Alice sends a message to Bob and adds the hash code to the message. Can an attacker manipulate the message without Bob noticing? (Only Alice and Bob have the hash key)

What is the second rule of identity? You have an online store. How does this rule affect it?

Given is a Kerberos system. The attacker intercepted a TGT from Alice and their session key.

a) Can the attacker now request services on behalf of Alice?

b) Can the attacker request services on behalf of other users?