How does bitcoin solve the problem of double spending

1.

In the discussion of blockchain, bitcoin and other digital currencies, we often hear the word "bifurcation". So what is bifurcation? What is the effect of bifurcation

blockchain

before talking about bifurcation, popularize a little knowledge of blockchain, so as to help us understand what bifurcation is more easily (if you don't have any concept of blockchain, please read my previous articles, which are all popular words to help you understand what blockchain is)

blockchain, as the name suggests, is a chain composed of blocks. Of course, this kind of chain is just a figurative metaphor. To put it bluntly, data blocks are connected orderly. In bitcoin, the transaction records of bitcoin are stored in the block. The size of the block and the space occupied by the transaction records determine how many transactions can be stored in a block. These transaction records are packaged into blocks, and then the blocks are connected one by one to form a blockchain

We know that bitcoin software, like other software, needs to be updated and modified regularly in order to make it better. So a new version will appear, but not everyone will download the new version, so one miner will run the old version, and some will run the new version. If the old and new versions are not compatible, the blockchain will bifurcate. Because there may be differences between the version blocks and the old version blocks, they cannot be connected to the same blockchain, so there will be two or even more chains, which is called bifurcation

soft forking

soft forking refers to that when the new consensus rules are released, nodes that have not been upgraded will proce illegal blocks because they do not know the new consensus rules, resulting in temporary forking. This kind of bifurcation will be graally repaired with the upgrading of nodes

hard fork

hard fork refers to the permanent divergence of the blockchain. After the release of the new consensus rules, some nodes that have not been upgraded cannot verify the blocks proced by the upgraded nodes, and usually hard fork occurs. Therefore, in the field of digital currency, hard bifurcation often leads to the emergence of new currencies. For example, the hard bifurcation of Ethereum led to the emergence of eth

What is bifurcation? What is bitcoin bifurcation

2. After six confirmations, the probability of double flower is almost zero

3. You are right. Indeed, it will be rolled back. If the transaction is unfortunately packaged on the fork, the transaction is likely to be cancelled after the main chain is synchronized

the reason why we need six confirmations is that it is more difficult to obtain the optimal solution (to prevent single node fraud). One block may also be able to get an optimal solution, and it is basically impossible to get six blocks together. It has nothing to do with bifurcation

4.

Transaction mode of bitcoin

bitcoin is e-cash similar to e-mail, and both parties need "bitcoin wallet" similar to e-mail and "bitcoin address" similar to e-mail address. Just like sending and receiving e-mail, the remitter pays bitcoin directly to the other party through a computer or smart phone according to the recipient's address. The following table lists some websites that download bitcoin wallets and addresses for free

a bitcoin address is a string of about 33 characters long, consisting of letters and numbers, always starting with 1 or 3, such as & quot& quot; Bitcoin software can generate address automatically, and it doesn't need to exchange information online, so it can be offline. More than 2 bitcoin addresses are available. Figuratively speaking, there are about two grains of sand in the world. If there is an earth in each grain of sand, then the total number of bitcoin addresses far exceeds the number of all the sand on all these "earths"

the bitcoin address and private key appear in pairs, and their relationship is just like the bank card number and password. A bitcoin address is like a bank card number, which records how much bitcoin you have on it. You can generate bitcoin address at will to store bitcoin. When each bitcoin address is generated, a corresponding private key of the address will be generated. This private key proves that you have ownership of the bitcoin at that address. We can simply understand the bitcoin address as the bank card number, and the private key of the address as the password of the corresponding bank card number. Only when you know the bank password can you use the money on the bank card number. Therefore, please keep your address and private key when using bitcoin wallet

after the transaction data of bitcoin is packaged into a "data block" or "block", the transaction is initially confirmed. When a block is linked to a previous block, the transaction is further confirmed. After six block confirmations in a row, the transaction was irreversibly confirmed. Bitcoin P2P stores all transaction history in a "blockchain.". The blockchain continues to extend, and once new blocks are added to the blockchain, they will not be removed. Blockchain is actually a distributed database composed of a group of scattered client nodes and all participants, which is a record of all bitcoin transaction history. Nakamoto predicts that when the amount of data increases, users hope that not all the data will be stored in their own nodes. In order to achieve this goal, he uses the hash function mechanism. In this way, the client will be able to automatically eliminate those parts that it will never use, such as some very early bitcoin transactions

