Key Management For Secure Communication

Key Management For Secure CommunicationPresentation By: Garrett Lund

Paper By: Sandro Rafaeli and David HutchisonOverviewBackground InformationIP MulticastAssumptionsRequirementsRekeying MethodsCentralized Group Key Management ProtocolsDecentralized ArchitecturesDistributedEthicsSources

IP MulticastBetween Unicast and BroadcastNetwork Switches and Routers are responsible for replication and distribution

IP Multicast Applications

IP Multicast Applications

Encryption ReviewObviously some of these applications require limited access.No public key, but a group key

AssumptionsWhen a user joins, we have a way to get them their first keyWhen a user leaves there is a possibility of them continuing to acquire messagesEvery user eventually gets the intended messagesMembership ChangesGroups need to be dynamic, allowing (authorized) members to join the group and allowing administrators to expel members from the groupBackwards SecrecyForward Secrecy

RekeyingWe need a way to get new keys to the usersSince multicast is being used for group transmission, it is assumed that multicast should be used for rekeying the groupThree ApproachesCentralizedDecentralizedDistributedRekeying RequirementsStorage RequirementsSize of Rekey MessagesBackwards SecrecyForwards SecrecyCollusionBackground InformationIP MulticastAssumptionsRequirementsRekeying MethodsCentralized Group Key Management ProtocolsDecentralized ArchitecturesDistributedEthicsSources

OverviewCentralized ApproachesWe have a Key Distribution Center (KDC)KDC is in charge of managing all of the groups keysSimple Assign a secret key to each memberUse a group key to send group messagesEach member can recover the group key from the appropriate segment of the rekey message using its secret key

Simple ExampleRekey MessageDSFDBSAFSDFREGEFDSFAGFASFD@#DSGFDGFDPGGFDSFDHJHFTY546GFD5FGS&GF5REYHH. . .User FGFDSFDH

Secret KeyGroup Key

Simple ExampleUser F

Secret KeyGroup Key

DFDS#@FDSA

Secret MessageSimple Problems1. The KDC has to encrypt the new key n times2. The message could potentially be hugeIf n = 1 million and K is 56 bitsThe message would be 10 MB long3. You have to develop a protocol so that each user knows which part of the message is appropriate for them to decrypt with their secret key

Group Key Management Protocol (GKMP)Have 2 group keys and no secret keyOne Group Transmission Encryption Key (GTEK)One Group Key Encryption Key (GKEK)GKEK used to encrypt the GTEK when it changesSince GKEK will never change, the system lacks forward secrecy, you cannot kick a member out since they will always know the GKEK

Logical Key Hierarchy (LKH)Use a balanced Binary Tree to store keys hierarchically

LKH ExampleRekey MessageDSFDBSAFSDFREGEFDSFAGFASFD@#DSGFDGFDPGGFDSFDHJHFTY546

User u3

k3We Want k34Use k3 on 5th lineWe get k34Corresponds to: k

K14

K58

K12

K34

K56

K78

k34We Want k14Use k34 on 2nd lineWe get k14

k14We Want kUse k14 on first lineWe get k

kLogical Key Hierarchy (LKH)

Other Centralized ApproachesOne-Way Function Trees (OFT)One-Way Function Chain Trees (OFCT)ClusteringCentralized Flat Table (FT)Efficient Large-Group Key (ELK)Centralized Approach Summary

Decentralized ApproachesSplit the group into subgroups

Decentralized Approaches

Distributed ModelsTwo methodsEvery member contributesPick a member at randomDistributed Example LKH

Distributed Summary

Ethics

Sources"IP Multicast Technical Overview." Cisco Systems, Inc. Web.. Rafaeli, Sandro, and David Hutchison. "A Survey of Key Management for Secure Group Communication." ACM Digital Library. Lancaster University, Sept. 2003. Web. . Wikipedia