Network System and Web Security Quiz (100% Solved)

Q.1. If the electronic codebook (ECB) cryptographic mode is used to encrypt a long message made of many blocks of data, and a single bot in the third block of the cipher-text gets corrupted which of the following is true?

  • The decryption algorithm will not be able to decrypt only the first block
  • The decryption algorithm will not be able to decrypt only the third block
  • The decryption algorithm will not be able to decrypt only the last block
  • The decryption algorithm will not be able to decrypt only the fifth block

Q.2. In order to receive an encrypted message from Alice, Bob has to send the following information to Alice <n, e> denotes public key, <n,d> denotes private key, p and q are two prime numbers.

  • Sends <e, d> to Alice on an unsecure channel
  • Sends <p, q> to Alice on an unsecure channel
  • Sends <n, e> to Alice on an unsecure channel
  • Sends <n, d> to Alice on an unsecure channel

Q.3. For RSA, which of the following are the valid public exponents for n = 209 (p = 11 and q = 19)

  • 2
  • 7
  • 4
  • 9

Q.4. The Cipher Block Chaining (CBC) mode is used for encrypting long messages using symmetric block ciphers. The CBC uses an initialization vector (IV)

  • IV is not kept secret, but it is a fixed value known to both the parties and this value is used along with the keys in all confidential communication between them.
  • In every session of confidential communication between the two parties, the sender choose a new (previously not used) value for the IV and this value is included unencrypyed at the begning of the message.
  • IV is a vale derived from the secret key
  • IV like the key is shared secret between the tei communiction parties.

Q.5 Advance Encryption Standard (AES) does not use Feistel Structure.

  • True
  • False

Q.6. An application requires a block cipher (e.g. DES, AES) to be used to ensure confidentiality and integrity of message sent over an insecure public channel which mode of operation is best suited to meet the requirement?

  • Galoris Counter Mode (CTR)
  • Counter mode (CTR)
  • Output Feedback mode(OFB)
  • Cipher Feedback mode (CFB)

Q.7. Public key algorithms are based on mathematical functions rather than on single operations on bit patterns.

Select on:

  • True
  • False

Q,8, Which of the following sets is the set Z12* .

(Hint: Which elements has inverse)

  • {1,2,3,4,5,6,7}
  • {1,2,6,7,8,9}
  • {1,2,3,4,5,6,7,8,9,10,11}
  • {1,5,7,11}

Q.9. DES (Data Encryption Standard) is a

  • a symmetric key stream cipher
  • an asymmetric key stream cipher
  • an asymmetric key block cipher
  • a symmetric key block cipher

Q.10. The counter mode allows parallelization of encryption which is thus suitable for high-speed implementations.

Select one:

  • True
  • False

Q.11. Which of the following pair <e,d>, where e is public exponent and d is the private exponent for n = 451 (p=41 and q=11) are valid?

Select one or more

  • <10, 240>
  • <16, 383>
  • <7, 343>
  • <3, 267>

Q.12. Product Cipher is a concatenation of

  • A round of Substituation and Permutation
  • A round of Diffusion and Permutation
  • A round of Diffusion and Confussion
  • A round of Substituation and Confussion

Q.13. What is the encryption of the message m = 9 in the RSA system which has <n= 91, e= 3> as a public key?

Cipher Text: ☐

Q.14. Square and multiply algorithm for exponentiation of a number in modular arithmetic. You will compute (on paper) the given expression by applying the algorithm, and the, fill in the numerical values that are required in the empty boxes provided in the question. Make sure that you enter an integer in each of these boxes.

44^59 mod 23

Whats are the Square and multiply values for i = 1 ^ ☐ * ☐

Q.15. For generating pseudo-random number (PRN) streams for use in encryption applications, which of the following algorithms/schemes can be used?

  • RC4
  • Publicly avaliable numbers such as the daily lottery draws
  • Locally observable random physical phenomena such as radioactive decay.
  • AES

Q.16. Alice and Bob want to use RSA for the transmission of confidential messages from Alice to Bob. Bob has to generate a pair of keys, kpub, and kpri. He chooses two sufficiently large prime numbers 5 and 11. The public exponent is 3

Public key used them is <n,e> = < ☐, >

Generate a private jet <n,d> = <☐, ☐>

Whats is the plain text if cipher text is 17 ☐

Q.17. The question about the extended Euclidean algorithm for computing the greater common divisor (GCD) of two given positive integers, m and a

if m= 301 and a = 15 are first and second integers in the row, what is the third integer

From your computation, fill in the value of the coefficients in the boxes to complete the equation:

GCD(301, 15) = x301 + x15

Q.18. Alice and Bob want to use RSA for the transmission of confidential messages from Alice to Bob. Bob has to generate a pair of keys, kpub and kpri. He chooses two sufficiently large prime numbers 29 and 31.

Generate a public modular value they both agree upon

Generate a private modular value they both agree upon

Q.19. Alice and Bob want to use RSA for the transmission of a confidential messages from Alice to Bob. Bob has to generate a pair of keys, kupb and kpri. He s=chooses two sufficiently large prime numbers 13 * 17

Generate a private exponent for Alice, if she chooses 5 as the public exponent

Generate a private key <n,d> = <☐, ☐>

Q.20. The question about the extended Euclidean algorithm for computing the greater common divisor (GCD) of two given positive integers, m and a

if m= 53 and a = 14 are first and second integers in the row, what is the third integer

From your computation, fill in the value of the coefficients in the boxes to complete the equation:

GCD(53, 14) = x53 + x14

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