The original text is from BREAD

Compiled by | Odaily Planet Daily Golem (@web3golem)_

Editor’s note: Ethereum founder Vitalik mentioned in his new article today, “Possible futures of the Ethereum protocol, part 1: The Merge,” the areas where Ethereum's technology still needs improvement, the reasons, and the paths forward. The primary focus is to change the block finality from 2-3 epochs (~15 minutes) to be completed within a single slot (~12 seconds). So, what exactly is the finality (Finality) that Vitalik emphasizes so much? How is it achieved in Ethereum and L2?

Crypto researcher BREAD's article “WTF is Finality?” explains the finality of blocks and the implementation process through analogy. Odaily Planet Daily has specially compiled it below, hoping to help readers understand.

Analogy of Finality

Following the tradition of my “WTF is……” series, I like to start with analogies from real life, allowing people to grasp the key points without delving into the underlying details. For finality, we can use the example of concrete hardening over time, as shown in the image:

This is the highest-level explanation of “finality” in blockchain; like concrete, over time, from pouring (initial confirmation) to initial set (multiple confirmations), it becomes increasingly difficult to deem the initial block as “false” until it is fully hardened (finalized). Once it reaches the end, it is almost impossible to change.

The corresponding specific sequence in blockchain is:

Submitted > Confirmed > Finalized

If you want to delve deeper into the methods, content, and reasons for finality (in the Ethereum environment), feel free to continue reading.

What is Finality?

Let’s try to understand some structure around this concept. Here’s an explanation of finality and related concepts:

• Slot (also known as block time): Its alternative name, block time, might be easier to understand. A slot or block time is the amount of time allocated for the system to generate new transaction blocks and attach them to the current chain. For example, Ethereum's slot is 12 seconds, Base is 2 seconds, and Solana is 0.4 seconds.

• Confirmation: Confirmation occurs when a transaction is officially added to a block that has been added to the current chain. It is now “confirmed” as part of the ledger, and as subsequent blocks are continuously added to the ledger, the number of confirmations will increase.

• Epoch: Every 32 slots is referred to as an epoch. This is a secondary structure in blockchain used for delegating roles and responsibilities. Slots are used to build blocks, while epochs are used for data propagation, reward distribution, validator selection, etc.

• Checkpoint Block: A checkpoint block is the first block created in an epoch, serving as a reference point for checking the chain's history.

• Finality: Finality is the point at which a transaction is considered irreversibly added to the ledger of a given chain. However, in terms of technical attributes, the use of this term varies across different chains, so it’s best not to assume uniform standards in all cases. In the Ethereum ecosystem, finality is reached after 2 epochs (~13 minutes); in Optimistic L2, it requires waiting for the fraud dispute period to pass (~7 days); in ZK L2, due to the guarantees provided by validity proofs, there are two disputed finality moments: local (when the proof is generated on L2 [~a few minutes]) and global finality (when the proof is published to Ethereum and finalized there [~13 minutes]).

• Block Reorganization (“Reorg”): Block reorganization refers to a situation where a block that was once confirmed as part of the chain is no longer considered valid for some reason, resulting in the formation of a new chain. This usually comes with penalties.

The following image attempts to visualize all these terms in a single image for easier understanding:

How is Finality Achieved?

Now that we understand finality and related concepts, how do they work together? What are the rules?

For Ethereum

• Validator Voting: Validators for each epoch (32 blocks) will vote on the checkpoint blocks (Checkpoint Block) of the current and previous epoch until the checkpoint block receives 2/3 of the votes from staked ETH;

• Reasonable Checkpoint: Once the checkpoint block reaches the 2/3 voting threshold, it is considered “reasonable”;

• Absolute Majority Chain: Once two subsequent checkpoint blocks a and b are both reasonable and b has connected to the next block, the blocks included in the epoch prior to the first epoch will become final blocks, and they will no longer be affected by simple block reorganization.

For L2

L2 is built on Ethereum, so are they basically the same?

The answer can be both yes and no. In the article “Will Based Rollups Have a Place in the Future of Ethereum?,” it was mentioned that L2 is an independent blockchain, but they rely on Ethereum for finality settlement. This means their finality is layered just like the chain.

There are two types:

• Local Finality: This is the finality of L2 itself and applies only to L2s that utilize validity proofs (also known as ZK Rollups). This is because validity proofs are mathematically supported, and when the proof itself is generated, it means it is correct. Therefore, once ZK L2 generates its proof, the L2 state can be considered finalized without waiting for the proof to be published to Ethereum and settled there. However, this still carries risks and trust assumptions, which can be judged based on one’s risk tolerance.

• Global Finality: Once the state is determined, L2 confirms its local state and generates proofs (fraud or validity), publishes that proof to Ethereum, and then Ethereum confirms the block containing that proof. Even so, for L2s using optimistic methods, there is still a chance to revert transactions until the 7-day challenge period has passed. This is a trade-off made to reduce the computational load required when creating proofs.

L2 networks can have local finality in certain cases, but generally, they must wait until Ethereum completes its published validity proof (ZK) or the challenge window for fraud proofs has passed (Optimistic rollups).

For Bitcoin/POW Chains

In Bitcoin's PoW mechanism, there is no concept of finality because anyone can produce the longest chain and become the main ledger. This means that, although it is somewhat impractical, as long as there is enough computing power, one can rewrite Bitcoin's history from the last day, week, or year.

However, despite this method being costly in terms of resources and time, and impractical in operation, it does create a meaningful distinction between different systems and gives rise to several unique types of MEV (Maximum Extractable Value), such as “Long-Ranged Attacks” and “Block Withholding.” In these cases, miners can choose to produce and hide a block, then append a subsequent block, or continuously mine multiple blocks, thereby creating and capturing unique profit opportunities.

Why is Finality Needed?

From the above, we know how finality is achieved in POS chains, and it requires a significant amount of work. So, why do we need to do this? The answer is that there are indeed some benefits to doing so:

• Economic Security: The system (and we) can review a certain point and confidently determine that it will not change, which gives ecosystem participants confidence in the "real situation." For example, in large transfers and loans, once users are assured that the system cannot be altered without extreme, protocol-exceeding interventions, it instills confidence for users to participate in the ecosystem based on this authenticity. This is also why cross-chain bridges often wait for a certain number of confirmations or complete finality before releasing funds on the secondary chain.

• Faster Settlement: Because there is a moment in the system that formally establishes the state as permanent, it means that participants within the ecosystem only need to wait for this settlement time, whereas in PoW (Proof of Work) systems, this moment never arrives and is entirely dependent on individual subjective judgment.

• Reduced Attack Factors: Earlier, some MEV opportunities present on PoW chains were mentioned. PoW chains only address the "Nothing at Stake" problem, meaning that anyone who takes malicious actions against the system may also face losses. However, in PoS chains, if you are a validator and attempt to alter an already finalized state, you must violate protocol rules, thus facing the risk of slashing.

Conclusion

This article briefly explains what finality is, aiming to make people aware that it is a frequently used but often misunderstood blockchain mechanism. The process of finality is akin to blocks in the system hardening like concrete, ultimately becoming as solid as a rock.

免责声明：本文章仅代表作者个人观点，不代表本平台的立场和观点。本文章仅供信息分享，不构成对任何人的任何投资建议。用户与作者之间的任何争议，与本平台无关。如网页中刊载的文章或图片涉及侵权，请提供相关的权利证明和身份证明发送邮件到support@aicoin.com，本平台相关工作人员将会进行核查。