Problem:

1. An authenticator is:

a. A value used to authenticate a message
b. The party in a protocol who first authenticates the other party
c. Proof of the authenticity of a certificate
d. The output of a hash function to be signed

2. Why should data compression be performed before encryption rather than after?

a. Compression is less effective on random data
b. Compressing after encryption interferes with feedback modes for block ciphers
c. The numeric format of RSA cannot be changed after encryption
d. It is redundant as commercial compression software includes encryption.

Additional Information:

These multiple choice questions is from Computer Science. The 1st question discusses about authenticator. The 2nd question is about why data compression should be performed before encryption.