Decipher the following messages which in English that have been encrypted.

Describe in not more than two or three sentences on the method used for deciphering.

i) RKZ'Y NGBK YUSK LAT COZN IOVNKXY

ii) POWTCDQR KSIK SIGD AODIKDO KSIF PWCVFWQJIC KJQD ICAWOJKSQ IOD JFKOINKITCD.

iii) VOKAIKAGGRSSFJRIQEVVKMUBJCWWYFGNWVFMCMXDLLTTGZB

iv) IRTLLRHCBSU NAAEGIMAEEL TCBAOTSNUF