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RSA Encryption

  1. Jul 30, 2013 #1
    1. The problem statement, all variables and given/known data
    "You are to receive a message using the RSA system. You choose p = 5,
    q = 7 and E = 5. Verify that D = 5 is a decoder. The encoded message
    you receive is 17. What is the actual (decoded) message?"

    2. Relevant equations

    3. The attempt at a solution
    N= pq = 35, our E = 5 --> M^E is congruent to R (mod35) where R is the remainder.

    The decoder (D=5) is being given to me, so this shouldn't be that hard, but how can I use it to help me find M, the sent message?
  2. jcsd
  3. Jul 31, 2013 #2


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    The coded message R was computed as M^E mod N. To decode, you use the same procedure but with D instead of E. Is your problem finding an efficient way to do the computation?
  4. Jul 31, 2013 #3
    Also, even though D was given to you, you should still check that D is indeed what it is supposed to be.
    I mean, to check if ED = 1 (mod the totient function).
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