Here's the ciphertext to decode.

1.  Find the keylength
2.  Find the key

CIHYKTKSDCKSLXVVAROXSUYXGXSJORUVRVXXUJCISESSFVVIXJSTZYTMCEKWZEPCOWNNIJZMIIWEYYXIRFSIYXWTZVGRELOPOXMGXSBMRVLSXXVVISSQCEJILIBJKTXSAFZIZLSXKRKVOCCIRJOIKETHGVIYXIHYKFRIGJORMWCWRMHIFKEXUSIIYIRZSJGRJSIIVSYXSIOXEHCFXHGMBRTHKWHRHPOWVKNMYGCEYXOXIKOSTJCIZLKYBZZIJWHRZIYSTRSIXMQRQT

Or, with lines cut off

CIHYKTKSDCKSLXVVAROXSUYXGXSJORUVRVXXUJCISESSFVVIXJSTZYTMCEKWZEPCOWNNIJZMIIWEY
YXIRFSIYXWTZVGRELOPOXMGXSBMRVLSXXVVISSQCEJILIBJKTXSAFZIZLSXKRKVOCCIRJOIKETHGV
IYXIHYKFRIGJORMWCWRMHIFKEXUSIIYIRZSJGRJSIIVSYXSIOXEHCFXHGMBRTHKWHRHPOWVKNMYGC
EYXOXIKOSTJCIZLKYBZZIJWHRZIYSTRSIXMQRQT