Which of the following attacks could be used to initiate a subsequent man-in-the-middle attack?

A.
ARP poisoning

B.
DoS

C.
Replay

D.
Brute force

Explanation:
A replay attack (also known as playback attack) is a form of network attack in which a valid data
transmission is maliciously or fraudulently repeated or delayed. This is carried out either by the
originator or by an adversary who intercepts the data and retransmits it, possibly as part of a
masquerade attack by IP packet substitution (such as stream cipher attack).
For example: Suppose Alice wants to prove her identity to Bob. Bob requests her password as
proof of identity, which Alice dutifully provides (possibly after some transformation like a hash
function); meanwhile, Eve is eavesdropping on the conversation and keeps the password (or the
hash). After the interchange is over, Eve (posing as Alice) connects to Bob; when asked for a
proof of identity, Eve sends Alice’s password (or hash) read from the last session, which Bob
accepts thus granting access to Eve.
Countermeasures: A way to avoid replay attacks is by using session tokens: Bob sends a one
time token to Alice, which Alice uses to transform the password and send the result to Bob (e.g.
computing a hash function of the session token appended to the password). On his side Bob
performs the same computation; if and only if both values match, the login is successful. Now
suppose Eve has captured this value and tries to use it on another session; Bob sends a different
session token, and when Eve replies with the captured value it will be different from Bob’s
computation.
Session tokens should be chosen by a (pseudo-) random process. Otherwise Eve may be able to
pose as Bob, presenting some predicted future token, and convince Alice to use that token in her
transformation. Eve can then replay her reply at a later time (when the previously predicted token
is actually presented by Bob), and Bob will accept the authentication.
One-time passwords are similar to session tokens in that the password expires after it has been
used or after a very short amount of time. They can be used to authenticate individual transactions
in addition to sessions. The technique has been widely implemented in personal online banking
systems.
Bob can also send nonces but should then include a message authentication code (MAC), which
Alice should check.
Timestamping is another way of preventing a replay attack. Synchronization should be achieved
using a secure protocol. For example Bob periodically broadcasts the time on his clock together
with a MAC. When Alice wants to send Bob a message, she includes her best estimate of the time
on his clock in her message, which is also authenticated. Bob only accepts messages for which
the timestamp is within a reasonable tolerance. The advantage of this scheme is that Bob does
not need to generate (pseudo-) random numbers, with the trade-off being that replay attacks, if
they are performed quickly enough i.e. within that ‘reasonable’ limit, could succeed.