Peking University Xiao Zhen teacher "block chain technology and application" open class notes 11 - BTC Review Q & A article

Peking University Xiao Zhen teacher "block chain technology and application" open class notes

Bitcoin review quiz papers, correspondence Xiao teacher video: https: //www.bilibili.com/video/av37065233 p = 11?
Full range of notes, see: https: //blog.csdn.net/Mu_Xiaoye/article/details/ 104 299 664

Data in this chapter unfold in a question and answer format, you need to understand the content before.

Some questions and answers

1. Transfer transaction time, if the recipient is not online (not attached to the Bitcoin network) how to do?
   Transfer transactions need only be recorded on the block chain, will be a Bitcoin account to another account, and whether the recipient has no effect online.
2. Suppose a node receives a full transfer transactions, will not be possible to transfer the payee address the whole transaction node never heard of.
   Probably because Bitcoin account requires only local produce can be. Only the account for the first time received the money, the other nodes in order to know the existence of the node.
3. If the account private key is lost how to do?
   No way. Because Bitcoin is a decentralized currency, no third party central authority can reset the password, so the money on the account will become a dead money.
   By encrypting Currency Exchange (centralized organization) usually need to provide proof of identity, the private key can be found if you forget Exchange for the recovery of the private key. But this type of currency exchange, still in its lack of supervision of the state, does not necessarily have a credible force. Moreover, the play itself is only "intermediary" role, the answer to the question "private key is lost can not be recovered inside the Bitcoin" is not a conflict.
   Historically, many times there are a lot of things were stolen encrypted exchange currency hacker attacks, most famous of which is Mt. GOX (Chinese translation: Mentougou) event. The exchange was once the world's largest Bitcoin exchange, trading accounted for about 70% of the global Bitcoin trading volume, located in Japan. Later, due to the loss of a large number of bitcoins being attacked, resulting in the exchange of bankruptcy, its CEO was sentenced to prison.
   In addition, there are exchange embezzlement, staff escaped on foot (somewhat similar to rm -rf * / delete library on foot series).
4. Private key is revealed how to do?
   The remaining BTC will soon be transferred to other security accounts, no third party central institutions to freeze accounts or reset passwords only responsible for themselves.
   BTC system account is the public-private key pair, the private key password that can not be changed.
5. Transfer wrong address how to do?
   No way, nothing with, you can not cancel the transaction has been released. If the transferred address does not exist, the part Bitcoin will become dead money. Of course, the Bitcoin system UTXO permanently save the transaction, record the address does not exist. Therefore, the whole node, it is unfriendly.
6. Before the introduction of the BTC OP_RETURN instruction in the script, we mentioned that this method provides content to write a bitcoin network you want to have saved for the average user. But OP_RETURN execution result is the unconditional return an error, and the transaction returns an error, blocks, how will it contain? Block chain and how to receive this block?

1 idea: a special mechanism, even if the script returns an error, still write block chain. (Not real)
idea 2: Even if a failure is returned, still write block chain, not just the specific processing time to calculate. (A large number of malicious nodes thrown transaction fails, attack the block chain how to do? Last article mentioned, can only handle an average of 7 transactions per second)

In fact, there is a need to think clearly detail (my second time back here when watching the video, encounter this problem still forget why, really tears left to their own stupidity .55555 ....) to make it clear, OP_RETURN is written in where. OP_RETURN actually written in the script output in the current transaction, while verifying the legitimacy of the transaction, enter the script used in the current transaction and the output of the script before a transaction (transaction currency origin) to verify. In other words, verify the legitimacy of the current transaction, and does not execute the statement. (I am not feeling very wonderful ah ???) only when someone wants to spend the money, will execute the statement.

6. BTC system mining, the miners will have to "steal" the answer? For example: some miners found other miners released a nonce, after receiving legal verify the block, the nonce nonce as he found out the release.
   In fact, this is impossible. Blocks contain coins issued in the transaction, the payee whose address is dug ore miner address, if you want to steal the answers, we need to modify the payment address, and the address change, coins, trading content is changed, causing Merkle Tree Root hash value changes. Resulting in the original nonce void. In other words, it may not "steal" the answer.
7. Transaction fees are traders for their own transactions can be given on the chain and "tip", then how you can know which miners dug mine?
   Without knowing in advance who dug the mine, the transaction total input and total output is the difference between a transaction fee. Which miners dug mine, when package deal, you can collect a transaction fee as a transaction fee up their own access.

BTC statistics

• Figure 1: BTC block chain size changes (to 2018)
  because the block chain can only add, not delete. For the current contents of the hard disk, it saves it no problem.
  
• Figure 2: UTXO set size changes (to 2018)
  increase in trading, private key is lost, and this will lead to increased UTXO.
  
• Figure 3: BTC ore mining pool case (2018)
  centralization trend seriously!
  
• Figure 4: BTC price changes (to 2018)
  
• FIG 5: BTC market changes (2018)
  and 4 remained the same
  
• Figure 6: BTC volume changes (to 2018) - obtained as described in US dollars, prices
  
• Figure 7: BTC changes in the number of transactions (2018)
  
• Figure 8: changes in the number of transactions for each block (2018)
  generated every day the number of blocks almost all the same, so the number of transactions and changes in the basic block comprises a number of transactions the same trend.

Can be seen, the theoretical upper limit for each trading block may comprise 4000, and which is far from the upper limit in FIG. So many people say that's too small 1MB block, on the other hand, many of the actual block is not full.