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Understanding the Playfair Cipher Basics
Aug 31, 2024
Playfair Cipher - Part 1
Session Outcomes
Understand the basic working of Playfair Cipher
Learn about diagrams and their generation with and without filler characters
Classical Encryption Techniques
Substitution Technique
Transposition Technique
Focus: Substitution Technique (Playfair Cipher)
Introduction to Playfair Cipher
Also known as Playfair Square or Wheatstone Playfair Cipher
Type
: Manual symmetric encryption technique
Symmetric encryption
: Same key used for both encryption and decryption
Example: Sender encrypts with a key, and the receiver decrypts using the same key
First literal diagram substitution technique
Invented
: 1854 by Charles Wheatstone
Named after Lord Playfair for promoting its use
Characteristics of Playfair Cipher
Multi-letter encryption technique
Unlike single-letter techniques (e.g., Caesar cipher)
Example: Letter 'D' can be encrypted to different characters at different occurrences
Improves security compared to classical ciphers
Diagrams Approach
Plain text letters are split into diagrams (pairs of letters)
Key
: A keyword used to construct a 5x5 matrix
Example: Using "monarchy" as the key
Constructing the 5x5 Matrix
Fill matrix with keyword letters (no repeating letters)
Example:
M O N A R
C H Y
Fill remaining letters of the alphabet, combining I and J
Resulting matrix example:
M O N A R
C H Y B D
E F G I/K L
M N O P Q
R S T U V
W X Y Z
Rules for Encryption
Creating Diagrams
Split plaintext into pairs of letters (diagrams)
Example: "hello" becomes HE LL O
Inserting Filler Character
Insert a filler character (e.g., 'X') if repeating letters are found or if the last letter is left alone
Example:
"attack" → AT TA CK
"balloon" → BA LX LO ON
Encryption Logic
Same Column
: Move down (wrap around if at bottom)
Same Row
: Move right (wrap around if at end)
Rectangle
: Swap letters
Summary of Diagram Creation
Create diagrams from plaintext
Handle repeating letters with filler characters
Ensure all letters are included in diagrams
Conclusion
Basic working of Playfair cipher understood
Diagrams generation rules covered
Next presentation: Encryption using Playfair cipher
Notes
Remember the importance of the filler character and its agreed selection by sender and receiver.
Explore more examples in the next session.
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Full transcript