probable-word method

cryptanalysis

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

July 21, 2026

Quick Summary

The probable-word method is a technique used in cryptanalysis, specifically for breaking running-key Vigenère ciphers. This method involves guessing words that are likely to appear in the original plaintext.1

Here's how it generally works:
* Guessing: The cryptanalyst identifies words they believe are probably in the message.1
* Subtraction: These guessed words are then "subtracted" from the ciphertext.1
* Analysis: This process helps reveal meaningful English fragments within the ciphertext, which can then be further analyzed to decrypt the entire message.1

This technique relies on the fact that even with encryption, patterns and redundancies in language can survive, aiding the cryptanalyst.2

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

6 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

Vigenère cipher
…is commonly known as the probable-word method. In this approach, words that are thought most likely to occur in the text are subtracted from the cipher. For example, suppose that an encrypted message to President Jefferson Davis of the Confederate States of America was intercepted. Based on a statistical analysis…
Read More
…is commonly known as the probable-word method. In this approach, words that are thought most likely to occur in the text are subtracted from the cipher. For example, suppose that an encrypted message to President Jefferson Davis of the Confederate States of America was intercepted. Based on a statistical analysis…
Read More