TheCodeBreakers
unearthing prehistoric graves, and reporting on his work to learned
journals. (One of his scholarly articles was cited in the Encyclopaedia
Britannica.) Kasiski died on May 22, 1881, almost certainly without
realizing that he had wrought a revolution in cryptology.
That revolution began when Kasiski shrewdly noted a phenomenon:
the conjunction of a repeated portion of the key with a repetition in the
plaintext produces a repetition in the ciphertext:
key RTJNRTJNRUNRUNRTJNRUNRUNRTJNRtJNRUN
plaintext tobeornot tobethatisthequestion ciphertext KIO v i EE io K Io
v NUB N v J N u VKHVMQZ I A
Each time that the key RUNR engages the repeated plaintext to be, the
repeated ciphertext tetragraph KIOV results. Like causes produce like
effects. Similarly, when the repeated key-fragment UN operates upon the
repeated th's, the ciphertext registers repeated NU'S.
Clearly, the keyword must repeat one or more times for a given part of
annaabi.ee 
