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Unformatted text preview: cannot break the encryption within reasonable time frame. All current encryption methods (with the exception of the one-time pad) are computationally secure. 17) Check for letter frequency of the expected language. If the frequency of the letters matches the target language then it is probably transposition. Note, it the same frequency is present but with different letters then mono-alphabetic substitution is likely. 33) Changing the encryption key from time to time: 1) Limit the available cipher text encrypted with the same key, thus reducing the amount of info the cryptanalyst can use, also remove potential patterns. 2) Provide backward or/and forward secrecy (i.e., limit the scope of the compromise) Frequency of changes: depends on the security need of the domain/application/etc....
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- Fall '11
- Information Security