Rangdom

Encode text with a keyword

The della Porta cipher (1563) repeats your keyword across the message and uses each keyword letter to pick a tableau row that exchanges the A–M and N–Z halves of the alphabet. It belongs to the same keyword-driven family as Vigenère and Beaufort, but every letter always crosses between the two halves.

When to use this tool

Reach for the della Porta cipher when a puzzle, CTF challenge, or cryptography course uses this classic 1563 polyalphabetic cipher, in which each keyword letter selects a tableau row that exchanges the A–M and N–Z halves of the alphabet. It shares the same repeating-keyword mechanic as Vigenère and Beaufort but always crosses each letter between the two halves, and like Beaufort it is self-reciprocal — the same operation both encodes and decodes. Pick a keyword, then encode or decode on a single page.

Privacy and limitations

Everything runs locally in your browser; nothing is sent anywhere. This is a classical polyalphabetic cipher, not real encryption — it only transforms A–Z and a–z, leaves digits and symbols untouched, and implements only the modern A/B-paired Porta tableau with no alternate variants or auto-solving features. Because the transform is its own inverse, encode and decode produce identical results; you still need the exact keyword to recover a message.

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