Rail Fence Cipher

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A transposition cipher written in a zigzag that simulates the pattern of rails on a fence.

A few months ago, I gave in and clicked on a persistent facebook ad for the Mystery Experiences Company.  At the risk of sounding like an infomercial, it sends me a new puzzle story every month with lots of cool props and was totally worth it.  At the very least, I have learned a ton about cryptography, which will be the subject of several new posts.

This cipher works by writing out a message on a “rail fence” of a set number of posts, descending then ascending in a zig-zag fashion.  So the message: “This is a cipher” might look like this in a three rail cipher:

T—I—P—

-H-S-A-I-H-R

–I—C—E

The code then is created straight across, top to bottom.  So in the case above: TIPHSAIHRICE.

It is not considered a particularly difficult cipher to break once identified as a rail fence cipher, because one would only need know the number of “rails.” One tip that is is a rail fence cipher is that because it is simply an anagram, the frequency of letters will remain consistent with the rest of the English language.

Some information about Rail Fence Ciphers was found at Sophia Knight’s page at Trinity College: http://www.cs.trincoll.edu/~crypto/historical/railfence.html

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