Below is an example of constant repeated ATTACK and FIX (Take a certified key establishment protocol protocols for automated key establishment using encryption)
Prot2.1: protocol "from alice to bob"
Alice Generates Kat, And Sends To Trent: Alice, Bob, {K} Kat; Trent Finds Keys Kat, KBT, Decrypts {K} Kat To Reveal K, Creates {K} KBT and Sends To Bob: Alice, Bob, {K} Kbt; Bob Decrypts {K} Kbt To Reveal K, Forms and sends to alice: {Hello Alice, I'm bob!} K.
Since K may not be safe enough, the K can could not obtain the trust of BOB, so changed to Trent to generate K
Prot2.2: protocol "session key from trent"
Alice Sends to Trent: Alice, Bob; Trent Finds Keys Kat, KBT, Generates K at Random and Sends To Alice: {K} Kat, {K} Kbt; Alice Decrypts {K} Kat, And Sends To Bob: Trent, Alice , {K} kbt; bob decrypts {k} KBT to Reveal K, Forms and sends to alice: {Hello, I'm bob!} K.
Attack2.2: an attack on prot2.2
Alice -> Malice ("Trent"): Alice, Bob;
Malice ("alice" -> Trent: Alice, Malice;
Trent Finds Kat, KMT, Generates Kam, -> Alice: {Kam} Kat, {Kam} KMT;
Alice decrypts {kam} kmt, -> malice ("bob"): trent, alice, {kam} kmt;
Malice ("Bob") -> Alice: {Hello, IM Bob!} Kam;
