Fully demonstrates the creativity of the team
Author: Chloe
Arbitrum transfers the calculation engineering originally performed on Ethereum to Layer 2, and then assumes that the calculation results are correct without any verification, and publishes the data back to Ethereum. But in order to prevent someone from doing evil, a 7-day challenge period is set to buffer (if someone is found to be fraudulent, the deposit will be deducted).
Arbitrum launched an upgraded version of Nitro on August 31 last year. It has lower fees, better compatibility with Ethereum, and simpler zk proofs. In short, it is a comprehensive upgrade (rather than targeting specific problems). However, because it did not reissue a new chain, but seamlessly upgraded from Arbitrum One, it is still called Arbitrum One.
The key innovations supporting Nitro can be summarized into four points: the proof program, Geth as the core, separation of execution and proof, and Optimistic Rollup for interactive fraud proof.
Proof program that does not require a consensus mechanism
Nitro executes transactions using two phases.
The first stage: self-processing in Layer2
The user creates a transaction, which will be sent to Nitro's Sequencer (sequencer) after wallet signature confirmation.
Sequencer receives the information, filters out invalid transactions through the "state transition function", and queues up the remaining transactions fairly.
Then, without any additional confirmation on the chain (such as L1 Ethereum), the node is directly and unconditionally executed locally and provides transaction receipts to customers (including users who submit malicious or wrong information). This process usually only takes one two seconds.
But at this time, the transaction has not been submitted to L1 Ethereum, and there is room for change, so it is called "soft confirmation". However, for users, this step is over. In fact, there are still many steps to ensure security. .
second stage
Sequencer publishes the queuing sequence to Ethereum and finally confirms it, that is, "hard termination".
One way to do this is to publish instant notifications to all subscribers as each transaction is sequenced. Another way is to aggregate them and publish them in batches (every few minutes) on L1 Ethereum.
It should be emphasized that the "state transition function" operation of Sequencer in the first stage is public. Anyone can calculate the state transition function according to their known transaction sequence, and all honest parties get the same result.
Therefore, Nitro's nodes do not need a consensus mechanism, but only need to obtain transaction sequences (instant extraction and batch extraction on Ethereum) and run them locally by themselves, so the cost will be significantly reduced.
Node software Geth rewritten in Go language
Geth is go-ethereum. As the name suggests, it is the Ethereum node software written in Go language, which allows miners to execute transactions. This is the core part of Nitro.
Arbitrum's old solution is to simulate EVM through a customized Arbitrum virtual machine (AVM). Some of its internal logic is inconsistent in EVM (such as the calculation of Gas), so it is limited to low-level instructions.
Geth basically fully supports the data structure, format and virtual machine of Ethereum, so it can achieve a high degree of compatibility with Ethereum.
It is worth mentioning that Geth abandoned the stack accumulated by the old solution (using its own custom language mini to implement custom logic), and directly started from scratch and wrote it in Go language. Most of the development work was based on the existing out-of-the-box Out-of-the-box code, and overall leaner.
Two sets of codes for execution and proof
There are two tasks in Layer 2—execution and proof. These are two emphases and cannot be taken care of at the same time. Therefore, Nitro uses different codes to implement them.
However, they are all the same set of source codes. The node software Geth mentioned earlier that allows miners to execute transactions uses source codes, and the execution speed is faster.
However, the code for fraud proofs is compiled into a binary wasm format, which is characterized by portability, small size, fast loading, and compatibility with the Web. Moreover, Nitro has fine-tuned the wasm format to make it more suitable for interacting with the chain, which is called WAVM code.
Performing Arbitrum's interactive fraud proof on WASM code replaces the architecture of the Arbitrum Virtual Machine (AVM), and directly builds and compiles it with standard languages and tools.
Interactive fraud proofs for reporting each other
The proof system adopted by Nitro is their first-of-its-kind "Interactive Fraud Proof".
To put it simply, after all the transactions are completed, there will be 7 days to be checked by the verifier (whether it is fraudulent or invalid), and if there is indeed a problem, it will be re-executed.
The verifier is equivalent to a bounty hunter who makes a living by reporting, but in order to prevent someone from disturbing the order through false accusations, bounty hunters are also allowed to report and expose each other, so that both parties continue to provide evidence until one party no longer follows up.
Finally, submit the reported transaction to Ethereum for execution and verify who is wrong, and distribute the deposit of the false accuser to the bounty hunter who challenges the false accuser.
This is the interactive fraud proof, which is equivalent to introducing external regulators by means of marketization. It is an innovation in the governance mechanism, which can greatly improve the efficiency and accuracy of verification.
Summarize
As an iterative version of Arbitrum, Nitro has assisted in the launch of hundreds of projects, accumulated hundreds of thousands of unique users, millions of transactions and billions of dollars in bridging assets, and currently occupies a dominant position in the market.
In addition to using Nitro technology to upgrade Arbitrum One, the Arbitrum team also hopes to use it to create application-specific Rollups. They also want to absorb resources from Solana and Cosmos ecology (especially developers) in the future.
Arbitrum's ability in ecological incubation operations is obvious to all. At the same time, it has also overcome a large number of technical bottlenecks (especially in a non-blockchain way), which fully demonstrates the creativity of the team. I believe that they who have come all the way from Layer2 will move towards a larger ecology.
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