Table of Contents
Introduction
What is DAG?
Features of DAG
Benefits of DAG
Aleph Zero’s DAG Architecture
What is Consensus Mechanism?
Types of Consensus Mechanism
Byzantine Fault Tolerant Consensus Mechanism
Aleph Zero’s Consensus Mechanism - AlephBFT
Aleph Zero: DAG and BFT Consensus Mechanism
Conclusion
Introduction
Since its inception in 2018, Aleph Zero has been true to its mission of advancing the adoption and growth of decentralized systems by building a secure blockchain ecosystem and developing secure smart contracts that power the decentralized world. So far, the blockchain has been able to attain some great heights for its goals, and the protocol will continue to expand and be updated in the years to come.
In this article, we’ll be taking a look at how Aleph Zero is ensuring a secure ecosystem with the implementation of the BFT (Byzantine Fault Tolerant) consensus protocol and the DAG (Directed Acyclic Graph) structure as its auxiliary data.
What is DAG?
DAG stands for Directed Acyclic Graph and it is a type of distributed ledger technology that uses edges and vertices in storing transactions instead of blocks as is the case in blockchains. DAGs have nodes that perform tasks to create and submit transactions but unlike blockchains, transactions are not sent into a block to be added to a chain of other blocks, rather, transactions in DAG are stored atop one another as vertices (vertex for a single transaction). And no, DAGs don’t form chains - blockchains do.
Features of DAG
Vertices and edges: unlike blockchain blocks, DAGs store transactions in edges that connect to form vertices, giving a graph-like structure.
High level of centralization: most DAGs are centralized and, hence require permission before nodes can participate. Most DAGs are run by a small group of people. Hedera Hashgraph, for example, is governed by the Hedera Council and contains just 39 node operators.
Benefits of DAG
Highly scalable: DAGs, typically, can handle a larger number of transactions than the average blockchain. This is possible because the architecture on which DAG technology is built is akin to that of a tree, where linked nodes are the branches and they can validate transactions simultaneously unlike blockchains where transactions are processed block by block. This way users don’t have to wait long hours for one transaction to validate before executing another. Scalability is very attainable in this model of processing transactions.
For instance, Constellation Network (a form of DAG) can perform 11,000 transactions per second; while Hedera Hashgraph can perform 10,000 tps.
Faster transaction speed: transactions are processed faster because there are blocks to be created and nodes process transactions parallel to each other. For example, Aleph Zero which utilizes DAG reached a transaction speed of 100,000 per second on a test network of 128 nodes.
Low transaction costs: There are no miners to validate transactions so users are not required to pay much for transaction fees.
Greater flexibility: DAG-based DLTs are more favorable since they can be used in various use cases, such as payments, gaming, healthcare, supply chain management, IoT, databases, and much more.
Rising traffic improves performance: Unlike blockchains that get congested during high traffic, with DAGs, the case is different.
Less energy consumption: Even though DAGs use PoW approach, they consume way less energy than the average PoW blockchains.
Aleph Zero’s DAG Architecture
Although DAG is known mainly to be used in permissioned settings, in Aleph Zero, it is permissionless. The blockchain utilizes DAG to develop a leaderless (one in which no single node controls the entirety of the activities that take place on the network) protocol that mitigates the threats of malicious block producers. Some of the many advantages of DAG technology which Aleph Zero adopts are increased throughput, faster transaction speed, and reduced transaction fees. Aleph Zero believes that these will make mass adoption more feasible.
What is a Consensus Mechanism?
The blockchain, as we know it, is a distributed ledger technology that works when a group of nodes work together to ensure the system runs. Every participating node has a record of every transaction and they are in charge of validating and broadcasting every transaction that takes place on the network. To ensure that all nodes follow the rules and agree on a singular mode of validating transactions, we have what we call a consensus mechanism or consensus protocol.
A consensus mechanism is an algorithm embedded into a blockchain’s code to ensure all the nodes participating in a network agree on the state of the blockchain. The state of the blockchain in this case refers to the mode by which transactions are validated in the blockchain and security is achieved.
