Permissioned Blockchain - (Byzantine General Problem)

Byzantine Generals Problem

Three Byzantine Generals Problem : Lieutenant Faulty

Round 1 :
→ Commander correctly sends same message to Lieutenants

Round 2 :
→ Lieutenant1 correctly echoes to Lieutenant2
→ Lieutenant2 incorrectly echoes to Lieutenant1

• Lieutenant1 received differing message
• By integrity condition, Lieutenant1 bound to decide on Commander message
• What if Commander is faulty ??
• This contradicts the agreement condition
• No solution possible for three generals including one faulty

Four Byzantine Generals Problem : Lieutenant Faulty

• Lieutenant1 decides on majority (Retreat, Attack, Retreat) = Retreat
• Lieutenant2 decides on majority (Attack, Retreat,Retreat)=Retreat
• Lieutenant3 decides on majority (Retreat,Retreat,Attack)=Retreat

Round 1 :
→ Commander sends differing message to Lieutenants
Round 2 :
→ Lieutenant1, Lieutenant2 and Lieutenant3 correctly echo the message to others

Byzantine Generals Model

• N number of process with at most f faulty
• Receiver always knows the identity of the sender
• Fully connected
• Reliable communication medium
• Synchronous system

Lamport-Shostak-Pease Algorithm

• Base Condition : 

           Broadcast (N, t-=0)
            - N : number of processes
            - t : algorithm parameter

• Commander decides on its own value

• All lieutenants broadcast their values to the other lieutenants except the senders