Word: ciphertext
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Dates: during 1968-1968
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Since "every letter has a cluster of preferred associations that constitute its most distinguishing characteristic," the next step is to set up a contact chart. This shows how often each letter precedes and is succeeded by each other letter. From this it is clear that N in the ciphertext stands for plaintext e: it is the most frequently used letter, and associates more often with more different characters than does any other letter...
...other high-frequency plaintext vowels, a, i and o, tend to avoid one another. A contact chart would show that three of the most common letters in the ciphertext -O, U and A-are the most mutually exclusive. OA appears twice, OU once, and UO, UA, AO and AU not at all. But NU appears five times in the cryptogram. It happens that the most frequent English vowel diagraph is ea. Thus it is a good bet that U = a. Similarly, since the combination io is most frequent among the three dissident vowels in English, assume that it is represented...
...four most common vowels have been tentatively identified. Now for consonants. An easy-to-spot characteristic of plaintext n is that it is preceded 80% of the time by vowels. The contact chart shows that ciphertext T is preceded 17 times out of 23 by ciphertext N, O, U, or A. Put T down...
...cryptanalyst, ciphertext Y is also significant. In the cryptogram, it runs before N and never follows it; at the same time, it always follows H and never precedes it. This is the usual behavior of plaintext h: the diagraph he is commonplace, but eh is unusual; th is the most frequent diagraph of all, but ht less so. Therefore, in the cryptogram, Y=h and H should equal...
...becomes possible to find familiar words in plain English. For example, the letters ith appear near the beginning. Guessing that this could stand for with, the analyst assumes that M = w. He tries that idea out in other places where M appears in the ciphertext. Down the line this produces the sequence with-n-nown. This suggests: with unknown, in which case J would equal u, and K would equal...