Vigenere Cipher Cryptanalysis Graded Lab

Consider the following ciphretext that was ecrypted using Vigenere cipher and the key of length 5. Find the key and decipher the message.

You MUST explain your answer in detail.

Ciphertext

WSPGM HHEHM CMTGP NROVX WISCQ TXHKR VESQT IMMKW BMTKW CSTVL TGOPZ XGTKS CXHCX HSMGX WMNIA XPLVY GROWX LILNF JXTJI RIRVE XRTAX WETUS BITJM CKMCO TWSGR HIRGK PVDNI HWOHL DAIVX JVNUS JX

Optional: Write the program that performing Vigenere Cipher cryptanalysis in general. Input: Ciphretext, Output: Key Length, Key and plaintext.

You can implement an easier variation that inputs the Key Length instead of calculating an estimate value. This will reduce the number of calculations.