About this app

Caesar and Vigen\u00E8re both ways, with the cryptanalysis alongside: a live letter-frequency histogram, the index of coincidence to tell a single shift from a keyed cipher, and a cracker that scores all twenty-six shifts against English frequencies by chi-squared and picks the winner with no dictionary and no guessing. Ends with why Vigen\u00E8re survived three hundred years and what Kasiski noticed that ended it.