Secret Codes — Defense Range

The code wheel

A Caesar cipher slides every letter along the alphabet by the same amount. Pick a shift, type a message, and watch it turn into a secret.

Shift 3

Your message

Secret (shifted forward)

Decrypted again (shifted back the same amount)

Shift forward to lock it, shift back the same amount to unlock it. The shift number is the key. Here the only is a number from 1 to 25, so there are just 25 to try.

Crack it

Here is an intercepted secret. You do not know the shift. No problem: a Caesar cipher only has 25 keys, so just try them all until one reads like English.

Tap a row when you can read it.

Why real codes hold

A Caesar cipher fell because it had 25 keys. Real encryption does the same trick, just with a key so enormous that trying them all is hopeless.

Number of keys to try:

Caesar cipher: 25 · a few seconds by hand

Modern key (AES-256):

That is more keys than there are atoms in the whole visible universe.

Brute force gives up here. Even if every computer on Earth guessed billions of keys a second, working together, they would not finish trying them all before the Sun burns out, or even before the universe gets old. So a strong key cannot be guessed open. It has to be given.

That is the whole idea: keep the key secret and unpredictable, and make it long enough that the number of guesses is bigger than time itself.