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Homework Help: Protocols insecure against Replay Attack

  1. Nov 21, 2011 #1
    1. The problem statement, all variables and given/known data

    Determine which of the following protocols are insecure
    against replay attack , and explain why:

    (a) A → B : username, password

    (b) A → B : username, h(timestamp, password)

    (c) A → B : username, timestamp, h(password)

    (d) A → B : username, h(password), h(timestamp)

    3. The attempt at a solution

    I know a is insecure, b is secure but I am not certain about c and d.

    Off the cuff, in C it seems that h(password) can be replicated as its in the open, as can timestamp, but then if timestamp can be replicated so can h(timestamp). No?

    I guess my answer is that a,c and d are all insecure, so if possible can someone provide any input on this?
  2. jcsd
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