Blockchain 1.0 is called programmable currency, mainly based on Bitcoin. It mainly develops many businesses and peripheral services around the Bitcoin blockchain, such as wallets, tools, exchanges, mining, mining machine business, etc. In the 1.0 era, people pay too much attention to virtual currencies built on blockchain technology, their value, ways to obtain bitcoins, and ways to use bitcoins for transactions.
The emergence of smart contracts marks that the blockchain has entered the blockchain 2.0 era represented by the Ethereum blockchain. The blockchain 2.0 era refers to the development and application of smart contracts. The combination of smart contracts and electronic money also provides a wider range of application scenarios for the financial field. The 2.0 era is to create a broader protocol by forking the Bitcoin blockchain or building another set of blockchain-based technology and generate inherent new tokens. The blockchain 2.0 era is represented by the Ethereum blockchain. The Ethereum blockchain has established a more flexible and general framework system. Innovations at the protocol level and application level enable developers to Create new protocols on application sets, using smart contracts to build new functionality on its blockchain.
The future blockchain 3.0 may not only be limited to the financial field, but an ecological network composed of multiple chains, covering all aspects of human social life, including in various fields such as justice, medical care, and logistics. Blockchain 3.0 is In order to solve the problem of mutual trust in all walks of life and the landing and realization of security technology in the process of data transmission.
safety:
In order to achieve the security of the blockchain, the following three aspects should be considered when designing the blockchain:
1. Anti-hash collision:
Hash collision refers to two different input values, the hash value calculated by the hash function is the same, that is, there are two numbers x and y, where x!=y is calculated by hash to get H(x)=H( y). The hash algorithm used in the blockchain is SHA256, that is, the output space is 2^256. Although the input space is infinite, according to the pigeonhole principle, there must be two different inputs that will map to the same output. , however, we do not have an efficient algorithm to artificially create hash collisions. Violently creating hash collisions by brute force is not feasible under the conditions of existing computer computing power. Therefore, using the hash SHA256 algorithm can resist hash collisions. This property can be used in the blockchain to verify whether the blocks in the blockchain have been tampered with, and hash all transaction information to form an information summary. When verifying whether the information has been modified, the summary of the transaction information can be obtained first, and then the hash can be obtained, and the two hash results can be compared to determine whether the transaction has been modified.
2. The original hash value is hidden:
Another important property of the hash function is that it can hide the original hash value, that is, the hash function is one-way. When the input space is large enough and the value distribution of the input space is uniform, suppose there is a message x, and the message x is calculated by hash function to obtain the message digest H(x). This process is very easy, but it is very difficult to obtain the value x of the original message from H(x), that is, P(x→H(x))→1, P(H(x)→x)→0. In practical applications, the input space may be limited. In the case of limited input results, a pseudo-random number can be added behind it to make the input space large enough, so that you can avoid using brute force methods to get a certain hash summary. original hash value.
3. Correlation is unpredictable:
Given a hash function H that takes some input x from the user and produces an output H(x), a good "Puzzlefriendly" algorithm does not explicitly make any pre-determinable differences between the input x and the output H(x) definite correlation. In other words, you cannot choose a certain x and hope to return a certain H(x). In the actual blockchain network, to accept a block lower than a certain threshold value, the hash value of this block needs to meet the threshold value of the current network difficulty. At this point the user should not select an input based on any type of expected output value, the entire range of input values should have an equal chance of returning the desired output, otherwise, the user may differentiate between certain ranges of input values, thus narrowing their Search scope, and increase their chances of finding valid output. Allowing users to make "educated guesses" would defeat the desired functionality of POW cryptocurrencies.
Affected by market demand, some computers with higher computing power and more efficient have been produced continuously. Quantum computing has also gradually shifted from basic theoretical research to practical application research. This has caused great impact and challenge to classical cryptography. In addition, Grover's algorithm may also affect symmetric encryption and hashing algorithms. The excellent properties of anonymity, autonomy, openness, and traceability achieved by the blockchain are provided through public key encryption and hash functions. The rapid development of quantum computing makes the current consensus protocol more likely to be successfully attacked in the near future, thereby reducing the security of the blockchain. How to prevent the quantum attack of the blockchain and redesign the blockchain will be a development trend in the future. Utilizing cryptographic systems that can resist quantum attacks to create blockchain systems known as post-quantum, quantum-proof, quantum-safe or anti-quantum cryptographic systems is also a problem that needs to be solved urgently.
