Ever searching for a new way to attempt a K4 solution, I stumbled upon a series of ciphers that utilize a Polybius square.

In cryptography, the Polybius square, also known as the Polybius checkerboard, is a device invented by the Ancient Greek historian and scholar Polybius for fractionating plaintext characters so that they can be represented by a smaller set of symbols. (Wikipedia)

In classical cryptography, the bifid cipher is a cipher which combines the Polybius square with transposition, and uses fractionation to achieve diffusion. It was invented around 1901 by Felix Delastelle. (Wikipedia)

Using a Polybius square:

1 2 3 4 5
1 A B C D E
2 F G H I/J K
3 L M N O P
4 Q R S T U
5 V W X Y Z

I converted the text of K4 into numbers.

34-12-25-42-45-34-53-45-22-23-45-31-12-43-34-31-24-21-12-12-52-21-31-42-51

41-41-35-42-33-22-25-43-43-34-44-52-44-41-43-24-41-43-43-15-25-55-55-52-11

44-24-25-31-45-14-24-11-52-24-33-21-12-33-54-35-51-44-44-32-55-21-35-25-52

22-14-25-55-53-44-24-13-14-24-22-25-45-11-45-15-25-13-11-42

At this point the power went out. Now, it’s important to know exactly what you’re doing when trying a cipher technique for the first time. I thought I had the right method but ended up making a critical mistake which invalidates everything I did afterwards. It wasn’t until today that I realized this of course but it is what it is. In a Bifid cipher you write the coordinates vertically then read them off by rows then pair those numbers and use the Polybius square to translate. I used the first 97 for my first coordinate and the next 97 as my second coordinate which will not translate a Bifid ciphered text. Being bored with no power, I then padded the text into 7 columns under Kryptos and performed my first successful keyed columnar transposition. While I was working with flawed data, I would recommend each solver attempt the cryptology techniques with pen and paper because although I was having difficulties conceptualizing this type of transposition before, having done it – it feels quite logical.

As of this post, I can’t make a conclusive determination about the Bifid cipher solution but will include a link to a separate page when I’m done.

For those unfamiliar with why these types of ciphers caught my interest, it’s due to the fact that the methods used in enciphering text could potentially give rise to the letter frequencies observed in K4 where they are more flattened than you would see in a substitution or straight transposition.

Kryptos fan

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