I'm looking for detailed information on a statistical tool to aid in cryptanalysis called an "index of coincidence". I would appreciate it if someone could please explain what this is, how one builds such an index against a given ciphertext, and how it is valuable in the cryptanalysis of said ciphertext.
Given a ciphertext X with discrete components x[1], x[2], ... x[n], I[c] is the probability that two random elements of x are identical. Ben. Ben Samman..............................................samman@cs.yale.edu "If what Proust says is true, that happiness is the absence of fever, then I will never know happiness. For I am possessed by a fever for knowledge, experience, and creation." -Anais Nin Want to give a soon-to-be college grad a job? Mail me for a resume