Is it technically feasible to roll back the Bitcoin blockchain? Seeing Daxie's Discussion on Belief

Yesterday, Zhao Changpeng discussed the bitcoin blockchain rollback on Twitter, which caused a fierce debate in the currency circle.

Although many people think that Qian’an is not capable of carrying out this operation, Zhao Changpeng eventually said that it is impossible to reorganize bitcoin transactions. However, Zhao Changpeng still throws the idea of ​​“returning the bitcoin blockchain technically feasible”. .

From the point of view of technical feasibility, how to implement the reorganization of the Bitcoin blockchain, in reality, whether there is any risk or cost of such a situation, can only be achieved by the currency alone, and the reorganization block can be retrieved. Whether the stolen funds will be a good suggestion.

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Let's see what the big guys say.

can do

Yesterday, the reporter gave a detailed description of the events that occurred yesterday through an article entitled “Returning, letting the currency from rave reviews to fame and ruin”, but it did not mention the specifics of the rollback blockchain. Process.

Today, with the fermentation of this event, more and more analysis and opinions have been studied and discussed.

TamasBlummer, DAH's chief ledger architect, believes that it can be done from a technical and PoW economic perspective. Of course, the premise is to unite more than half of the miners and then reorganize.

Tamas Blummer said that if you want to recover the bitcoin stolen by hackers, the miner must build another replacement chain at block 575011 (the hacker steals 7,000 bitcoins at block height 575012).

"This alternative continuation chain does not contain hacking transactions and must grow faster than the current chain, and at some point it shows more work, and all Bitcoin clients reorganize it. After that, the hacker transaction will not exist in the network. That is, block 575012 and subsequent blocks will not exist in the network."

The founder of the Litecoin pool, Jiang Zhuoer, also said:

This rollback is technically feasible: as long as there is more than 51% of the calculation power, before the money trading block, restart a digging fork, and only remove the stolen transaction (and subsequent transactions), the normal package Other transactions on the chain, then block reorganization occurs after the new fork length exceeds the original stolen chain.

Currency can do it

Of course, the fundamental premise for block reorganization is to have at least half of the computing power.

Although Bitcoin has the largest and most extensive computing power and miners group to date, it is undeniable that most of Bitcoin’s computing power is still in the hands of major mining pools, and the impact of currency security For the sake of force, it is not an idiot to dream about trying to assemble these calculations.

In the early hours of the morning, Pan Zhiyu, the founder of the coin-printing pool, said in a statement that if you want to say the feasibility of the currency restructuring of the Bitcoin block, "more than half."

He said that CZ (Zhao Changpeng) contacted a certain land to calculate the computing power, and the calculation power of the system was estimated to be about 26E, which is slightly more than half of the whole network. Considering the participation in the mining pool has additional rewards, attracting the middle of the mining pool to join, and finally can stably win the entire network. “It’s easier to seduce miners than mines.”

However, all of the above are all about feasibility issues. There are many constraints on the specific operation.

On the one hand, as Zhao Changpeng said, if the block is rolled back, it will have a serious impact on the reputation of Bitcoin (speaking lightly, even if it is serious, it will even lead to the collapse of faith), on the other hand, it requires a lot of money to operate.

cost

If you want to reorganize the Bitcoin block, how much does it cost?

Yesterday, bitcoin core developer Jimmy Song issued seven tweets in a row, saying that from a mathematical point of view, it is unlikely that BTC will be stolen by using block reorganization to recover the stolen money. The specific tweets are as follows:

1. The block that has been confirmed by the hash value is currently borrowed from the currency piracy. From a mathematical point of view, if 58 blocks are reorganized and roughly calculated, it is assumed that each miner obtains the same hash fee on the new chain. 100% miners agree to reorganization, then the minimum cost of restructuring is 58*12.5 BTC=725 BTC.

2. If 75% of the miners agree to restructure, an average of 116 blocks, or 1450 BTC mining awards, will be required to replace the current main chain. Similarly, 60% of miners require an average of 290 blocks or 3625 BTC mining awards; 55% miners, this number becomes 580 blocks or 7250 BTC.

