Position based key exchange:definitions and implementations

Chandran,et al.introduce the direction of position based cryptography at CRYPTO 2009.In position based cryptography,the position of a party is used to be its unique“credential”in order to realize the cryptographic tasks,such as position based encryption,position based signature,position based key exchange and so on.Position based key exchange,as a basic primitive in position based cryptography,can be used to establish a shared key based on the position of the participant.To begin with,this paper presents the notions of the prover-to-verifier mode and the prover-to-prover mode for position based key exchange.In the prover-to-verifier mode,a secret key can be shared between a prover and the verifiers according to the position of the prover.While in the prover-to-prover mode,two provers located at the valid positions can negotiate a shared key with the help of the verifiers and any other party whose position is illegal cannot obtain the shared key.At the same time,this paper formalizes two security definitions against colluding adversaries:position based prover-to-verifier key exchange and position based prover-to-prover key exchange.Then,this paper introduces the bounded retrieval model and the implementations of position based key exchange in two modes based on the bounded retrieval model.Finally,this paper discusses the position based key exchange protocols in two modes from both security and performance perspectives.

Spontaneous positive exchange bias effect in SrFeO_(3-x)/SrCoO_(3-x) epitaxial bilayer

A novel phenomenon of spontaneous positive exchange bias(PEB)is reported in SrFeO_(3-x)/SrCoO_(3-x) epitaxial bilayer without undergoing any magnetic field treatment.When inserting a thick SrTiO3(STO)nonmagnetic spacer(about 6 nm)into the bilayer interface,this phenomenon still exists.Based on a series of testing means,the spontaneous PEB effect is supposed to be mainly related to short-range ferromagnetic(FM)exchange coupling at the interface when there is no STO spacer.As the STO interlayer reaches up to a certain thickness,shortrange coupling interaction basically disappears.At this time,the long-range dipole field may be responsible for the coupling of the FM and antiferromagnetic(AFM)layer across the nonmagnetic STO and then leads to the same bias effect.Our discoveries provide a new way to realize and manipulate spontaneous exchange bias-based spintronics devices,such as magnetic recording heads and spin valves.

RAO Logic for Multiagent Framework

In this paper, we deal with how agents reason about knowledgeof others in multiagent system. We first present a knowledge representation frame-work called reasoning about others (RAO) which is designed specifically to representconcepts and rules used in reasoning about knowledge of others. From a class ofsentences usually taken by people in daily life to reason about others, a rule calledposition exchange principle (PEP) is abstracted. PEP is described as an axiomscheme in RAO and regarded as a basic rule for agents to reason about others, andfurther it has the similar form and role to modus ponens and (K) axiom of knowl-edge logic. The relationship between speech acts and common sense is also discussedwhich is necessary for RAO. Based on ideas from situation calculus, this relationshipis characterized by an axiom schema in RAO. Our theories are also demonstrated byan example.