Cryptography is - in a nutshell - the study of how to protect information in systems where multiple agents (or players) interact. This can be in cases where mutually trusting players want to be protected against external attacks, or cases where the players do not trust each other and wish to be protected against those they interact with. In both cases, many fundamental open questions remain open.

Some of these questions relate to border areas between cryptography and other disciplines, such as rational cryptography and quantum cryptography, and these are treated in detail in the sections on Algorithmic game theory and Quantum informatics, respectively.