NSIS QoS-NSLP Authorization
(Next Steps In Signaling, Quality of Service NSIS Signaling Layer Application, Authorization process of the QoS reservation requests)


REFERENCE: [nsis-qos-nslp]



Authorization of the QoS resource requestor (Client),
Protection of the 3-party model against misbehavior of the Client (MITM attack), the Router and the Server


Tseno Tsenov for Siemens CT IC 3, June 2005



 1. R --- {Service.C.R}_K_CR ------------> C
 2. R <-- {{Service.C.S}_K_CS.C.R}_K_CR -- C
 3. R --------- {{Service.C.S}_K_CS.C.S.R}_inv(K_R) --> S
 4. R <-------- {C.R.S}_inv(K_S) ---------------------- S






G2, G20






  • Sessions between the Router and the Client are based on TLS and sessions between the Router and the Server are based on any AAA protocol. These protocols provide authentication, integrity and replay protection of the exchanged messages. The Client and its subscriber profile is known at the Server and is authenticated on the symmetric key shared between the Client and Server.

    The main goal of the model is the authorization aspect and not authentication of the involved peers. Therefore the above protocols are not modeled but services that their sessions provide are directly used. This implies:

  • There are two authorization goals that are modeled:

    Since AVISPA does not provide direct proof of authorization, but only proof of authentication % and secrecy, verification of the above goals is indirectly modeled by the following approach:

  • Due to the use of a TLS and AAA session, we can assume replay protection. Moreover it is assumed that the Routers authorized to provide the service do not misbehave. Thus only weak authentication is specified as goals. \end{enumerate}  


    role client(C,R,S          : agent,
                K_CR, K_CS     : symmetric_key,
                SND_CR, RCV_CR : channel(dy)
    played_by C
      local State   : nat,
            Service : text
      init  State := 1 
        1.  State   = 1 /\ RCV_CR( {Service'.C.R}_K_CR) =|> 
            State' := 2 /\ SND_CR({{Service'.C.S}_K_CS.C.R}_K_CR)
                        /\ witness(C,S,server_client_service,Service')
    end role
    role router(C,R,S : agent, K_CR : symmetric_key, K_S, K_R : public_key, Service : text, SND_CR, RCV_CR, SND_RS, RCV_RS: channel(dy) ) played_by R def= local State : nat, MessageCS : {text.agent.agent}_symmetric_key init State := 1 transition 1. State = 1 /\ RCV_CR(start) =|> State':= 2 /\ SND_CR({Service.C.R}_K_CR) 2. State = 2 /\ RCV_CR({MessageCS'.C.R}_K_CR) =|> State':= 3 /\ SND_RS({MessageCS'.C.S.R}_inv(K_R)) 3. State = 3 /\ RCV_RS({C.S.R}_inv(K_S)) =|> State':= 4 /\ wrequest(R,S,router_server_clientid,C) end role
    role server(R,S : agent, K_S, K_R : public_key, Service : text, KeyRing : (agent.symmetric_key) set, SND_RS, RCV_RS: channel(dy) ) played_by S def= local State : nat, C : agent, K_CS : symmetric_key, MessageCS : {text.agent.agent}_symmetric_key init State := 1 transition 1. State = 1 /\ RCV_RS({MessageCS'.C'.S.R}_inv(K_R)) /\ in(C'.K_CS', KeyRing) /\ MessageCS' = {Service.C'.S}_K_CS' =|> State':= 2 /\ SND_RS({C'.S.R}_inv(K_S)) /\ witness(S,R,router_server_clientid,C') /\ wrequest(S,C',server_client_service,Service) end role
    role session(C,R,S: agent, K_CR,K_CS : symmetric_key, K_S, K_R : public_key, Service: text, KeyRing: (agent.symmetric_key) set ) def= local SCR,RCR,SSR,RSR: channel(dy) composition client(C,R,S,K_CR,K_CS,SCR,RCR) /\ router(C,R,S,K_CR,K_S,K_R,Service,SCR,RCR,SSR,RSR) /\ server(R,S,K_S,K_R,Service,KeyRing,SSR,RSR) end role
    role environment() def= local KeyRing : (agent.symmetric_key) set const c, r, s : agent, k_cr, k_cs, k_is, k_ic, k_ir : symmetric_key, k_s, k_r, k_i : public_key, service : text, server_client_service, router_server_clientid : protocol_id init KeyRing := {c.k_cs, i.k_is} intruder_knowledge={c,r,s,service,k_is,k_ic,k_ir,k_s,k_r,k_i,inv(k_i)} composition session(c,r,s,k_cr,k_cs,k_s,k_r,service,KeyRing) /\ session(i,r,s,k_ir,k_is,k_s,k_r,service,KeyRing) /\ session(c,i,s,k_ic,k_cs,k_s,k_i,service,KeyRing) /\ session(c,r,i,k_cr,k_ic,k_i,k_r,service,KeyRing) end role
    goal %client authorization weak_authentication_on router_server_clientid % addresses G2: agreeement on C %router authorization weak_authentication_on server_client_service % addresses G2 and G20: % the router provides the service the client has asked (and payed) for end goal