Randy’s not expecting to find any HEILHITLER s in the Arethusa messages, but there might be other predictable words. He’s been making a list of cribs in his head: MANILA , certainly. WATERHOUSE , perhaps. And now he’s thinking GOLD and BULLION . So, in the case of MANILA he could pick out any six-character string from the intercepts and say, "What if these characters are the encrypted form of MANILA ?" and then work from there. If he were working with an intercept only six characters long, then there would be only one such six-character segment to choose from. A seven-character-long message would give him two possibilities: it could be the first six or the last six characters. The upshot is that for a message intercept that is n characters long, the number of six-character-long segments is equal to (n - 5). In the case of a 105-character-long intercept, he will have 100 different possible locations for the word MANILA . Actually, a hundred and one: because it’s of course possible—even likely—that MANILA is not in there at all. But each of these 100 guesses has its own set of ramifications vis-à-vis all of the other characters in the message. What those ramifications are, exactly, depends on what assumptions Randy is making about the underlying algorithm.