This paper proposes fault tolerant algorithms for routing mobile agents in a single channel wireless sensor network which cover every node in the network. These algorithms use local knowledge (assume no knowledge of g...This paper proposes fault tolerant algorithms for routing mobile agents in a single channel wireless sensor network which cover every node in the network. These algorithms use local knowledge (assume no knowledge of global deployment or topology, etc). We propose the algorithms and show mathematical analysis to support our claims. The paper ends with simulation studies and discussion of results.展开更多
In this paper,we employ genetic algorithms to solve the migration problem(MP).We propose a new encoding scheme to represent trees,which is composed of two parts:the pre-ordered traversal sequence of tree vertices and ...In this paper,we employ genetic algorithms to solve the migration problem(MP).We propose a new encoding scheme to represent trees,which is composed of two parts:the pre-ordered traversal sequence of tree vertices and the children number sequence of corresponding tree vertices.The proposed encoding scheme has the advantages of simplicity for encoding and decoding,ease for GA operations,and better equilibrium between exploration and exploitation.It is also adaptive in that,with few restrictions on the length of code,it can be freely lengthened or shortened according to the characteristics of the problem space.Furthermore,the encoding scheme is highly applicable to the degree-constrained minimum spanning tree problem because it also contains the degree information of each node.The simulation results demonstrate the higher performance of our algorithm,with fast convergence to the optima or sub-optima on various problem sizes.Comparing with the binary string encoding of vertices,when the problem size is large,our algorithm runs remarkably faster with comparable search capability.展开更多
The security problem of mobile agents is widely being discussed. The problem which protects mobile agents from malicious hosts is difficult to solve, because a host has access to the complete internal state of an agen...The security problem of mobile agents is widely being discussed. The problem which protects mobile agents from malicious hosts is difficult to solve, because a host has access to the complete internal state of an agent. Forward integrity in mobile agents guarantees that offers contained in a mobile agent from previously visited host can not be modified by a malicious host. Itinerary secrecy can prevent mobile agent from being passively attack. This paper proposes a new forward integrity and itinerary secrecy protocol for mobile agent. The protocol can also resist collusion truncation attack.展开更多
Even with attractive computational advantages,mobile agent technology has not developed its full potential due to various security issues.This paper proposes a method called Private Key Consignment to solve the proble...Even with attractive computational advantages,mobile agent technology has not developed its full potential due to various security issues.This paper proposes a method called Private Key Consignment to solve the problem of how to protect the data carried by mobile agents.It exploits new functionalities and mechanism provided by the trusted computing technology,and adopts both public key and symmetric key cryptographic means for data and key protection.The most notable feature of this method is that it protects the private key of the agent by consigning it to a tamper proof hardware,thus,enabling convenient and secure use of the private key.It provides a new scheme of mobile agents'data protection.展开更多
Current workflow management systems usually adopt the existing technologies such as TCP/IP-based Web technologies and CORBA as well to fulfill the bottom communications. Very often it has been considered only from a t...Current workflow management systems usually adopt the existing technologies such as TCP/IP-based Web technologies and CORBA as well to fulfill the bottom communications. Very often it has been considered only from a theoretical point of view, mainly for the lack of concrete possibilities to execute with elasticity. MAT (Mobile Agent Technology) represents a very attractive approach to the distributed control of computer networks and a valid alternative to the implementation of strategies for workflow system. This paper mainly focuses on improving the performance of workflow system by using MAT. Firstly, the performances of workflow systems based on both CORBA and mobile agent are summarized and analyzed; Secondly, the performance contrast is presented by introducing the mathematic model of each kind of data interaction process respectively. Last, a mobile agentbased workflow system named MAWMS is presented and described in detail. Key words workflow - Mobile Agent - Contract Net Protocol - CORBA - Web CLC number TP 393 Foundation item: Supported by the National Natural Science Foundation of China (60272024) and National Natural Science Foundation of Henan Province (0411014100)Biography: LI Jie, (1975-), male, lector, Ph. D., research direction: workflow, mobile agent, network management.展开更多
This paper considers the formation control problem of multi-agent systems in a distributed fashion. Two cases of the information propagating topologies among multiple agents, characterized by graphics model, are consi...This paper considers the formation control problem of multi-agent systems in a distributed fashion. Two cases of the information propagating topologies among multiple agents, characterized by graphics model, are considered. One is fixed topology. The other is switching topology which represents the limited and less reliable information exchange. The local formation control strategies established in this paper are based on a simple modification of the existing consensus control strategies. Moreover, some existing convergence conditions are shown to be a special case of our model even in the continuous-time consensus case. Therefore, the results of this paper extend the existing results about the consensus problem.展开更多
