Formal Analysis of Fairness for Optimistic Multiparty Contract Signing Protocol

Algorithm 5

Modeling of five-party CKS abort and recovery subprotocols.

T_process()=

Modeling of the five-party CKS abort subprotocol

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//(1)T agrees with the abort requirement from P₂

[][!T_Respond2 && P₂_Abort_Send && !T_Validated ]TP₂abort1{T_S2=true; T_Abort_Send_P₂=true;

T_Respond2=true; T_h2=0; T_l2=1}->P₂H_process()

//(2)T refuses the abort requirement from P₂

[][!T_Respond2 && P₂_Abort_Send && T_Validated ]TP₂abort2{T_S2=true; T_Recovery_Send_P₂=true;

T_Respond2=true}->P₂H_process()

Modeling of the five-party CKS recovery subprotocol

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//(3)T agrees with the recovery requirement from P₃

[][P₃_recovery_1_1_3_3 && !T_Respond5 && !T_Respond4 && !T_Respond3 && !T_Respond2 && !

T_Respond1] P₃reco1{T_Recovery_Send_P₃=true;T_Respond3=true; T_Validated=true;}->P₃_process()

//(4)T refuses the recovery requirement from P₃

[][P₃_recovery_1_1_3_3 && !T_Respond3 && (T_Respond5∣∣T_Respond4∣∣T_Respond3∣∣T_Respond2∣∣

T_Respond1)&& !T_Validted && ((T_S5 && T_l5>0 ∣∣T_S4 && T_l4>0 ∣∣ T_S2 && T_h2>2∣∣T_S1 &&

T_h1>2 ))]P₃reco3{T_Respond3=true;T_S3=true;T_Abort_Send_P₃=true;T_h3=3;T_l3=3}->P₃_process()