Digital Communications Multiple Choice Questions on “Pretty good privacy”.
1. Pretty good privacy (PGP) security system uses
A. Public key cryptosystem
B. Private key cryptosystem
C. Public & Private key cryptosystem
D. None of the mentioned
Answer: C
Clarification: PGP uses many encryption techniques such as private key cryptosystem and also public key cryptosystem.
2. Public key cryptosystem is used for the encryption of
A. Messages
B. Session key
C. Session key & Messages
D. None of the mentioned
Answer: B
Clarification: Public key cryptosystem is used for encryption of messages and private key cryptosystem is used for encryption of messages.
3. For digital signatures private key cryptosystem is used.
A. True
B. False
Answer: B
Clarification: Public key cryptosystem is used for the creation of digital signatures.
4. Data compression includes
A. Removal of redundant character
B. Uniform distribution of characters
C. Removal of redundant character & Uniform distribution of characters
D. None of the mentioned
Answer: C
Clarification: Data compression removes redundant character strings in a file and produces a more uniform distribution of characters.
5. PGP offers _____ block ciphers for message encryption.
A. Triple-DES
B. CAST
C. IDEA
D. All of the mentioned
Answer: D
Clarification: Pretty good privacy security system offers three block ciphers for message encryption – Triple-DES, IDEA and CAST.
6. Which block cipher has key length of 128 bits?
A. IDEA
B. CAST
C. IDEA & CAST
D. None of the mentioned
Answer: C
Clarification: The block ciphers IDEA and CAST has key length of 128 bits where as Triple-DES has key size of 168 bits.
7. These three ciphers can operate of ______ of plaintext and cipher text.
A. 128 bit blocks
B. 64 bit blocks
C. 256 bit blocks
D. 156 bit blocks
Answer: B
Clarification: The three ciphers – Triple-DES, IDEA and CAST can operate on 64 bit blocks of plain text and cipher text.
8. The key size of DES is
A. 56 bits
B. 64 bits
C. 128 bits
D. 168 bits
Answer: A
Clarification: The key size of DES algorithm is 56 bits and with Triple-DES, the message to be encrypted is run on DES algorithm 3 times.
9. Which operation is used in encryption using IDEA?
A. Addition modulo 216
B. Bit wise XOR
C. Addition modulo 216 & Bit wise XOR
D. None of the mentioned
Answer: C
Clarification: The arithmetic operations used in IDEA are addition modulo 216, multiplication modulo 216+1, and bit wise XOR.
10. What is the key size allowed in PGP?
A. 1024-1056
B. 1024-4056
C. 1024-4096
D. 1024-2048
Answer: C
Clarification: Pretty good privacy security system allows 1024 to 4096 bits of key size.
11. Which algorithm is used for public key encryption?
A. RSA
B. Diffie-Hellman
C. RSA & Diffie-Hellman
D. None of the mentioned
Answer: C
Clarification: The two algorithms used for public key encryption in PGP are RSA and Diffie-Hellman algorithms.
12. Which should be used first to decrypt?
A. Public key
B. Private key
C. Public & Private key
D. None of the mentioned
Answer: B
Clarification: The recipient should first decrypt the message using private key and then with the public key.
13. The digital signature provides authentication to the
A. Sender
B. Message
C. Sender & Message
D. None of the mentioned
Answer: C
Clarification: The digital signature provides authentication to both the sender and the message.
14. In hash function output length is fixed.
A. True
B. False
Answer: A
Clarification: In hash function the output length is fixed and it is easy to compute.
15. The hash function
A. Is collision free
B. Has manageable collision
C. Has high unmanageable level of collision
D. None of the mentioned
Answer: A
Clarification: Hash function is collision free and it is unfeasible that two different messages will create the same hash value.
16. DSA protocol is based on
A. Discrete logarithm problem
B. Continuous logarithm problem
C. Discrete & Continuous logarithm problem
D. None of the mentioned
Answer: A
Clarification: The DSA algorithm uses and is based on discrete logarithm problem.