Need help with a past exam question: Alice and Bob want to establish a shared key KAB with the help of a trusted server D. Presume Bob and Alice share their secret keys KAD and KBD with D and that nonces is 64 bits long and keys are 128 bits long.

  1. A > B = Alice,NA
  2. B > D = Bob,NB,{A,NA,NB}KBD
  3. D > A = {B,KAB,NA,NB}KAD,{A,KAB}KBD
  4. A > B = {A,KAB}KBS,{NB}KAB

Question is: Explain 2 attacks that can be applied to this protocol.