recent years, computational complexity theory has led to a revolution in the designs of secret codes. The field of cryptography, as this area is known, now extends well beyond secret codes for private communications and addresses a broad range of issues concerning the security of information.
             Modern cryptography is concerned with four chief objectives:
             1. Confidentiality; the information cannot be understood by anyone other than the intended recipient.
             2. Integrity; the information cannot be altered during storage or transit without the alteration being detected.
             3. Non-repudiation; the creator cannot deny at a later stage his intention in the creation and transmission of the information.
             4. Authentication: the sender and receiver can confirm each other's identity and the origin or destination of the information.
             The advances that have been made in technology such as Internet e-Commerce, communications
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