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University of Twente The Netherlands Centre for Telematics and Information Technology Verification of Security Protocols Sandro Etalle

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University of Twente The Netherlands Centre for Telematics and Information Technology Outline Day 2: Practice analysis of many flawed protocol......using the online demo Resources: The online tool, reachable at wwwes.cs.utwente.nl/24cqet The Clark-Jacob library www-users.cs.york.ac.uk/~jac/papers/drareviewps.ps

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University of Twente The Netherlands Centre for Telematics and Information Technology Security Protocols & the Attacks Otway-Rees Secrecy+type-flaw attack Kao-chow replay-attack Woo-Lam authentication+type flaw attack NSL (as bonus protocol) auth+type-flaw attack

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University of Twente The Netherlands Centre for Telematics and Information Technology Otway-Rees Protocol 1. A->B : [M,A,B,[Na,M,A,B]+Kas] 2. B->S : [M,A,B,[Na,M,A,B]+Kas], [Nb,M,A,B]+Kbs 3. S->B : [M, [Na,Kab]+Kas, [Nb,Kab]+Kbs 4. B->A : [M,[Na,Kab]+Kas ] Aim: key distribution using a trusted server. Kab: short-term key. Could be guessed. Na and Nb serve as challenges.

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University of Twente The Netherlands Centre for Telematics and Information Technology Attack upon Otway-Rees a.1 A->e(B) : [M,A,B,[Na,M,A,B]+Kas] a.4 e(B)->A : [M,A,B,[Na,M,A,B]+Kas] Type flaw attack A takes [M,A,B] to be the key The intruder just replies the first message. It is an authentication flaw. It is also a secrecy flaw (the intruder knows the key, now).

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University of Twente The Netherlands Centre for Telematics and Information Technology Otway-Rees in the tool initiator(A,B,Na,Nb,M,X,Kas,Kab,[ recv([A,B]), % for origination assumption send([M,A,B,[Na,M,A,B]+Kas]]), recv([M,[Na,Kab]+Kas]), send(X+Kab)]). % another way of checking secrecy responder(A,B,Na,Nb,M,X,Kas,Kab,[ %NOT RELEVANT recv([M,A,B,[Na,M,A,B]+Kas]), send([[M,A,B,[Na,M,A,B]+Kas], [Nb,M,A,B]+Kbs]), recv([[M,Na,Kab]+Kas, [Nb,Kab]+Kbs]), send([M,[Na,Kab]+Kas]), recv(X+Kab) ]).

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University of Twente The Netherlands Centre for Telematics and Information Technology Otway-Rees in the tool cont’d secrecy(N,[recv(N)]). server(A,B,Na,Nb,M,X,Kas,Kab,[ recv([[M,A,B,[Na,M,A,B]+Kas]]], [Nb,[M,[A,B]]]+Kbs]), send([[M,[Na,Kab]]+Kas, [Nb,Kab]+Kbs])]).

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University of Twente The Netherlands Centre for Telematics and Information Technology Scenario One initiator is enough. And the secrecy check. We could not check secrecy the “usual” way because Kab is not instantiated anywhere (it is given by the server). scenario([[sec1,St],[a,Sa1]]) :- initiator(a,b,na,Nb,m,x,kas,Kab,Sa1), secrecy(x, St). initial_intruder_knowledge([a,b,e]). has_to_finish([sec1]).

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University of Twente The Netherlands Centre for Telematics and Information Technology The Attack Output Trace: [a,recv([a,b])] [a,send([m,[a,[b,[na,[m,[a,b]]] + kas]]])] [a,recv([m,[na,[m,[a,b]]] + kas])] [a,send(x + [m,[a,b]])] [sec1,recv(x)]

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University of Twente The Netherlands Centre for Telematics and Information Technology Kao-Chow authentication Protocol 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 Assumption: Kab is compromised

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University of Twente The Netherlands Centre for Telematics and Information Technology Attack upon Kao-Chow a.1 A->S : [A,B,Na] a.2 S->B : [A,B,Na,Kab]+Kas, [A,B,Na,Kab]+Kbs a.3 B->A : [A,B,Na,Kab]+Kas,[Na+Kab,Nb] a.4 A->B : Nb+Kab b.2 e(S)->B : [A,B,Na,Kab]+Kas,[A,B,Na,Kab]+Kbs b.3 B->e(A) : [A,B,Na,Kab]+Kas, [Na+Kab,Nb’] b.4 e(A)->B : Nb’+Kab

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University of Twente The Netherlands Centre for Telematics and Information Technology How it works Two sessions. First a normal session is carried out. We assume the intruder “guesses” Kab. This is something we have to implement manually. In a second session, the intruder can impersonate both A and the server S.

