I am required to create an cipher that encrypted a message using a certain keyword with assumption that user will not repeat any alphebet for the keyword.(if user repeat any alphebet the program will not run.)it also requires user input of keyword and message for the program to run.

example
keyword : TIGER
alphebet in original order:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
these letter will be encrypted as such :
T I G E R Z Y X W V U S Q P O N M L K J H F D C B A
originally message will be:
I HAVE ATE AN APPLE.
after encrypting it will be:
B XTFR TJR TP TNNSR.

spacing and punctuation will be ignored in this case.