Implementing Cryptography Using Python

CHAPTER 2Cryptographic Protocols and Perfect Secrecy

Cryptography has been used since 1900 BC to ensure message secrecy. Up until the 1970s, the use of cryptography was primarily found in government and military applications; the use expanded to telecommunication and financial industries over the following decade. In today's world, we find cryptography in cell phones, emails, web browsers, and bank cards. Over the next few years, we can expect cryptography to play a role in how we communicate with our refrigerators, cars, and other devices connected through the Internet of Things.

It is important to ensure the use of strong encryption of sensitive data and that we provide integrity and confidentiality of the data. In this chapter, we will look at the study of cryptology and its components and then dive into perfect secrecy. Claude Shannon, often regarded as the father of information theory, defined perfect secrecy for secret-key systems and showed that perfect secrecy exists. Basically, perfect secrecy is the idea that no matter how much ciphertext you have, it will not convey anything about the contents of the plaintext or key. It can be proved that any such scheme must use at least as much key material as there is plaintext to encrypt. In terms of probabilities, this means that the probability distribution of the possible plaintexts is independent of the ciphertext.

In this chapter, you will continue your journey into understanding the importance of message perfect secrecy. ...