Recall that for the shift cipher, we have M = C = K = Z/26Z (the integers
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Recall that for the shift cipher, we have M = C = K = Z/26Z (the integers modulo 26). Encryption is given by EK(M) ≡ M +K (mod 26) (modular addition of message and key).
(i) Give a formal mathematical proof that double encryption for the shift cipher under two keys K1, K2 results again in a shift cipher. What is the key of the double encipherment?
(ii) Give a formal mathematical proof that superencipherment (i.e. multiple encryptions) for the shift cipher results again in a shift cipher. Use induction on the number of encipherments (solutions that do not use induction will be penalized). What is the key of the multiple encipherments?
Related Book For
Ethics in Accounting A Decision Making Approach
ISBN: 978-1118928332
1st edition
Authors: Gordon Klein
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