User blog:Peacexfreedom/Vigenère cipher

Vigenère cipher
To encrypt or decrypt a Vigenère cipher without using the chart, use the following equations:
 * α= the number the coded letter is in the alphabet (example: s is 19)
 * β= the number the key letter (corresponding to the coded letter) is in the alphabet (example: g is 7)
 * λ= the number the encoded (message) letter is in the alphabet (example: m is 13)

Example message:
 * Message: MABELEATSSPRINKLES
 * Key: GRAVITYGRAVITYGRAV
 * Cipher: SRBZTXYZJSKZBLQCEN
 * Where s is 19, g is 7, and m is 13
 * Calculation: (19+1)-7=13

Decrypt
Equation: (α + 1) – β = λ

Requirements/Rules:

a>b

Encrypt
 Equation: (β-1) +  λ =  α 

 If [ (β-1) +  λ] > 26, then  (β-1) +  λ -26 =  α

If  β =  λ, then  β =  λ =  α