Group items tagged

Cryptanalysis and Frequency Analysis

An in-depth description of Julius Caesar's shift cipher and how it works. Also shows how to use frequency analysis and chi-square values to quickly break the cipher.

For longer ciphers, Kasiski analysis is useful for determining possible keywords using a modified frequency analysis and repetition analysis. This is an online tool to find repeat sequences in a ciphertext, and can be used to quickly decrypt a Vigenere ciphertext.

A more user-friendly way to work on monoalphabetic substitution ciphers, includes frequency charts

I'm just going to resubmit the bookmark directly to this page so I'll be sure it ends up publicly in the group. This wasn't mentioned in Singh chapter 2, but it was created around the time period discussed in the chapter. (Plus, it's one of my favorite articles I've read in Wired so I really wanted to use it as a bookmark.) The article discusses the strategies used to break this cipher, some of which, such as frequency analysis, we have talked about in class. It's also just fascinating to read about the Oculists and their history.

Here's the paper that Robert Ward of Maryland shared with me via email last year. The stats look solid to me, although I didn't check his p-values. Let me know if you work this into any of your projects this fall!