contains a normal central region coupled to multiple superconducting leads, a general expression of the current is derived by using nonequilibrium-Green-function method. This current formula can be used to describe the case with time-dependent external fields applied to any parts of the system, arbitrarily finite voltages, and any kinds of interactions in the central region. For a normal two-terminal interacting electron system, this expression reduces to the general time-dependent current formula previously obtained by Wingreen et al. [Phys. Rev. B 98, 8487 (1993)]. As an application, we use this current formula to study a special case of a noninteracting single-level central region coupled to two or three superconducting leads, respectively.published_or_final_versio

Control of the supercurrent in a mesoscopic four-terminal Josephson junction

We study the control of the supercurrent in a mesoscopic four-terminal superconductor–normal-metal–superconductor (SNS) junction, in which the N region is a quantum dot connected via tunneling barriers to two superconducting electrodes and two normal electrodes, respectively. By using the nonequilibrium Green’s function method, the current flowing into the quantum dot from each electrode is derived. We find that the supercurrent between two superconducting electrodes can be suppressed and even reversed by changing the dc voltage applied across the two normal terminals, similar to recent experiments of diffusive SNS junctions and previous theories for both the ballistic and diffusive SNS junctions. Then we investigate a three-terminal SNS junction, reduced from the four-terminal junction by decoupling the dot from one normal terminal. We find that even at zero bias of the normal terminal, the supercurrent still can be controlled by changing the coupling strength between the dot and the normal terminal. In addition, both the Andreev reflection current and Andreev quasibound states depend on the phase difference of two superconductors and the coupling strength between the dot and superconducting electrodes. Finally, the behavior of the supercurrent is discussed in the limit when the normal terminals are decoupled from the system.published_or_final_versio

Breaking of phase rigidity by a time-varying field for a two-terminal modified Aharonov-Bohm ring

For a two-terminal modified Aharonov-Bohm (AB) ring with a quantum dot inserted in one arm and threaded by a magnetic flux, the phase rigidity is observed experimentally in the linear response regime, and also established theoretically. We show that this phase rigidity can be broken, even in the linear response regime, by applying a time-varying field on the dot, together with the magnetic flux through the AB ring. This provides another way of observing the continuous variation of the transmission phase through a two-terminal mesoscopic system.published_or_final_versio

Lack of quenching for the resonant transmission through an inhomogeneously oscillating quantum well

The spectral weights of the wave-function sidebands for a quantum well in the presence of an inhomogeneous electromagnetic (EM) field are studied by introducing a wave function with the form of a Floquet state and then solving the time-dependent Schrödinger equation approximately. The two cases of radiation direction of the EM field parallel and perpendicular to the well axis are considered. We find that the inhomogeneity of the EM field may eliminate the sideband quenching. Based on the spectral weight, the transmission probability through the well is investigated. The energy-level splitting for a special case, the averaged vector potential equal to zero, is also studied.published_or_final_versio