SOLUTION to Challenge 2: Shedding Light

Congratulations to Bill Briere for solving Challenge 2, the first code to be solved on Code a Week!

I’ll reveal the secrets below, but if you haven’t tried your hand at solving it, read this first.

The ciphertext is:

gurjnlgbevtug
jebatfvfgbghe
aguryvtugbsge
hguhcbagurzvq
nojryyf

“Shedding Light” is a ROT13 cipher, one of the simplest coding techniques. To encipher a message, you number the alphabet where A = 1, B = 2, etc.

A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z
1  2  3  4  5  6  7  8  9  10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Then you take each letter in your message and add 13 letters. If the result is over 26, simply subtract 26. So, “A” would be “N”; “X” would be “K”; etc.

Thus, the message “HAT” becomes “UNG”.

ROT13 is a form of the Caesar Cipher, in which a shift of fixed length occurs, just not necessarily a shift of 13. What makes ROT13 the most popular form of Caesar is the fact that 13 is half of 26, the number of letters in the English alphabet. To decipher, you can perform the same operation that was used to encipher. That’s not the case with any other shift length.

For example, using a shift of +4, “A”=”D”. To decode, you have to reverse the operation and subtract 4.

But using a shift of 13, you always get back to where you started. Here’s a great article on how the Caesar Cipher helps to understand the concept behind Modular Arithmetic.

So what’s the solution? Give it a try and scroll below to see the answer.

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thewaytoright
wrongsistotur
nthelightoftr
uthuponthemid
abwells

Formatted, this becomes: “The way to right wrongs is to turn the light of truth upon them.” ― Ida B. Wells

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