7. In symmetric key cryptography, what is the number of keys required for secure communication between 100 parties? (a) 2000 symmetric keys (b) 10000 symmetric keys (c) 9900 symmetric keys (d) None of the above 8. What is the most significant advantage of Diffie-Hellman? (a) Fast key exchange (b) Easy to implement (c) Encrypt/Decrypt messages (d) Key exchange among a group of nodes 9. A digital signature is obtained by the following procedure: (a) Hash the message Mand encrypt it with sender's public key (b) Hash the message Mand encrypt it with sender's private key (e) Hash the message Mand encrypt it with recipient's public key (d) Hash the message M and encrypt it with recipient's private key 10. In the Advanced Encryption Standard (AES) cipher, "Sub-Byte" provides (a) Concealment (b) Confusion (e) Diffusion (d) None of the above to the cipher 11. The is an example of polyalphabetic substitution. (a) Vigenere cipher (b) S-box (e) Product block (d) Caesar cipher 12. Which of the following describes symmetric key algorithm? (a) Encryption and decryption is performed using the same key (b) Does not require secure exchange of a secret key (c) Can be used to ensure non-repudiation (d) Require two separate keys 13. Which of these is true for CBC mode? (a) Specific plaintext always generates the same cipher text every time. (b) Every plaintext has a defined corresponding cipher text (c) It can support a different key for every block type (d) The IV must be unpredictable at eneryption time