Cryptography or cryptology (of kryptós κρυπτός Greek, "hidden, secret", and grafein γράφειν, "writing", or -logía -λογία, "estudio", respectively) is the practice and study of techniques of secure communication in presence Of the third parties called opponents. More generally, cryptography consists of constructing and analyzing protocols that prevent third parties or the public from reading private messages; Various aspects of information security, such as data confidentiality, data integrity, authentication and non-repudiation, are fundamental to modern cryptography. Modern cryptography exists at the intersection of mathematics, computer science and electrical engineering. Cryptography applications include military communications, e-commerce, ATM cards, and computer passwords.
Pre-modern cryptography was synonymous with encryption, converting information from a readable state to apparent nonsense. The originator of an encrypted message (Alice) shared the decoding technique necessary to retrieve the original information only with recipients (Bob), thereby preventing unwanted persons (EVE) from doing the same. The cryptography literature often uses Alice ("A") for the sender, Bob ("B") for the recipient, and Eva ("spy") for the adversary. Since the development of rotor encryption machines in World War I and the advent of computers in World War II, the methods used to carry out cryptology have become increasingly complex and their application more widespread.
Modern cryptography relies heavily on mathematical theory and computer practice; Cryptographic algorithms are designed around computational hardness assumptions, making such algorithms difficult to break in practice by any adversary. Theoretically it is possible to break such a system, but it is impossible to do so by any known practical means. Therefore, these schemes are called safe from the computational point of view; Theoretical advances, for example, improvements in integer factorization algorithms and faster computing technology require these solutions to be continuously adapted. There are theoretically secure information schemes that demonstrably can not be broken even with unlimited computing power: one example is the platform, but once these schemes are more difficult to implement than the theoretically better mechanisms that can break, but are computationally secure .
The growth of cryptographic technology has raised a number of legal issues in the information age. The potential of cryptography for use as a tool for espionage and sedition has led many governments to classify it as a weapon and to limit or even prohibit its use and export. In some jurisdictions where the use of cryptography is legal, the law allows investigators to force disclosure of encryption keys for documents relevant to an investigation. Cryptography also plays an important role in the management of digital rights and copyright infringement of digital media.