Cybersecurity of Industrial Systems

Appendix 1Cryptography Basics

A1.1. Introduction

Cryptography is one of the basic techniques for securing information systems. Content is encrypted using a method or algorithm that transforms a message to make it unintelligible. This technique is old and has existed since ancient times. Its weak point was the need to transmit the encryption and decryption method to all parties. In 1976, Whitfield Diffie and Martin Hellman (Diffie et al. 1976), of Stanford University, proposed an entirely new encryption principle: public key or asymmetric cryptography. This technique allows you to distribute a key to encrypt a message, but this key does not allow you to decrypt it. This principle has been incorporated into the RSA system (Rivest–Shamir–Adleman, names of inventors).

A1.1.1. Definitions of the terms

Encryption is about transforming a message in such a way that it becomes incomprehensible. Only authorized correspondents will be able to decipher it.

Data encryption consists of applying a function F configurable by a key k to a message M, so that the message cannot be decrypted.

Decryption consists of transforming a previously encrypted message to reconstitute the original message. The objective is that only authorized correspondents can carry out this action.

Unauthorized correspondents aims at reconstituting the original message by trying to “break” the cryptographic code or algorithm.

Signing a document consists of creating an electronic signature unique to the document and ...