WHY THIS MATTERS
Caesar and substitution operate on visible symbols.
USE EXAMPLE TEXT — DO NOT ENTER REAL SECRETS. Everything here is transformed locally in your browser; this lab does not contact or access external systems.
LETTERS → ALPHABET MAPPING
CAESAR SHIFT
“Caesar cipher” names the historically associated shift-cipher concept: each alphabetic letter moves by a fixed number of positions. Spaces, punctuation, and numbers stay put.
CIPHERTEXT
SHIFT
PLAIN
ABCDEFGHIJKLMNOPQRSTUVWXYZSHIFTEDLETTER SHIFT · 13 POSITIONS
ROT13
ROT13 is a Caesar shift of exactly 13 positions. In a 26-letter alphabet, applying it twice returns every letter to its original position.
ROT13(TEXT)
ROT13(ROT13(TEXT))
FIXED SHIFT → ARBITRARY MAPPING
SUBSTITUTION
A monoalphabetic substitution replaces each letter with one chosen counterpart. It has vastly more possible mappings than a Caesar cipher—but repeated language patterns still leak structure.
PLAIN ALPHABET
ABCDEFGHIJKLMNOPQRSTUVWXYZSUBSTITUTION ALPHABETTRANSFORMED TEXT
CHARACTER CODES → BITS → LOGIC
XOR BITS
PLAINTEXT XOR KEY = CIPHERTEXT (BYTES)
CIPHERTEXT XOR KEY = PLAINTEXT
XOR TRUTH TABLE
| A | B | XOR |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
FIRST BYTE, BIT BY BIT
SECURITY TODAY
XOR is a fundamental operation used throughout computing and cryptography—not a complete secure cipher by itself. Security depends on its construction and key handling. A one-time pad is information-theoretically secret only with a truly random, message-length key used once and kept secret. This repeating-key illustration is not AES or secure messaging.
WHAT CHANGED?
Computers represent symbols as numbers, then as bits.
THE PAYOFF
XOR combines bits according to logic and can reverse itself with the same key.