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Shift = 4
The number twenty six is truly brilliant. It is the smallest number that isn't a palindrome but has a square which is. It is the only number that is squeezed between two cube numbers and an unsolved rubicks cube can be solved in no more than twenty six moves.
The Rail Fence Cipher involves writing messages so that alternate letters are written on separate upper and lower lines. To create the final encrypted message, the sequence of letters on the upper line is then followed by the sequence on the lower line. The code maker improves the security of the cipher by choosing more than two lines to encrypt the message.
Take the plaintext "pancakes for breakfast" for example. It can be enciphered using a shift of two by writing it as follows:
The ciphertext is then created by reading across the rows as follows:
Ciphertext: pnaefrra fsa cksobekat
In this case, a shift of two was used ie. two lines. In order to decipher it, the ciphertext must be split into two parts. If the shift was three, then the ciphertext must be split into three lines, four lines for a shift of four etc.
More information on the railfence cipher can be found at here http://www.simonsingh.net/The_Black_Chamber/railfence.html