Caesar Cipher

The game supports two alphabets: Russian (А-Я, Ё) and English (A–Z). All letters are automatically converted to uppercase. Spaces are kept but not encrypted. Digits and punctuation marks are not allowed.

Alice enters the original message. Each character is checked against the chosen alphabet. Invalid characters are filtered out automatically.

A shift (0-90) and direction (left/right) are chosen. The disk visually shows the character mapping.

For each character of the message:

• The letter's position on the inner disk is found
• The disk is rotated by the given shift
• The encrypted character is read from the outer disk
• Spaces are copied unchanged

Formula: C = (P + K) mod N, where P is the plaintext position, K is the shift, N is the alphabet size.

The key (shift) is transmitted over a secure channel, the ciphertext over an open one.

Bob applies the reverse shift to the ciphertext, recovering the original message.

Formula: P = (C − K + N) mod N