I am looking for a comprehensive list of the IOC values of any or all classical ciphers. I can't find a list, only pieces. Each cipher has an average IOC value, and I was wondering if there was a comprehensive list of these values for every classical cipher available. Can anyone share a list of these IOC values?
The index of coincidence (IOC) measures the likelihood of drawing two matching characters by randomly selecting two characters from a given ciphertext. It also applies to digraphs, etc.
So, the chance of drawing a given character or grouping from a given ciphertext is: (number of times that character or grouping appears / length of the text).
The index of coincidence applies to ciphertexts, not to ciphers. Friedman's IOC does not apply to a cipher itself--not to the Alberti cipher, the Vigenère cipher, etc.
See: William F. Friedman, The Index of Coincidence and Its Applications in Cryptanalysis, Aegean Park Press, 1996.
A declassified NSA document about the IOC that links to that august institution.