Cryptography is the practice and study of techniques for secure communication in the presence of third parties or adversaries. So it is nothing but the art of protecting information by transforming it (encrypting it) into an unreadable format, called cipher text. Thus it is in general an idea of constructing and analyzing protocols that overcome the influence of adversaries and which are related to various aspects in information security such as data confidentiality, data integrity, and authentication. A person who possesses the secret key, which can be even his biometric information, can decrypt/decipher the message to readable/understandable format. Encrypted messages can sometimes be broken by cryptanalysis, also called codebreaking, although modern
cryptography techniques are virtually unbreakable or rather claim to be so till some hacker breaks into it.
Cryptography systems can be broadly classified into symmetric-key systems that use a single key that both the sender and recipient have, and public-key systems that use two keys, a public key known to everyone and a private key that only the recipient of messages uses. Modern
cryptography intersects the disciplines of mathematics, computer science, and electrical engineering. Applications of
cryptography include ATM cards, computer passwords, and electronic commerce.
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Watermarking of Data Using Biometrics