Objectives of cryptography, Symmetric Key Encryption- Stream ciphers & Block ciphers, Public-Key cryptography: RSA, Hash-functions, Discrete logarithm, Modular Squaring, Cryptographic Protocols: Key exchange & entity authentication, identification schemes, commitment schemes, electronic elections, Probabilistic algorithms, probably secure encryption & Digital signatures. Mathematical Models for Internet: Design and control communication networks that respond to: randomly fluctuating demands and failures by adapting rates, by rerouting traffic and by reallocating resources, stability and fairness of rate control algorithms for the Internet; economic issues, scalable models of simulation of such networks, Quantum Cryptography