Cryptanalysis

Cryptanalysis (from the Greek "kryptós", "hidden", and "analýein", "to loosen" or "to untie") is the study of methods for obtaining the meaning of encrypted information, without access to the secret information which is normally required to do so. Typically, this involves finding a secret key. In non-technical language, this is the practice of codebreaking or cracking the code, although "break" can also mean just a part of a complete solution.
People have been making and breaking codes for many centuries. In the 1930s specialized machines were invented to do the calculations. Code-breaking machines such as the Colossus computer were important during World War II. Computers were the main tool of cryptanalysis in the Cold War and later.