Authentication in which a random value is presented to a user, who
then returns a calculated number based on that random value is called:

A.
Man-in-the-middle

B.
Personal identification number (PIN) protocol

C.
One-time password

D.
Challenge-response

Explanation:
In challenge-response authentication, the user enters a random value
(challenge) sent by the authentication server into a token device. The
token device shares knowledge of a cryptographic secret key with the
authentication server and calculates a response based on the challenge
value and the secret key. This response is entered into the authentication
server, which uses the response to authenticate the identity of the
user by performing the same calculation and comparing results.
Answer “man-in-the-middle” is a type of attack in which a cracker is

interposed between the user and authentication server and attempts to
gain access to packets for replay in order to impersonate a valid user.
A “one-time password” is a password that is used only once to gain
access to a network or computer system. A typical implementation is
through the use of a token that generates a number based on the time of
day. The user reads this number and enters it into the authenticating
device. The authenticating device calculates the same number based on
the time of day and uses the same algorithm used by the token. If the
token’s number matches that of the authentication server, the identity of
the user is validated. Obviously, the token and the authentication server
must be time-synchronized for this approach to work. Also, there is
allowance for small values of time skew between the authorization
device and the token. Answer d refers to a PIN number that is something
you know used with something you have, such as an ATM card.