Cryptography—What Is It and How Does It Work?

A High-Level Overview With Examples Using Ruby + OpenSSL

Cryptography—Not Just a Digital Thing

As defined by Bruce Schneier in his book Applied Cryptography, “The art and science of keeping messages secure is cryptography […].” Cryptography, while now considered fundamental in our digital lives, is not specifically related to computing. It has existed in various forms for millennia. From Wikipedia’s article on the history of cryptography:

The earliest known use of cryptography is found in non-standard hieroglyphs carved into the wall of a tomb from the Old Kingdom of Egypt circa 1900 BCE. These are not thought to be serious attempts at secret communications, however, but rather to have been attempts at mystery, intrigue, or even amusement for literate onlookers. These are examples of still other uses of cryptography, or of something that looks (impressively if misleadingly) like it. Some clay tablets from Mesopotamia somewhat later are clearly meant to protect information — one dated near 1500 BCE was found to encrypt a craftsman’s recipe for pottery glaze, presumably commercially valuable. Later still, Hebrew scholars made use of simple monoalphabetic…