The Cryptography-What it is
Cryptography is the field concerned with linguistic and mathematical techniques for securing information, particularly in communications. Historically, cryptography was concerned solely with encryption; that is, means of converting information from its normal, comprehensible form into an incomprehensible format, rendering it unreadable without secret knowledge. Encryption was used primarily to ensure secrecy in important communications, such as those of spies, military leaders, and diplomats. In recent decades, however, the field of cryptography has expanded its remit: modern cryptography provides mechanisms for more than just keeping secrets and has a variety of applications including, for example, authentication, digital signatures, electronic voting and digital cash. Moreover, people without extraordinary needs for secrecy use cryptographic technology, which is often built transparently into much of computing and telecommunications infrastructure.
Cryptography is an interdisciplinary subject, drawing from several fields. Older forms of cryptography were chiefly concerned with patterns in language. More recently, the emphasis has shifted, and cryptography makes extensive use of mathematics, particularly discrete mathematics, including topics from number theory, information theory, computational complexity, statistics and combinatorics. Cryptography is also considered a branch of engineering, but it is considered to be an unusual one as it deals with active, intelligent and malevolent opposition (see cryptographic engineering and security engineering). Cryptography is a tool used within computer and network security