Julian Zelizer: Public-key cryptography is a mathematical system for scrambling information. Zelizer says encryption is performed with two mathematical keys: one that users keep secret, one that they can freely distribute. He says in the 1970s, the inventors thought that people would one day publish their public keys in some kind of directory such as a phone directory but with hundred-digit keys instead of phone numbers. Digital signatures can be used to sign any kind of digital information, such as an e-mail message or a purchase order.”]
Source: https://www.csoonline.com/article/2116278/technologies–tools-and-tactics.html