CS435 - Classical Cryptography Flashcards

Study Notes

Ciphers and Keys

A cipher is a cryptographic algorithm that enables the processes of encryption and decryption.
A key is essential data utilized by a cipher for executing encryption and decryption processes.
Keyspace refers to the total range of potential values that a key can adopt.

Cryptography Principles

Kerckhoffs's principle asserts that the security of a cryptographic system should rely solely on the confidentiality of the key, not the cipher algorithm itself.
Cryptanalysis is the skill and discipline focused on identifying and exploiting vulnerabilities in cipher algorithms.

Types of Attacks on Cryptography

Different types of cryptography attacks include:
- Ciphertext-only attacks: Analyzing ciphertext without any known plaintext.
- Known-plaintext attacks: Ciphertext is paired with its corresponding plaintext.
- Chosen-plaintext attacks: The attacker can choose arbitrary plaintexts for encryption.
- Chosen-ciphertext attacks: The attacker can manipulate ciphertext to analyze the associated plaintext.

Specific Attack Goals

In a chosen-ciphertext attack, the objective is to deduce the key through the analysis of chosen ciphertexts.

Shannon's Principles

Claude Shannon recommended two primary principles to obscure redundancies in plaintext messages:
- Confusion: Aims to hide the relationship between plaintext and ciphertext.
- Diffusion: Disperses plaintext redundancy across the ciphertext to enhance security.

Confusion and Diffusion

Confusion emphasizes the complex correlation between ciphertext and plaintext, making decryption more challenging.
Diffusion involves spreading out plaintext data, reducing predictability and redundancy within the ciphertext.

Ciphers Classification

ROT13 and the Caesar cipher are classified as examples of monoalphabetic ciphers, employing a fixed substitution for letters.

Mathematical Representation

Zₘ denotes the set comprising integers from 0 to m - 1, commonly used in modular arithmetic.

Shift Cipher

A shift cipher is formally defined as a method whereby each letter in the plaintext is shifted by a fixed number of places down or up the alphabet.

Description

Test your knowledge of classical cryptography with these flashcards. Covering key concepts such as ciphers, keys, keyspace, and Kerchoff's principle, this quiz will help reinforce your understanding of fundamental cryptographic principles. Perfect for students of CS435 or anyone interested in the basics of cryptography.