Wireless Personal Communications22:213–228,2002.
©2002Kluwer Academic Publishers.Printed in the Netherlands.
Security in Wireless Communicationmerci
MOHAMMAD GHULAM RAHMAN and HIDEKI IMAI
Faculty of Information and Communication Engineering,University of Tokyo,Institute of Industrial Science,
4-6-1,Komaba,Tokyo,153-8505,Japan
E-mail:rahman@imailab.iis.u-tokyo.ac.jp.imai@iis.u-tokyo.ac.jp
Abstract.Security is a critical issue in mobile radio applications both for the urs and providers of such systems. Although the same may be said of all communications systems,mobile application have speci
dancersal requirements and vulnerabilities,and are therefore of special concern.Emerging wireless networks share many common char-acteristics with traditional wire-line networks such as public switch telephone/data networks,and hence many curity issues with the wire-line networks also apply to the wireless environment.However the integration of curity features into wireless communication must take into account restrictions that may apply to their u such as small packet size,low bandwidth,high transmission costs,limited processing and storage resources and real time constraints.In this paper curity requirements in wireless communications along with curity features in 2G and3G systems are described.
Keywords:wireless communication,encryption,authentication,anonymity.
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1.Introduction
With the implementation of1st generation analog system in mobile communication mobility is incorporated in communication system.2nd generation system moves to the digital era from analog system still with only voice communication and some sort of data communications. And the3rd generation brings in multi media communication,mobile commerce etc.in wire-less environment.Hence we e that advances in wireless technologies have brought us many new mobil
e applications and rvices.The boundary between wireless network and wired networks have been become blurred with the easy access to the Internet through the mobile devices.In the meantime such advances have also introduced new curity problems that are specific to the wireless environment.For certain problems,existing curity technologies are sufficient,while for others new solutions are need to be developed.The types of curity in the mobile environments are similar to wired system such as Internet,the main differences are constraints in bandwidth,memory and processing power.Therefore more lightweight and efficient solutions are generally required.
Mobile devices are designed to be ,light and small.Until a more suitable alter-native is found,mobile devices will more than likely be battery powered within the foreeable future.In order to conrve energy,processing speeds need to be slower and processor cycles reduced.Data transmissions also consume energy therefore it must be reduced.The former impos limits on the computational complexity of encryption algorithms and the number of messages involved in curity protocols.Even though using special purpo circuitry or encryption chips can alleviate this problem,it still faces the hurdle of the public’s suspicion towards any devices that claim to protect the privacy of their communication or data.
专四成绩2021什么时候出
214Mohammad Ghulam Rahman and Hideki Imai
The rest of the paper is organized as follows.In Section2curity threats in a general communication networks are pointed out.Security issues in mobile system are described in Section4.Security of2G and3G systems are portrayed in Sections5and6respectively.In Section7we prented our approach of anonymous mutual authentication of mobile ur and the rver with ssion key generation and also the analysis of the propod protocol.
2.Security Threats in a Network
A network environment is in general susceptible to a number of curity threats.The include the following:
•Masquerading or ID spoofing:The pretence of one entity to be another entity.By mas-querading,an entity can get hold of privileges that it is not authorized to have in the first place.Within a computer system,a ur process might masquerade as another to gain access to afile or memory to which it is not authorized,while over a network,a masquerading ur or host may deceive the receiver about its real identity.•Unauthorized u of resources:This includes unauthorized access to both resources on the networks as well as computer system.For instance,within a computer system,this threat corresponds to us or process accessingfiles,memory or processor without authorization.Over the network the threat may be in the form of accessing a network resource.si wa
•Unauthorized disclosure andflow of information:This threat involves unauthorized dis-closure and illegalflow of information stored,procesd or transferred in a network system both internal and external to the ur organizations.Within a system,such an attack may occur in the form of unauthorized reading of stored information,while over the network,the means of attack may be wire tapping or traffic analysis.•Unauthorized alteration of resources and information:Unauthorized alteration of infor-mation may occur both within a system(by writing into memory)and over the network (through active wire-tapping).The latter attack may be ud in combination with other attacks such as replay whereby a message or part of a message is repeated intentionally to produce an unauthorized effect.This threat may also involve unauthorized introduction (removal)of resources into(from)a distribution system.
