Our exploration of the cybersecurity world starts with a look at the different ways in which information is converted into secret code and back (encryption and decryption), as well as at the various tricks used to reveal content that had been intended to remain secret. Understanding encryption is a prerequisite to grasping a lot of what follows in subsequent chapters. This is because most non-public information of any consequence is communicated – and often also stored – in forms that are designed to be unreadable to eavesdroppers.

Encryption is quite an apt topic with which to pick up the reader who is not a computer expert. Unlike most other aspects of cybersecurity, it has a long history that stretches back over two millennia. Encoding and decoding messages rarely requires any specific technology. In theory, the steps required to convert an original text into a secure code and back could be carried out using a pen, paper and a pocket calculator, even if, in practice, the complexity of modern encryption and the amount of information involved precludes using it without a computer.

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Next section: The Sicilian Mafia and the Caesar cipher