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ARCH consensus

Archethic Blockchain is using a new consensus called ARCH (Atomic Rotating Commitment Heuristic) for an uncompromising consensus to support high scalability and high throughput.

Archethic Blockchain is based on three properties:

  • Security: Each transaction is validated atomically
  • Data consistency: Algorithms ensure to access the latest write and maximum availability
  • Fault tolerance: Allow nodes to operate independently even in case of disaster

ARCH consensus is defined by three concepts:

  • Atomic Commitment: The most absolute form a consensus which implies 100% of concordant responses for the acceptance or refusal of the transaction validation
  • Heuristic: Set of algorithms which manages the entire network, allowing to elect in a decentralized and coordinated way the nodes in charge to validate or store the transaction chains
  • Rotating: Node election is constantly changing. No nodes can predict which nodes will validate the transaction before its arrives.

Atomic Commitment​

Archethic Blockchain is based on Hypergeometric distribution laws which from an unpredictable election and formal consensus make it possible to obtain with certainty (99.99999999%) the same answer by querying 197 nodes as would be obtained by querying 100 000 nodes.

Therefore, it makes possible the consensus establishment with a small part of nodes and can resist to attacks of 90% of malicious nodes.

The risk of related availability is ensured by a strict management of the disruptive nodes, which are banished after investigation of the origin of the disagreement.

By supporting more 90% of malicious nodes into its network, ARCH consensus is above aeronautical or nuclear standard, thanks to the Atomic Commitment which request the total agreement of the validation nodes and from a Malicious Detection algorithm to detect the malicious nodes.

Rotating Election​

Each rotating election is unpredictable, but still verifiable and reproducible. The rotating algorithm sort a list of nodes based on:

  • Hash of transaction: Unpredictable until the transaction arrives
  • Daily nonce: Secret shared between the authorized nodes and renewed daily
  • Node public key: Last node public key

The rotating election produces a proof, named: Proof of Election which can be verified by any other nodes to ensure the right election of nodes.

From this algorithm, we get a list of nodes which can be filtered according to the constraints of the validation of the transaction.

  • P2P availability
  • Geographical distribution

Workflow​

When a transaction is willing to be validated, its follows the given workflow:

  1. The transaction is received by any node (aka Welcome node)
  2. The Welcome Node determines the validation nodes from the Rotating Election algorithm and forward the transaction
  3. The validation nodes after receiving the transaction start some preliminary job to gather the context of the transaction:
    • Previous transaction
    • List of unspent outputs
  4. After the context building, the Cross Validation Nodes communicate to the Coordinator Node the list of storage nodes involved to gather this information.
  5. The Coordinator Node can build the Validation Stamp and compute the replication tree. Then it transmits them to the Cross Validation Nodes.
  6. The Cross Validation Nodes verify the content of the Validation Stamp, sign with or without inconsistencies, and send the Cross Validation Stamp to all the validation nodes involved.
  7. Once all the Cross Validation Stamps are received and if the Atomic Commitment is reached, the replication phase starts.
  8. Validation nodes send the transaction to the respective storage nodes:
  • Storage nodes responsible for the new transaction chain
  • Storage nodes responsible for the outputs of the transactions (transaction's movements addresses, recipients)
  • Storage nodes responsible for the Beacon Chain
  1. The storage for the new transaction chain will notify the validation nodes and the Welcome Node about the replication, and the Welcome Node will notify the client about it.
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