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Questions and Answers
What are the two basic building blocks of all encryption techniques?
What are the two basic building blocks of all encryption techniques?
- Substitution and transposition (correct)
- Caesar and transposition
- Transposition and Caesar
- Substitution and Caesar
In a substitution technique, how are the letters of plaintext replaced?
In a substitution technique, how are the letters of plaintext replaced?
- By shifting each letter by 3 places (correct)
- By using random symbols
- By repeating the same letter
- By removing certain letters
What was the earliest known substitution cipher known as?
What was the earliest known substitution cipher known as?
- Shift cipher
- Transposition cipher
- Vigenère cipher
- Caesar cipher (correct)
What is the general formula for the Caesar cipher algorithm?
What is the general formula for the Caesar cipher algorithm?
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In the Caesar cipher, how many places is each letter of the alphabet shifted?
In the Caesar cipher, how many places is each letter of the alphabet shifted?
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What does the decryption algorithm do in a substitution technique like the Caesar cipher?
What does the decryption algorithm do in a substitution technique like the Caesar cipher?
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Study Notes
Classical Encryption Techniques
- Two fundamental building blocks of encryption techniques: substitution and transposition
Substitution Techniques
- Replace plaintext letters with other letters, numbers, or symbols
- Substitute plaintext bit patterns with ciphertext bit patterns when viewed as a sequence of bits
Caesar Cipher (Shift Cipher)
- Earliest known use of a substitution cipher
- Simplest substitution cipher
- Replace each letter of the alphabet with the letter standing 3 places further down the alphabet
- Alphabet is wrapped around, so the letter following "z" is "a"
- Example: plaintext "pay more money" → ciphertext "SDB PRUH PRQHB"
- General formula: C = E(p) = (p+k) mod 26, where k is a value in the range 1 to 25
- Decryption algorithm: reverse of the encryption process
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