With Trusted Third Party-Version 4 Alice A Bob n Authentication {n,Bk Center A,(n,BiKA> {B,kabjKA (n,A,kabikB (B,kabKa We are almost there-except having mutual authentication. 1212 With Trusted Third Party – Version 4  We are almost there – except having mutual authentication. Alice A Bob n {n, B}KA A, {n, B}KA {n, A, kab}KB, {B, kab}KA Authentication Center {B, kab}KA