RSD2 ALERT: Reading and Media Literacy
  • Blog
    • About Mr. Durden
    • ALERT
    • SPARK
    • Mr. D. Celebrations
  • e-Reading
    • Classic Chapter Books for eReading
    • Bookman Road Media Center
    • Lake Carolina Upper Campus Media Center
    • Langford Elementary Media Center
    • Lonnie B. Nelson Media Center
    • Read Alouds >
      • AA History Read-Alouds
      • Architecture Read-Alouds
      • Creative Inspiration
      • Dr. Seuss!
      • Engineering Stories
      • Family Stories
      • Folktales >
        • Halloween Tales
        • Holidays Around the World
      • Habits of Mind >
        • Applying Past Knowledge to New Situations
        • Creating, Imagining, Innovating
        • Finding Humor
        • Gathering Data Through All the Senses
        • Learning Continuously
        • Listening with Understanding and Empathy
        • Managing Impulsivity
        • Metacognition (Thinking about Thinking)
        • Persisting
        • Questioning and Problem Solving
        • Responding with Wonderment and Awe
        • Striving for Accuracy and Precision
        • Taking Responsible Risks
        • Thinking and Communicating with Clarity and Precision
        • Thinking Flexibly
        • Thinking Interdependently
      • Math Read-Alouds
      • Research Unit Connections
      • Sustainable Living
      • U.S. Government in Storybooks
  • Reference
    • Atlas of Science Literacy
    • Digital Research Tools
    • Etymology Dictionary
    • Fallacies
    • Philosophy >
      • Stoicism
    • Project 2061: Science Literacy
    • Real World Research Connections
  • Music
    • Adventure Music
    • Classical Music
    • Fantasy Music >
      • Wild About Harry
    • Historical Eras in Music >
      • Colonial Era Music
      • Georgian Music
      • Federal Period Music
      • Greek Revival Music
      • Victorian Era Music >
        • Italianate Music
        • Romanesque Revival Music
        • Gothic Revival Music
        • Second Empire
        • Queen Anne Music
      • Stick, Shingle, Arts and Crafts Music
      • Prairie Style Inspired Music
      • Early 20th Century Revivals >
        • French Revival Music
        • Spanish Revival
        • Tudor Revival
        • Mediterranean Revival
      • Art Deco Music
    • Journaling Music
    • Literature-Music Connections
    • Mystery Music
    • Science Fiction Music >
      • Star Wars
    • Stage Musicals >
      • Blue Man Group
      • Hamilton!
    • WeVideo Safe Music Tracks
    • World Music >
      • Ancient Egypt
      • Arabic Music--Southwest Asia
      • Indian Music--South Asia
      • Persian Music--South Central Asia
      • Russian Music
  • Imagery
    • The Physical Universe
    • The Living Environment
    • The Human Experience
    • The Designed World
    • The Life of Strength and Grace
    • The Life of the Mind
  • Languages
    • Language Learners
    • Language Tech Tools
    • Language Grammar
    • Language Pronunciation >
      • Pronunciation: Getting Started
      • Arabic Pronunciation
      • Brazilian Portuguese Pronunciation
      • Cantonese Chinese Pronunciation
      • French Pronunciation
      • German Pronunciation
      • Italian Pronunciation
      • Japanese Pronunciation
      • Korean Pronunciation
      • Mandarin Chinese Pronunciation
      • Russian Pronunciation
      • Spanish Pronunciation
  • Breakout!
    • Breakout EDU Overview
    • Breakout EDU Coaching
    • Breakout EDU Timers
    • Breakout EDU Tools and Templates
    • Codes and Ciphers >
      • Caesar Shift and Wheel Ciphers
      • International Maritime Signals
      • Hidden Writing
      • Morse Code
      • Pigpen Ciphers
      • Substitution Ciphers
      • Vigenere Polyalphabetic Cipher
      • Semaphore Flag Signals
      • Signals and Noise: The Importance of Taking Note
    • Breakout ALERT Architecture 1 >
      • Breakout EDU ALERT Architecture 01 Logic Alpha >
        • Breakout EDU ALERT Architecture 01 Logic Bravo
        • Breakout EDU ALERT Architecture 01 Logic Charlie
        • Breakout EDU ALERT Architecture 01 Logic Delta
        • Breakout EDU ALERT Architecture 01 Logic Echo
        • Breakout EDU ALERT Architecture 01 Logic Foxtrot
      • Breakout EDU ALERT Architecture 01 Gallery
      • Breakout EDU ALERT Architecture 01 Geoguessr
      • Breakout EDU ALERT Architecture 01 Quotes Alpha >
        • Breakout EDU ALERT Architecture 01 Quotes Bravo
        • Breakout EDU ALERT Architecture 01 Quotes Charlie
        • Breakout EDU ALERT Architecture 01 Quotes Delta
        • Breakout EDU ALERT Architecture 01 Quotes Echo
        • Breakout EDU ALERT Architecture 01 Quotes Foxtrot
      • Breakout EDU ALERT Architecture 1 Taking Note Alpha >
        • Breakout EDU ALERT Architecture 1 Taking Note Bravo
        • Breakout EDU ALERT Architecture 1 Taking Note Charlie
        • Breakout EDU ALERT Architecture 1 Taking Note Delta
        • Breakout EDU ALERT Architecture 1 Taking Note Echo
        • Breakout EDU ALERT Architecture 1 Taking Note Foxtrot
      • Breakout EDU ALERT Architecture 01 Timeline Alpha >
        • Breakout EDU ALERT Architecture 01 Timeline Bravo
        • Breakout EDU ALERT Architecture 01 Timeline Charlie
        • Breakout EDU ALERT Architecture 01 Timeline Delta
        • Breakout EDU ALERT Architecture 01 Timeline Echo
        • Breakout EDU ALERT Architecture 01 Timeline Foxtrot
Picture

Vigenère Polyalphabetic Cipher


The Vigenère Cipher is one of the truly great breakthroughs in the development of cryptography, much stronger than other ciphers that preceded it. The birth of the cipher can be traced back to the work of Leon Alberti. Born in 1404, Alberti was one the leading figures of the Renaissance; a painter, composer, poet and philosopher. 

