lecture12-broadcast-keydist

lecture12-broadcast-keydist - Lecture 12 Key Distribution...

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1 1 Lecture 12 Key Distribution in Large-scale Broadcast Networks Adrian Perrig 18-731: Network Security Spring 2009 2 Overview Administrative issues Office hours Friday as usual, stop by to discuss your project if you like (most likely no office hours next week) Crypto overview Upcoming lectures Broadcast authentication and signatures Midterm exam!
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2 3 Challenges for Broadcast Security Broadcast applications need security Packet injection or eavesdropping is easy Security solutions for point-to-point communication not secure for broadcast Broadcast challenges Scale to large audiences Dynamic membership Low overhead (computation & communication) Packet loss How to achieve reliability in broadcasts? Lost packets are not retransmitted 4 Scale & Dynamics Small groups contain up to ~100 members Medium-size groups contain 100-1000 members Large groups contain 1000-10 9 members How does scale affect security? Dynamic membership: members may join and leave at any time How do dynamics affect security?
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3 5 Communication Pattern Group can be single-source broadcast One-to-many SSM: Single-source multicast, source-specific multicast Multiple-source broadcast Some-to-many All members broadcast Many-to-many Which one is most common? Examples? 6 Reliable Broadcast Transmission How to reliably and scalably disseminate data to large numbers of receivers? Challenges Ack implosion problem if receivers return Ack to sender for received packets Nack implosion problem is severe as well For large numbers of receivers, there usually is a fraction of them that do not obtain message Local repair mechanisms (create tree topology and ask upstream parent for packet) faced numerous scalability difficulties End-system multicast builds data dissemination graph so receivers forward information to each other, for example Rinera startup
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4 7 Forward Error Correction Forward Error Correction (FEC) is a mechanism to reliably transmit data to a receiver without a back channel from receiver to sender Sender adds redundant information that enables receiver to tolerate message loss Ideal for broadcast setting because receiver
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lecture12-broadcast-keydist - Lecture 12 Key Distribution...

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