Byzantine Agreement

• N vessels, each general controls one vessel

• For each general (vessel)

  • Decide on a profile "honest" or "Byzantine"

  • For honest generals decide on a vote "attack" or "retreat"

  • Start the Byzantine agreement algorithm on all generals, through a webpage interface

• When the algorithm ends, the result and result vector should appear on each webpage (upon refresh)

  • Honest generals should agree on the same votes among them

  • It is not required any agreement for the Byzantine generals

The interface

• Each node has a webpage interface of three buttons:

  • "Attack", "Retreat", "Byzantine"

• If a general is honest, start the Byzantine agreement algorithm on that general (vessel) by clicking the "Attack" or "Retreat" button, depending on the initial vote that you have assigned to that general

• If a general is Byzantine, start the Byzantine agreement algorithm on that general (vessel) by clicking the "Byzantine" button

How it works

Byzantine agreement algorithm runs in two steps:

• (step 1) When voting starts:

  • Honest nodes start by sending out their votes

  • Byzantine nodes wait until they collect all the honest votes and send out different votes to the honest nodes in order to break agreement (if possible).

• (step 2) When a vessel has received all votes

  • if honest, it sends to other vessels a vector of all votes received

  • if Byzantine, it sends to other vessels a vector of Byzantine votes

• Voting and outcome:

  • When a vessel has received all the messages from step 2, it computes the (majority vote) result vector and the result

  • Then, it adds the result vector and the result to the webpage (to be seen upon refresh)

Task 1 https://youtu.be/ll78bKLLGl4

• Select 4 nodes for this subtask. Using the interface set:

  • 3 honest nodes and 1 Byzantine (N=4, k=1)

• Demonstrate that agreement is reached. That is, no matter what the honest nodes vote for, agreement can always be reached

  • The result vectors of the honest generals should match on the entries corresponding to the honest generals

  • Hence, the honest generals agree on the same result.

• Note that the Byzantine node must respect the agreement protocol, but it can change the votes to be sent to the honest nodes (e.g. it cannot sent garbage – in this implementation, not in general)

Task 2 https://youtu.be/7aMSQQhaOMk

• Select 3 nodes for this subtask. Using the interface set:

  • 2 honest nodes and 1 Byzantine (N=3, k=1)

• Set different votes for the two honest nodes. The Byzantine node must be able to convince one node to attack and another one to retreat

• The Byzantine node can only change the votes to be sent to other nodes, but always respects the agreement protocol