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University of Twente The Netherlands Centre for Telematics and Information Technology Kao-Chow in the tool initiator(A,B,Na,Nb,Kas,Kab,Kbs,[ recv([A,B]), % for origination assumption send([A,[B,Na]]), recv([ [A,[B,[Na,Kab]]]+Kas,[ Na+Kab, Nb ]]), send(Nb+Kab) ]). responder(A,B,Na,Nb,M,Kab,Kbs,[ recv([M, ([A,[B,[Na,Kab]]]+Kbs)]), %M because he cannot decipher it send([M, [ Na+Kab, Nb ]]), recv(Nb+Kab), send(Kab) % we model that the key kab was compromised... ]).

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University of Twente The Netherlands Centre for Telematics and Information Technology Scenario scenario([[a1,Sa1],[a2,Sb1],[a3,Sb2],[s1,Ss1]]) :- initiator(a,b,na,Nb,kas,Kab,Kbs,Sa1), responder(a,b,Na1,nb1,M,Kab1,kbs,Sb1), responder(a,b,Na2,nb2,M2,Kab2,kbs,Sb2), server(a,b,Na3,kas,kab,kbs,Ss1). initial_intruder_knowledge([a,b,e]). has_to_finish([a2,a3]). session consisting of: initiator, two responders, one server. any larger session will do. If both responders can finish there is certainly an attack.

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University of Twente The Netherlands Centre for Telematics and Information Technology The Attack Output Trace: [a1,recv([a,b])] [a1,send([a,[b,na]])] [s1,recv([a,[b,na]])] [s1,send([[a,[b,[na,kab]]] + kas,[a,[b,[na,kab]]] + kbs])] [a2,recv([_h381,[a,[b,[na,kab]]] + kbs])] % a variable here [a2,send([_h381,[na + kab,nb1]])] [a1,recv([[a,[b,[na,kab]]] + kas,[na + kab,nb1]])] [a1,send(nb1 + kab)] [a2,recv(nb1 + kab)] [a2,send(kab)] [a3,recv([_h433,[a,[b,[na,kab]]] + kbs])] [a3,send([_h433,[na + kab,nb2]])] [a3,recv(nb2 + kab)] [a3,send(kab)]

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University of Twente The Netherlands Centre for Telematics and Information Technology Woo-Lam Mutual Authentication Protocol 1. A->B : [A,Na] 2. B->A : [B,Nb] 3. A->B : [A,B,Na,Nb]+Kas 4. B->S : [A,B,Na,Nb]+Kas, [A,B,Na,Nb]+Kbs 5. S->B: [B,Na,Nb,Kab]+Kas,[A,Na,Nb,Kab]+Kbs 6. B->A: [B,Na,Nb,Kab]+Kas, [Na,Nb]+Kab 7. A->B: Nb+Kab

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University of Twente The Netherlands Centre for Telematics and Information Technology Attack upon Woo-Lam Attack upon Woo-Lam a.1 e(A)->B : [A,B] a.2 B->e(A) : [B,Nb] a.3 e(A)->B : [A,B,B,Nb]+Kes a.4 B->e(S) : [A,B,B,Nb]+Kes, [A,B,B,Nb]+Kbs b.1 e(A)->B : [A,Nb] b.2 B->e(A) : [B,Nb' ] b.3 e(A)->B : [A,B,Nb,Nb' ]+Kes b.4 B->e(S) : [A,B,Nb,Nb' ]+Kes,[A,B,Nb,Nb' ]+Kbs a.5 e(S)->B: [B,B,Nb,Nb' ]+Kes,[A,B,Nb,Nb' ]+Kbs a.6 B->e(A): [B,B,Nb,Nb' ]+Kes,[ B,Nb]+Nb' a.7 e(A)->B: Nb+Nb'

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University of Twente The Netherlands Centre for Telematics and Information Technology Comments There is one complete session and one incomplete session. Which agents do we actually have to implement to find this attack?

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University of Twente The Netherlands Centre for Telematics and Information Technology One Responder will do: Woo-Lam in the Tool responder(A,B,Na,Nb,Kab,Kas,Kbs,[ recv([A,B]), % for origination assumption recv([A,Na]), send([B,Nb]), recv([A,[B,[Na,Nb]]]+Kas), send([([A,[B,[Na,Nb]]]+Kas), ([A,[B,[Na,Nb]]]+Kbs) ]), recv([([B,[Na,[Nb,Kab]]]+Kas), ([A,[Na,[Nb,Kab]]]+Kbs) ]), send([([B,[Na,[Nb,Kab]]]+Kas), ([Na,Nb]+Kab) ]), recv(Nb+Kab) ]).

