Towards Scalable and Reliable Towards Scalable and Reliable Secure Multicast Secure Multicast Presenter: Yang Richard Yang Presenter: Yang Richard Yang Network Research Lab Network Research Lab Department of Computer Sciences Department of Computer Sciences The University of Texas at Austin The University of Texas at Austin 11/02/2000 11/02/2000 Project Director: Simon S. Lam Project Director: Simon S. Lam Other Members: Steve Li, Xincheng Zhang Other Members: Steve Li, Xincheng Zhang Past member: C. K. Wong Past member: C. K. Wong
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Towards Scalable and Reliable Secure Multicast Presenter: Yang Richard Yang Network Research Lab Department of Computer Sciences The University of Texas.
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Towards Scalable and ReliableTowards Scalable and ReliableSecure MulticastSecure Multicast
Presenter: Yang Richard YangPresenter: Yang Richard Yang
Network Research LabNetwork Research Lab
Department of Computer SciencesDepartment of Computer Sciences
The University of Texas at AustinThe University of Texas at Austin
11/02/200011/02/2000
Project Director: Simon S. LamProject Director: Simon S. Lam
Other Members: Steve Li, Xincheng ZhangOther Members: Steve Li, Xincheng Zhang
Past member: C. K. WongPast member: C. K. Wong
11/02/2000 Towards a Scalable and Reliable Group Key Management 2
What is a Group What is a Group Key Management System?Key Management System?
• Provide access control to the symmetric Provide access control to the symmetric
group key that is shared by all group group key that is shared by all group
membersmembers
• Two types of access control services:Two types of access control services: Backward access control:Backward access control:
•Change the group key after a new user joinsChange the group key after a new user joins
Forward access control: Forward access control:
•Change the group key after a member leavesChange the group key after a member leaves
11/02/2000 Towards a Scalable and Reliable Group Key Management 3
Key TreesKey Trees
k1-9
k123 k456
k1
k789
k2 k3 k4 k5 k6 k7 k8
u2 u3 u4 u5 u6 u7 u8 u9u1
k9
(changed to k78)
(changed to k1-8)
[Wong et al. SIGCOMM ’98, Wallner et al. Internet Draft]
{k78}k7 {k78}k8
{k1-8}k123 {k1-8}k456 {k1-8}k78
11/02/2000 Towards a Scalable and Reliable Group Key Management 4
Group Key Management System Components
registration
rekey encoding
rekey transport
individualkeys
join leave
11/02/2000 Towards a Scalable and Reliable Group Key Management 5
Registration ComponentRegistration Component
• Issue: authentication can have large Issue: authentication can have large
overheadoverhead
• Solution: allow multiple registrars in our Solution: allow multiple registrars in our
Keystone prototype Keystone prototype
encoding
transport
Reg.
11/02/2000 Towards a Scalable and Reliable Group Key Management 6
11/02/2000 Towards a Scalable and Reliable Group Key Management 7
Rekey Encoding ComponentRekey Encoding Component
• Issue: rekey for each request in real-Issue: rekey for each request in real-time may not be desiredtime may not be desired Rekey for each request is not efficientRekey for each request is not efficient Rekey in real-time have out-of-sync problemRekey in real-time have out-of-sync problem
• Solution: use periodic batch rekeyingSolution: use periodic batch rekeying
• Periodic batch rekeying provides Periodic batch rekeying provides tradeoffs between performance and tradeoffs between performance and how effective group access control is how effective group access control is
Reg.encoding
transport
11/02/2000 Towards a Scalable and Reliable Group Key Management 8
User send re-synchronization at the end User send re-synchronization at the end
of rekey intervalof rekey interval
11/02/2000 Towards a Scalable and Reliable Group Key Management 16
How to Determine Proactivity How to Determine Proactivity Factor?Factor?
0.00
0.50
1.00
1.50
2.00
2.50
3.00
1.00 1.10 1.20 1.50 1.60 1.70 1.80 2.00 2.50
Proactivity factor
ban
dw
idth
overh
ead
0.00
1.00
2.00
3.00
4.00
5.00
6.00
reco
very
late
ncy
bw overhead
Latency
11/02/2000 Towards a Scalable and Reliable Group Key Management 17
Two Remaining QuestionsTwo Remaining Questions
• Questions:Questions: How to determine the rekey interval T?How to determine the rekey interval T?
How to determine the number of users a How to determine the number of users a
key server can support?key server can support?
• These answers to these questions will These answers to these questions will
be tradeoff decisionsbe tradeoff decisions
Reg.encoding
transport
11/02/2000 Towards a Scalable and Reliable Group Key Management 18
Bandwidth Requirement vs Bandwidth Requirement vs Rekey IntervalRekey Interval
11/02/2000 Towards a Scalable and Reliable Group Key Management 19
Determine System Parameters Determine System Parameters by Constraintsby Constraints
• Two types of constraints:Two types of constraints: Performance constraints give lower bounds on TPerformance constraints give lower bounds on T
• Upper bounds of key server and receiver bandwidth Upper bounds of key server and receiver bandwidth requirementrequirement
• Rekey latencyRekey latency System effectiveness constraints give upper bound on T:System effectiveness constraints give upper bound on T:
• E.g. T/m < 0.1, m is the mean time each user in the E.g. T/m < 0.1, m is the mean time each user in the groupgroup
• If the lower bounds < upper bound, choose the If the lower bounds < upper bound, choose the upper bound as T, otherwise, have to reduce the upper bound as T, otherwise, have to reduce the number of users in the groupnumber of users in the group
11/02/2000 Towards a Scalable and Reliable Group Key Management 20
Extend to Distributed Key Extend to Distributed Key ServersServers
• Objective: improve scalability and Objective: improve scalability and
reliabilityreliability
• Issue: how to coordinate different Issue: how to coordinate different
groups?groups?
• Two distributed architectures:Two distributed architectures: Multiple key servers based on clock Multiple key servers based on clock
synchronization, larger virtual groupsynchronization, larger virtual group
iolus agents with RMX like topologyiolus agents with RMX like topology
11/02/2000 Towards a Scalable and Reliable Group Key Management 21
ConclusionConclusion
• Investigated scalability and reliability issues of Investigated scalability and reliability issues of
a single key server systema single key server system Registration: distributed registarsRegistration: distributed registars
Rekey encoding: period batch processingRekey encoding: period batch processing