Symmetric Encryption

Flashcards covering core concepts of symmetric encryption, including definitions, historical ciphers, attack types, and algorithm categories like block and stream ciphers, and key principles like Kerckhoff’s Principle.

Active attack

An attempt to alter system resources or affect their operation.

Passive Attack

An attempt to learn or make use of information from a system without affecting its resources.

Man-in-the-Middle (MitM) Attack / On-Path Attack

An attack where the adversary intercepts traffic between two communicating parties.

Plaintext

The original, unencrypted form of a message.

Ciphertext

The encrypted form of a message.

Key

A piece of information used to encrypt or decrypt messages/data.

Key space

The set of all possible keys.

Symmetric Encryption

An encryption method that uses the same key for both encryption and decryption.

Asymmetric Encryption

An encryption method that uses separate keys (a pair) for encryption and decryption.

Caesar Cipher / Shift Cipher

A simple substitution cipher where each letter in the plaintext is replaced by a letter a fixed number of positions down the alphabet.

Substitution cipher

A method of encryption where units of plaintext are replaced with ciphertext, according to a regular system, often using symbols or shifted letters.

Frequency analysis

A method for breaking ciphers, especially substitution ciphers, by studying the frequency of letters or patterns in the ciphertext.

Vigenère cipher / Polyalphabetic cipher

An encryption method that uses a series of different Caesar ciphers based on the letters of a keyword, making it more resistant to frequency analysis.

One-to-many plaintext to ciphertext

A property of ciphers like Vigenère where a single plaintext letter can be encrypted to multiple different ciphertext letters, depending on its position and the key.

Kerckhoff’s Principle

A cryptosystem should be secure even if everything about the system, except the key, is public knowledge; security relies solely on the secrecy of the key.

Security through Obscurity

The belief that a system is secure if its inner workings are unknown to the public; considered not a secure method.

Stream Cipher

An encryption method that encrypts data bit by bit as it is transmitted, without breaking it into chunks.

Block Cipher

An encryption method that encrypts data by grouping it into fixed-size chunks (blocks).

Enigma Cipher

A historical stream cipher used by Germany in WWII.

Data Encryption Standard (DES)

An older block cipher, deprecated around 2017 and prohibited for federal government interaction by 2023 due to its limited key length.

Advanced Encryption Standard (AES)

A modern and frequently used block cipher, adopted as a standard after 'Rijndael'.

Diffusion

A property of a cipher where a change in a single plaintext character statistically results in about half of the bits of the ciphertext changing.

Confusion

A property of a cipher that aims to obscure the relationship between the ciphertext and the key, making it difficult to determine which part of the key created which part of the ciphertext.

Padding

Adding extra data to a message in a block cipher to make its length exactly match a multiple of the block size.

Double DES (2DES)

A DES variant that uses two 56-bit keys to encrypt data twice, increasing strength.

Two-key Triple DES (3DES)

A DES variant that uses two 56-bit keys in a three-step encryption process (Encrypt-Decrypt-Encrypt), offering increased strength.

Three-key Triple DES (3DES)

A DES variant that uses three distinct 56-bit keys in a three-step encryption process (Encrypt-Decrypt-Encrypt), providing significantly higher strength.

Rijndael

The original name of the algorithm that was adopted as the Advanced Encryption Standard (AES).

ECB (Electronic Codebook)

A block cipher mode where each block of plaintext is encrypted independently with the same key.

CBC (Cipher Block Chaining)

A block cipher mode where each block of plaintext is XORed with the previous ciphertext block before encryption, using an Initialization Vector (IV).

CFB (Cipher Feedback)

A block cipher mode that makes a block cipher into a stream cipher, where ciphertext depends on all preceding plaintext.

OFB (Output Feedback)

A block cipher mode that makes a block cipher into a stream cipher, where feedback for encryption is independent of plaintext or ciphertext.

XOR (Exclusive OR)

A logical bitwise operation that outputs true (1) if inputs differ, and false (0) if inputs are the same; often used in symmetric encryption.

PEBKAC (Problem Exists Between Keyboard And Chair)

A humorous acronym indicating that user error is the cause of a problem, highlighting humans as a weak link in cybersecurity.

Brute Force Attack

An attack that tries every possible key until the correct one is found.

Ciphertext Only Attack

An attack where the adversary has only a collection of ciphertexts and attempts to deduce the plaintext or the key.

Known-Plaintext Attack (KPA)

An attack where the adversary has access to both the plaintext and its corresponding ciphertext.

Chosen-Plaintext Attack (CPA)

An attack where the adversary can choose arbitrary plaintexts to be encrypted and obtain their corresponding ciphertexts.

Adaptive-Chosen-Plaintext Attack

A type of chosen-plaintext attack where the attacker can choose subsequent plaintexts based on information learned from previous encryptions.

Chosen-Ciphertext Attack (CCA)

An attack where the adversary can choose arbitrary ciphertexts and obtain their corresponding plaintexts (decryptions).

Chosen-Key Attack

An attack where the adversary has some control over or knowledge of the key used for encryption.

Wrench Attack

A non-technical, human-factor attack where a person is physically coerced to reveal a password or key.