From Crib to Menu

Introduction

A crib tells you what a piece of the plaintext probably says. A valid crib position tells you which cypher letters those plaintext letters became.

Link each crib letter to the cypher letter above it and you have a menu. The Bombe does not think about words; it thinks about whether a set of rotor settings can make every link in the menu true at once.

Key ideaAt every valid crib position, the crib and intercept letters form a menu — a graph that the Bombe can test electrically.