Caesar Cipher: The Cryptographic Disk

The Caesar cipher shifts every letter by the same number of positions in the alphabet. It is the simplest cipher there is, which makes it a good place to see the parts every cipher has: a message, a key, encryption, transmission and decryption.

Alice writes a message, sets the shift on a two-ring disk and encrypts the text one letter at a time: find the letter on the inner ring, read the result on the outer ring. The key goes to Bob over a secure channel, the ciphertext over an open one, and Bob turns the disk back.

Works with the English alphabet (A–Z) and the Russian one.

Part of Ludus Lab: small browser games about cryptography and quantum key distribution, each with a short article. Theory and the other games: https://ludus-lab.com. Languages: English, Spanish, Chinese and Russian (buttons in the top-right corner).