Cryptography and Network Security Chapter 14Chapter 14 – Key Management and DistributionKey Management and DistributionKey DistributionSlide 5Key Distribution TaskKey HierarchySlide 8Key Distribution ScenarioKey Distribution IssuesSymmetric Key Distribution Using Public KeysSimple Secret Key DistributionMan-in-the-Middle AttackSecret Key Distribution with Confidentiality and AuthenticationHybrid Key DistributionDistribution of Public KeysPublic AnnouncementPublicly Available DirectoryPublic-Key AuthoritySlide 20Public-Key CertificatesSlide 22X.509 Authentication ServiceX.509 Certificate UseX.509 CertificatesSlide 26Obtaining a CertificateCA HierarchyCA Hierarchy UseCertificate RevocationX.509 Version 3Certificate ExtensionsPublic Key InfrastructurePKIX ManagementSummaryCryptography and Cryptography and Network SecurityNetwork SecurityChapter 14Chapter 14Fifth EditionFifth Editionby William Stallingsby William StallingsLecture slides by Lawrie BrownLecture slides by Lawrie BrownChapter 14 – Key Management Chapter 14 – Key Management and Distributionand DistributionNo Singhalese, whether man or woman, No Singhalese, whether man or woman, would venture out of the house without a would venture out of the house without a bunch of keys in his hand, for without such bunch of keys in his hand, for without such a talisman he would fear that some devil a talisman he would fear that some devil might take advantage of his weak state to might take advantage of his weak state to slip into his body. slip into his body. ——The Golden Bough, Sir James George The Golden Bough, Sir James George FrazerFrazerKey Management and Key Management and DistributionDistributiontopics of cryptographic key management / topics of cryptographic key management / key distribution are complex key distribution are complex cryptographic, protocol, & management issuescryptographic, protocol, & management issuessymmetric schemes require both parties to symmetric schemes require both parties to share a common secret keyshare a common secret keypublic key schemes require parties to public key schemes require parties to acquire valid public keysacquire valid public keyshave concerns with doing bothhave concerns with doing bothKey DistributionKey Distributionsymmetric schemes require both parties to symmetric schemes require both parties to share a common secret keyshare a common secret keyissue is how to securely distribute this keyissue is how to securely distribute this keywhilst protecting it from otherswhilst protecting it from othersfrequent key changes can be desirablefrequent key changes can be desirableoften secure system failure due to a break often secure system failure due to a break in the key distribution scheme in the key distribution schemeKey DistributionKey Distributiongiven parties A and B have various given parties A and B have various key key distributiondistribution alternatives: alternatives:1.1.A can select key and physically deliver to BA can select key and physically deliver to B2.2.third party can select & deliver key to A & Bthird party can select & deliver key to A & B3.3.if A & B have communicated previously can if A & B have communicated previously can use previous key to encrypt a new keyuse previous key to encrypt a new key4.4.if A & B have secure communications with a if A & B have secure communications with a third party C, C can relay key between A & Bthird party C, C can relay key between A & BKey Distribution TaskKey Distribution TaskKey HierarchyKey Hierarchytypically have a hierarchy of keystypically have a hierarchy of keyssession keysession keytemporary keytemporary keyused for encryption of data between usersused for encryption of data between usersfor one logical session then discardedfor one logical session then discardedmaster keymaster keyused to encrypt session keysused to encrypt session keysshared by user & key distribution centershared by user & key distribution centerKey HierarchyKey HierarchyKey Distribution ScenarioKey Distribution ScenarioKey Distribution IssuesKey Distribution Issueshierarchies of KDC’s required for large hierarchies of KDC’s required for large networks, but must trust each othernetworks, but must trust each othersession key lifetimes should be limited for session key lifetimes should be limited for greater securitygreater securityuse of automatic key distribution on behalf use of automatic key distribution on behalf of users, but must trust systemof users, but must trust systemuse of decentralized key distributionuse of decentralized key distributioncontrolling key usagecontrolling key usageSymmetric Key Distribution Symmetric Key Distribution Using Public KeysUsing Public Keyspublic key cryptosystems are inefficientpublic key cryptosystems are inefficientso almost never use for direct dataso almost never use for direct data encryptionencryptionrather use to encrypt secret keys for distributionrather use to encrypt secret keys for distributionSimple Secret Key DistributionSimple Secret Key DistributionMerkle proposed this very simple schemeMerkle proposed this very simple schemeallows secure communicationsallows secure communicationsno keys before/after existno keys before/after existMan-in-the-Middle AttackMan-in-the-Middle Attackthis very simple scheme is vulnerable to this very simple scheme is vulnerable to an active man-in-the-middle attackan active man-in-the-middle attackSecret Key Distribution with Secret Key Distribution with Confidentiality and Confidentiality and AuthenticationAuthenticationHybrid Key DistributionHybrid Key Distributionretain use of private-key KDCretain use of private-key KDCshares secret master key with each usershares secret master key with each userdistributes session key using master keydistributes session key using master keypublic-key used to distribute master keyspublic-key used to distribute master keysespecially useful with widely distributed usersespecially useful with widely distributed usersrationalerationaleperformanceperformancebackward compatibilitybackward compatibilityDistribution of Public KeysDistribution of Public Keyscan be considered as using one of:can be considered as using one of:public announcementpublic announcementpublicly available directorypublicly available directorypublic-key authoritypublic-key authoritypublic-key certificatespublic-key