Sniffing-and-replay the attacker eve eavesdrops to the

Question

For the following types of possible attacks:

Sniffing-and-replay: the attacker Eve eavesdrops to the communications between Alice and Bob. Later, Eve re-uses Aliceâs messages to impersonate Alice against Bob.

Trojan-horse: the attacker Eve impersonates Bob by interacting with Alice, who authenticates herself to him. Later, Eve re-uses the values Alice sent her, to impersonate Alice to Bob.

(a) Which attacks are possible with the normal Unix (crypt) login?

(b) Which attacks are possible with the S/key identification-authentication method?

(c) Which attacks are possible with the the time-based token scheme?