Alberti Cipher Disk

How Alberti Cipher Disk works

Alberti Cipher Disk handles letters between a fixed outer alphabet and an editable inner disk whose alignment changes by a chosen step after each completed interval. Encoding reads the inner alphabet at the outer letter position plus the current offset. Decoding reverses that lookup, and both modes advance the disk after the same count of letters. The Alberti Cipher Disk exposes its message, inner alphabet, initial offset, letters per rotation, rotation step, operation controls so this particular convention stays inspectable instead of hiding behind an unexplained preset.

With an ordinary inner alphabet, offset one, period three, and step one, ABCDEF becomes BCDFGH because the disk advances again before encoding D. Cipher students can experiment with a movable-disk principle using fully explicit rotation timing rather than an undocumented hand signal or hidden random movement. The Alberti Cipher Disk presents a deterministic plain-text result that can be copied and compared with the worked value before it enters another workflow.

Limits and private processing

Historical Alberti operation allowed operator-selected indicator changes; this tool uses the stated periodic convention for reproducibility. It is educational, not secure. The Alberti Cipher Disk performs its complete operation locally in your browser; neither the source text nor its settings are uploaded, stored remotely, or sent through an external request.