Moreover, hacker attacks caused by the loopholes in the blockchain system are hard to guard against. As long as there are bifurcation attacks, cryptography-based attacks, consensus mechanism-based attacks, smart contract-based attacks, and other attacks
Cross-chain technology:
Most of today's blockchain systems are heterogeneous and not interconnected. A large number of blockchain systems with different characteristics form a large number of value islands, and direct value circulation cannot be carried out between chains, which largely limits The functional expansion and development space of the block chain.
Today, there are four mainstream cross-chain technologies:
1. Notary mechanism:
The notary mechanism is a technical framework created based on the Interledger protocol. It is similar to the intermediary mechanism in the real world. It assumes that the two parties to the transaction cannot trust each other, and then introduces a third party trusted by both parties to act as the notary as an intermediary. This or this A group of trusted groups can not only automatically monitor and respond to transaction requests and confirmation information from the chain, but also actively monitor and respond to events or requests that occur.
2. Side chain and relay mechanism:
The side chain refers to another blockchain system with completely independent functions, which can actively sense the information of the main chain and take corresponding actions. Through the side chain, new functions such as transaction supervision, privacy protection and smart contracts can be added on the basis of the main chain, and the work of the main chain is not affected while developing new services. When the main chain and the side chain exchange value and information, the repeater is equivalent to the communication channel between them. The repeater will combine the side chain with the notarization mechanism to complete the functions of collecting messages, verifying messages and forwarding messages. If the repeater itself is a blockchain, it can also be called a relay chain, which is more flexible and easy to expand. After the target chain receives the data, it verifies and completes the transaction confirmation. This work does not require third-party certification. Depending on the system structure of the target blockchain, the verification methods used are also different. The relay method supports functions such as cross-chain asset exchange, mortgage, and cross-chain contract implementation.
3. Hash locking:
Hash locking is a technical implementation mode proposed in Lightning Network, which has been widely used in Lightning Network technology architecture. Lightning network is a typical application of hash locking technology, which is essentially a mechanism that uses hash time-locked smart contracts to securely conduct zero-confirmation transactions. There are currently two well-designed smart contracts, including expiry sequence revocable contracts and hash timelock contracts.
The expiry sequence revocable contract assumes that there is a "micropayment channel" between the transaction objects, and requires both parties to sign and authenticate each transaction plan. Both parties can request cash withdrawal at any time, and if the other party fails to submit the latest version of the transaction result, they can be punished. Through this method, both parties can be restricted from tampering with the results. After the withdrawal is successful, a series of transaction results recognized by both parties will be written into the blockchain.
The hash time lock contract uses hash locks and time locks to ensure that the transaction recipient either confirms that he has received the payment before the deadline by generating an encrypted proof, or loses the ability to accept the payment and returns the payment to the transaction initiator, while receiving The encrypted proof generated by the party can also be used for other payment operations. In hash-locked transactions, the transaction initiator has the initiative and is the more advantageous party.
4. Distributed private key control:
Distributed private key control is to map encrypted currency assets to the chain of built-in asset templates based on the blockchain protocol through private key generation and control technology, and then deploy new smart contracts based on cross-chain transaction information to create new A technology of encrypted currency assets, and its representative projects include Wanchain and Fusion. In order to make the assets on the original blockchain still tradeable in the cross-chain system, the distributed private key control technology introduces two operations of locking and unlocking. By locking and unlocking, the tokens on the original blockchain can be managed. Locking is to implement distributed control management and asset mapping operations on key-controlled digital currency assets; unlocking is to use the distributed private key that has been mastered to unlock the locked tokens, so that the tokens are changed from the original The inoperable state becomes the present transferable, operable state.
Cross-chain technology comparison:
The problems that cross-chain technology needs to solve include cross-chain transaction management, multi-chain compatibility and verification, cross-chain security and supervision, privacy protection, concurrent transaction execution, technical implementation, etc.
Consensus mechanism:
The consensus mechanism still needs to be improved:
(1) The consensus efficiency of the blockchain still needs to be improved, which can be studied from the perspective of improving the consensus speed of the blockchain.
(2) In the consensus process of the blockchain, there are still cases where participating nodes do not cooperate, which may affect the fairness of the consensus process, and improvements can be made in this regard in the future.