TheCodeBreakers
We
lost no time in sending a ship, and late on an October afternoon
Prince Louis [of Battenberg, First Sea Lord] and I received from the
hands of our loyal allies these sea-stained priceless documents.
The date was October 13. But even this astounding windfall—the
luckiest in the whole history of cryptology—did not enable Ewing's team
to read the German naval messages, for the four-letter codewords in that
book did not appear in the dispatches. Finally, Fleet Paymaster Charles
J. E. Rotter, a principal German expert, discovered that the code had
been superenciphered with a monoalphabetic substitution. Solution of
such a superencipherment is not too difficult a problem with the
codebook in one's possession. As in ordinary plaintext, certain codewords
recur more frequently than others and in familiar clusters, letters in one
codeword reappear in others in different arrangements, and the
codewords themselves possess some structural regularities: in the case
annaabi.ee 