He is probably best known as an architect, having designed Rome's first Trevi Fountain and having written 'De Re Aedificatoria", the first printed book on architecture, which acted as a catalyst for the transition from Gothic to Renaissance design.

Sometime in the 1460's, Alberti had a conversation with Leonardo Dato, the Pope's secretary, about some of the finer points of cryptography. This prompted Alberti to write an essay on the subject, outlining what he believed to be a new form of cipher. Up until this point, a substitution cipher involved establishing a single cipher alphabet for encrypting each message. However, Alberti proposed using two or more cipher alphabets and switching between them during encipherment, thereby confusing potential cryptanalysts.

Although he had hit upon the most significant breakthrough in encryption for over one thousand years, he failed to develop his concept into a fully formed system of encryption. 

Blaise de Vigenère, a French diplomat, became acquainted with the writings of Alberti when he was sent to Rome on a two-year diplomatic mission in 1549. Initially, his interest in cryptography was purely practical and was linked to his diplomatic work. Then, at the age of 39 in 1565, Vigenère decided that he had accumulated enough money to be able to abandon his career and concentrate on a life of study. It was only then that his powerful new cipher reached its final form.


The cipher Alberti shared in his writings used 2 or at most 3 cipher alphabets. However, the Vigenère cipher uses 26 cipher alphabets! The 26 cipher alphabets are contained in the Vigenère Square, shown below, which has a plaintext alphabet followed by 26 cipher alphabets, each one shifted by one more letter with respect to the previous one. Hence, row number 1 represents a cipher alphabet with a Caesar shift of 1, row number 2 represents a cipher alphabet with a Caesar shift of 2, and so on.

​A different column of the square can be used to encrypt each letter of the message. In other words, the sender might encrypt the first letter according to column E, the second according to column M, and the third letter according to column U, and so on. In order to unscramble the message, it is important that the intended receiver knows which column of the Vigenère Square has been used to encipher each letter, and so there must be an agreed system of switching between columns. This agreement is achieved via a keyword.


  • The plaintext is written out;
  • The keyword is written above the plaintext in letter-to-letter correspondence, with the  keyword repeated as many times as needed to match the plaintext length;
  • The cryptographer uses the column of the keyword letter and the row of the plaintext letter to find the ciphertext;
  • The cryptographer can then send the message to the intended recipient, who knows the keyword by prior arrangement and can decrypt the message. 


The strength of the Vigenère Cipher is that the same letter can be encrypted in different ways.

For example, if the keyword is KING, then every plaintext letter can be encrypted in 4 ways, because the keyword contains 4 letters. Each letter of the keyword defines a different cipher alphabet in the Vigenère Square. Longer keywords with more unique letters make the cryptanalyst's task more difficult; by the time they have broken the cipher and read the message, the information may no longer need to be protected.


Picture

At first glance the Vigenère Cipher appears to be unbreakable, due to its use of up to 26 different cipher alphabets. Ciphers like this, which use more than one cipher alphabet are known as polyalphabetic (multiple alphabet) ciphers. These can be incredibly difficult to decipher, because of their resistance to the frequency analysis that makes vulnerable Caesar ciphers. Indeed, over time, the Vigenère cipher became known as "Le Chiffre Undechiffrable," or "The Unbreakable Cipher."

It wasn't until 1854, about two hundred years later, that the Vigenère Cipher was finally cracked independently by Polish Major Friedrich Kasiski and British cryptographer Charles Babbage. Both realized that looking for repeated sets or "runs" of letter patterns in the stream of ciphertext would give a fair idea of the length of the keyword setting for the message. If the cryptanalyst knows the target language and often-used phrases in the context of the likely subject of the message then the same approach to the Caesar cipher can work, made more difficult, but not impossible, by the added degree of difficulty of multiple Caesar ciphers.


Vigenère Ciphers Resources Online

Picture
https://www.dcode.fr/vigenere-cipher
Picture
https://www.guballa.de/vigenere-solver

​Kasiski Analysis
http://pages.mtu.edu/~shene/NSF-4/Tutorial/VIG/Vig-Kasiski.html
​


Charles Babbage, computer pioneer

Picture
Active Learning Experiences in Resourceful Thinking: Our  Mission

​The Richland School District Two ALERT program for academically gifted students, in association with families, the district and global community, affords each learner unique challenges to inspire the pursuit of highest academic standards by providing rigorous, differentiated curricula that cultivates excellence in leadership and life-long learning.
​


Website Updated:
15 April 2018
Webpage maintained by the Active Learning Experiences in Resourceful Thinking (ALERT)  and Scholarly Pursuits Always Reveal Knowledge (SPARK) classes of Richland School District Two, Columbia, South Carolina.
Please direct queries to Mr. Kevin Durden.
✕