gen-define-a-one-time-pad-and-give-one-short-worked-example-e1a6

Define a one-time pad and give one short worked example.

# One-Time Pad A **one-time pad** is a theoretically unbreakable encryption method where: - The key is truly random - The key is at least as long as the message - The key is used only once - Encryption combines message and key using XOR (⊕) ## Worked Example **Message:** `HI` **Step 1:** Convert to binary (ASCII) - H = 72 = `01001000` - I = 73 = `01001001` **Step 2:** Generate random key (same length) - Key: `10110101 11100110` **Step 3:** Encrypt (XOR message ⊕ key) ``` Message: 01001000 01001001 Key: 10110101 11100110 ───────────────── Cipher: 11111101 10101111 ``` **Ciphertext:** `11111101 10101111` (or 253, 175 in decimal) **Step 4:** Decrypt (XOR cipher ⊕ key) ``` Cipher: 11111101 10101111 Key: 10110101 11100110 ───────────────── Message: 01001000 01001001 → "HI" ``` The security relies on the key being truly random and never reused. Without the key, the ciphertext reveals nothing about the plaintext.