Pattern Recognition Flashcards

What is a Caesar cipher?

Answer: A substitution cipher that shifts each letter by a fixed number of positions

The Caesar cipher shifts each letter in the plaintext by a fixed number of positions in the alphabet. For example, with a shift of 3, A becomes D.

What is frequency analysis used for in cryptography?

Answer: To break substitution ciphers by analyzing letter frequency patterns

Frequency analysis exploits the fact that certain letters (like E, T, A in English) appear more often, allowing codebreakers to identify substitution patterns.

What is the difference between a cipher and a code?

Answer: A cipher transforms individual characters; a code replaces entire words or phrases

Ciphers operate on individual characters (letter by letter substitution or transposition), while codes replace entire words or phrases with other words or symbols.

What is a transposition cipher?

Answer: A cipher that rearranges the order of letters without changing them

Transposition ciphers keep the original letters but rearrange their positions. Examples include rail fence and columnar transposition ciphers.

What is a one-time pad?

Answer: A theoretically unbreakable cipher using a random key as long as the message

The one-time pad uses a truly random key at least as long as the message, XORed with the plaintext. When used correctly, it is mathematically proven to be unbreakable.

What is the Enigma machine?

Answer: A WWII German cipher machine using rotors for polyalphabetic encryption

The Enigma machine used a series of rotating wheels (rotors) to create complex polyalphabetic substitution ciphers, famously broken by Allied codebreakers.