By using Pedersen's verifiable secret sharing scheme and the theory of crossvalidation, we propose an a-nonymous payment protocol which have following features: protecting theconfidentiality of sensitive payment i...By using Pedersen's verifiable secret sharing scheme and the theory of crossvalidation, we propose an a-nonymous payment protocol which have following features: protecting theconfidentiality of sensitive payment information from spying by malicioushosts; using a trustedthird party in a minimal way; verifying the validity of the share by the merchant; allowing agent toverify that the product which it is a-bout to receive is the one it is paying for; keeping thecustomer anonymous.展开更多
Within an agent server, the model introduces a trusted third party entity called Secure Service Station(SSS). The SSS is a non\|hardware component and is intended to prevent most attacks performed by malicious hosts, ...Within an agent server, the model introduces a trusted third party entity called Secure Service Station(SSS). The SSS is a non\|hardware component and is intended to prevent most attacks performed by malicious hosts, by providing mechanisms that ensure attack detection and provide integrity to mobile agents. This noble technique involves encapsulating partial results obtained on each intermediate host and binding these results together using a hash function, thus forming a strong bonded chain that cannot be compromised. An analytical model to explore the system performance was also developed.展开更多
Mobile agent technology has drawn a tremendous amount of attention from researchers in distributed computing recently as it promises to provide an elegant and efficient way of solving complex distributed problems, as ...Mobile agent technology has drawn a tremendous amount of attention from researchers in distributed computing recently as it promises to provide an elegant and efficient way of solving complex distributed problems, as well as offering a new approach to human-computer-interaction. In mobile agent systems, the mobile agent travels autonomously from one computer to another within the agent enabled networks, executes itself in the agent execution environment, collects useful information and makes its own decision or behalf of its owner. This mobility nature of mobile agent demands its unique name in the whole network otherwise it gets lost or conflicts with other mobile agent having same name. This paper proposes a naming scheme which promises a unique name for a mobile agent within that network. Key words mobile agent - mobile agent platform - naming scheme展开更多
The Quality of Service （QoS） has received more and more attention since QoS becomes increasingly important in the Internet development. Mobile software agents represent a valid alternative to the implementation of s...The Quality of Service （QoS） has received more and more attention since QoS becomes increasingly important in the Internet development. Mobile software agents represent a valid alternative to the implementation of strategies for the negotiation. In this paper, a QoS negotiation and renegotiation system architecture based on mobile agents is proposed. The agents perform the task in the whole process. Therefore, such a system can reduce the network load, overcome latency, and avoid frequent exchange information between clients and server. The simulation results show that the proposed system could improve the network resource utility about 10%.展开更多
The word“spatial”fundamentally relates to human existence,evolution,and activity in terrestrial and even celestial spaces.After reviewing the spatial features of many areas,the paper describes basics of high level m...The word“spatial”fundamentally relates to human existence,evolution,and activity in terrestrial and even celestial spaces.After reviewing the spatial features of many areas,the paper describes basics of high level model and technology called Spatial Grasp for dealing with large distributed systems,which can provide spatial vision,awareness,management,control,and even consciousness.The technology description includes its key Spatial Grasp Language(SGL),self-evolution of recursive SGL scenarios,and implementation of SGL interpreter converting distributed networked systems into powerful spatial engines.Examples of typical spatial scenarios in SGL include finding shortest path tree and shortest path between network nodes,collecting proper information throughout the whole world,elimination of multiple targets by intelligent teams of chasers,and withstanding cyber attacks in distributed networked systems.Also this paper compares Spatial Grasp model with traditional algorithms,confirming universality of the former for any spatial systems,while the latter just tools for concrete applications.展开更多
The nature of adhoc networks makes them vulnerable to security attacks. Many security technologies such as intrusion prevention and intrusion detection are passive in response to intrusions in that their countermea- s...The nature of adhoc networks makes them vulnerable to security attacks. Many security technologies such as intrusion prevention and intrusion detection are passive in response to intrusions in that their countermea- sures are only to protect the networks, and there is no automated network-wide counteraction against detected intrusions, the architecture of cooperation intrusion response based multi-agent is propose. The architecture is composed of mobile agents. Monitor agent resides on every node and monitors its neighbor nodes. Decision agent collects information from monitor nodes and detects an intrusion by security policies. When an intruder is found in the architecture, the block agents will get to the neighbor nodes of the intruder and form the mobile firewall to isolate the intruder. In the end, we evaluate it by simulation.展开更多
