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Questions and Answers
Cryptography is the art and science of keeping messages public.
Cryptography is the art and science of keeping messages public.
False (B)
Decryption is the process of encoding the contents of a message.
Decryption is the process of encoding the contents of a message.
False (B)
Cryptanalysis is the art of breaking ciphers.
Cryptanalysis is the art of breaking ciphers.
True (A)
Symmetric key encryption uses different keys for encryption and decryption.
Symmetric key encryption uses different keys for encryption and decryption.
Cryptographers are people who practice cryptanalysis.
Cryptographers are people who practice cryptanalysis.
Public-key encryption is a type of symmetric key encryption.
Public-key encryption is a type of symmetric key encryption.
Asymmetric Key Encryption uses only one key for both encryption and decryption.
Asymmetric Key Encryption uses only one key for both encryption and decryption.
Public-key cryptography allows anyone to decrypt a message.
Public-key cryptography allows anyone to decrypt a message.
Substitution cipher replaces each element of the plaintext with a different element in the alphabet.
Substitution cipher replaces each element of the plaintext with a different element in the alphabet.
Monoalphabetic ciphers use different substitutions across the entire message.
Monoalphabetic ciphers use different substitutions across the entire message.
Vigenère cipher is an example of a polyalphabetic cipher.
Vigenère cipher is an example of a polyalphabetic cipher.
Product cipher is classified as a transposition cipher.
Product cipher is classified as a transposition cipher.
The Playfair Cipher is a monoalphabetic cipher.
The Playfair Cipher is a monoalphabetic cipher.
In the Caesar cipher, each letter is replaced by the letter one position further down the alphabet.
In the Caesar cipher, each letter is replaced by the letter one position further down the alphabet.
The Vigenère Cipher is a polyalphabetic substitution cipher.
The Vigenère Cipher is a polyalphabetic substitution cipher.
The keyword 'LEMON' was used to encrypt the plaintext 'ATTACK AT DAWN' in the Vigenère Cipher.
The keyword 'LEMON' was used to encrypt the plaintext 'ATTACK AT DAWN' in the Vigenère Cipher.
In the Caesar cipher, decryption formula is p = (c - k) mod 26.
In the Caesar cipher, decryption formula is p = (c - k) mod 26.
The Vigenère Cipher uses a table together with a keyword for encryption and decryption.
The Vigenère Cipher uses a table together with a keyword for encryption and decryption.
In Playfair Cipher, if there is a repeated letter in a pair, a filler like 'Z' is inserted.
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 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.
In Playfair Cipher, if both letters of a pair fall in the same column, they are replaced with the letter below them.
Row Transposition Ciphers involve shuffling the plaintext without altering the actual letters used.
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.
Rail Fence cipher involves writing message letters out diagonally over a number of columns.
In Rail Fence cipher, if the depth is 3, the ciphertext is read off vertically instead of row by row.
In Rail Fence cipher, if the depth is 3, the ciphertext is read off vertically instead of row by row.
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.
