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# Lesson 5 - A Tough-To-Break Code For Words Up To 8 Letters Long

Note: To use the Javascript programs in these lessons, you will need to use a FireFox browser or other non-Internet Explorer browser due to the "feature" in the IE browser disallowing Javascript prompts.

Introduction
This coding algorithm will encode words in such a way that they will be nearly impossible for the casual observer to decode.  You should read through the previous coding instructions for background and information on how to use the coding program.

The Formula For This Encoding Algorithm
In this code, the first operation performed is that the number order of each letter is inverted.  An "A" becomes a "Z", a  "B" becomes a "Y", a "C" becomes an "X", "D" becomes "W" and so on.  To achieve this, you assign each letter a number from 1 to 26, subtract that value from 27, and then assign the new number back to a letter. The function that does this is simply y = 27 - x.

The second operation performed is to simply "bump up" the letter two places (after being reversed). This amounts to adding 2 to its position value.  So, we modify the formula y = 27 - x and write it as

y = 27 - x + 2

Here, again, we run into the problem of obtaining number values like 27 or 28 that do not correspond to letters.  So again we use the MOD 26 operation to correct this and our formula becomes

y = (27 - x + 2)(Mod 26)

Give This Encoding Formula a Try!
Go to the coding program at this page and input an 8-letter message 1 letter at a time, hitting "Enter" after each letter.

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