1
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the protocol given in past exam paper:
(1) A → S : A, B, Na
(2) S → B : {A, B, Na,Kab}Kas, {A, B, Na,Kab}Kbs
(3) B → A : {A, B, Na,Kab}Kas, {Na}Kab, Nb
(4) A → B : {Nb}Kab

my answer when replaying the compromised session key to impersonate A:

(1)A -> S : A, B, Na
(2)S -> B : {A, B, Na, Kab}Kas, {A, B, Na, Kab}Kbs // comment assume Kab is compromised
(3)I(S) -> B : {A, B, Na, Kab}Kas, {A, B, Na, Kab}Kbs
(4)B -> I(A) : {A, B, Na, Kab}Kas, {Na}Kab, N’b
(5)I(A) -> B : {N’b}Kab
$\endgroup$
  • 2
    $\begingroup$ What is your question? Whether or not you got it right? $\endgroup$ – mikeazo Apr 6 '16 at 18:15
  • $\begingroup$ @mikeazo is the answer right or wrong? $\endgroup$ – john ab Apr 6 '16 at 19:20
  • $\begingroup$ So you are impersonating the server and A? $\endgroup$ – mikeazo Apr 6 '16 at 19:34
  • $\begingroup$ A is alice, B is Bob and S is the session key. I am replaying the compromised key so assume line 2 is compromised by secret key Kab. $\endgroup$ – john ab Apr 6 '16 at 19:37
  • $\begingroup$ line 3 is the replayed session key with intruder S impersonate B $\endgroup$ – john ab Apr 6 '16 at 19:38

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