How many public keys does a blockchain have

2. 1-contains a distributed database

2-The distributed database is the physical carrier of the blockchain, and the blockchain is the logical carrier of the transaction. All core nodes should contain the full of the blockchain data

3-The blockchain serializes the blocks according to time, and the blockchain is the only body of the whole network transaction data

4-The blockchain is only effective for adding, Invalid for other operations

5-public-private key verification based on asymmetric encryption

6-accounting node requires that Byzantine general problem can be solved / avoided

7-consensus progress is evolutionarily stable, that is, it will not collapse in the face of a certain amount of contradictory data of different nodes

8-consensus process can solve the problem of double spending

five characteristics of blockchain:
decentralized
e to the use of Distributed Accounting and storage, there is no centralized hardware or management organization, the rights and obligations of any node are equal, and the data blocks in the system are jointly maintained by the nodes with maintenance function in the whole system
thanks to the decentralization of blockchain, bitcoin also has the characteristics of decentralization [6]
openness
the system is open, in addition to the private information of all parties to the transaction is encrypted, the data of the blockchain is open to all, and anyone can query the blockchain data and develop related applications through the open interface, so the information of the whole system is highly transparent
autonomy
blockchain adopts consensus based specifications and Protocols (such as a set of open and transparent algorithms) to enable all nodes in the whole system to exchange data freely and safely in a de trusted environment, so that the trust in "people" is changed into the trust in machines, and any human intervention does not work
information cannot be tampered with
once the information is verified and added to the blockchain, it will be stored permanently. Unless more than 51% of the nodes in the system can be controlled at the same time, the modification of the database on a single node is invalid, so the data stability and reliability of the blockchain are extremely high<
anonymity
since the exchange between nodes follows a fixed algorithm, their data interaction does not need trust (the program rules in the blockchain will judge whether the activity is effective by themselves), so the counterparties do not need to let the counterparties generate their own trust by disclosing their identities, which is very helpful for credit accumulation.

3. Tell you what blockchain is and what can it do

what is a blockchain? How does it work

bitcoin has become the trend of modern Internet, followed by blockchain. It is said that blockchain technology will lead to fundamental changes in Internet operation, enterprise operation and everything else

but what is blockchain? Most of us don't know much about blockchain. If you want to understand blockchain, you can read this article carefully

what is a blockchain? In the simplest terms, blockchain is a distributed ledger

to understand what this means, let's first look at its opposite: a centralized ledger. Because blockchain technology starts from finance, we will also use the bank as an example

the following is the process of our bank debit card transaction:

you can buy goods by swiping your card in the store

the merchant sends the bill to your bank to get the agreed amount

your bank will verify whether you are likely to authorize the purchase

banks remit money to businesses

finally, the bank records this information in its ledger

there are a lot of technologies involved here, but basically that's it. The last step is important - the bank keeps track of all transactions made by the customer. This ledger goes all the way back to the first transaction the bank made

the ledger is kept, maintained and supervised by the bank. You can read it in your online bank account, but you can't change it. The bank is in full control. If it decides to make a change, there's nothing you can do

it is crucial that if hackers can access the bank's ledger, it may lead to many problems. They can change the account balance to make it look like some transaction never happened, and so on

that's why distributed ledger is so cool

blockchain network visualization

if the bank operates on a distributed ledger, each member of the bank will have a of the ledger. Whenever any member of the bank makes a purchase, they will tell all other members of the bank

each member validates the transaction and adds it to the ledger (the added record is called a "block"). This has some important benefits because there are no centralized permissions to manipulate records. Hacker access to one ledger won't be a big problem because other ledgers can easily verify it

on the other hand, it requires a lot of work. In short, the second system is blockchain (at least in the financial scenario)

as mentioned above, blockchain is a decentralized transaction list. If I send Xiaoming two bitcoins, I will send a message to everyone in the network, saying "I am sending Xiaoming two bitcoins", and they will record the transaction<

bitcoin and blockchain

let's take bitcoin as an example to illustrate

bitcoin transaction

but the transaction must be verified. This is where blockchain technology has become a bit more complex. Each bitcoin wallet (which we will complete in one second) has a public and private key

you use your private key to send transaction requests to other members of the network and confirm that you have cryptocurrency in your account. If they do, they allow transactions to register on the ledger

the mechanism of public / private key system is very complex, but it comes down to that every transaction is verifiable and secure< However, the computing cost of the whole system is very high. Everyone who updates the ledger needs a lot of authority to validate transactions and modify the ledger. This is where mining comes in. People who verify and modify use their own computing resources, and each time they get a small transaction fee

and they're using a lot of electricity to do it

in this way, each transaction will be verified and added to the ledger, and the person who performs the verification and modification will be paid. This is a reasonable system

at the same time, it is also very safe. To change a single block, you have to change each subsequent block. After all this is done, validation will fail because other copies of the chain will show someone tampered with one

how to define blockchain is a difficult problem

although the mechanism behind blockchain technology is not always intuitive, it seems that it is not too difficult to explain what blockchain is. But what we're describing here is the traditional definition

we can use this special type of blockchain for a wide range of applications;, Such as cryptocurrency, sharing medical information, sending security messages and so on. But more blockchain like technologies are being developed for other uses

for example, companies may use internal blockchains to manage problem tracking in software. Each block in the chain may represent a problem, and users can publish updates to the network. But is this a blockchain? In this case, the ledger is not public, it is only visible within the company

some people will say that this is not a blockchain

other blockchain like technologies are not encrypted. Are they still blockchain? What if it's centrally managed but uses other blockchain features? What defines the lowest level of blockchain technology? There is no consensus on these issues

what is a blockchain wallet

we usually hear people talk about bitcoin wallets, Ethernet wallets and other cryptocurrency specific wallets. But wallet technology can be used in any system that uses blockchain

