The index of coincidence (IC) is a measure of the relative frequency of letters in a cipher text sample, which facilitates cryptanalysis of poly-alphabetic ciphers by allowing determination of the period t, length of the key, as an alternative to Kasiski’s method.
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Expectation Value of the Index of Coincidence
Can Anybody tell me why the expectation value of the Index of Coincidence is the following?
For a cipher text string of length $L$, where $n$ is the number of
alphabet characters, $k_r = 1/n$, and ...
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How does the index of coincidence work in the Kasiki test?
I'm starting to learn about cryptanalysis and I am having a bit of difficulty understanding the Kasiski test's index of coincidence. I have a book (Cryptography Theory And Practice by Douglas Stinson) ...
