Twisting the Keyword Length from a Vigenère Cipher

Abstract

Researchers give an alternate method to the standard Friedman and Kasiski techniques for determining the length of a keyword in Vigenère-type ciphers using a comparison twist on the sorted frequency vectors of the letter usage in a message.

Keywords:

• coset
• cryptanalysis
• Friedman test
• Kasiski test
• sample signature
• signature
• twist difference
• Vigenerè cipher

Additional information

Notes on contributors

Thomas H. Barr

Thomas H. Barr is currently a faculty member at Indian Springs School where he teaches such courses as Linear Algebra, Discrete Math (with some cryptology in the mix), and Differential Equations. He also manages the school's internship program, teaches Entrepreneurship, and works with students on independent studies, competitions, and outdoor expeditions. He started and manages Entreventures Consulting, which provides strategic planning for startup and early-stage companies. Longer term, he served for many years as professor and chairperson of the Mathematics and Computer Science Department at Rhodes College.

Andrew J. Simoson

Andrew J. Simoson is a professor of mathematics at King University (which just happens to be the alma mater of Thomas H. Barr, who graduated the year before Andrew arrived at King in 1980). Nevertheless, this disjuncture prompted a life-long friendship, many mathematical discussions, and most recently, this article on a topic with which many undergraduate cryptology students have wrestled, oftentimes in vain.