Criptografía (del griego κρύπτos '(criptos), «oculto», y γραφη (grafé), «grafo» ó «escritura», literalmente «escritura oculta»). Tradicionalmente se ha definido como el ámbito de la criptología el que se ocupa de las técnicas de cifrado o codificado destinadas a alterar las representaciones lingüísticas de ciertos mensajes con el fin de hacerlos ininteligibles a receptores no autorizados. Estas técnicas se utilizan tanto en el Arte como en la Ciencia. Por tanto, el único objetivo de la criptografía era conseguir la confidencialidad de los mensajes. Para ello se diseñaban sistemas de cifrado y códigos. En esos tiempos la única criptografía existente era la llamada criptografía clásica.[cita requerida] La aparición de la Informática y el uso masivo de las comunicaciones digitales, han producido un número creciente de problemas de seguridad. Las transacciones que se realizan a través de la red pueden ser interceptadas, y por tanto, la seguridad de esta información debe garantizarse. Este desafío ha generalizado los objetivos de la criptografía para ser la parte de la criptología que se encarga del estudio de los algoritmos, protocolos (se les llama protocolos criptográficos), y sistemas que se utilizan para proteger la información y dotar de seguridad a las comunicaciones y a las entidades que se comunican. Para ello los criptógrafos investigan, desarrollan y aprovechan técnicas matemáticas que les sirven como herramientas para conseguir sus objetivos. Los grandes avances que se han producido en el mundo de la criptografía, han sido posibles gracias a los grandes avances que se han producido en el campo de la matemática y la informática.

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Cryptography or cryptology (from Greek κρυπτός kryptós, "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, cryptography is about constructing and analyzing protocols that prevent third parties or the public from reading private messages; various aspects in information security such as data confidentiality, data integrity, authentication, and non-repudiation are central to modern cryptography. Modern cryptography exists at the intersection of the disciplines of mathematics, computer science, and electrical engineering. Applications of cryptography include ATM cards, computer passwords, and electronic commerce. Cryptography prior to the modern age was effectively synonymous with encryption, the conversion of information from a readable state to apparent nonsense. The originator of an encrypted message (Alice) shared the decoding technique needed to recover the original information only with intended recipients (Bob), thereby precluding unwanted persons (Eve) from doing the same. The cryptography literature often uses Alice ("A") for the sender, Bob ("B") for the intended recipient, and Eve ("eavesdropper") for the adversary. Since the development of rotor cipher 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 its application more widespread. Modern cryptography is heavily based on mathematical theory and computer science practice; cryptographic algorithms are designed around computational hardness assumptions, making such algorithms hard to break in practice by any adversary. It is theoretically possible to break such a system, but it is infeasible to do so by any known practical means. These schemes are therefore termed computationally secure; theoretical advances, e.g., improvements in integer factorization algorithms, and faster computing technology require these solutions to be continually adapted. There exist information-theoretically secure schemes that provably cannot be broken even with unlimited computing power—an example is the one-time pad—but these schemes are more difficult to implement than the best theoretically breakable but computationally secure mechanisms. The growth of cryptographic technology has raised a number of legal issues in the information age. Cryptography's potential 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, laws permit investigators to compel the disclosure of encryption keys for documents relevant to an investigation. Cryptography also plays a major role in digital rights management and copyright infringement of digital media.

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