hw2-s08 - 18-731Homework 210 April 2008Due 22 April...

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Unformatted text preview: 18-731Homework 210 April 2008Due 22 April 2008NOTE: Please hand in a hard copy with this cover page attached at the beginning of theclass. Please keep your answers concise.Name:Andrew user id:Scores:Problem 1 (15 points):Problem 2 (15 points):Problem 3 (20 points):Problem 4 (20 points):Problem 5 (20 points):Problem 6 (10 points):Total:1Problem 1: Intrusion Tolerant Systems (15 points)a) (3 points) List one advantage and disadvantage of using MACs instead of digital signa-tures to authenticate the messages in the Castro-Liskov Protocol for Intrusion TolerantSystems.b) (4 points) In a distributed system with 3f + 1 nodes that uses a primary backup approach asthe replica co-ordination protocol, how would you ensure liveness (i.e. ensuring the clienteventually receive replies to their requests) if a primary and f-1 replicas are malicious i.e.they are under the control of the adversary?c) (4 points) Explain one method to correctly integrate a server into the system using astate-machine approach when other servers are already running?d) (4 points) Give an example of a request that could result in different replies from differentservers in a state-machine approach. Assume that there are no malicious nodes in thesystem and there are no faults. How would you solve this inconsistency?2Problem 2: Distance Bounding (15 points)Alice and Bob want to establish a secure key over a wireless network. They do not share anysecrets, nor do they have any PKI certificates. To evade the man-in-the-middle attack, they de-cide to use Diffie-Hellman scheme with distance bounding as follows:AliceBobGivengaGivengbPickNa∈ {,1}kPickNb∈ {,1}kma←||ga||Namb←1||gb||Nb(ca,da)←commit(ma)(cb,db)←commit(mb)caa45cba27daa45ma←open(ca,da)Verify 0 inmadba27mb←open(cb,db)Verify 1 inmbα1=Nb1α1a45β1a27β1=Na1⊕α1......
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This note was uploaded on 04/19/2008 for the course ECE 18731 taught by Professor Perrig during the Spring '08 term at Carnegie Mellon.

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hw2-s08 - 18-731Homework 210 April 2008Due 22 April...

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