kryptosfan, I like your site. I just started looking at Kyrptos4 yesterday. Frequency distribution looks exactly like a bifid with an even period because it is leveled out to some extent, but not entirely. There is a high count of period 21 bigram repeats, and another small spike at 42. Redraft the message into 21 columns and you will see what I mean. At that period, there are two repeating trigrams. I find it interesting that the clue BERLINCLOCK starts at the 64th position, which is 21*3+1. A bifid that encodes plaintext in chunks of 42 plaintext would create period 21 bigram repeats, but not so many at period 42. I shuffled the message 500 times to see if you could have as many period 21 bigram repeats, and that was easy to duplicate. However, out of the 500 shuffles, there were only four where there were as many period x repeats as with period 21, and also as many period x * 2 repeats as with period 42. Given that there are so many period 21 bigram repeats, and the clue starts at the 64th position, I think that the period 21 repeats may be significant.
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