3. Protocole :

a) Common ground : the gossip protocole

The gossip protocole is used in the blockchain and in the Hashgraph to spread the informations through the network. Basically each time a node is sent a new transaction it communicates it to its neighbours nodes and so on.

b) Consensus protocole

In this section we will describe the Proof of work consensus protocole which is used by the most famous blockchains as Bitcoin and Ethereum. The nodes are competing on a very complex mathematical challenge to gain the right to add their data to the blockchain. It takes on average 10 min to validate a block and consume a ridiculous amount of energy equivalent to the electricity required to power 8.61 US household for 1 day. In the Bitcoin and Ethereum protocole nodes have to run a safety algorithm which verifies all transactions to make sure they do not accept a malicious transaction. Although if the node try to fraud and add a block with a double spend transaction for instance, the next node to add a block to the blockchain will reject it, connect with the node before it and so the transactions of the fraud block will be deleted. The cost of mining is supposed to dissuade miners to try these kinds of attacks on a blockchain however if several nodes are dishonest the “fraud chain” can gain in length. This means that in the Proof of work consensus the consensus is actually never reached but only approached which also explain why a receiver of a transaction usually wait for the confirmation of several nodes to validate a transaction.

The Hashgraph breakthrough is nested in the validation protocole. The hasgraph consensus protocole is based on the connection graph we described earlier and does not require any additional effort from the network nodes. The process is the following :

STEP 0: The Hashgraph is divided in rounds. One round is created each time one event is able to connect more than 2/3 of the firsts events of the current round by more paths than 2/3 of the node population.

By doing so one event « strongly sees » another event.

In the example B4 strongly sees A3. (Node population = 4, number of connecting path = 3)

STEP 2 : Each time a new round is created the first new nodes of the new round will vote to say if they would agreed upon the data contained in the first row of events of the preceding round. To do so they just need to verify that they are connected to these nodes.

In this example all the 3rd round first nodes would have agreed upon the data in A2

STEP : 3 The last stage is to collect the 3rd round nodes answers. To do so the 4th round nodes are required. They need to strongly see the 3rd round node (cf example). If one of the 4th round node succeed to collect a super majority (more than 2/3 of the population) of positive votes (STEP 2) upon the data in the 2nd round then the consensus is found this data.

For more details on the Hashgraph consensus process, please visit : https://hashgraph.com/