Secrecy of Cipher System MCQ [Free PDF] – Objective Question Answer for Secrecy of Cipher System Quiz

1. Cryptosystems are used for

A. Privacy
B. Authentication
C. Privacy & Authentication
D. None of the mentioned

Answer: C

Cryptosystems which include the process of encryption and decryption are used for both privacy and authentication.

 

2. The key also contains a

A. Plaintext
B. Ciphertext
C. Plaintext & Ciphertext
D. None of the mentioned

Answer: C

The key is supplied along with a plaintext message for encryption and a cipher text message for decryption.

 

3. The system which has insufficient information available to crypt-analyst is

A. One-time pad
B. Unconditionally secure
C. One-time pad & Unconditionally secure
D. None of the mentioned

Answer: C

An unconditionally secure system is one that has insufficient information available to the crypt-analyst. One such system is a one-time pad.

 

4. Caesar’s cipher was a monoalphabetic cipher.

A. True
B. False

Answer: A

The earliest example of a monoalphabetic cipher was the Caesar cipher.

 

5. In Caesar cipher, each plain text is replaced by

A. Alphabet shift
B. Numerals
C. Symbols
D. None of the mentioned

Answer: A

In Caesar cipher, each plain text is replaced with a new letter obtained by an alphabetic shift.

 

6. The trithemius cipher is a mono alphabetical cipher.

A. True
B. False

Answer: B

The Trithemius cipher is a poly alphabetical cipher.

 

7. In the auto key method

A. Feedback is necessary
B. Feedback is not necessary
C. Can be either necessary or not
D. None of the mentioned

Answer: A

In the auto key method feedback is necessary for the encryption process.

 

8. In the Vigenere method ______ is provided.

A. Priming key
B. Feedback
C. Priming key & Feedback
D. None of the mentioned

Answer: C

Vigenere method which is also called the vigenere auto method priming key and feedback is used.

 

9. A cipher system is said to have perfect secrecy if

A. Posteriori probability is equal to the prior probability
B. Posteriori probability is greater than the prior probability
C. Posteriori probability is less than the prior probability
D. None of the mentioned

Answer: A

A cipher system is said to have perfect secrecy if for every message and cipher text the posterior probability is equal to the prior probability.

 

10. The conditions for perfect secrecy are

A. Only one key transforming message should exist
B. All keys should be equally likely
C. One key transforming message to each cipher text & all keys should be equally likely
D. None of the mentioned

Answer: C

The conditions for perfect secrecy are, that there is only one key transforming message to each cipher text and all keys should be equally likely.

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