This set of Computer Networks Multiple Choice Questions & Answers (MCQs) focuses on “Symmetric Key Cryptography”.

1. Which of the following is not an alternative name for symmetric key cryptography?

a) Secret key cryptography

b) Public key cryptography

c) Conventional encryption

d) Private key cryptography

View Answer

Explanation: Cryptography is mainly categorized into two types; symmetric key cryptography and asymmetric key cryptography(public key cryptography). Symmetric key cryptography uses only one key for both encryption and decryption.

2. What is the cipher text for the text “GREET HER”, if Caesar Cipher is used(key=3)?

a) KVIIY LIV

b) KVIIX LIV

c) LWJJY MJW

d) JUHHW KHU

View Answer

Explanation: Caesar cipher is the substitution cipher, which belongs to classical cryptography. Cipher text will be obtained by replacing the plain text letters with letters three places further from them. If further letter is ‘z’, then process will circularly follows ‘a’.

3. What is the cipher text for the message “TAKE ME TO THE PARTY”, id Rail Fence technique is used with two rows?

a) TKMTTEATAEEOHPRY

b) TAKEMETOTHEPARTY

c) TAEKMEOTTHPEARYT

d) YRPHOEEATAETTMKT

View Answer

Explanation: Rail fence is the transposition technique, that belongs to classical cryptography. First the plain text is written in a sequence of diagonals with defined number of rows, then the cipher text is read off as a sequence of all the rows from starting to end.

4. What are the two broad categories of symmetric key cryptography?

a) Transposition and substitution

b) Classical and modern

c) Stream and Block

d) Classical and Block

View Answer

Explanation: Symmetric key cryptography has two types; classical and modern. Classical cryptography again divided into two types; transposition and substitution. Modern cryptography is of two types; stream cipher and block cipher.

5. Which of the following algorithm does not belong to symmetric key ciphers?

a) DES

b) RC4

c) AES

d) Diffie-Hellman

View Answer

Explanation: Diffie-Hellman is the first asymmetric cipher and well known for its logarithm computations. It is used at its best to transmit the secret key between users for further symmetric encryption of messages.

6. Which of the following is an advantage of symmetric cipher?

a) (N(N-1))/2 keys are required for N people

b) sharing secret key over communication channel

c) Brute force attack for small key size

d) Quick encryption and decryption

View Answer

Explanation: Quick encryption and decryption is done in symmetric key cryptography. Because, it uses less resources and cipher text length will be small or same as plain text. It encrypts huge amount of data quickly and provides confidentiality.

7. Which of the following is incorrect about symmetric key cryptography?

a) It uses common key for both encryption and decryption

b) It is a secret key cryptography

c) It uses single fixed length key for each algorithm

d) Symmetric key can be combined with asymmetric key to achieve more security

View Answer

Explanation: An algorithm can make use of number of random keys and the keys can be any size. If the key length is increased, then it will become difficult to crack the key.

8. Which of the following is a disadvantage of symmetric cipher?

a) Quick encryption

b) Less computational power

c) High level of security

d) Transmission of secret key

View Answer

Explanation: Symmetric key cryptography uses single key to encrypt and decrypt messages. If the secret key is shared through an unsecured channel, then there will be a chance for attacking the key.

9. Which of the following is not an application of symmetric encryption algorithms.

a) Data security

b) Cloud storage

c) User privacy

d) Bitcoin’s block chain

View Answer

Explanation: Unlike data security, cloud storage and user privacy, bitcoin uses elliptic-curve cryptography over symmetric key cryptography. Elliptic curve cryptography not only used for encryption, but also for digital signatures and random generators.

10. Asymmetric ciphers are complex than symmetric ciphers.

a) True

b) False

View Answer

Explanation: Asymmetric ciphers are much complex and slower than symmetric ciphers. Asymmetric ciphers have longer keys, which are more related to mathematics. As two keys are employed in asymmetric cipher, it is complex than symmetric ciphers.

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