March 31, 2009
The rail-fence cipher is a transposition cipher that rearranges the characters of a clear-text to form the cipher-text. The clear-text is arranged in up-and-down waves like the tops of the pickets on a rail fence; the cipher key is the height of the fence. For instance, the encipherment of “PROGRAMMING PRAXIS” with a key of 4 is shown below, using an underscore to make the space character visible:
P R O G R A M M I N G _ P R A X I S
P M P = P M P
R A M _ R S = R A M _ R S
O R I G A I = O R I G A I
G N X = G N X
The cipher-text is read at the right of the pickets: “PMPRAM RSORIGAIGNX”.
Your task is to write functions that encipher and decipher texts using the rail-fence method. When you are finished, you are welcome to read or run a suggested solution, or to post your solution or discuss the exercise in the comments below.
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