Security Requirements Confidentiality Data Integrity Availability User Authentication Non-repudiation Details of Theory of Secure Communication Condition of Perfect Secrecy P(M|C) = P(C|M)P(M) / P(C) P(M|C) = prob. of message M given C intercepted P(C|M) = prob. of cipher text C generated by M P(M) = prob. of M being selected P(C) = prob. of obtaining C Necessary and Sufficient Condition for Per..