You're a young detective. Every detective needs a function to decrypt a vigenère cipher. It's a modification of a caesar cipher.

Let's talk more about the algorithm:

• Every letter is a number. A=0, B=1, C=2, (...), Z=26
• Output should be presented in capital letters.
• Use ONLY letters. Without interpunction, spaces, etc
• Function has two arguments: encrypted text and key (both are strings). Your output will present a decrypted text. Let's show it on easy example from http://en.algoritmy.net/article/45623/Vigenere-cipher

Ciphertext : CTMCCD, Key : Cat

C – C = 2 – 2 = 0 = A

T – A = 19 – 0 = 19 = T

M – T = 12 – 19 = 19 = T

C – C = 2 – 2 = 0 = A

C – A = 2 – 0 = 2 = C

D – T = 3 – 19 = 10 = K

decrypted word: ATTACK

It's quite simple,right? Good luck!

You can read more about this cipher here. Click!