Volvelle

plain

key

cipher

↺ reversible — the same settings decode it. Type to turn the disk.

A real Alberti cipher disk — turn the lettered wheel and it performs three genuine classical ciphers. The outer ring is fixed plaintext A–Z; the inner disk is the cipher alphabet. Type to watch it step letter by letter.

Type to encipher

Mode

Shift — rotation of the disk (0–25)

Keyword — drives the rotation per letter

Seed — the mixed cipher alphabet

Index period N — re-key every N letters

Per-period step — cells the disk turns each re-key

Direction

Presets

Skin

Encipher: find a plaintext letter on the fixed outer ring; its cipher letter is on the rotating inner disk beneath it. Drag the inner disk to turn it by hand (snaps to letters; sets the shift in Caesar mode). Skins change only colour & material — never the cipher.

↔ This disk only adds. Every mode here is a shift — (P+k) mod 26 (the self-test proves it). The multiplicative twin — (k·P) mod m, the half that draws a cardioid and completes the affine cipher — lives in the Numbers Room: The Times-Table Cardioid →.