5. Because it comes from money. Virtual money is bought with real money. So it's also called coin there.

6. Detailed process of mining right price evaluation
1. Copy of the business license (plicate) of the mining enterprise of the evaluation client*
2. The of the mining license * or the approval document for delimiting the scope of the mining area, and the map of the mining area based on the topographic and geological map or geological map and demarcated by rectangular coordinates*
3. Reserve verification report, reserve review record certificate, *
4. Development and utilization scheme / (pre) feasibility study report / preliminary design and its review opinions or approval documents*
5. A complete set of financial statements for the three years before the base date of evaluation, at least providing the statistical table of output and sales price of mineral procts, sales revenue, cost of fixed assets and current assets and other major technical and economic indicators*
6. Basic information of the mine (including the nature of the enterprise, technical personnel, staff, registered capital, historical evolution, evolution of subordinate relationship, acquisition method, time and change of mining right, evaluation purpose and related process of mining right, proction and operation, etc.)
7. Information on the previous evaluation and price disposal of mining rights, including copies of previous evaluation reports, confirmation or filing documents of evaluation results, and documents on price disposal of mining rights (contracts or agreements and payment vouchers)
8. The plan of the nearest roadway project and the plan of reserves of the mine; 9. Copies of the annual mineral proct settlement sheet (main batch) or sales contract or sales invoice on the base date of evaluation
10. Traffic location map of the mining area, comprehensive geological and mineral plan (topographic and geological map indicating the scope of the mining area), reserve calculation map, typical profile of main ore body (exploration line profile), development system plan diagram and mining and beneficiation process flow chart
11. The mining volume of the mine from the deadline of reserves calculated in the geological exploration report / reserves verification report to the base date of evaluation. The appraisal of mineral rights can be divided into three stages, namely, the entrusted appraisal stage, the appraisal stage and the appraisal result confirmation or filing stage
first, the stage of entrusted evaluation. In this stage, the evaluation client and the evaluation institution are the leading ones< The appraisal client and the appraisal trustee can be people with different appraisal purposes, mainly including the administrative authority of the mining right that intends to transfer the mining right, the applicant of the mining right that intends to apply for registration of the mining right, the mining right that intends to transfer the mining right, the transferee of the mining right that intends to transfer the mining right, and the creditor when setting the mortgage of the mining right, Mining right holders who plan to restructure or go public. Generally speaking, anyone can entrust the appraisal of mining right, but if the appraisal result is used as the basis for collecting the price of mining right when the mining right is transferred, the administrative organ that transfers the mining right must be the appraisal principal; If it is necessary to apply for confirmation or filing for the purpose of transferring the mining right of the state funded exploration of the mining origin, the mining right owner must be the evaluation client. In short, there are only the right holders (the administrative organ of mining right transfer and the right holder) who have the right to dispose of the mining right of the proved ore procing area, so the evaluation must be entrusted by the right holders. In addition, it is their own right and choice for the relevant person to entrust to evaluate the mining right, but the follow-up procere will be different from the former
2. Entrustment and entrustment are service economic and legal relations established through the contract signed by both parties or the power of attorney issued by the client. When dealing with the entrusted matters, the client should explain the purpose, object, scope, ownership and investment nature of the entrusted appraisal. The appraisal institution should also explain the relevant provisions of mining right appraisal to the client, ask relevant questions and remind relevant matters. When both parties reach an agreement on the entrustment matters, they can sign the entrustment contract for mining right evaluation, or the entrustment party can issue the entrustment letter. The entrustment contract of mining right appraisal should comply with the general provisions of the contract law of the people's Republic of China. In the contract of entrustment for appraisal, the appraisal object, appraisal scope, appraisal purpose, required items, completion time, appraisal base date, rights, obligations and commitments of both parties, legal responsibilities, etc. shall be specified
Second, the evaluation stage is dominated by the evaluation institution. The main work of this stage is as follows:
(1) the mining right appraisal organization accepting the entrustment should form an appraisal working group to determine a mining right appraiser as the project leader, and the professional composition of the members of the appraisal working group should be suitable for the characteristics of the appraisal object and the appraisal method. The evaluation team went to the client's place for the following preparatory work: (1) listen to the client's detailed introction of the evaluation object, including the registration and change history of the evaluation object, the historical evolution of geological work, and understand the working time, working unit, nature of work, exploration results obtained, nature of investment, amount of investment, etc. It also includes the exploration and mining activities around the assessment object and the relationship with the assessment object 2) We will go to the scene to investigate the situation of mining rights, understand the topography and mining activities, sample some exploration projects, and inspect mining and mineral processing facilities 3) Investigate and collect the market transaction and market price of local mineral procts 4) Draw up evaluation ideas or technical routes and determine evaluation methods. Collect documents, data and drawings related to the assessment 5) Summarize and sort out the data
