DESIGN OF CRYPTOSYSTEM USING SYMMETRIC KEY OF ADVANCED ENCRYPTION STANDARD ALGORITHM (A CASE STUDY OF EXAMS AND RECORD FEDERAL POLYTECHNIC BAUCHI) BY ISAH MOHAMMED YAKUBU ATBU/CS/B.TECH/13/33629/d/1 SUBMITTED TO THE DEPARTMENT OF COMPUTER SCIENCE, SCHOOL OF SCIENCE AND TECHNOLOGY, ABUBAKAR TAFAWA BALEWA UNIVERSITY BAUCHI. AUGUST, 2015. i