Mobile Ad hoc NETwork (MANET) consists of a set of mobile hosts which can operate independently without infrastructure base stations. Energy saving is a critical issue for MANET since most mobile hosts will operate on...Mobile Ad hoc NETwork (MANET) consists of a set of mobile hosts which can operate independently without infrastructure base stations. Energy saving is a critical issue for MANET since most mobile hosts will operate on battery powers. A cross layer coordinated framework for energy saving is proposed in this letter. On-demand power management, physical layer and medium access control layer dialogue based multi-packet reception, mobile agent based topology discovery and topology control based transmit power-aware and battery power-aware dynamic source routing are some of new ideas in this framework.展开更多
The method to remove bioavailable amounts of heavy metals from a contaminated soil by using plants is defined as bioavailable contaminant stripping （BCS） and could safely be applied if the soil＇s long-term ability ...The method to remove bioavailable amounts of heavy metals from a contaminated soil by using plants is defined as bioavailable contaminant stripping （BCS） and could safely be applied if the soil＇s long-term ability to replenish the bioavuilable pool is known. The aim of this study was to evaluate the ability of three common plant species selected, Brassica juncea, Poa annua, and Helianthus annus, to remove bioavailable amounts of mercury （Hg） from a contaminated industrial soil containing 15.1 mg kg-1 Hg. Trials were carried out under greenhouse conditions using pots （mesocosms）. According to the precautionary principle, we modified the BCS remediation approach by adding a new step, in which mercury bioavailability was increased by the addition of a strong mobilizing agent, ammonium thiosulphate, （NH4）28203, to obtain an estimate of the likely long-term bioavailable Hg pool. The modified BCS remediation approach was called enhanced bioavailable contaminant stripping （EBCS）. After one growth cycle, nearly all the bioavailable mercury （95.7%） was removed and the metal remaining in the soil was considered inert since it was neither extractable by （NH4）2S2O3 nor taken up by plants during a second growth cycle. The results demonstrated that EBCS appeared promising since it removed the most dangerous metal forms while substantially shortening the cleanup time.展开更多
This paper focuses on investigating immunological principles in designing a multi-agent security architecture for intrusion detection and response in wireless mesh networks.In this approach,the immunity-based agents m...This paper focuses on investigating immunological principles in designing a multi-agent security architecture for intrusion detection and response in wireless mesh networks.In this approach,the immunity-based agents monitor the situation in the network.These agents can take appropriate actions according to the underlying security policies.Specifically,their activities are coordinated in a hierarchical fashion while sensing,communicating,determining and generating responses.Such an agent can learn about and adapt to its environment dynamically and can detect both known and unknown intrusions.The proposed intrusion detection architecture is designed to be flexible,extendible,and adaptable so that it can perform real-time monitoring.This paper provides the conceptual view and a general framework of the proposed system.In the end,the architecture is illustrated by an example and by simulation to show it can prevent attacks efficiently.展开更多
The diversity of GISs and the wide spread availability of WWW have led to an increasing amount of research on integrating a variety of heterogeneous and autonomous GISs in a cooperative environment to construct a new...The diversity of GISs and the wide spread availability of WWW have led to an increasing amount of research on integrating a variety of heterogeneous and autonomous GISs in a cooperative environment to construct a new generation of GIS characterizing in open architecture, distributed computation, interoperability, and extensibility. Our on going research project MADGIS (Mobile Agent based Distributed Geographic Information System) is reported, in which we propose the architecture of MADGIS to meet the requirements of integrating distributed GIS applications under Internet environment. We first describe the architecture of MADGIS, and detailed discussions focusing on the structure of client site, server site and mobile agent in MADGIS. Then we explore key techniques for MADGIS implementation.展开更多
This paper focuses on investigating immunological principles in designing a multi-agent security architecture for intrusion detection and response in mobile ad hoc networks. In this approach, the immunity-based agents...This paper focuses on investigating immunological principles in designing a multi-agent security architecture for intrusion detection and response in mobile ad hoc networks. In this approach, the immunity-based agents monitor the situation in the network. These agents can take appropriate actions according to the underlying security policies. Specifically, their activities are coordinated in a hierarchical fashion while sensing, communicating, decision and generating responses. Such an agent can learn and adapt to its environment dynamically and can detect both known and unknown intrusions. The proposed intrusion detection architecture is designed to be flexible, extendible, and adaptable that can perform real-time monitoring. This paper provides the conceptual view and a general framework of the proposed system. In the end, the architecture is illustrated by an example to show it can prevent the attack efficiently.展开更多
文摘This paper proposes fault tolerant algorithms for routing mobile agents in a single channel wireless sensor network which cover every node in the network. These algorithms use local knowledge (assume no knowledge of global deployment or topology, etc). We propose the algorithms and show mathematical analysis to support our claims. The paper ends with simulation studies and discussion of results.
