区块链技术原理(转载)

哈希实现防篡改

这个就不多说了，技术都应该明白，主要我们看看它是怎么防篡改。在区块链中，每个区块头部包含了上一个区块数据的哈希值，这些哈希层层嵌套，最终将所有区块串联起来，形成区块链。区块链里包含了自该链诞生以来发生的所有交易，因此，要篡改一笔交易，意味着它之后的所有区块的父区块哈希全部要篡改一遍。这需要进行大量的运算。如果想要篡改数据，必须靠伪造交易链实现，即保证在正确的区块产生之前能快速地运算出伪造的区块。同时在以比特币为代表的区块链系统要求连续产生一定数量的区块之后，交易才会得到确认，即需要保证连续伪造多个区块。只要网络中节点足够多，连续伪造的区块运算速度都超过其他节点几乎是不可能实现的。另一种可行的篡改区块链的方式是，某一利益方拥有全网超过 的算力，利用区块链中少数服从多数的特点，篡改历史交易。然而在区块链网络中，只要有足够多的节点参与，控制网络中 的算力也是不可能做到的。即使某一利益方拥有了全网超过 的算力，那已经是既得利益者，肯定会更坚定地维护区块链网络的稳定性。

In the block chain, each block has its head that contains the Hash value of the previous block data, and these Hashi layers are embedded, and eventually all the blocks are bound together to form a block chain. The chain contains all the transactions that have taken place since the chain was born, so that it is necessary to tamper with a transaction that means that all of its subsequent sections have to be tampered with. This requires a lot of calculations. If the data are to be tampered with, it must be done quickly before the right block is created. At the same time, the chain system of blocks, represented by bitcoins, requires a number of blocks to be created.

通过哈希构建默克尔树，实现内容改变的快速检测

在区块链中默克尔树就是当前区块所有交易信息的一个哈希值。但是这个哈希值并不是直接将所有交易内容计算得到的哈希，而是一个 哈希二叉树。首先对每笔交易计算哈希值；然后进行两两分组，对这两个哈希值再计算得到一个新的哈希值，两个旧的哈希值就作为新哈希值的叶子节点，如果哈希值数量为单数，则对最后一哈希值再次计算哈希值即可；然后重复上述计算，直至最后只剩一个哈希值，作为默克尔树的根，最终形成一个二叉树的结构。

In the chain of blocks, the Merkel tree is a Hashi value for all transactions in the current block. But this Hashi value is not a Hashi that directly calculates all transactions, but a Hashi two-fork tree. First, the Hashi value is calculated for each transaction; then two groups, where the two Hashi values are recalculated to obtain a new Hashi value, then the two old Hashi values are used as a leaf node for the New Hashi value, and if the Hashi number is single, then the last Hashi value is counted again; and then the above calculation is repeated until there is only one Hashi value, which is the root of the Merkel tree, and eventually forms a two-fork tree structure.

在区块链中，我们只需要保留对自己有用的交易信息，删除或者在其他设备备份其余交易信息。如果需要验证交易内容，只需验证默克尔树即可。若根哈希验证不通过，则验证两个叶子节点，再验证其中哈希验证不通过的节点的叶子节点，最终可以准确识别被篡改的交易。

In the block chain, we just need to keep the transaction information that is useful to ourselves, delete it or back up the rest of the transaction information with other devices. If you need to verify the transaction, you just need to verify the Merkel Tree. If Genhashi does not pass, we need to verify the two leaf nodes, then we need to verify the node in which Hashi authenticates the node that is not passed, so that the altered transaction can eventually be accurately identified.

默克尔树在生活中其他领域应用也非常广泛。例如 ，数据一般会分成很多个小块，以保证快速下载。在下载前，先下载该文件的一个默克尔树，下载完成后，重新生成默克尔树进行对比校验。若校验不通过，可根据默克尔树快速定位损坏的数据块，重新下载即可。

Merkel trees are also very widely used in other areas of life. For example, data are usually divided into many small blocks to ensure quick downloads. Before downloading, a Merkel tree downloads the file and, after downloading it, regenerates the Merkel tree for a comparative check. If the check is not passed, re-downloading can be done on the Merkel tree as quickly as possible.