a wallet is the software or hardware that "saves" your cryptocurrency. But it doesn't really have anything, it's just a place to store public and private keys. This information allows you to access the currency shown in the public ledger

the wallet is the only record of the key. So if you lose it, you will no longer be able to access your cryptocurrency

in the future of blockchain, how will it change our lives

one important thing about blockchain is that it is a public resource and no one really owns it because everyone owns it

blockchain is more than science fiction. We don't need to understand the mechanism behind this technology, but you need to understand that it may completely change our lives in the next 20 years

that sounds bold, but remember, 20 years ago, we were browsing the Internet on Netscape, using the most advanced Motorola flip phone, and buying our first DVD player. At that time, if we imagined that the computer could be held in our hands, and that we could buy a car, pay for money and watch movies on it, it would be considered a fantasy

although the impact of blockchain may not be as obvious as the Internet or as tangible as mobile phones, blockchain will effectively solve many troubles in daily life. For example, intermediary entrapment, transaction delay and so on. In our present life, middlemen can be seen everywhere. We take it for granted that they are a part of our life. If one day, these intermediaries no longer exist, you will find that the world will become a different one

imagine that by 2040, blockchain may become a mature and widely used technology. One day, you can't do without blockchain, just as you can't do without the Internet now, you will be surprised that this decentralized accounting technology has become a part of your lifestyle<

first praise
+ 1

4. Of course it's true. But bitcoin is the representative of digital currency, cryptocurrency. According to the current 24-hour market of China currency, the highest price of bitcoin is 73900.00 QC (equivalent to RMB)
When did you buy 500? Now you make a lot of money

5.

As an emerging technology, blockchain has attracted more and more attention. It is a new application of traditional technology in the Internet era, including distributed data storage technology, consensus mechanism and cryptography. With the establishment of various blockchain research alliances, more and more funds and personnel support related research. Hash algorithm, zero knowledge proof, ring signature and other cryptographic algorithms used in blockchain:

hash algorithm

as the basic technology of blockchain, the essence of hash function is to map a set of data of any length (limited) to a set of defined length data stream. If this function satisfies the following conditions:

(1) the calculation of hash value for any group of data is very simple

(2) it is difficult to find two different data with the same hash value

hash functions satisfying the above two properties are also called encrypted hash functions. In case of no contradiction, hash functions usually refer to encrypted hash functions. For the hash function, finding such that is called a collision. The current popular hash functions are MD5, SHA1, Sha2, Sha3

bitcoin uses sha256, and most blockchain systems use sha256 algorithm. So here's sha256< Step 1: additional filling bits. The length of the message is congruent with that of 448 mod512 (length = 448 mod512). The number of bits to be filled ranges from 1 to 512. The highest bit of the filled bit string is 1, and the rest bits are 0

Step2: additional length value. The bit length of the initial message (before filling) represented by 64 bit is appended to the result of step 1 (the low byte takes precedence)

Step3: initialize cache. A 256 bit cache is used to store the intermediate and final results of the hash function

Step 4: process 512 bit (16 word) packet sequence. The algorithm uses six basic logic functions and consists of 64 steps of iterative operation. Each step takes the 256 bit cache value as the input, and then updates the cache content. Each step uses a 32-bit constant KT and a 32-bit wt. Where WT is the packet after the packet, t = 1,2,..., 16

step5: after all 512 bit packets are processed, the output of the last packet of sha256 algorithm is 256 bit packet< In 2001, Rivest, Shamir and TauMan proposed ring signature for the first time. It is a simplified group signature, only ring members have no manager, and it does not need the cooperation between ring members. In the ring signature scheme, the signer first selects a temporary signer set, which includes signers. Then the signer can generate the signature independently by using his private key and the public key of others in the signature set without the help of others. Members of the signer collection may not know that they are included in it

ring signature scheme consists of the following parts:

(1) key generation. A key pair (public key PKI, private key ski) is generated for each member of the ring

(2) signature. The signer uses his private key and the public keys of any n ring members (including himself) to generate the signature a for the message M

(3) signature verification. According to the ring signature and message M, the verifier verifies whether the signature is signed by the member in the ring. If it is valid, it will be received, otherwise it will be discarded

ring signature satisfies the following properties:

(1) unconditional anonymity: the attacker can not determine which member of the ring generated the signature, even if the private key of the ring member is obtained, the probability is not more than 1 / n

(2) Correctness: the signature must be verifiable by all others

(3) unforgeability: other members of the ring can't forge the real signer's signature, and even if an external attacker obtains a valid ring signature, he can't forge a signature for message M

(1) anonymity. The verifier can verify that the signature is signed by a member of the group, but can't know which member it is, so that the signer can be anonymous< (2) traceability. In group signature, the existence of group administrator ensures the traceability of signature. The group administrator can revoke the signature and expose the real signer. The ring signature itself cannot reveal the signer unless the signer wants to expose or add additional information to the signature. A verifiable ring signature scheme is proposed. In this scheme, the real signer wants the verifier to know his identity. At this time, the real signer can confirm his identity by disclosing his secret information< (3) management system. Group signature is managed by group administrator, ring signature does not need to be managed, signer can only select a set of possible signers, obtain its public key, and then publish the set, all members are equal

the Xueshuo innovation blockchain Technology Workstation of Lianqiao ecation online is the only approved "blockchain Technology Specialty" pilot workstation of "smart learning workshop 2020 Xueshuo innovation workstation" launched by the school planning, construction and development center of the Ministry of ecation of China. Based on providing diversified growth paths for students, the professional station promotes the reform of the training mode of the combination of professional degree research, proction, learning and research, and constructs the applied and compound talent training system< br />

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