In this key establishment protocol, - A interacts with a trusted server T and a party B. - A and T share a symmetric key KAT, and B and T share a symmetricikey KBT. - T will choose a key k to be shared by A and B. - NA and NB are nonces chosen by A and B respectively. - We wil write EK(x) to mean encrypting a message x using a symmetric key encryption algorithm E with key K. The protocol runs as follows: 1. AT:A,B,NA 2. T A:EKAF(NA,B,k,EKAF(k,A)). 3. AB:EKm(k,A). 4. BA:Ek(NB) 5. AB;E(NB1). What guarantees the freshness of the message A receives from T ? A in message 1. NA in message 1. KAT in message 2. KBT in message 2. B in message 1. NA in mossage