Podcast
Questions and Answers
What are the two basic building blocks of all encryption techniques?
In a substitution technique, how are the letters of plaintext replaced?
What was the earliest known substitution cipher known as?
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?
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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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Description
Explore the basic building blocks of encryption techniques including substitution and transposition. Learn about substitution techniques where plaintext letters are replaced by other letters, numbers, or symbols, such as the Caesar cipher (shift cipher).
