Question

Which of these systems use timestamps as an expiration date?

(a) Public-Key Certificates

(b) Public announcements

(c) Publicly available directories

(d) Public-Key authority

This question was posed to me in a national level competition.

I'm obligated to ask this question of Public Keys and X.509 Certificates-I in portion Message Authentication Codes, Whirlpool Algorithm and Key Management and Distribution of Cryptograph & Network Security

Answer 1

Right choice is (a) Public-Key Certificates

The best explanation: Public key certificates use timestamps as expiration dates.