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1、ComputerSecurityMuchofthismaterialappearsin[NRC1991]inarevisedform.Section1isjointworkwithDougMcIlroy.Anumberofpeoplecontributedtosection3.ButlerW.LampsonDigitalEquipmentCorporationJuly1990Thisdocumentisadraftofchapters2and3oftheNationalAcademyofScience’sreportoncomputersecurity[NRC1991],alongw
2、iththetechnicalappendix,references,andglossary.Section1describesrequirementsforsecurity,andsection2thetechnologyavailableformeetingthem.Section3containsmoretechnicaldetailonanumberofspecifictopics.Thereisalistofreferencesandaglossaryattheend.1RequirementsOrganizationsandpeoplethatusecomputersca
3、ndescribetheirneedsforinformationsecurityunderfourmajorheadings:secrecyOftencalled'confidentiality',asevensyllablejawbreaker.:controllingwhogetstoreadinformation;integrity:controllinghowinformationchangesorresourcesareused;accountability:knowingwhohashadaccesstoinformationorresources;availabili
4、ty:providingpromptaccesstoinformationandresources.Eachuserofcomputersmustdecidewhatsecuritymeanstohim.Forexample,adefenseagencyislikelytocaremoreaboutsecrecy,acommercialfirmmoreaboutintegrityofassets.Adescriptionoftheuser’sneedsforsecurityiscalledasecuritypolicy.Asystemthatmeetsthoseneedsiscall
5、edasecuresystem.Sincetherearemanydifferentsetsofneeds,therecan’tbeanyabsolutenotionofasecuresystem.Anexamplefromarelatedfieldmayclarifythispoint.Wecallanactionlegalifitmeetstherequirementsofthelaw.Sincethelawisdifferentindifferentjurisdictions,therecan’tbeanyabsolutenotionofalegalaction;whatisl
6、egalunderthelawsofBritainmaybeillegalintheUS.Havingestablishedasecuritypolicy,ausermightwonderwhetheritisactuallybeingcarriedoutbythecomplexcollectionofpeople,hardware,andsoftwarethatmakeuptheinformationprocessingsystem.Thequestionis:canthesystembetrustedtomeettheneedsforsecuritythatareexpresse
7、dbythepolicy?Ifso,wesaythatthesystemistrustedPerhapsweoughttosaythatitistrustworthy,butwedon't..Atrustedsystemmustbetrustedforsomething;inthiscontextitistrustedtomeettheuser’sneedsforsecurity.Insomeothercontextitmightbetrustedtoco
