Cryptography is the science of writing and reading secret communications. Each cryptogram, or message, is prepared in a special form intended to hide its meaning so that it can be understood only by people who are familiar with both the method and the key being used. The term "cryptography" comes from two Greek words: "kryptos," meaning hidden, and "graphein," meaning to write.
Cryptography is as old as writing itself, and from the earliest days of civilization messages have been sent by secret methods. Today cryptography is used in human enterprises of all sorts, including commerce, banking, industry, espionage, diplomacy, and warfare.
It is sometimes possible to find the meaning of a cryptogram without having a prior knowledge of the system and key being used. The science of solving cryptograms in this way is called cryptanalytics and the procedures used constitute cryptanalysis. Cryptology is the name of the science that includes both cryptography and cryptanalysis.