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University of Twente The Netherlands Centre for Telematics and Information Technology Scenario scenario([[b1,Sb1],[b2,Sb2]]) :- responder(a,b,Na1,nb1,Kab1,Kas,kbs,Sb1), responder(a,b,Na2,nb2,Kab2,Kas,kbs,Sb2). initial_intruder_knowledge([a,b,e]). has_to_finish([b1]). The definition of the responder is sufficient, but we need two responders here. If one of the two finishes, there is certainly an attack. RULE: if a role can finish when no corresponding role is defined we are in certainly presence of an authentication problem.

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University of Twente The Netherlands Centre for Telematics and Information Technology The Attack Output (after 30s!) Trace: [b1,recv([a,b])] [b1,send([b,nb1])] [b1,recv([a,[b,[b,nb1]]] + _h97)] [b1,send([[a,[b,[b,nb1]]] + _h97,[a,[b,[b,nb1]]] + kbs])] [b2,recv([a,b])] [b2,recv([a,nb1])] [b2,send([b,nb2])] [b2,recv([a,[b,[nb1,nb2]]] + _h97)] [b2,send([[a,[b,[nb1,nb2]]] + _h97,[a,[b,[nb1,nb2]]] + kbs])] [b1,recv([[b,[b,[nb1,nb2]]] + _h97,[a,[b,[nb1,nb2]]] + kbs])] [b1,send([[b,[b,[nb1,nb2]]] + _h97,[b,nb1] + nb2])] [b1,recv(nb1 + nb2)]

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University of Twente The Netherlands Centre for Telematics and Information Technology Exercises Explain the attack in the Woo-Lam protocol. Say why it is a type flaw attack. Implement and find the flaw of the Needham- Schroeder with Conventional keys (see Clark- Jacob Survey). Implement and find the flaw of the Yahalom protocol (see Clark-Jacob Survey). Write a small article over how to find security bugs in protocols using the COProVe tool.

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University of Twente The Netherlands Centre for Telematics and Information Technology Extra: Needham-Schroeder- Lowe Protocol 1. A->B : [A,Na]*pk(B) 2. B->A : [Na,Nb,B]*pk(A) 3. A->B : Nb*pk(B) Corrected version of the other one. Still contains an (unrealistic) flaw

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University of Twente The Netherlands Centre for Telematics and Information Technology Attack upon NSL a.1 A->e(B) : [A,Na]*pk(B) a.1' e(A)->B : [A,e]*pk(B) a.2 B->e(A) : [e,Nb,B]*pk(A) b.1 e->A : [e, [Nb,B] ]*pk(A) b.2 A->e: [[Nb,B], Na',A] *pk(e) Message a.2 is passed as b.1. Notice that a.2 has three fields, while b.1 has two. It is a type flaw attack. Rather unrealistic.

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University of Twente The Netherlands Centre for Telematics and Information Technology NSL in the tool initiator(A,B,Na,Nb,[ recv([A,B]), % for origination assumption send([A,Na]*pk(B)), recv([Na,[Nb,B]]*pk(A)), send(Nb*pk(B)) ]). responder(A,B,Na,Nb,[ recv([A,Na]*pk(B)), send([Na,[Nb,B]]*pk(A)), recv(Nb*pk(B)) ]). secrecy(N,[recv(N)]).

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University of Twente The Netherlands Centre for Telematics and Information Technology Scenario scenario([[a1,Sa],[a2,Sb],[a3,Sa2],[b1,Sb2],[sec1,St]]):- initiator(a,b,na,Nb,Sa), responder(a,b,Na,nb,Sb), initiator(A1,B1,na2,Nb2,Sa2), responder(A2,B2,Na2,nb2,Sb2), secrecy(nb,St). initial_intruder_knowledge([a,b,e]). has_to_finish([sec1]).

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University of Twente The Netherlands Centre for Telematics and Information Technology NSL output Trace: [a1,recv([a,b])] [a1,send([a,na] * pk(b))] [a2,recv([a,e] * pk(b))] [a2,send([e,[nb,b]] * pk(a))] [a3,recv([_h414,e])] [a3,send([_h414,na2] * pk(e))] [a3,recv([na2,[_h416,e]] * pk(_h414))] [a3,send(_h416 * pk(e))] [b1,recv([e,[nb,b]] * pk(a))] [b1,send([[nb,b],[nb2,a]] * pk(e))] [a2,recv(nb * pk(b))] [b1,recv(nb2 * pk(a))] [sec1,recv(nb)]

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