Initial knowledge of blockchain (II.)

Several key issues in blockchain technology

First, to be centralized

The centrality is not a fashionable noun, simply the point-to-point exchange of information, there is no third-party intermediary. Our daily use of the Internet, Email Service, SMTP and so on have used the idea of central.

Second, the distributed consensus

In decentralized distributed systems, if a trusted accounting system is to be reached, it is necessary to consider a consensus issue, that is, how to make the point-to-point communication parties agree, and solve the problem of traitors or malicious nodes.

The distributed consensus is to ensure that the input of all honest nodes is consistent, and that the consensus is achieved by all honest points. The Byzantine general problem is a typical case, but when the number of traitors exceeds the total number of 1/3, the consensus problem cannot be solved. There are some vulnerabilities in these algorithms.

In the blockchain technology, the former distributed consensus algorithm is not fully applied, but it combines the unique incentive mechanism and the step-confirmation mechanism. It can be said that Satoshi is using an overt one to deal with conspiracy.

　　The consensus algorithm is brief:

One, the broadcast transaction.

Second, the Honest node packs the transaction into chunks. (miners, see who is strong)

Three, a random node broadcasts the chunk.

Four, if all the transactions in the chunk are valid (with a validation algorithm), then the other nodes accept the chunk and add the hash of the chunk (the chain-in algorithm) to the newly created new district.

Thirdly, the reward mechanism

Bitcoin is a currency in which most nodes are willing to be rewarded for maintaining the system's normal operation, thus ensuring that most of the points are honest.

Currently consists of two parts: block bonuses and trading tips.

IV, the progressive confirmation mechanism

The consensus in the blockchain is not an immediate confirmation, but a two-step walk.

The first step is to wait one hours for confirmation of the first chunk (a transaction), which basically determines that the transaction is legal (for example, A send to B, which buys the goods of B, and that after the chunk is generated, B waits for the time to link to the 6 chunks again before the transaction is completed and the goods are handed to A, This time can be considered as basic cannot be changed before the block to be confirmed.

The second step, as the number of links into the more, the block representing the transaction has been changed the probability of a smaller, more legitimacy gradually enhanced.

Five, double payment issues

What is double payment?

Suppose a broadcasts a trading message, a send BTC to B, a miner (the other node) packs the chunk into a blockchain, B discovers the chunk, and if the goods are immediately given to a (0 confirmation mechanism), a may use its own powerful calculation to quickly add another chunk to the blockchain, a Send BTC to A, if a can successfully add this chunk, and use the force to continue adding new chunks after this chunk, the real chunk will be ignored. Because an honest node will create chunks along the longest blockchain.

What's the deal?

Based on two basic points: first, replace the 0 confirmation mechanism with the step-up confirmation mechanism mentioned above. Second, a is difficult to achieve under the gradual confirmation mechanism, can still be in the false block after the control chain into more than 6 blocks of the calculation of the power. Third, even if this calculation can be achieved, then the entire Bitcoin system will lose its credibility because of a powerful bug, that is, trust collapse, the loss of trust BTC is worthless, then the control of a powerful force of a will also have no income, the cost is higher than the income. This is also naked an overt one, that is, want to play together good fun, want to trouble, we all do not play.

(The article is only the blockchain technology learning record, if there is a mistake or textual research is not rigorous place, please advise.) ）

(Reference: https://www.zhihu.com/people/ustcsse308)

Initial knowledge of blockchain (II.)