Polygraphic Ciphers: Playfair and Caesar Cipher

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Questions and Answers

Cryptography is the art and science of keeping messages public.

False (B)

Decryption is the process of encoding the contents of a message.

False (B)

Cryptanalysis is the art of breaking ciphers.

True (A)

Symmetric key encryption uses different keys for encryption and decryption.

<p>False (B)</p> Signup and view all the answers

Cryptographers are people who practice cryptanalysis.

<p>False (B)</p> Signup and view all the answers

Public-key encryption is a type of symmetric key encryption.

<p>False (B)</p> Signup and view all the answers

Asymmetric Key Encryption uses only one key for both encryption and decryption.

<p>False (B)</p> Signup and view all the answers

Public-key cryptography allows anyone to decrypt a message.

<p>False (B)</p> Signup and view all the answers

Substitution cipher replaces each element of the plaintext with a different element in the alphabet.

<p>True (A)</p> Signup and view all the answers

Monoalphabetic ciphers use different substitutions across the entire message.

<p>False (B)</p> Signup and view all the answers

Vigenère cipher is an example of a polyalphabetic cipher.

<p>True (A)</p> Signup and view all the answers

Product cipher is classified as a transposition cipher.

<p>False (B)</p> Signup and view all the answers

The Playfair Cipher is a monoalphabetic cipher.

<p>False (B)</p> Signup and view all the answers

In the Caesar cipher, each letter is replaced by the letter one position further down the alphabet.

<p>False (B)</p> Signup and view all the answers

The Vigenère Cipher is a polyalphabetic substitution cipher.

<p>True (A)</p> Signup and view all the answers

The keyword 'LEMON' was used to encrypt the plaintext 'ATTACK AT DAWN' in the Vigenère Cipher.

<p>True (A)</p> Signup and view all the answers

In the Caesar cipher, decryption formula is p = (c - k) mod 26.

<p>True (A)</p> Signup and view all the answers

The Vigenère Cipher uses a table together with a keyword for encryption and decryption.

<p>True (A)</p> Signup and view all the answers

In Playfair Cipher, if there is a repeated letter in a pair, a filler like 'Z' is inserted.

<p>False (B)</p> Signup and view all the answers

In Playfair Cipher, if both letters of a pair fall in the same row, they are replaced with the letter above them.

<p>False (B)</p> Signup and view all the answers

In Playfair Cipher, if both letters of a pair fall in the same column, they are replaced with the letter below them.

<p>True (A)</p> Signup and view all the answers

Row Transposition Ciphers involve shuffling the plaintext without altering the actual letters used.

<p>True (A)</p> Signup and view all the answers

Rail Fence cipher involves writing message letters out diagonally over a number of columns.

<p>False (B)</p> Signup and view all the answers

In Rail Fence cipher, if the depth is 3, the ciphertext is read off vertically instead of row by row.

<p>False (B)</p> Signup and view all the answers

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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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