Types of Consensus Mechanisms
There are several consensus mechanisms but the most popular of them are Proof of Work and Proof of Stake consensus protocols. The former involves miners competing to perform complex computational tasks to be able to create blocks, put transactions into the blocks, validate them, and then ensure that the network’s security is maintained. Only the fastest node to get the problem right gets to create the block and get rewarded. However, the latter involves stakers delegating their tokens to validators who then validate transactions and maintain the network's security.
Other consensus mechanisms are Proof of History (PoH), Delegated Proof of Stake (DPoS), Proof of Authority (PoA), Proof of Importance (PoI), Proof of Elapsed Time (PoET), Proof of Capacity (PoC), Proof of Burn (PoB), Byzantine Fault Tolerance (BFT), etc.
Byzantine Fault Tolerant (BFT) Consensus Mechanism's
Byzantine Fault Tolerant (BFT) is a consensus mechanism that ensures the safety of the blockchain network despite faulty or malicious nodes assuming the number of malicious nodes doesn’t exceed the honest nodes or even equal one-third of all nodes in the network. BFT can be attained if the network's correctly functioning nodes come to an understanding regarding their values.
The Byzantine Fault Tolerant (BFT) consensus mechanism is derived from the Byzantine Generals’ problem, which is a game theory problem that describes how difficult it is for decentralized parties to reach an agreement without depending on a reliable central party. The image below provides a better explanation of Byzantine Generals’ Problem:
Byzantine Fault Tolerant is advantageous in that it ensures that the system still functions even when some nodes on the network are faulty or start acting maliciously.
Aleph Zero’s Consensus Mechanism - AlephBFT
Aleph Zero utilizes the Byzantine Fault Tolerant consensus protocol and is referred to as AlephBFT. Aleph Zero operates by having a group of nodes known as validators propose and vote on blocks. A validator must first construct a unit, which is a tiny bit of data that includes some of the transactions and the block header before they can submit a block. After that, the unit is transmitted to every validator in the network. After that, the units are voted on by the validators. Every validator must confirm that the unit is legitimate and hasn't been tampered with before they can cast a vote for it. The unit is added to the blockchain if the majority of validators vote for it.
AlephBFT is one of the key ingredients that power the Aleph Zero blockchain and it is peer-reviewed. It ensures that even amid malicious nodes, communication between the other nodes is transparent and efficient. Aleph Zero can withstand up to 33% of malicious or dishonest node members without its validation process or outcome being affected. Every transaction is approved by 67% of the members before it is finalized.
In Aleph Zero, the validators who determine the state of the network are rotated
Aleph Zero: DAG and BFT Consensus Mechanism
Aleph Zero combines the BFT consensus protocol and DAG architecture at the core level. Aleph Zero has three qualities that make it the secure blockchain it is: asynchronous, leader-free, and the consensus mechanism it employs - Byzantine Fault Tolerant. It is worth noting that Aleph Zero is not a DAG, rather it employs the integration of its data structure in its development.
The DAG in Aleph Zero is used in collating data on the ordering of the transactions, and then the network’s validators build blocks of chains based on these transaction data. In Aleph Zero, the blocks are developed using the DAG as an auxiliary structure in the parallel process, so it is clear that DAG has an impact on the chain's development but it is not the chain itself. Hence, Aleph Zero cannot be regarded as a DAG but rather a blockchain.
Although Aleph Zero utilizes the DAG, it doesn’t adopt its permissioned feature. It implements a process that designates a rotating committee of randomly selected individuals to make decisions regarding the state of the network to ensure that the protocol stays decentralized.
Conclusion
While Aleph Zero can attribute its privacy to ZK-SNARKS and sMPC, its security can be credited to its implementation of the BFT consensus mechanism and DAG architecture. As a result of this integration, the blockchain can withstand coordinated attacks by some of its participating nodes as well as downtime in others.
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