T : Target (subsumes Location Generator, Mobile User and Rule Maker)
LR : Location Recipient
LS : Location Server (subsumes Rule Holder)
LI : Location Information
PR : Privacy Rule
1. LR ---- LR.{LR.K_LR.N_LR}_K_T_LR ---------------------------------> T
2. LR <- {Psi_LR.Psi_T.N_LR}_K_T_LR ---------------------------------- T
3. LS <- {Psi_LR.Psi_T.PR.LI.K_LR}_K_LS - T
% some time later, LR requests the location information of T:
4. LR -- {Psi_LR.Psi_T}_K_LS -> LS
5. LR <- {PR(LI).Psi_T}_K_LR -- LS
A further (minor) difference is that we model the Location Generator as part of the Target and transmit in the third message both the pseudonyms and the location of the Target because the Location Server cannot associate these values since he is not allowed to know the identity of the Target.
role locationRecipient(
T, LR, LS : agent,
K_T_LR : symmetric_key,
K_LS : public_key,
Snd, Rcv : channel(dy)) played_by LR def=
local
State : nat,
N_LR : text,
Psi_LR : text,
Psi_T : text,
K_LR : symmetric_key, % could also be: public_key
Filtered_LI : message
init State := 0
transition
0. State = 0 /\ Rcv(start)
=|> State':= 2 /\ N_LR' := new()
/\ K_LR' := new()
/\ secret(K_LR' , k_LR, {T, LR, LS})
/\ Snd(LR.{LR.K_LR'.N_LR'}_K_T_LR)
/\ witness(LR, T, t_LR_LR, LR)
2. State = 2 /\ Rcv({Psi_LR'.Psi_T'.N_LR}_K_T_LR)
=|> State':= 8 /\ Snd({Psi_LR'.Psi_T'}_K_LS)
/\ witness(LR, LS, ls_LR_K_LR, K_LR)
/\ request(LR, T , lr_T_N_LR, N_LR)
8. State = 8 /\ Rcv({Filtered_LI'.Psi_T}_K_LR)
=|> State':= 10/\ request(LR, T, lr_T_filtered_LI, Filtered_LI')
end role
role target(
T, LS : agent,
K_T_LR : symmetric_key, % should be determined by a lookup
K_LS : public_key,
Snd_LR, Snd_LS, Rcv: channel(dy)) played_by T def=
local
State : nat,
LR : agent,
N_LR : text,
K_LR : symmetric_key, % could also be: public_key
Psi_LR : text,
Psi_T : text,
LI : text,
PR : hash_func
init State := 1
transition
1. State = 1 /\ Rcv(LR'.{LR'.K_LR'.N_LR'}_K_T_LR)
=|> State':= 3 /\ Psi_LR' := new()
/\ Psi_T' := new()
/\ Snd_LR({Psi_LR'.Psi_T'.N_LR'}_K_T_LR)
/\ witness (T, LR', lr_T_N_LR, N_LR')
/\ wrequest(T, LR', t_LR_LR, LR')
/\ PR' := new() % chooses some privacy (accuracy) rule
/\ LI' := new()
/\ secret(LI', li, {T, LS})
/\ secret((PR'.LI'), filtered_LI, {T, LR', LS})
/\ Snd_LS({Psi_LR'.Psi_T'.PR'.LI'.K_LR'}_K_LS)
/\ witness (T, LR', lr_T_filtered_LI, (PR'.LI'))
end role
role locationServer(
T, LR, % but LS does not actually use identity of T and LR
LS : agent,
K_LS : public_key,
Psi_Table: (text.text.hash_func.text.symmetric_key) set,
Snd, Rcv : channel(dy)) played_by LS def=
local State : nat,
Psi_LR : text,
Psi_T : text,
K_LR : symmetric_key,
LI : text,
PR : hash_func
init State := 5
transition
5. State = 5 /\ Rcv({Psi_LR'.Psi_T'.PR'.LI'.K_LR'}_K_LS)
=|> State':= 7 /\ Psi_Table':=
cons(Psi_LR'.Psi_T'.PR'.LI'.K_LR', Psi_Table)
7. State = 7 /\ Rcv({Psi_LR'.Psi_T'}_K_LS)
/\ in(Psi_LR'.Psi_T'.PR'.LI'.K_LR', Psi_Table)
% uses the information Psi_LR and Psi_T to look up PR, LI and K_LR in the table.
=|> State':= 9 /\ Snd({(PR'.LI').Psi_T'}_K_LR')
/\ wrequest(LS, LR, ls_LR_K_LR, K_LR')
end role
role session(T, LR, LS : agent,
K_T_LR : symmetric_key,
K_LS : public_key,
Psi_Table : (text.text.hash_func.text.symmetric_key) set) def=
local SLR, RLR, STLR, STLS, RT, SLS, RLS: channel(dy)
composition
locationRecipient(T, LR, LS, K_T_LR, K_LS, SLR, RLR)
/\ target (T, LS, K_T_LR, K_LS, STLR, STLS, RT)
/\ locationServer (T, LR, LS, K_LS, Psi_Table, SLS, RLS)
end role
role environment() def=
local Psi_Table: (text.text.hash_func.text.symmetric_key) set
% shared between all instances of LS
const psi_LR,
li, filtered_LI,
lr_T_N_LR,
k_LR, t_LR_LR,
lr_LS_filtered_LI : protocol_id,
t, lr, ls : agent,
k_LS : public_key,
k_T_LR, k_T_i, k_i_LR : symmetric_key
init Psi_Table := {}
intruder_knowledge = {t, lr, ls, k_LS, k_T_i, k_i_LR}
composition
session(t, lr, ls, k_T_LR, k_LS, Psi_Table)
/\ session(t, lr, ls, k_T_LR, k_LS, Psi_Table)
% repeat session to check for replay attacks
% /\ session(i, lr, ls, k_i_LR, k_LS, Psi_Table)
% It does not make much sense to let the intruder play the role of T
% since then the intruder would know its location information anyway.
% /\ session(t, i, ls, k_T_i, k_LS, Psi_Table)
% It does not make sense to let the intruder play the role of LR
% since then the intruder is allowed to know the (secret) location of T.
end role
goal
secrecy_of li, filtered_LI, k_LR % addresses G12
% strong authentication and integrity of the Location Information,
% (including replay protection):
authentication_on lr_T_filtered_LI % addresses G2 and G3
% the Location Server (weakly) authenticates the Location Recipient:
% weak_authentication_on ls_LR_K_LR % addresses G2 and G3
% additional authentication goals, not in RFC3693:
authentication_on lr_T_N_LR % addresses G1 and G3
weak_authentication_on t_LR_LR % addresses G1
% and G20: T authorizes LR to receive the location via LS
end goal
environment()