MONO-ALPHABETIC AND POLY-ALPH……
1. Mono-alphabetic Cipher
1. Mono-alphabetic Cipher
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Definition
1. Mono-alphabetic Cipher…
Definition
Mono-alphabetic Cipher என்பது ஒரு substitution cipher. இதில்: ஒரே plaintext alphabet-க்கு முழு message-……
Explanation
Example
A → Q என்றால்: A A A ↓ ↓ ↓ Q Q ……
List
1. Poly-alphabetic Cipher…
Explanation
Poly-alphabetic Cipher என்பது multiple substitution alphabets பயன்படுத்தும் substitution technique. இதில்: ஒர……
Explanation
Word meaning
இந்த இரண்டு words-ஐ புரிந்துகொண்டால் concept easy. Mono Mono = One Therefore: Mono-alphabetic = O……
Simple Explanation
Plaintext: BANANA இதில்: A மூன்று முறை வருகிறது. Mono-alphabe……
Explanation
Example
A → Q A → Q A → Q அதாவது: Same plaintext letter → Same ciphertext letter. Poly-alphabetic Same plaintext: BAN……
Flow
Mono-alphabetic Cipher Plainte……
Explanation
Example
A → D B → E C → F Entire message-க்கும் இந்த same mapping. Poly-alphabetic Cipher Plain……
Definition
Detailed definition
Mono-alphabetic substitution cipher-ல்: Plain……
Explanation
Example
Plain : ABCDEFGHIJKLMNOPQRSTUVWXYZ Cipher: QWERTYUIOPASDFGHJK……
Real Life Example
Mono example
Plain alphabet: ABCDEFGHIJKLMNOPQRSTUVWXYZ Cipher alphabet……
Real Life Example
Another mono example
Plaintext: APPLE Suppose: A → Q P → H L → S E → T Then: A → Q P → H P → H L → S E →……
Important
Important property
Mono-alphabetic cipher: Same ……
Explanation
Example
E → X என்றால் message முழுவதும்: E → X……
Real Life Example
Examples of mono-alphabetic ciphers
Important examples: Caesar Cipher Simple Substitutio……
Explanation
Caesar as mono-alphabetic
Suppose Key = 3. Plain : ABCDEFGHIJKLMNOPQRSTUVWXYZ Cipher: DEFGHIJKLMNOPQRSTUVWXY……
Explanation
Mono key space
General mono-alphabetic substitution cipher-ல் alphabet letters எந்த permutation-லும் arrange செய்யலாம். Engl……
Explanation
Frequency analysis
Mono-alphabetic cipher-ன் major weakness: Frequency Analysis English language-ல் சில letters அதிகமாக வருகின்ற……
Explanation
Why frequency is preserved
Suppose plaintext: EEEEEE Mono cipher mapping: E → X Then ciphertext: XXXXXX Pl……
Explanation
Pattern preservation
Mono-alphabetic cipher word patterns-ஐயும் hide செய்ய முடியாமல் இருக்கலாம். LETTER Pattern: L E T T……
Explanation
Advantages of mono-alphabetic
Simple to understand. Easy to implement. Caesar cipher-……
Explanation
Disadvantages of mono-alphabetic
Same plaintext letter always maps to same ciphertext letter. Letter freque……
Definition
Poly-alphabetic cipher என்பது: More than one substitution alphabet பயன்பட……
Concept
Core concept
Mono: A → D A → D A → D Poly:……
Explanation
Why poly-alphabetic was developed
Mono-alphabetic cipher-ன் weakness: Same letter ↓ Same cipher letter ↓ Frequency preserved இந்த problem-ஐ red……
Explanation
Multiple alphabets
Suppose நாம் மூன்று Caesar alphabets வைத்துள்ளோம். Alphabet 1: A → B B → C C → D Alphabet 2: A → D B → E C → ……
Real Life Example
Most important example
Most famous poly-alphabetic c……
Explanation
Vigenère cipher
Vigenère cipher: Keyword + Multiple Caesar Shifts பயன்படுத்துக……
Output
Result
Explanation
Why same letter changes in vigenere
Plaintext: ATTACKATDAWN இதில் A multiple times வருகிறது. ஆனால் ஒவ்வொரு A-க்கும் கீழே வரும் key lette……
Formula
Vigenere formula
Standard numeric representation: A = 0 B = 1 ... Z = 25 Encryption: Cᵢ = (Pᵢ + Kᵢ) mod……
Explanation
Vigenere first letter
Plaintext: A Value: A = 0 Key……
Formula
C = (0 + 11) mod 26 C = 11 11……
Real Life Example
Second example
Plaintext: T T = 19. Key: E E = 4.……
Explanation
Why poly is stronger
Mono: Same plaintext frequency ↓ Visible in ciphertext Poly: Same plaintext character ↓ Dis……
Explanation
Poly does not mean unbreakable
