# Classical Encryption Technique MCQs

1. In brute force attack, on average half of all possible keys must be tried to achieve success..

A. TRUE.

B. FALSE.

C. Nothing can be said.

D. None of the mentioned.

2. If the sender and receiver use different keys, the system is referred to as conventional cipher system..

A. TRUE.

B. FALSE.

C. Nothing can be said.

D. None of the mentioned.

3. Divide (HAPPY)26 by (SAD)26. We get quotient

A. KD.

B. LD.

C. JC.

D. MC.

4. Dividing (11001001) by (100111) gives remainder

A. 11.

B. 111.

C. 101.

D. 110.

5. pi in terms of base 26 is.

A. C.DRS.

B. D.SQR.

C. D.DRS.

D. D.DSS.

6. The time required to convert a k-bit integer to its representation in the base 10 in terms of big-O notation is.

A. O(log2 n).

B. O(log n).

C. O(log2 2n).

D. O(2log n).

7. In base 26, multiplication of YES by NO gives

A. THWOE.

B. MPAHT.

C. MPJNS.

D. THWAE.

8. Division of  (131B6C3) base 16 by (lA2F) base 16 yeilds

9. An encryption scheme is unconditionally secure if the ciphertext generated does not contain enough information to determine unily the corresponding plaintext, no matter how much cipher text is available..

A. TRUE.

B. FALSE.

C. Nothing can be said.

D. None of the mentioned.

10. The estimated computations required to crack a password of 6 characters from the 26 letter alphabet is

A. 308915776.

B. 11881376.

C. 456976.

D. 8031810176.

11. Reduce the following big-O natations:O[ ax7 + 3 x3 + sin(x)] = .

A. O[ax7]..

B. O[sin(x)]..

C. O[x7]..

D. O[x7 + x3]..

12. Reduce the following big-O natations:O[ en + an10] = .

A. O[ an10 ]..

B. O[ n10 ]..

C. O[ en ]..

D. O[ en + n10 ]..

13. Reduce the following big-O natations:O [ n! + n50 ] = .

A. O [ n! + n50 ]..

B. O [ n! ]..

C. O [ n50]..

D. None of the Mentioned.

14. Use Caesar's Cipher to decipher the followingHQFUBSWHG WHAW.

A. ABANDONED LOCK.

B. ENCRYPTED TEXT.

C. ABANDONED TEXT.

D. ENCRYPTED LOCK.

15. Caesar Cipher is an example of.

A. Poly-alphabetic Cipher.

B. Mono-alphabetic Cipher.

C. Multi-alphabetic Cipher.

D. Bi-alphabetic Cipher.

16. Monoalphabetic ciphers are stronger than Polyalphabetic ciphers because frency analysis is tougher on the former..

A. TRUE.

B. FALSE.

C. Nothing can be said.

D. None of the mentioned.

17. Which are the most frently found letters in the English language ?.

A. e,a.

B. e,o.

C. e,t.

D. e,i.

18. Choose from among the following cipher systems, from best to the worst, with respect to ease of decryption using frency analysis..

A. Random Polyalphabetic, Plaintext, Playfair.

B. Random Polyalphabetic, Playfair, Vignere.

C. Random Polyalphabetic, Vignere, Playfair, Plaintext.

D. Random Polyalphabetic, Plaintext, Beaufort, Playfair.

Answer= Random Polyalphabetic, Vignere, Playfair, Plaintext

19. On Encrypting "thepepsiisintherefrigerator" using Vignere Cipher System using the keyword "HUMOR" we get cipher text

A. abqdnwewuwjphfvrrtrfznsdokvl.

B. abqdvmwuwjphfvvyyrfznydokvl.

C. tbqyrvmwuwjphfvvyyrfznydokvl.

D. baiuvmwuwjphfoeiyrfznydokvl.

20. On Encrypting "cryptography" using Vignere Cipher System using the keyword "LUCKY" we get cipher text.

A. nlazeiibljji.

B. nlazeiibljii.

C. olaaeiibljki.

D. mlaaeiibljki.

21. The Index of Coincidence for English language is approximately.

A. 0.068.

B. 0.038.

C. 0.065.

D. 0.048.

22. If all letters have the same chance of being chosen, the IC is approximately.

A. 0.065.

B. 0.035.

C. 0.048.

D. 0.038.

23. Consider the cipher text message with relative frencies:4 0 10 25 5 32 24 15 6 11 5 5 1 2 6 6 15 19 10 0 6 28 8 2 3 2The Index of Coincidence is.

A. 0.065.

B. 0.048.

C. 0.067.

D. 0.042.

24. Consider the cipher text message:YJIHX RVHKK KSKHK IQQEV IFLRK QUZVA EVFYZ RVFBX UKGBP KYVVB QTAJK TGBQO ISGHU CWIKX QUXIH DUGIU LMWKG CHXJV WEKIH HEHGR EXXSF DMIIL UPSLW UPSLW AJKTR WTOWP IVXBW NPTGW EKBYU SBQWSRelative Frencies –3 7 2 2 5 5 7 9 11 4 14 4 2 1 3 4 6 5 6 5 7 10 9 8 4 2 The Index of Coincidence is

A. 0.065.

B. 0.048.

C. 0.067.

D. 0.044.