History of Cryptography to the 1800s

Abstract

Cryptography is an integral part of information security. Thus, the need to understand cryptography is substantial. The study of cryptography can be daunting, particularly for readers who do not have a rigorous mathematical background. It is often useful to begin with studying ancient ciphers. While these ciphers lack sufficient security to be useful today, they are effective at teaching the fundamental concepts of cryptography. These ancient ciphers still have a plaintext, an algorithm, and a key, used to produce the ciphertext. For this reason, ancient ciphers are an appropriate starting point for the study of cryptography.

Test Your Knowledge

A few questions are provided here to aid you in testing your knowledge before you proceed.

• 1. What is the most obvious weakness in a mono-alphabet cipher?

  • A. They preserve word frequency.

  • B. They can be cracked with modern computers.

  • C. They are actually quite strong.

  • D. They don’t use complex mathematics.

• 2. The total number of possible keys for a given cipher is referred to as the _______________.

  • A. key group

  • B. key domain

  • C. key space

  • D. key range

• 3. Which of the following methods used a cylinder with text wrapped around it?

  • A. Vigenère cipher

  • B. Jefferson disk

  • C. Cipher disk

  • D. Scytale

• 4. What is an affine cipher?

  • A. Any cipher of the form ax + b (≡ m)

  • B. Only single-substitution ciphers

  • C. Any single-substitution cipher

  • D. A multi-alphabet cipher

• 5. What are the key features of homophonic substitution?

  • A. Multiple substitution alphabets are used.

  • B. A single plaintext letter may have several ciphertext representations.

  • C. The ciphertext is phonically similar to the plaintext.

  • D. It combines substitution with transposition.