## Podcast Beta

## 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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VigenÃ¨re 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 VigenÃ¨re Cipher is a polyalphabetic substitution cipher.

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

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

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The VigenÃ¨re 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.
- VigenÃ¨re 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.

### VigenÃ¨re Cipher

- The VigenÃ¨re Cipher is a polyalphabetic substitution cipher.
- The VigenÃ¨re 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 VigenÃ¨re 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.