PKI.docx

PKI.docx

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PKI

OperatingSystem

MicrosoftWindows 2000PublicKeyInfrastructure

WhitePaper

Abstract

Microsoft®Windows®2000introducesacomprehensivepublic-keyinfrastructure（PKI）totheWindowsplatform.ThisinfrastructureextendstheWindows-basedpublic-key（PK）cryptographicservicesintroducedoverthepastfewyears,providinganintegratedsetofservicesandadministrativetoolsforcreating,deploying,andmanagingPK-basedapplications.Thisallowsapplicationdeveloperstotakeadvantageoftheshared-secretsecuritymechanismsorPK-basedsecuritymechanisminWindows,asappropriate.Enterprisesalsogaintheadvantageofbeingabletomanagetheenvironmentandapplicationswithconsistenttoolsandpolicies.

©1999MicrosoftCorporation.Allrightsreserved.

TheinformationcontainedinthisdocumentrepresentsthecurrentviewofMicrosoftCorporationontheissuesdiscussedasofthedateofpublication.BecauseMicrosoftmustrespondtochangingmarketconditions,itshouldnotbeinterpretedtobeacommitmentonthepartofMicrosoft,andMicrosoftcannotguaranteetheaccuracyofanyinformationpresentedafterthedateofpublication.

ThisWhitePaperisforinformationalpurposesonly.MICROSOFTMAKESNOWARRANTIES,EXPRESSORIMPLIED,INTHISDOCUMENT.

Microsoft,ActiveX,Authenticode,Outlook,TheBackOfficelogo,Windows,andWindows NTareregisteredtrademarksofMicrosoftCorporation.

Otherproductorcompanynamesmentionedhereinmaybethetrademarksoftheirrespectiveowners.

MicrosoftCorporation•OneMicrosoftWay•Redmond,WA98052-6399•USA

0499

Contents

Introduction1

Concepts2

PublicKeyCryptography2

Public-KeyFunctionality2

DigitalSignatures2

Authentication3

SecretKeyAgreementviaPublicKey3

BulkDataEncryptionwithoutPriorSharedSecrets3

ProtectingandTrustingCryptographicKeys4

Certificates4

CertificateAuthorities4

TrustandValidation5

Windows 2000PKIComponents6

CertificateAuthorities8

CertificateHierarchies8

DeployinganEnterpriseCA9

TrustInMultipleCAHierarchies11

EnablingDomainClients12

GeneratingKeys12

KeyRecovery12

CertificateEnrollment13

Renewal13

UsingKeysandCertificates13

Recovery14

Roaming15

Revocation15

Trust15

PKSecurityPolicyinWindows 200017

TrustedCARoots17

CertificateEnrollmentandRenewal17

Smart-CardLogon18

ApplicationsOverview19

WebSecurity19

SecureE-mail20

DigitallySignedContent21

EncryptingFileSystem21

Smart-CardLogon22

IPSecurity（IPSec）22

Interoperability23

Criteria23

InternetStandards23

PreparingforWindows 2000PKI26

S/MIME-basedE-mailUsingExchangeServer26

ForMoreInformation27

Introduction

TheMicrosoftWindows 2000operatingsystemintroducesacomprehensivepublic-keyinfrastructure（PKI）totheWindowsplatform.ThisinfrastructureextendstheWindows-basedpublic-key（PK）cryptographicservicesthatwereintroducedoverthepastfewyears,providinganintegratedsetofservicesandadministrativetoolsforcreating,deploying,andmanagingPK-basedapplications.Thisallowsapplicationdeveloperstotakeadvantageoftheshared-secretsecuritymechanismsorPK-basedsecuritymechanism,asappropriate.Enterprisesalsogaintheadvantageofbeingabletomanagetheenvironmentandapplicationswithconsistenttoolsandpolicies.

TheremainderofthispaperprovidesanoverviewofthePKIinWindows 2000.

Concepts

PublicKeyCryptography

Cryptographyisthescienceofprotectingdata.Cryptographicalgorithmsmathematicallycombineinputplaintextdataandanencryptionkeytogenerateencrypteddata（ciphertext）.Withagoodcryptographicalgorithm,itiscomputationallynotfeasibletoreversetheencryptionprocessandderivetheplaintextdata,startingwithonlytheciphertext;someadditionaldata,adecryptionkey,isneededtoperformthetransformation.

Intraditional,secret（orsymmetric）keycryptography,theencryptionanddecryptionkeysareidenticalandthussharesensitivedata.Partieswishingtocommunicatewithsecret-keycryptographymustsecurelyexchangetheirencryption/decryptionkeysbeforetheycanexchangeencrypteddata.

Incontrast,thefundamentalpropertyofpublic-key（PK）cryptographyisthattheencryptionanddecryptionkeysaredifferent.Encryptionwithapublickeyencryptionkeyisaone-wayfunction;plaintextturnsintociphertext,buttheencryptionkeyisirrelevanttothedecryptionprocess.Adifferentdecryptionkey（related,butnotidentical,totheencryptionkey）isneededtoturntheciphertextbackintoplaintext.Thus,forPKcryptography,everyuserhasapairofkeys,consistingofapublickeyandaprivatekey.Bymakingthepublickeyavailable,itispossibletoenableotherstosendyouencrypteddatathatcanonlybedecryptedusingyourprivatekey.Similarly,youcantransformdatausingyourprivatekeyinsuchawaythatotherscanverifythatitoriginatedwithyou.Thislattercapabilityisthebasisfordigitalsignatures,discussedbelow.

