Beaufort Cipher
[INTRODUCTION]
The Beaufort Cipher, created by Sir Francis Beaufort, is based on the Beaufort square which is essentially the same as a Vigenère's tabula recta but in reverse order starting with the letter Z in the first row, wjere the first row and the last column serve the same purpose.
[ALGORITHM]
The Beaufort Cipher uses Beaufort square, a 26 x 26 table contains 26 possible shifts of alphabet arranged into rows and columns. (Refer to the attached picture)
The cipher is similar to the Vigenère cipher as it both needs a keyword which is repeated so that the total length of it is in equal length to the plaintext.
The letters in the leftmost column of the table serves as keys, while the upper row are the letters to plot for your plaintext. The intersection of given key and the letter of your plaintext will be a cipher letter.
[ENCRYPTION]
For example, the plaintext to be encrypt is:
"AVE FELLOW WELL MET"
With a key of "WATSON"
It will be:
AVEFEL--LOWWEL-LMET (plaintext)
WATSON-WATSON-WATS (keyword)
The first plaintext letter is A and the first keyword letter is W.
Using the Beaufort Square, find plaintext A at the upper row and keyword W at the leftmost part of the table. Now its intersection will give you the cipher text which is letter W.
Proceeding:
Plaintext V + Keyword A = F
Plaintext E + Keyword T = P
The same process is repeated for all the characters.
So, the ciphertext for the above plaintext is:
"WFPNKC-LMXWKC-LOPZ"
AVEFEL--LOWWEL-LMET (plaintext)
WATSON-WATSON-WATS (keyword)
WFPNKC-LMXWKC-LOPZ (ciphertext)
[DECRYPTION]
Let's use the given above.
WFPNKC-LMXWKC-LOPZ (ciphertext)
WATSON-WATSON-WATS (keyword)
To decrypt the code, find keyword W in the leftmost of the square, move down to the its cipher text which is letter W. Now, letter A, that is on the upper row, is the plaintext.
Following:
Keyword A + Cipher Text F = V
Keyword T + Cipher Text P = E
Do the same procedure in the remaining letters and you'll finally decode it.
WFPNKC-LMXWKC-LOPZ (ciphertext)
WATSON-WATSON-WATS (keyword)
AVEFEL--LOWWEL-LMET (plaintext)
[GAME]
1. IULMRCOBHDJXBVZAE (Keyword: Vice)
2. SWTERQSRESFOYRG (Keyword: Jamie)
3. XAEXDTKKUAAYYTSNOJVWYSKLNAJS (Keyword: Yellow)