You need to ensure that a session key derived from a set of long-term public and private keys will not be compromised if one of the private keys is compromised in the future?

A.
Perfect forward secrecy

B.
Secure socket layer

C.
Secure shell

D.
Security token

Explanation:
Perfect forward secrecy (or PFS) is the property that ensures that a session key derived from a set of long-term public and private keys will not be compromised if one of the (long-term) private keys is compromised in the future.

Forward secrecy has been used as a synonym for perfect forward secrecy, since the term perfect has been controversial in this context. However, at least one reference distinguishes perfect forward secrecy from forward secrecy with the additional property that an agreed key will not be compromised even if agreed keys derived from the same long-term keying material in a subsequent run are compromised.

Answer option C is incorrect. Secure Shell (SSH) is a program that is used for logging into a remote computer over a network. Secure Shell can be used to execute commands on a remote machine and to move files from one machine to another. SSH uses strong authentication and secure communications over insecure channels.

Answer option B is incorrect. Secure Sockets Layer (SSL) is a protocol that was developed by Netscape for transmitting private documents via the Internet. It uses a cryptographic system thatuses public and private keys to encrypt data. A public key is globally available and a private key is known only to the recipient of the message. Both Netscape Navigator and Internet Explorer support the SSL protocol. Several web sites use this protocol to obtain confidential user information. When the SSL protocol is used to connect to a Web site, the URL must begin with https instead of http.

Answer option D is incorrect. Security token can be a physical device that an authorized user of computer services is given to ease authentication. The term may also refer to software tokens. Security tokens are used to prove one’s identity electronically (as in the case of a customer trying to access his bank account). The token is used in addition to or in place of a password to prove that the customer is who he claims to be. The token acts like an electronic key to access something.