In 1967, David Kahn, an American historian, journalist, and writer, published a book titled The Codebreakers – The Story of Secret Writing, which is considered to be the first extensive treatment and a comprehensive report of the history of cryptography and military intelligence from ancient Egypt to modern times [93]. Kahn’s book introduced cryptology to a broader audience. Its content was, however, necessarily restricted to symmetric cryptography. In symmetric cryptography, the sender and receiver of a message share a common secret key and use it for both encrypting and decrypting. The problem of how sender and receiver should exchange the secret in a secure way was considered out of scope.