Encryption & Ciphers – AP CSP | ShowMeClass

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Encryption & Ciphers

AP CSP · Unit 2: The Internet

Learning Objectives

Understand symmetric vs asymmetric encryption

Apply Caesar cipher encryption & decryption

Explain public/private key concepts

Recognize why encryption matters for security

Cipher Types

Caesar Cipher: Shift each letter by N positions. Symmetric key.

Vigenère Cipher: Polyalphabetic — uses keyword for variable shifts.

Substitution: Each letter maps to a different letter via a key alphabet.

Encryption Concepts

Symmetric: Same key to encrypt & decrypt (Caesar, AES)

Asymmetric: Public key encrypts, private key decrypts (RSA)

Key Space: Caesar = 25 keys; modern = 2²⁵⁶ keys

Colors

Plaintext

Ciphertext

Key / shift

EncryptionCaesarCipher

Cipher:Caesar

Key/Shift:3

Mode:Encrypt

Plaintext

↓ Encrypt ↓ Shift: 3

Ciphertext

CIPHER WHEEL

Input Text

Shift / Key Value 3

Cipher Type

Vigenère Keyword

Mode

Brute Force

Analysis

Quick Quiz▼

1. A Caesar cipher with shift 3 turns 'A' into:

B C D Z

2. Symmetric encryption means:

No key is needed Same key encrypts and decrypts Two different keys are used Data cannot be decrypted

3. Caesar cipher's main weakness is:

It only works with numbers Only 25 possible keys — easy to brute force It requires a computer It changes the message length