Introduction

Implementation Attack: Try to extract key through reverse engineering or power measurement, e.g., for a banking smart card.

Social Engineering: E.g., trick a user into giving up her password

Cryptology is the science of secret messages. Therefore, anything that has to do with making or breaking codes falls into cryptology’s domain.

• The scientific study of cryptography and cryptanalysis.

<aside> 💡 Prime numbers are the heart of cryptography.****

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Simply put, Cryptography provides a method for secure communication. By using cryptography, we can send secret messages to others across an insecure medium (like the internet), and be sure that only the intended recipients will be able to read the message.

Implementations of the cryptographic algorithms are available here.

Cryptanalysis is the inverse of cryptography. It's the study of how to break secret codes, not make them. Having a solid understanding of cryptanalysis is fundamental in cryptography.

History of Cryptography

The art of secret communication is not new and has been done for centuries.

Secret communication achieved by hiding the existence of a message is known as steganography, derived from the Greek words steganos, meaning “covered,” and graphein, meaning “to write.”

In parallel with the development of steganography, there was the evolution of cryptography, derived from the Greek word kryptos, meaning “hidden.”

The aim of cryptography is not to hide the existence of a message, but rather to hide its meaning, a process known as encryption.

In turn, cryptography itself can be divided into two branches, known as transposition and substitution.

• In transposition, the letters of the message are simply rearranged, effectively generating an anagram.
• In transposition each letter retains its identity but changes its position, whereas in substitution each letter changes its identity but retains its position.

A cipher is the name given to any form of cryptographic substitution in which each letter is replaced by another letter or symbol.

It is possible to have substitution at a much higher level, whereby each word is represented by another word or symbol—this is called code.

• Technically, a code is defined as substitution at the level of words or phrases, whereas a cipher is defined as substitution at the level of letters.