The expanded needham-schroeder protocol can be shortened to a 6-message protocol without loss of security by merely removing the 7thmessage. why is this true? (hint: the purpose of the 7thmessage is to prove to bob that he is talking to alice, but he already knows that. why?)

Question

Jonathan Lamb

Computers & Technology

16 June, 13:57

The expanded needham-schroeder protocol can be shortened to a 6-message protocol without loss of security by merely removing the 7thmessage. why is this true? (hint: the purpose of the 7thmessage is to prove to bob that he is talking to alice, but he already knows that. why?)

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Jordon Perkins · Answer 1

This is true since the ticket issued by KDC is enciphered by Alice's key, KAlice, so the one who can decrypt the fourth message and get the ticket to Bob is Alice only, which means that the one who is sending the ticket to Bob is Alice and nobody else ... (No one can get the ticket from the fourth message.)