Digital Communications

Cipher Systems and Secrecy of Cipher Systems

Question 1
Marks : +2 | -2
Pass Ratio : 100%
The system which has insufficient information available to crypt-analyst is
One-time pad
Unconditionally secure
One-time pad & Unconditionally secure
None of the mentioned
Explanation:
Unconditionally secure system is the one which has insufficient information available to crypt-analyst. One such system is one-time pad.
Question 2
Marks : +2 | -2
Pass Ratio : 100%
The key also contains a
Plaintext
Ciphertext
Plaintext & Ciphertext
None of the mentioned
Explanation:
The key is supplied along with a plaintext message for encryption and cipher text message for decryption.
Question 3
Marks : +2 | -2
Pass Ratio : 100%
Caesar cipher was a mono alphabetic cipher.
True
False
Explanation:
An earliest example of a mono alphabetic cipher was the Caesar cipher.
Question 4
Marks : +2 | -2
Pass Ratio : 100%
A cipher system is said to have perfect secrecy if
Posteriori probability is equal to priori probability
Posteriori probability is greater than priori probability
Posteriori probability is less than priori probability
None of the mentioned
Explanation:
A cipher system is said to have perfect secrecy if for every message and cipher text the posteriori probability is equal to priori probability.
Question 5
Marks : +2 | -2
Pass Ratio : 100%
The conditions for perfect secrecy are
Only one key transforming message should exist
All keys should be equally likely
One key transforming message to each cipher text & all keys should be equally likely
None of the mentioned
Explanation:
The conditions for perfect secrecy are, there is only one key transforming message to each cipher text and all keys should be equally likely.
Question 6
Marks : +2 | -2
Pass Ratio : 100%
In auto key method
Feedback is necessary
Feedback is not necessary
Can be either necessary or not
None of the mentioned
Explanation:
In auto key method feedback is necessary for the encryption process.
Question 7
Marks : +2 | -2
Pass Ratio : 100%
The trithemius cipher is a mono alphabetical cipher.
True
False
Explanation:
The Trithemius cipher is a poly alphabetical cipher.
Question 8
Marks : +2 | -2
Pass Ratio : 100%
In Vigenere method ______ is provided.
Priming key
Feedback
Priming key & Feedback
None of the mentioned
Explanation:
Vigenere method which is also called as vigenere auto method priming key and feedback are used.
Question 9
Marks : +2 | -2
Pass Ratio : 100%
Cryptosystems are used for
Privacy
Authentication
Privacy & Authentication
None of the mentioned
Explanation:
Cryptosystems which includes the process of encryption and decryption is used for both privacy and authentication.
Question 10
Marks : +2 | -2
Pass Ratio : 100%
In Caesar cipher, each plain text is replaced by
Alphabet shift
Numerals
Symbols
None of the mentioned
Explanation:
In Caesar cipher each plain text is replaced with a new letter obtained by an alphabetic shift.