(2) the appraisers shall exchange opinions with the client on the first draft of the appraisal report and make necessary adjustments, modifications or supplements. After the final draft, submit the formal evaluation report to the client. The necessary information provided by the client includes: assignment evaluation: the area and geographical coordinates of the exploration area or the opinion on delimiting the mining area; Transfer evaluation: exploration license, or mining license, the supporting documents that can explain the nature of exploration investment; Geological reports and maps of each stage; Relevant documents proving the resources / reserves within the scope of exploration license or mining license; Mine enterprise registration, statistics and reported reserves change report. The main data collected by the appraisal institution include: the development and utilization plan of mineral resources or (pre) feasibility study report or preliminary design and relevant approval documents; Mineral processing process and proct plan; Statistical report of actual indicators such as mining recovery rate, ore dilution rate, beneficiation recovery rate, concentrate yield, etc; Statistical report on recovery of associated and symbiotic ores, etc< According to the three regulations of the State Council on the management of mining rights and the provisions of relevant documents of the State Council, the appraisal results of the mining rights formed by state funded exploration, whether the appraisal is transfer or transfer, must be confirmed or filed by the Department in charge of Geology and mineral resources of the State Council. Therefore, the confirmation and filing stage of the evaluation results only corresponds to the broken property rights formed by the state funded exploration; It is a necessary procere and is evaluated by the obligee as the client. In addition, according to the Interim Provisions of the Ministry of land and resources on the administration of the transfer of mining rights, no matter what the nature of the original investment is, the administrative organs of mining rights need to evaluate and confirm or record the evaluation results< (1) the three regulations of the State Council on the management of mining rights have explicitly authorized the Department in charge of Geology and mineral resources of the State Council to confirm the evaluation results of mining rights funded by the state, that is, the Ministry of land and resources. The confirmation of mining right evaluation results can be divided into two forms: direct confirmation by the Ministry of land and resources and entrusted confirmation. The Ministry of land and resources confirmed that the mining right issued by the Ministry of land and resources, the mining right stocks listed, and the proction scale of large and medium-sized enterprises transferred in the form of bidding. Entrustment confirmation: other mining right appraisal and confirmation work other than that confirmed by the Ministry of land and resources shall be entrusted to the mining right administrative organs of all provinces, autonomous regions and municipalities directly under the central government. After confirmation, the mining right administrative organs of all provinces, autonomous regions and municipalities directly under the central government shall fill in the letter of responsibility and submit it to the Ministry of land and resources together with the appraisal report. The Ministry of land and resources shall uniformly number, seal and issue the confirmation letter
(2) according to the three regulations of the State Council on the management of mining rights and the relevant documents of the State Council, the evaluation results of the mining rights formed by state funded exploration, whether it is transfer evaluation or transfer evaluation, must be filed by the Department in charge of Geology and mineral resources of the State Council
1. The Ministry of land and resources records the evaluation report of exploration rights according to the proceres of verification, filing and filing
1) according to Article 14 of the Interim Measures for the administration of the evaluation of exploration rights and mining rights and the requirements of the guidelines for the evaluation of mining rights on the format of the evaluation report of mining rights, the staff responsible for the verification and filing of the evaluation report of exploration rights shall carry out the verification. The specific verification contents include: (1) whether the evaluation report is within the scope of filing. The appraisal report of mineral exploration right transfer within the scope of filing must be: the appraisal is entrusted by the organ of mineral exploration right transfer (the valid certificate is the appraisal power of attorney of the organ of mineral exploration right transfer or the appraisal power of attorney contract of both parties); The appraisal object is the mineral land that has been invested and explored by the state (according to the announcement of the Ministry of land and resources on the mineral land that has been invested and explored by the state). The nature of exploration funds is contributed by the State Finance (Geological Exploration fee, resource compensation fee and special fund) The effective proof document is the mission statement of exploration project. For the newly registered exploration right after the State Council Order No. 240 was issued in 1998, whether the price of exploration right was charged or not at the time of transfer depends on the nature of the exploration fund after this registration, and whether it is within the scope of filing or not, rather than retrospecting the nature of the investment of exploration work before registration. For the exploration rights acquired before February 12, 1998 and extended up to now, it depends on the nature of exploration funds in the whole exploration history.) 2) (3) check whether the format and attachments of the evaluation report are complete and standardized. Whether the evaluation object is an effective exploration right. No problem is found in the above verification, and the next procere will be carried out. In case of any problems found in the above verification, the applicant for record shall be informed in writing, and the evaluation report shall be returned to the applicant for record. The filing applicant shall apply for filing again after solving the problem. If the re verification has met the requirements, enter the next procere
2) the staff responsible for the filing of the evaluation report of exploration right will submit the verified evaluation report together with the approval form for the filing of the evaluation result of exploration right to the director, who will make a decision on whether to approve the filing after review. If the record is approved, the "record verification certificate of prospecting right evaluation report" shall be issued to the record applicant. If the record is not approved, the reasons shall be explained to the applicant in writing, and the evaluation report and relevant documents shall be returned
3) filing: the evaluation reports approved for filing are registered and filed for future reference
2. Evaluation of exploration rights other than those recorded by the Ministry of Geology and mineral resources of provinces, autonomous regions and municipalities directly under the central government.

7. There are two main cases of double payment: one is to let the miner help to achieve, the other is to become a miner. In November 2013, we found that betcoin has double payment in ghash.io mine pool, and every transaction used by the website can be carried out without waiting for confirmation<
solution:
analyze transaction risk
payment channel
signed by trusted third party
remote authentication
ID verification
block waiting for confirmation
punish double payment

8. Because there has been an irreconcilable spear in the bitcoin community, and this contradiction is still difficult to solve. Expansion team: the classic bitcoin scheme proposed by Gavin Andresen, the successor of Nakamoto, and the Bu scheme supported by Chinese miners. Sw: supporting SW is mainly the core team and the BS company behind it. The debate between the two parties has been going on. The two parties once reached a consensus in Hong Kong, but later the core went back on its words and the two parties became even more incompatible. The core party has strong strength abroad. It has captured western public opinion by using the water army to fight public opinion. In China, there are also many water armies. However, in China, the core does not have an advantage in fighting against the core.

9. Not too clear,