•Repudiation of actions:This is a threat against accountability in organizations.For in-stance,a repudiation attack can occur whereby the nder(or the receiver)of a message denies having nd(or received)the information.For instance,a customer engages in transaction with a bank to withdraw a certain amount from his account,but later denies having nt the message.A similar attack can occur at the receiving end;for instance a firm denying the receipt of a particular bid offer for the tender even though it actually did receive that offer.
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•Unauthorized denial of rvice:Here the attacker acts to deny resources or rvices to entities,which are authorized to u them.For instance,within a computer system an entity may lock afile thereby denying access to other authorized entities.In the ca of the network,the attack may involve blocking the access to the network by continuous deletion or generation of messages so that the target is either depleted or saturated with meaningless messages.
Security in Wireless Communications215
Figure1.Mobile communication architecture.
3.Mobile Environment
A very general architecture of mobile communication system is prented in Figure1.The radio port is the element that connects the Air-Interface to the Fixed(Home or Serving) Network.All the communication between the Mobile Station(MS)and thefixed network takes place through the Radio port.The Home Network(belonging to the Home Service Provider) is the where the Mobile ur is registered and has the billing and location information of the ur.The Serving Network(SN),from ur’s point of view,is one that is currently providing him rvice in the area in which he has roamed.Typically a rving network has to query the ur’s Home Network for information about the ur for curity and authentication purpo.
The wireless medium is intrinsically a broadcast-bad medium.An eavesdropper is able to tap into the wireless communications channels by positioning himlf anywhere within the area of the cell.Since all transmitted data travel directly between a mobile host and the ba station,it is possible to copy all the data of a particular message transmitted through the air.
如何提高自己的口才It is also harder to control visiting hosts overloading the network with excessive trans-missions,resulti
ng in a sudden decrea in network performance.This may lead to denial of rvice to other mobile hosts becau of the congested network.
There is a curity threat during channel tup.When a mobile host“pops-up”in a cell, the ba station(or any other network entity carrying out network management tasks and has jurisdiction over that cell)needs to update information on the network in order to al-low messages to be routed to that mobile host correctly.This means that information on the physical location of the mobile host are available to entities that are able to e the routing information,and this may be undesirable if that mobile would like to keep his location private.An impostor may also able to disgui as another mobile ur by monitoring that mobile ur and immediately connecting to the network using that mobile ur’s identity after
216Mohammad Ghulam Rahman and Hideki Imai
a disconnection.The impostor will then have access to all the resources that is available to the real ur.The real ur may even be denied connection later becau the ba station might think that it is trying to re-connect again for the cond time.
4.Security Issues in Mobile Systems
英文数字In this ction,four major areas of mobile systems curity are discusd,namely authentica-tion,anonymity,device vulnerability and domain crossing.
4.1.A UTHENTICATION
As with current distributed systems,authentication is a necessary procedure for verifying an entity’s identity and authority as well.The level of trust for a particular entity depends on the outcome of this authentication process.Ideally,ur authentication should be carried out transparently,without disruption to whatever the ur’s task is at the moment.Authentication protects the rvice provider from unauthorized intrusion.By mutual authentication[1]mobile station also authenticate the ba station.This could be of importance for two reasons:Firstly it prevents a malicious station from pretending to be a ba station.Secondly it permits the MS to choo the rvices of a particular ba station in the prence of co-located networks.
Most authentication protocols in practice require the home authentication authority(or authentication rver)to be contacted during the execution of the protocol.Consider the over-head that will be incurred when this has to be done for many mobile urs entering the foreign domain.Furthermore,the“transparency”requirement for authentication protocols would be difficult to
meet the completion time for the each protocol now also depends on the quality of the link between the visited domain and the mobile ur’s home authentication rver.This also means that the home authentication rver must always be up and its rvice must be available all the time).The last two factors,the link quality between the visited domain and the ur’s home authentication rver and the availability of the authentication rver itlf,is unpredictable and therefore cannot be guaranteed.