Public-KeyFunctionality

TheseparationbetweenpublicandprivatekeysinPKcryptographyhasallowedthecreationofanumberofnewtechnologies.Themostimportantofthesearedigitalsignatures,distributedauthentication,secret-keyagreementviapublickey,andbulkdataencryptionwithoutpriorsharedsecrets.

Thereareanumberofwell-knownPKcryptographicalgorithms.Some,suchasRivest-Shamir-Adleman（RSA）andEllipticCurveCryptography（ECC）,aregeneral-purpose;theycansupportalloftheaboveoperations.Otherssupportonlyasubsetofthesecapabilities.SomeexamplesincludetheDigitalSignatureAlgorithm（DSA,whichispartoftheU.S.government’sDigitalSignatureStandard,FIPS186）,whichisusefulonlyfordigitalsignatures,andDiffie-Hellman（D-H）,whichisusedforsecretkeyagreement.

ThefollowingsectionsbrieflydescribetheprincipalusesofPKcryptography.Theseoperationsaredescribedintermsoftwousers,BobandAlice.ItisassumedthatBobandAlicecanexchangeinformationbutdonothaveanypre-arranged,sharedsecretsbetweenthem.

DigitalSignatures

Perhapsthemostexcitingaspectofpublickeycryptographyiscreatingandvalidatingdigitalsignatures.Thisisbasedonamathematicaltransformthatcombinestheprivatekeywiththedatatobesignedinsuchawaythat:

Onlysomeonepossessingtheprivatekeycouldhavecreatedthedigitalsignature.

Anyonewithaccesstothecorrespondingpublickeycanverifythedigitalsignature.

Anymodificationofthesigneddata（evenchangingonlyasinglebitinalargefile）invalidatesthedigitalsignature.

Digitalsignaturesarethemselvesjustdata,sotheycanbetransportedalongwiththesigneddatathattheyprotect.Forexample,Bobcancreateasignede-mailmessagetoAliceandsendthesignaturealongwiththemessagetext,providingAlicetheinformationthatisrequiredtoverifythemessageorigin.Inaddition,digitalsignaturesprovideawaytoverifythatdatahasnotbeentamperedwith（eitheraccidentallyorintentionally）whileintransitfromthesourcetothedestination.Therefore,theycanbeexploitedtoprovideaverysecuredata-integritymechanism.

Authentication

PKcryptographyprovidesrobustdistributedauthenticationservices.Entityauthenticationguaranteesthatthesenderofdataistheentitythatthereceiverthinksitis.IfAlicereceivesdatafromBob,andthensendshimachallengeencryptedwithBob’spublickey,BobthendecodesthischallengeandsendsitbacktoAlice,provingthathehasaccesstotheprivatekeyassociatedwiththepublickeythatAliceusedtoissuethechallenge.AlicecanalsosendaplaintextchallengetoBob.Bobthencombinesthechallengewithotherinformation,whichisdigitallysigned.AlicethenusesBob’spublickeytoverifythesignatureandprovethatBobhastheassociatedprivatekey.Thechallengemakesthismessageuniqueandpreventsreplayattacksbyahostilethirdparty.Ineithercase,thisisknownasaproof-of-possessionprotocolbecausethesenderprovesthathehasaccesstoaparticularprivatekey.

SecretKeyAgreementviaPublicKey

AnotherfeatureofPKcryptographyisthatitpermitstwopartiestoagreeonasharedsecret,usingpublic,andnonsecure,communicationnetworks.Basically,BobandAliceeachgeneratearandomnumberthatformshalfofthesharedsecretkey.Bobthensendshishalfofthesecret,encrypted,toAlice,usingherpublickey.Alicesendsherhalf,encrypted,toBobwithhispublickey.Eachsidecanthendecryptthemessagereceivedfromtheotherparty,extractthehalfofthesharedsecretthatwasgeneratedbytheother,andcombinethetwohalvestocreatethesharedsecret.Oncetheprotocoliscompleted,thesharedsecretcanbeusedforsecuringothercommunications.

BulkDataEncryptionwithoutPriorSharedSecrets

ThefourthmajortechnologyenabledbyPKcryptographyistheabilitytoencryptbulkdatawithouttheestablishmentofpriorsharedsecrets.ExistingPKalgorithmsarecomputationallyintensiverelativetosecret-keyalgorithms.Thismakesthemillsuitedforencryptinglargeamountsofdata.TogettheadvantagesofPKcryptographyalongwithefficientbulkencryption,PKandsecret-keytechnologiesaretypicallycombined.

Thisisaccomplishedbyfirstselectingasecret-keyencryptionalgorithmandgeneratingarandomsessionkeytousefordataencryption.IfBobissendingthemessage,hefirstencryptsthissessionkey,usingAlice’spublickey.TheresultingciphertextkeyisthensenttoAlicealongwiththeencrypteddata.Alicecanrecoverthesessionkey,usingherprivatekey,andthenusethesessionkeytodecryptthedata.

ProtectingandTrustingCryptographicKeys

Insecret-keycryptography,Alic