Cryptography (or cryptology; from Greek κρυπτός, "hidden, secret"; and γράφειν, graphein, "writing", or -λογία, -logia, "study", respectively) is the practice and study of techniques for secure communication in the presence of third parties (called adversaries). More generally, it is about 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. Modern cryptography intersects the disciplines of mathematics, computer science, and electrical engineering. Applications of cryptography include ATM cards, computer passwords, and electronic commerce.
Cryptology prior to the modern age was almost synonymous with encryption, the conversion of information from a readable state to apparent nonsense. The sender retained the ability to decrypt the information and therefore avoid unwanted persons being able to read it. Since World War I and the advent of the computer, the methods used to carry out cryptology have become increasingly complex and its application more widespread.
Modern cryptography follows a strongly scientific approach, and designs cryptographic algorithms around computational hardness assumptions, making such algorithms hard to break by an adversary. It is theoretically possible to break such a system but it is infeasible to do so by any practical means. These schemes are therefore computationally secure. There exist information-theoretically secure schemes that provably cannot be broken—an example is the one-time pad—but these schemes are more difficult to implement than the theoretically breakable but computationally secure mechanisms.
Cryptology-related technology has raised a number of legal issues. In the United Kingdom, additions to the Regulation of Investigatory Powers Act 2000 requires a suspected criminal to hand over their encryption key if asked by law enforcement. Otherwise the user will face a criminal charge. The Electronic Frontier Foundation is involved in a case in the Supreme Court of the United States, which will ascertain if requiring suspected criminals to provide their encryption keys to law enforcement is unconstitutional. The EFF is arguing that this is a violation of the right of not being forced to incriminate oneself, as given in the fifth amendment.