Computer Security : Generic name for collection of tools designed to protect data and frustrate hackers.Network Security : measures to protect data during transmission.Internet Security : measures to protect data during transmission over interconnnected networks.3 aspects of Information Security : Security attack : Any action that compromises the security of the information owned by organization. Security mechanism : Mechanism that is designed to detect, prevent or recover from security attack. Security service : Service that enhances security of data processing system and information transfer. Makes use of one or more security mechanism to provide the services. Each security service is implemented using one or more security mechanism. There are 14 difference security service : Authentication : Assurance that the communicating entity is the one claimed. Access Control : prevention of unauthorized use of resource. Data Confidentiality : protection of data from unauthorized disclosure. Data Integrity : Assurance that data received is sent by authorized person. Non repudiation : protection against denial by one of the parties in communication. 4 basic task in designing security service Design an algorithm : Opponent must not be able to defeat its purpose. Generate secret information. Develop methods of distribution and sharing of secret information. Specify protocol to be used by SR as security algorithm. Cryptographic techniques underlies many of the security mechanism.