Attacks on Version 3 with 3rd Party Robert Bob A 凸R Provoke B to talk to A B Alice Robert (g A)KB X Authentication Robert A.x Center (ng:A)KB How to defend against this attack? -Break symmetry. 1111 Attacks on Version 3 with 3rd Party  How to defend against this attack? ─ Break symmetry. Robert Bob A nR x Provoke B to talk to A Alice nA nR {nR, A}KB Robert B A, x Robert Authentication Center {nR, A}KB