Abstract: Cryptography is a tool that guards a network and data transmission over a network. Data Security is the core aspect of secure data transmission over untrustworthy network. Network security encompasses the authorization of access to data in a network, which is organized by the network administrator. Users select or are assigned an ID and password or other authenticating information that permits them access to information and programs within their control. Network security covers a wide range of computer networks, both public and private, that are used in ordinary jobs performing transactions and communications among businesses, government agencies and individuals. Networks may be private, such as within a company, or private which allow access to the public. Network security is involved in every type of institutions. In this article we concisely outlined Network security and cryptography along with its basic principles. Keywords: Network, Network Security, Cryptography, Asymmetric Cryptosystems, Symmetric Cryptosystems