1. Use Caesar’s Cipher to decipher the following

HQFUBSWHG WHAW

a) ABANDONED LOCK

b) ENCRYPTED TEXT

c) ABANDONED TEXT

d) ENCRYPTED LOCK

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2. Caesar Cipher is an example of

a) Poly-alphabetic Cipher

b) Mono-alphabetic Cipher

c) Multi-alphabetic Cipher

d) Bi-alphabetic Cipher

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3. Monoalphabetic ciphers are stronger than Polyalphabetic ciphers because frequency analysis is tougher on the former.

a) True

b) False

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4. Which are the most frequently found letters in the English language ?

a) e,a

b) e,o

c) e,t

d) e,i

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

a) Random Polyalphabetic, Plaintext, Playfair

b) Random Polyalphabetic, Playfair, Vignere

c) Random Polyalphabetic, Vignere, Playfair, Plaintext

d) Random Polyalphabetic, Plaintext, Beaufort, Playfair

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6. On Encrypting “thepepsiisintherefrigerator” using Vignere Cipher System using the keyword “HUMOR” we get cipher text-

a) abqdnwewuwjphfvrrtrfznsdokvl

b) abqdvmwuwjphfvvyyrfznydokvl

c) tbqyrvmwuwjphfvvyyrfznydokvl

d) baiuvmwuwjphfoeiyrfznydokvl

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7. On Encrypting “cryptography” using Vignere Cipher System using the keyword “LUCKY” we get cipher text

a) nlazeiibljji

b) nlazeiibljii

c) olaaeiibljki

d) mlaaeiibljki

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8. The Index of Coincidence for English language is approximately

a) 0.068

b) 0.038

c) 0.065

d) 0.048

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9. 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

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10. Consider the cipher text message with relative frequencies:

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 2

The Index of Coincidence is

a) 0.065

b) 0.048

c) 0.067

d) 0.042

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11.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 SBQWS

Relative Frequencies –

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

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12. A symmetric cipher system has an IC of 0.041. What is the length of the key ‘m’?

a) 1

b) 3

c) 2

d) 5