基金Supported by the National Natural Science Foundation of China(90104005)the Natural science Foundation of Hubei Province and the Hong Kong Poly-technic University under the grant G-YD63
文摘In this paper,we employ genetic algorithms to solve the migration problem(MP).We propose a new encoding scheme to represent trees,which is composed of two parts:the pre-ordered traversal sequence of tree vertices and the children number sequence of corresponding tree vertices.The proposed encoding scheme has the advantages of simplicity for encoding and decoding,ease for GA operations,and better equilibrium between exploration and exploitation.It is also adaptive in that,with few restrictions on the length of code,it can be freely lengthened or shortened according to the characteristics of the problem space.Furthermore,the encoding scheme is highly applicable to the degree-constrained minimum spanning tree problem because it also contains the degree information of each node.The simulation results demonstrate the higher performance of our algorithm,with fast convergence to the optima or sub-optima on various problem sizes.Comparing with the binary string encoding of vertices,when the problem size is large,our algorithm runs remarkably faster with comparable search capability.
基金Supported by the National Natural Science Foun-dation of China (60373087 ,60473023 ,90104005)
文摘The security problem of mobile agents is widely being discussed. The problem which protects mobile agents from malicious hosts is difficult to solve, because a host has access to the complete internal state of an agent. Forward integrity in mobile agents guarantees that offers contained in a mobile agent from previously visited host can not be modified by a malicious host. Itinerary secrecy can prevent mobile agent from being passively attack. This paper proposes a new forward integrity and itinerary secrecy protocol for mobile agent. The protocol can also resist collusion truncation attack.
文摘Even with attractive computational advantages,mobile agent technology has not developed its full potential due to various security issues.This paper proposes a method called Private Key Consignment to solve the problem of how to protect the data carried by mobile agents.It exploits new functionalities and mechanism provided by the trusted computing technology,and adopts both public key and symmetric key cryptographic means for data and key protection.The most notable feature of this method is that it protects the private key of the agent by consigning it to a tamper proof hardware,thus,enabling convenient and secure use of the private key.It provides a new scheme of mobile agents'data protection.
文摘Current workflow management systems usually adopt the existing technologies such as TCP/IP-based Web technologies and CORBA as well to fulfill the bottom communications. Very often it has been considered only from a theoretical point of view, mainly for the lack of concrete possibilities to execute with elasticity. MAT (Mobile Agent Technology) represents a very attractive approach to the distributed control of computer networks and a valid alternative to the implementation of strategies for workflow system. This paper mainly focuses on improving the performance of workflow system by using MAT. Firstly, the performances of workflow systems based on both CORBA and mobile agent are summarized and analyzed; Secondly, the performance contrast is presented by introducing the mathematic model of each kind of data interaction process respectively. Last, a mobile agentbased workflow system named MAWMS is presented and described in detail. Key words workflow - Mobile Agent - Contract Net Protocol - CORBA - Web CLC number TP 393 Foundation item: Supported by the National Natural Science Foundation of China (60272024) and National Natural Science Foundation of Henan Province (0411014100)Biography: LI Jie, (1975-), male, lector, Ph. D., research direction: workflow, mobile agent, network management.
基金the National Natural Science Foundation of China (No.60674071).
