If Alice wants to talk to Bob, Alice will ask KDC for a key to be used with Bob. To do this, Alice will contact the KDC with a message $$Alice wants to talk to Bob$.$ This message is not cryptographically protected, so an attacker could change the message to $$Alice wants to talk to Trudy$,$ and then the KDC will actually issue a session key to be used between Alice and Trudy. Without knowing the message has been changed before it reaches to the KDC$,$ Alice will mistakenly think the session key she received from the KDC is to be used between Alice and Bob.

How does Kerberos protocol ensure that Alice will not be tricked into thinking Trudy is Bob? Demonstrate your answer in words, add pictures$/$diagrams if necessary. Note: this question asks Kerberos, not Needham$-$Schroeder.