Poly-alphabetic cipher mono-alphabetic cipher-ஐ விட stronger. ஆனால் அது completely secure அல்ல. If short keyw……
Explanation
Historical attacks
1. Kasiski Examination…
Explanation
Repeated ciphertext sequences வைத……
Explanation
1. Index of Coincidence…
Explanation
Statistical technique மூலம் key le……
Common Mistake
Key repetition problem
Suppose keyword: CAT Then: CATCATCATCATCAT... என்று repeat ஆகும். இ……
Explanation
Poly-alphabetic advantages
Multiple substitution alphabets. Same letter different ciphertext letters-ஆக மா……
Explanation
Poly-alphabetic disadvantages
Repeated short keys pattern உருவாக்கும். Kasiski examination போன்ற attacks poss……
Comparison
Mono vs poly - core difference
இந்த ஒரு concept மட்டும் strong-ஆக நினைவில் வ……
Explanation
Example
A A A ↓ ↓ ↓ D D D Poly Same Plaintext Le……
Comparison
Detailed comparison
Real Life Example
Example side-by-side
Plaintext: AAAA Mono, Key 3 Caesar A → D A → D A → D A → D Ciphertext: DDDD Clearly pattern remains. ……
Real Life Example
Another example
Plaintext: BANANA Mono example Suppose: B → W A → Q N → F Then: B A N A N A ↓ ↓ ↓ ↓ ↓ ↓ W Q F Q F Q Ciphertex……
Comparison
Frequency analysis comparison
Suppose plaintext has: E = 20% Mono If: E → X then ciphertext-ல்: X ≈ 20% This gives attacker clue. Poly ……
Concept
Substitution alphabet concept
Mono One table மட்டும்: Plain : ABCDEFGHIJKLMNOPQRSTUVWXYZ Cipher: QWERTYUIOPASDFGH……
Explanation
Tabula recta
Vigenère போன்ற polyalphabetic cipher-ஐ……
Concept
Row 0 : ABCDEFGHIJKLMNOPQRSTUVWXYZ Row 1 : BCDEFGHIJKLMNOPQRSTUVWXYZA Row 2 : CDEFGHIJKLMNOPQRSTUVWXYZAB Row ……
Explanation
Mono → frequency
One alphabet ↓ Fixed substitu……
Explanation
Poly → frequency hiding
Multiple alphabets ↓ Changing substit……
Explanation
Security level
Conceptual order: Caesar ↓ Simple Mono-alphabetic ↓ Poly-alphabetic Security generally increase……
Common Mistake
Error 1
"Mono-alphabetic means one key letter." Wro……
Common Mistake
Error 2
"Poly-alphabetic means each letter has one f……
Common Mistake
Error 3
"Caesar is poly-alphabetic." ……
Common Mistake
Error 4
"Vigenère is mono-alphabetic.……
Common Mistake
Error 5
"Mono-alphabetic cannot have large key space." Wrong. General mono……
Common Mistake
Error 6
"Large key space alone guarantees security." Wrong. Cryptographic ……
Memory Trick
Very easy memory: MONO = ONE POLY = MANY Then: MONO One alpha……
Remember
Mono = A always becomes D. A → D A → D A → D Poly = A can become ……
TRB Point
TRB / NET / SET exams-க்கு மிகவும் important: Mono means one substitution alphabet. Poly means many substitut……
Interview Point
Question
Why is poly-alphabetic cipher stronger than mono-alphabetic cipher? Answer: Because mono-alphabetic cipher ma……
MCQ
"Mono" in Mono-alphabetic mea……
MCQ
Mono-alphabetic cipher uses:…
MCQ
In a mono-alphabetic cipher, ……
MCQ
Which is a mono-alphabetic ci……
MCQ
A major weakness of mono-alph……
MCQ
General mono-alphabetic substitution ……
MCQ
"Poly" means:…
MCQ
Poly-alphabetic cipher uses:…
MCQ
Which is a poly-alphabetic ci……
MCQ
In poly-alphabetic cipher, th……
MCQ
Which cipher is more resistan……
MCQ
Vigenère cipher uses:…
MCQ
Vigenère cipher is essentiall……
MCQ
Which statement is correct?…
MCQ
Kasiski examination is mainly……
Practice
Question 1
Which one is mono-alphabetic? A → D A → D A → D Answer: ……
Practice
Question 2
Which one is poly-alphabetic? A → D A → K A → P Answe……
Practice
Question 3
Classify: HELLO → KHOOR Key = 3 Ans……
Practice
Question 4
Classify: Plaintext : ATTACKATDAWN Key : LEMONLEMONLE……
TRB Point
Exam short answer
Mono-alphabetic Cipher Mono-alphabetic cipher என்பது entire plaintext message-க்கும் ஒரே fixed substitution a……
Summary
SUBSTITUTION CIPHERS | ----------------------- | | Mono-alphabetic Poly-alphabetic | | One alphabet Many alph……
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