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Questions and Answers
Cryptography is the art and science of keeping messages public.
False
Decryption is the process of encoding the contents of a message.
False
Cryptanalysis is the art of breaking ciphers.
True
Symmetric key encryption uses different keys for encryption and decryption.
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Cryptographers are people who practice cryptanalysis.
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Public-key encryption is a type of symmetric key encryption.
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Asymmetric Key Encryption uses only one key for both encryption and decryption.
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Public-key cryptography allows anyone to decrypt a message.
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Substitution cipher replaces each element of the plaintext with a different element in the alphabet.
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Monoalphabetic ciphers use different substitutions across the entire message.
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Vigenère cipher is an example of a polyalphabetic cipher.
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Product cipher is classified as a transposition cipher.
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The Playfair Cipher is a monoalphabetic cipher.
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In the Caesar cipher, each letter is replaced by the letter one position further down the alphabet.
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The Vigenère Cipher is a polyalphabetic substitution cipher.
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The keyword 'LEMON' was used to encrypt the plaintext 'ATTACK AT DAWN' in the Vigenère Cipher.
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In the Caesar cipher, decryption formula is p = (c - k) mod 26.
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The Vigenère Cipher uses a table together with a keyword for encryption and decryption.
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In Playfair Cipher, if there is a repeated letter in a pair, a filler like 'Z' is inserted.
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In Playfair Cipher, if both letters of a pair fall in the same row, they are replaced with the letter above them.
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In Playfair Cipher, if both letters of a pair fall in the same column, they are replaced with the letter below them.
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Row Transposition Ciphers involve shuffling the plaintext without altering the actual letters used.
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Rail Fence cipher involves writing message letters out diagonally over a number of columns.
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In Rail Fence cipher, if the depth is 3, the ciphertext is read off vertically instead of row by row.
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Study Notes
Cryptography Basics
- Cryptography is the art and science of keeping messages secret, not public.
Encryption and Decryption
- Decryption is the process of decoding the contents of a message, not encoding.
- Symmetric key encryption uses the same key for both encryption and decryption.
- Asymmetric Key Encryption, also known as public-key encryption, uses a pair of keys: one for encryption and another for decryption.
Cryptanalysis
- Cryptanalysis is the art of breaking ciphers, not making them.
Cryptographers
- Cryptographers are people who practice cryptography, not cryptanalysis.
Ciphers
Substitution Ciphers
- Substitution cipher replaces each element of the plaintext with a different element in the alphabet.
- Monoalphabetic ciphers use a single substitution across the entire message.
- Polyalphabetic ciphers use multiple substitutions.
- Vigenère cipher is an example of a polyalphabetic cipher.
Transposition Ciphers
- Product cipher is classified as a transposition cipher.
- Row Transposition Ciphers involve shuffling the plaintext without altering the actual letters used.
- Rail Fence cipher involves writing message letters out diagonally over a number of columns.
Specific Ciphers
Playfair Cipher
- The Playfair Cipher is a monoalphabetic cipher.
- In Playfair Cipher, if there is a repeated letter in a pair, a filler like 'Z' is inserted.
- In Playfair Cipher, if both letters of a pair fall in the same row, they are replaced with the letter above them.
- In Playfair Cipher, if both letters of a pair fall in the same column, they are replaced with the letter below them.
Vigenère Cipher
- The Vigenère Cipher is a polyalphabetic substitution cipher.
- The Vigenère Cipher uses a table together with a keyword for encryption and decryption.
- The keyword 'LEMON' was used to encrypt the plaintext 'ATTACK AT DAWN' in the Vigenère Cipher.
Caesar Cipher
- In the Caesar cipher, each letter is replaced by the letter one position further down the alphabet.
- In the Caesar cipher, decryption formula is p = (c - k) mod 26.
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Description
Learn about polygraphic ciphers, specifically focusing on the Playfair and Caesar cipher. Understand how the Playfair cipher substitutes two-letter groups, and how the Caesar cipher shifts each letter by a fixed number of positions.