Task Four: $4-$bit OFB $(2$ marks$)$

This task comprises three parts. Part one. This task is to implement a $4-$bit OFB TEA algorithm.

See the code for TEA in the lecture notes. Part two. Encrypt your student number using $4-$bit OFB

TEA algorithm as devised above. Part three. Add all the digits of your student number mod $7.$ Let

the result be c$.$ Then implement c$-$bit OFB TEA algorithm and encrypt your student numberusing

this algorithm. Compare the time needed to encrypt using $4-$bit OFB TEA algorithm and c$-$bit

OFB TEA algorithm and write your result in Task$4$Report.PDF$.$ Explain what has happened.

Remark: If the result of the modulo operation is $0$ or $4,$ that is c $=0$ or c $=4,$ then you need to

implement $3-$bit OFB TEA instead.