The u of certificates may relax the requirement of contacting the ur’s home authen-tication rver.Unfortunately,this scheme also has some undesirable properties.Firstly,it is irrational to assume that the certifying authority that signed the certificate is globally and unconditionally trusted by every entity.A mobile ur also cannot be expected tofind out be-forehand which domains it will be visiting and then obtain certificates that will be accepted by them.Another problem is that certificates do not reflect the current status of its owner/carrier, e.g.the current balance of his bank account or a record of his behavior in previously visited domains.It is difficult to embed some information about the current status of the ur into the certificate by the rver and at the same time be sure that the ur cannot alter that information or prent only certificates which provides the most positive credentials.Revocation of certifi-cates will also become a harder conce
rned with scalability,becau mobile urs move around a lot and their locations could be anywhere in the world.
Engineering good authentication protocols for mobile systems have been blesd with an extra burden of anonymity requirements.It is imperative that authentication protocols give out as little information as possible relating to the principals involved in the protocol execution.
Security in Wireless Communications217 4.2.A NONYMITY
Information about a particular person or organization is private and should only be known to its owner and whoever its owner grants access rights to.Privacy should be prerved in any kind of information system,be itfixed or mobile.The kinds of information that a ur may want to keep private include his real ur identity when on-line,his activities,his current location and his movement patterns.Prerving anonymity[2]is of greater concern in mobile systems for veral reasons.Mobile systems yield more easily to eavesdropping and tapping, compared tofixed networks,making it easier to tap into communication channels and get to ur information.As urs move around,a new kind of information immediately becomes detailed information about the movement and location of the ur.This may also provide clues to whom that ur interacted with at a given point in system update
time.Urs will also move in and out of foreign domains which the ur may not have prior knowledge about,hence may not be fully trustworthy.Moving across foreign domains thus results in incread risk to ur information.Current network implementers of mobile communication systems store a lot of ur related information on network databas,especially for mobile telecommunication networks.This is done to assist in ur mobility support as well as billing and authentication. This makes the ur information more widespread and highly available.It is also uncertain whether the environment where this data is stored is safe and trustworthy.The following issues should be considered to solve the anonymity problem:
mykonos•Preventing any association of the ur with messages that he nt or received.•Preventing any association of the ur with communication ssions that it participates in.
•Prerving the privacy of location and movement information of urs.•Preventing the disclosure of the relationship between a ur and his home domain.•Preventing any association of the ur with the foreign domains that were visited.•Disallowing the exposure of a ur’s activities,by hiding the relationship between him and the visited domains.
Urs can be denied rvice by various mechanisms,usually by either“cutting off”the communication
channel between the client and the rver or byflooding the network to the extent that no more bandwidth is available for u,rendering the network effectively unoperational.With unlective denial of rvice,whole rvices or large parts of a network are using explosives),and the are usually detectable.Selective denial is less evident and its victims are usually well defia particular client on the network). Anonymity is an obvious solution to the latter problem.
A common solution that has been adopted,providing a certain degree of anonymity in current systems,is by means of an alias,or a temporary identity.Alias or nicknames allow a ur to be referenced without revealing their real identity.Alias could be short-or long-lived, and there are no general specifications on their life span.Short-lived alias for a particular ur usually change as frequently as his inter-cell or inter-domain handoffs.A long-lived alias is more dangerous as it allows ur tracking.Even though the real ur might not be known at the moment of tracking the alias,that information can be kept and then matched at a later time to the real identities and their corresponding activity history that the subverted party manages to get hold of.
The alias scheme can be broken in some of its current implementations.For example,once a mobile ur is disconnected in mid-conversation in the GSM system,the mobile ur is re-
