18 Questions
Which concept involves exchanging one letter for another?
Polyalphabetic substitution cipher
What type of substitution cipher involves using a key letter to shift the cipher alphabet for encryption?
Auto key cipher
Which of the following ciphers involve using a 5x5 square of letters for encryption?
Playfair cipher
Which cipher technique involves matrix multiplication for encryption and decryption?
Hill cipher
Which type of cipher relies on a keyword to determine the shifting of alphabets for encryption?
Auto key cipher
Which type of substitution cipher uses multiple alphabets to encrypt plaintext?
Polyalphabetic substitution cipher
What is the defining characteristic of an Auto key cipher?
The key is a stream of subkeys where the 1st subkey is predefined.
How is encryption performed in a Playfair cipher when two letters are in the same row of the secret key?
The encrypted character for each letter is the next letter to the right.
What is the key stream used in a Vigenere cipher?
A repetition of the initial secret key stream of a certain length.
In an Auto key cipher, what value does the 3rd subkey take?
The value of the 2nd character of the plain text.
What happens in a Playfair cipher when two letters are neither in the same row nor in the same column?
The encrypted character is in its own row but in the same column as the other character.
What makes Hill cipher different from a Playfair cipher?
Hill cipher encrypts pairs of letters based on their positions in a matrix.
What is the main characteristic of a Polyalphabetic substitution cipher?
Each occurrence of a character may have different substitution
What is the characteristic of an Auto key cipher?
The next letter of the key is used as part of the key itself
Which cipher is known for using a 5x5 grid of letters to encrypt messages?
Playfair cipher
In the context of encryption, what does the Vigenere cipher rely on?
Rotating alphabet key
What differentiates Hill cipher from other ciphers?
It involves matrix operations for encryption and decryption
Which type of substitution cipher involves shifting letters based on a keyword?
Poly alphabetic substitution cipher
Study Notes
Ciphers
- Autokey cipher: uses a stream of subkeys, where each subkey is used to encrypt the corresponding character in the plaintext.
- In Autokey cipher, the first subkey is predefined, and subsequent subkeys are the values of previous plaintext characters.
Playfair Cipher
- The secret key is a 5x5 matrix of 25 characters.
- Rules for encryption:
- If two letters are in the same row, the corresponding encrypted character is the next letter to the right.
- If two letters are in the same column, the corresponding encrypted character is the next letter below in the same column.
- If two letters are neither in the same row nor in the same column, the encrypted character is in its own row but in the same column as the other character.
Vigenere Cipher
- The key stream is the repetition of the initial secret key stream of length m.
- Example: Plaintext - ABCDEFGHK, Key - 0, 5, 8
Cryptography Basics
- Encryption: transforming plaintext into ciphertext using an encryption algorithm and a key.
- Decryption: transforming ciphertext back into plaintext using a decryption algorithm and a key.
- Cryptosystem: a set of rules for encryption and decryption, often using a device called a key.
- Cryptanalyst: a person who studies encryption and tries to find hidden meanings.
Substitution Ciphers
- Substitution: replacing plaintext characters with different ciphertext characters.
- Types:
- Monoalphabetic substitution cipher: 1:1 relationship between plaintext and ciphertext characters.
- Polyalphabetic substitution cipher: 1 to many relationships between plaintext and ciphertext characters.
Monoalphabetic Substitution Cipher
- Additive cipher: key value is added to plaintext, with numeric values ranging from 0 to 25.
- Example: Plain text - HELLO, Key - 15, Cipher text - WTAAD.
Affine Cipher
- Combines additive and multiplicative properties: C = (P + K) mod 26.
- Decryption: P = (C - K) mod 26.
Combination Cipher
- Combination of additive and multiplicative properties: C = [(P x K1) + K2] mod 26.
- Decryption: P = [(C - K2) x K1-1] mod 26.
Test your knowledge on various ciphers including Auto Key, Playfair, Vigenere, and Hill ciphers. Learn about the encryption and decryption techniques along with examples for each cipher.
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