Bifid Cipher Tool

Encrypt and decrypt using the Bifid Cipher, combining Polybius square substitution with vertical transposition fractionation.

Deep-Dive Educational Guide

Bifid Cipher: Polybius Fractionation, Delastelle’s Breakthrough & Modern Diffusion

An exhaustive educational breakdown of the Bifid Cipher: Félix Delastelle’s 1901 invention, Polybius square coordinate decomposition, horizontal stream fractionation, Claude Shannon’s concept of diffusion, and runnable Python auto-solvers.

Read Companion Guide →

How to Use Bifid Cipher Tool

  1. Enter Message and Polybius Keyword: Type your message and enter a keyword to construct the 5x5 Polybius square matrix (I/J combined).
  2. Vertical Coordinate Fractionation: Each letter is mapped to (row, column) coordinates, written vertically underneath the plaintext.
  3. Read Horizontally & Substitute: The coordinate numbers are read horizontally in periodic groups and converted back into ciphertext letters.

Frequently Asked Questions

What makes the Bifid cipher unique in classical cryptography?

Invented by Félix Delastelle around 1901, Bifid was the first classical cipher to achieve both substitution and transposition simultaneously through a process called fractionation.

Why does Bifid use a 5x5 Polybius square?

A 5x5 grid contains 25 cells, exactly enough to hold the 26 letters of the English alphabet when I and J share a single cell.