3, 7250BTC> 7000 BTC, so at least 55% of miners need to agree to reorganization. For more than 58 blocks, this figure is up to 60%; for 116 blocks, it is 65%; for 174 blocks, it is 70%; for 232 blocks, it is 75%. Assuming each miner agrees, the cost will rise quickly.

4. But for any miner who chooses to reorganize and abandon the main chain, this will greatly increase the risk of wasting the hash power, and this part of the hash power can be used to effectively mine the longer main chain.

5. The extra cost charged by the miner for this risk means that the decision is made much shorter than the 232 block. If restructured, it will eventually pay the miners from the hands of the hackers. The currency has not benefited too much from it.

6. The minimum loss is still 725BTC, which is still a big change.

7. The currency security is subject to double squeeze of time and risk. Each new block is another block that needs to be surpassed, with a minimum cost of 12.5 BTC. It may not be easy to quickly coordinate with existing funding pools. It may take more than one day or 144 blocks to reach an agreement alone.

Bad influence of block reorganization

Compared to other traditional finances, the characteristic of digital currency is that any time period can be rolled back at any time as long as the cost is sufficient.

At first glance, there is a kind of "all mistakes can come back", but this is precisely the taboo of cryptocurrency.

It should be known that with the blockchain that is irreversible and irreversible, the cryptocurrency is based on consensus. Once the "coin king" bitcoin rolls back and the faith is lost, the entire cryptocurrency market will be devastated. of.

Yesterday, V Shenfa responded that Zhao Changpeng did not recover the stolen bitcoin through the rollback block. "Ethernet has done a state change that does not conform to the rules." "The resulting collateral damage will be huge, even It is fatal."

And V God said that "the state of non-conformity changes" means:

On June 15, 2016, due to the DAO vulnerability, the $600 million worth of Ethereum was stolen at the current price. V God proposed a soft fork to "freeze" all stolen coins at that address. On, another hard fork will be used to retrieve these Ethereum. Thus, the ETC's forked coin ETH is produced.

How to prevent

For the time being, there is no motivation or reason for the currency security to do such a “better than good” thing, but this does not mean that people can sit back and relax.

The internal worry has been solved, and there are external problems.

Today, Pan Zhiwei proposed further consideration:

1. If the money is lost, is it a government or even an institution like the FBI? What happens if the agency asks for a pool of mines, regardless of company or individual?

2. If the money is stolen by a world-renowned terrorist organization? Suppose they take 7K coins to buy a nuclear bomb?

Such concerns are enough to make people think about how to prevent rollback and thus better protect the irreversible cryptocurrency.

In this regard, Pan Zhiyi suggested:

Run the whole node, and then actively play the full node patch (UASF) before the reorganization occurs. The patch can forcibly recognize the stolen transaction, so that even if the winning reorganization chain is high, the existing data cannot be rewritten.

However, Jiang Zhuoer believes that Pan Zhiyi's approach does not prevent the BTC transaction from being modified, but only by actively patching and splitting a forked chain where the transaction has not been modified.

He believes that according to Pan Zhiyi's process, only a few people (the ability to notice the event in a short time and play a full patch) retain an unmodified chain, and may eventually form an ETH-like (rollback DAO money) And the double chain of ETC (retaining DAO stolen money).

At the same time, Jiang Zole’s suggestion is that deep reorganization is not allowed.

He said that in addition to the BUG in the history of Bitcoin, there has never been a reorganization of more than 6 blocks, and users have generally not confirmed it as safe. Therefore, it can be written directly in the code: Reorganization without more than 10 blocks is not accepted.

On December 5, 2010, WikiLeaks was financially blocked due to the disclosure of the US diplomatic cable. At the time, the Bitcoin community called WikiLeaks to accept bitcoin donations to break the financial blockade. However, Nakamoto was resolutely opposed, and he believed that Bitcoin was still in the cradle and could not withstand the conflict and controversy.

“Bitcoin is just a small-scale community experiment in infancy. You use it at most is a small payment, and the heat you bring may ruin us at this stage.”

Nowadays, Bitcoin has been developed for ten years, but what has not changed is that in the face of governments, people have grown into a cryptocurrency of giants, and still have a long way to go. (shared finance)

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