Security and Cryptography - Chapter 3: Classical Encryption Techniques

block cipher

A type of encryption that operates on data as a sequence of blocks, typically with transformation depending on the current data block, secret key, and content of preceding blocks

brute-force attack

A cryptanalysis technique that involves trying every possible key until the correct one is found

cipher

An algorithm for performing encryption or decryption

ciphertext

The encrypted form of a message

computationally secure

A cipher is computationally secure if the cost of breaking it exceeds the value of the encrypted information or the time required exceeds the useful lifetime of the information

conventional encryption

Traditional encryption method using the same key for encryption and decryption (also known as symmetric encryption)

cryptanalysis

The study of methods to break or bypass cryptographic security without knowing the key

cryptographic system

The entire system used for encryption and decryption, including algorithms, keys, and protocols

cryptography

The art and science of keeping messages secure, including encryption and decryption techniques

digram

A pair of consecutive letters in text

enciphering

The process of converting plaintext into ciphertext

encryption

The process of converting plaintext into ciphertext using a cipher and a key

monoalphabetic substitution cipher

A cipher that replaces each letter in the plaintext with a corresponding letter in the ciphertext, using the same substitution throughout the message

one time pad

A cipher that uses a random key the same length as the message, where the key is used only once

permutation

A rearrangement of the positions of characters in plaintext to produce ciphertext

plaintext

The original, unencrypted message

polyalphabetic substitution cipher

A cipher that uses multiple substitution alphabets to encrypt the plaintext

single-key encryption

Encryption system where the same key is used for both encryption and decryption

stream cipher

A cipher that operates on data as a sequence of bits, with transformation depending on a secret key

symmetric encryption

Encryption where the same key is used for both encryption and decryption

unconditionally secure

A cipher that cannot be broken even with unlimited computational resources (mathematically proven to be secure)