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MCQ | Cryptography Ciphers (Level: Easy)

Here, we have a set of multiple-choice questions and answers (quiz) on ciphers in Cryptography (basic concepts of Cryptography Techniques and different types of ciphers).
Submitted by Monika Sharma, on February 02, 2020

1) We are provided the plain text “SUN”. You need to convert the given plain text into ciphertext under the Ceasar cipher encryption technique. Which of the following options is the correct ciphertext for the given text if the key is 2?

  1. UWP
  2. NUS
  3. WUP
  4. QSL

Answer: a) UWP

Explanation:

In the Caesar cipher technique, the encryption is performed as follows,

    E ( P , K ) = ( P + K ) mod 26

    Therefore, 
    E ( S , 2 ) = ( 18 + 2 ) mod 26 = 20 = U
    E ( U , 2 ) = ( 20 + 2 ) mod 26 = 22 = W
    E ( N , 2 ) = ( 13 + 2 ) mod 26 = 15 = P
    Hence, the ciphertext is "UWP".

2) Which of the following cannot be chosen as a key in the Caesar cipher?

  1. An integer
  2. An alphabet (A-Z or a-z)
  3. A string
  4. None of the above

Answer: c) A string

Explanation:

In Caesar cipher, we can choose a number or a character which when performed addition modulo operation with the given letters of the plain text gives us ciphertext. However, a string cannot be chosen for encryption in this case.


3) Which of the following cipher techniques include the involvement of matrix operations in their algorithms of encryption and decryption?

  1. Hill Cipher
  2. Playfair cipher
  3. Both a and b
  4. None of the above

Answer: c) Both a and b

Explanation:

The hill cipher includes a square matrix as the key, and in Playfair cipher, we create a 5X5 matrix using the given key string. Hence, both these ciphers include the use of matrices.


4) Which of the following ciphers is a block cipher?

  1. Caesar cipher
  2. Vernam cipher
  3. Playfair cipher
  4. None of the above

Answer: c) Playfair cipher

Explanation:

The Playfair cipher uses a block of plain text, each block containing 2 characters.


5) Which of the following ciphers uses asymmetric key cryptography?

  1. Rail Fence Cipher
  2. Data Encryption Standard (DES)
  3. Diffie Hellman Cipher
  4. None of the above

Answer: c) Diffie Hellman Cipher

Explanation:

The Diffie Hellman cipher uses asymmetric key cryptography. It uses a pair of keys, one private and one public.


6) "Cipher" is synonymous with "code",

  1. True
  2. False

Answer: a) True

Explanation:

In cryptography, the terms "cypher" and "code" are synonymous since they both refer to a sequence of processes that encrypt a message; nonetheless, the ideas are separate in cryptography, particularly classical cryptography.


7) Block ciphers accumulate symbols in a message of a ______.

  1. Fixed size
  2. Variable
  3. Integration
  4. All of the mentioned above

Answer: a) Fixed size

Explanation:

Block cyphers amass symbols in a message of a fixed size (the block), whereas stream cyphers operate on a stream of symbols that is constantly changing. When a cypher employs the same key for both encryption and decryption, the algorithm or cypher is referred to as a symmetric key algorithm. Asymmetric key algorithms, also known as cyphers, encrypt and decrypt data using a different key for each operation.


8) With symmetric key algorithms, the ____ key is used for the encryption and decryption of data.

  1. Different
  2. Same
  3. Both A and B
  4. None of the mentioned above

Answer: b) Same

Explanation:

When using symmetric key techniques, the same key is utilized for both the encryption and decryption of the information being transmitted. Asymmetric key algorithms, which encrypt and decrypt data using public and private keys, are used to protect sensitive information.


9) ____ is the message or data that can be readable by the sender.

  1. Edited
  2. Main Text
  3. Plain text
  4. All of the mentioned above

Answer: c) Plain text

Explanation:

Plain text is a message or data that may be read by the sender, the receiver, or any third party who happens to come across it. When plain text is altered by the application of certain algorithms or procedures, the resulting data or message is referred to as ciphertext.


10) In the case of symmetric key encryption, the secret key that both the parties possess can be anything such as a _______.

  1. Passcode or a password
  2. Developed code
  3. Network set
  4. None of the mentioned above

Answer: a) Passcode or a password

Explanation:

With symmetric key encryption, the secret key that both parties have access to can be anything, such as a passcode or a password, depending on the circumstances. Also, a random string of characters or numbers generated using a secure Random Number Generator (RNG) can be used to represent it.


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