文摘This paper considers the formation control problem of multi-agent systems in a distributed fashion. Two cases of the information propagating topologies among multiple agents, characterized by graphics model, are considered. One is fixed topology. The other is switching topology which represents the limited and less reliable information exchange. The local formation control strategies established in this paper are based on a simple modification of the existing consensus control strategies. Moreover, some existing convergence conditions are shown to be a special case of our model even in the continuous-time consensus case. Therefore, the results of this paper extend the existing results about the consensus problem.
文摘By using Pedersen's verifiable secret sharing scheme and the theory of crossvalidation, we propose an a-nonymous payment protocol which have following features: protecting theconfidentiality of sensitive payment information from spying by malicioushosts; using a trustedthird party in a minimal way; verifying the validity of the share by the merchant; allowing agent toverify that the product which it is a-bout to receive is the one it is paying for; keeping thecustomer anonymous.
文摘Within an agent server, the model introduces a trusted third party entity called Secure Service Station(SSS). The SSS is a non\|hardware component and is intended to prevent most attacks performed by malicious hosts, by providing mechanisms that ensure attack detection and provide integrity to mobile agents. This noble technique involves encapsulating partial results obtained on each intermediate host and binding these results together using a hash function, thus forming a strong bonded chain that cannot be compromised. An analytical model to explore the system performance was also developed.
文摘Mobile agent technology has drawn a tremendous amount of attention from researchers in distributed computing recently as it promises to provide an elegant and efficient way of solving complex distributed problems, as well as offering a new approach to human-computer-interaction. In mobile agent systems, the mobile agent travels autonomously from one computer to another within the agent enabled networks, executes itself in the agent execution environment, collects useful information and makes its own decision or behalf of its owner. This mobility nature of mobile agent demands its unique name in the whole network otherwise it gets lost or conflicts with other mobile agent having same name. This paper proposes a naming scheme which promises a unique name for a mobile agent within that network. Key words mobile agent - mobile agent platform - naming scheme
基金Supported by Universities Natural Science Research Project of Jiangsu Province (No. 05KJB510101).
文摘The Quality of Service （QoS） has received more and more attention since QoS becomes increasingly important in the Internet development. Mobile software agents represent a valid alternative to the implementation of strategies for the negotiation. In this paper, a QoS negotiation and renegotiation system architecture based on mobile agents is proposed. The agents perform the task in the whole process. Therefore, such a system can reduce the network load, overcome latency, and avoid frequent exchange information between clients and server. The simulation results show that the proposed system could improve the network resource utility about 10%.
文摘The word“spatial”fundamentally relates to human existence,evolution,and activity in terrestrial and even celestial spaces.After reviewing the spatial features of many areas,the paper describes basics of high level model and technology called Spatial Grasp for dealing with large distributed systems,which can provide spatial vision,awareness,management,control,and even consciousness.The technology description includes its key Spatial Grasp Language(SGL),self-evolution of recursive SGL scenarios,and implementation of SGL interpreter converting distributed networked systems into powerful spatial engines.Examples of typical spatial scenarios in SGL include finding shortest path tree and shortest path between network nodes,collecting proper information throughout the whole world,elimination of multiple targets by intelligent teams of chasers,and withstanding cyber attacks in distributed networked systems.Also this paper compares Spatial Grasp model with traditional algorithms,confirming universality of the former for any spatial systems,while the latter just tools for concrete applications.
基金This project was supported by the National Natural Science Foundation of China (60672068)the National High Technology Development 863 Program of China (2006AA01Z436, 2007AA01Z452.)
文摘The nature of adhoc networks makes them vulnerable to security attacks. Many security technologies such as intrusion prevention and intrusion detection are passive in response to intrusions in that their countermea- sures are only to protect the networks, and there is no automated network-wide counteraction against detected intrusions, the architecture of cooperation intrusion response based multi-agent is propose. The architecture is composed of mobile agents. Monitor agent resides on every node and monitors its neighbor nodes. Decision agent collects information from monitor nodes and detects an intrusion by security policies. When an intruder is found in the architecture, the block agents will get to the neighbor nodes of the intruder and form the mobile firewall to isolate the intruder. In the end, we evaluate it by simulation.
