June 12, 2021

Stream Encryption Applications MCQ’s

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This set of Digital Communications Systems Multiple Choice Questions & Answers (MCQs) focuses on “Stream Encryption Applications”.

1. In which method cipher feedback is used?
a) Synchronous encryption method
b) Self synchronous encryption method
c) All of the mentioned
d) None of the mentioned

2. In substitution technique encryption protection is more.
a) True
b) False

3. One-time pad has
a) Random key
b) Unconditional security
c) Can be used only once
d) All of the mentioned

4. Which are called as substitution encryption techniques?
a) Caesar cipher
b) Trithemius cipher
c) Caesar & Trithemius cipher
d) None of the mentioned

5. For hybrid systems the minimum required processing gain is
a) 5db
b) 10db
c) 17db
d) 25db

6. Spread spectrum multiple access techniques allows the multiple signal to be transmitted
a) One after the other
b) Simultaneously
c) All of the mentioned
d) None of the mentioned

7. For direct sequence systems what is the minimum required processing gain?
a) 3db
b) 10db
c) 12db
d) 20db

8. Perfect secrecy can be achieved for
a) Finite number of messages
b) Infinite number of messages
c) Finite & Infinite number of messages
d) None of the mentioned

9. The 64 bit block input key has _____ number of parity bits.
a) 4
b) 6
c) 8
d) 16

10. In which method the key-stream is generated independently of the message?
a) Synchronous encryption method
b) Self synchronous encryption method
c) All of the mentioned
d) None of the mentioned

11. In CDMA, the users share the bandwidth
a) Synchronously
b) Asynchronously
c) Synchronously & Asynchronously
d) None of the mentioned

12. The segment of the key-stream of plaintext is obtained by _____ of two sequences together.
a) ANDing
b) ORing
c) Addition
d) Modulo 2 addition

13. Direct system allows detection of signals whose psd level is
a) Below noise level
b) Above noise level
c) All of the mentioned
d) None of the mentioned

14. The standard building block uses _______ of a key to transform 64-bit input into 64-bit output.
a) 32 bit
b) 48 bit
c) 64 bit
d) 128 bit

15. Multi paths may be because of
a) Reflections from buildings
b) Refraction
c) Atmospheric reflections
d) All of the mentioned

16. Frequency hopping system can provide reliable mitigation only if
a) Hopping rate is greater than the symbol rate
b) Hopping bandwidth is large
c) Hopping rate is greater than the symbol rate & its bandwidth is large
d) None of the mentioned

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