基金863" Project Fund (No.2002AA121068) National Natural Science Foundation of China(No.60272066)
文摘Mobile Ad hoc NETwork (MANET) consists of a set of mobile hosts which can operate independently without infrastructure base stations. Energy saving is a critical issue for MANET since most mobile hosts will operate on battery powers. A cross layer coordinated framework for energy saving is proposed in this letter. On-demand power management, physical layer and medium access control layer dialogue based multi-packet reception, mobile agent based topology discovery and topology control based transmit power-aware and battery power-aware dynamic source routing are some of new ideas in this framework.
基金Supported by the National Council of Research (CNR), Italy
文摘The method to remove bioavailable amounts of heavy metals from a contaminated soil by using plants is defined as bioavailable contaminant stripping （BCS） and could safely be applied if the soil＇s long-term ability to replenish the bioavuilable pool is known. The aim of this study was to evaluate the ability of three common plant species selected, Brassica juncea, Poa annua, and Helianthus annus, to remove bioavailable amounts of mercury （Hg） from a contaminated industrial soil containing 15.1 mg kg-1 Hg. Trials were carried out under greenhouse conditions using pots （mesocosms）. According to the precautionary principle, we modified the BCS remediation approach by adding a new step, in which mercury bioavailability was increased by the addition of a strong mobilizing agent, ammonium thiosulphate, （NH4）28203, to obtain an estimate of the likely long-term bioavailable Hg pool. The modified BCS remediation approach was called enhanced bioavailable contaminant stripping （EBCS）. After one growth cycle, nearly all the bioavailable mercury （95.7%） was removed and the metal remaining in the soil was considered inert since it was neither extractable by （NH4）2S2O3 nor taken up by plants during a second growth cycle. The results demonstrated that EBCS appeared promising since it removed the most dangerous metal forms while substantially shortening the cleanup time.
基金supported by National Natural Science Foundation of China under Grant No.60932003National High Technical Research and Development Program of China(863 program) Grant No.2007AA01Z452,No.2009AA01Z118+1 种基金Shanghai Municipal Natural Science Foundation under Grant No.09ZR1414900National Undergraduate Innovative Test Program under Grant No.091024812
文摘This paper focuses on investigating immunological principles in designing a multi-agent security architecture for intrusion detection and response in wireless mesh networks.In this approach,the immunity-based agents monitor the situation in the network.These agents can take appropriate actions according to the underlying security policies.Specifically,their activities are coordinated in a hierarchical fashion while sensing,communicating,determining and generating responses.Such an agent can learn about and adapt to its environment dynamically and can detect both known and unknown intrusions.The proposed intrusion detection architecture is designed to be flexible,extendible,and adaptable so that it can perform real-time monitoring.This paper provides the conceptual view and a general framework of the proposed system.In the end,the architecture is illustrated by an example and by simulation to show it can prevent attacks efficiently.
基金Supported by the Open Researches Fund Program of L IESMARS(WKL(0 0 ) 0 30 2 )
文摘The diversity of GISs and the wide spread availability of WWW have led to an increasing amount of research on integrating a variety of heterogeneous and autonomous GISs in a cooperative environment to construct a new generation of GIS characterizing in open architecture, distributed computation, interoperability, and extensibility. Our on going research project MADGIS (Mobile Agent based Distributed Geographic Information System) is reported, in which we propose the architecture of MADGIS to meet the requirements of integrating distributed GIS applications under Internet environment. We first describe the architecture of MADGIS, and detailed discussions focusing on the structure of client site, server site and mobile agent in MADGIS. Then we explore key techniques for MADGIS implementation.
基金Supported by the National High Technology Develop ment 863 Program of China (No.2003AA148010)Key Technologies R&D Program of China (No.2002DA103A03-07).
文摘This paper focuses on investigating immunological principles in designing a multi-agent security architecture for intrusion detection and response in mobile ad hoc networks. In this approach, the immunity-based agents monitor the situation in the network. These agents can take appropriate actions according to the underlying security policies. Specifically, their activities are coordinated in a hierarchical fashion while sensing, communicating, decision and generating responses. Such an agent can learn and adapt to its environment dynamically and can detect both known and unknown intrusions. The proposed intrusion detection architecture is designed to be flexible, extendible, and adaptable that can perform real-time monitoring. This paper provides the conceptual view and a general framework of the proposed system. In the end, the architecture is illustrated by an example to show it can prevent the attack efficiently.