图 3

在密码学领域，一套数字签名算法一般包含签名和验签两种运算，数据经过签名后，非常容易验证完整性，并且不可抵赖。只需要使用配套的验签方法验证即可，不必像传统物理签名一样需要专业手段鉴别。数字签名通常采用非对称加密算法，即每个节点需要一对私钥、公钥密钥对。所谓私钥即只有本人可以拥有的密钥，签名时需要使用私钥。不同的私钥对同一段数据的签名是完全不同的，类似物理签名的字迹。数字签名一般作为额外信息附加在原消息中，以此证明消息发送者的身份。公钥即所有人都可以获取的密钥，验签时需要使用公钥。因为公钥人人可以获取，所以所有节点均可以校验身份的合法性。

In the cryptography field, a digital signature algorithm typically contains both signatures and signatures, and the data are easy to verify integrity and irreconcilable once they have been signed. It only needs to be validated by an accompanying signature method, without the need for professional identification like traditional physical signatures. Digital signatures usually use asymmetric encryption algorithms, i.e., each node requires a pair of private keys and a public key pair. The so-called private key is only the key that the person can own, and the private key is required to be used when signing. The signature of the same paragraph of the data is completely different, similar to a physical signature. The digital signature is usually attached to the original message as additional information to prove the identity of the sender. The public key is the key that all people can access, and the public key is required to be used when signing. Because the public key is available, all the public key is valid for checking the legitimacy of the identity.

流程如下：

The process is as follows:

图 1

在区块链网络中，每个节点都拥有一份公私钥对。节点发送交易时，先利用自己的私钥对交易内容进行签名，并将签名附加在交易中。其他节点收到广播消息后，首先对交易中附加的数字签名进行验证，完成消息完整性校验及消息发送者身份合法性校验后，该交易才会触发后续处理流程。这对应到前文 比特币的通俗故事 一节中村民验证喊出交易者的声音，确保是张三自己发出的交易。

In the block chain network, each node has a public-private key pair. When a transaction is sent, the transaction is signed using its own private key and the signature is attached to the transaction. After the other node has received the broadcast message, the digital signature attached to the transaction is verified and the integrity of the message is verified and the sender's identity is authenticated before the transaction triggers the follow-up process. This will go to the popular story in the previous section of the < strong > bitcoin > to verify the sound of the caller and ensure that the transaction is made by Zhang San himself.

为什么要共识？

区块链通过全民记账来解决信任问题，但是所有节点都参与记录数据，那么最终以谁的记录为准？或者说，怎么保证所有节点最终都记录一份相同的正确数据，即达成共识？在传统的中心化系统中，因为有权威的中心节点背书，因此可以以中心节点记录的数据为准，其他节点仅简单复制中心节点的数据即可，很容易达成共识。然而在区块链这样的去中心化系统中，并不存在中心权威节点，所有节点对等地参与到共识过程之中。由于参与的各个节点的自身状态和所处网络环境不尽相同，而交易信息的传递又需要时间，并且消息传递本身不可靠，因此，每个节点接收到的需要记录的交易内容和顺序也难以保持一致。更不用说，由于区块链中参与的节点的身份难以控制，还可能会出现恶意节点故意阻碍消息传递或者发送不一致的信息给不同节点，以干扰整个区块链系统的记账一致性，从而从中获利的情况。因此，区块链系统的记账一致性问题，或者说共识问题，是一个十分关键的问题，它关系着整个区块链系统的正确性和安全性。

In traditional central systems, where there is an authoritative endorsement of central nodes, it is easy to reach a consensus. However, in a decentralized system such as a block chain, there is no central authority node, where all nodes are involved in the consensus process. Or, how is it possible to ensure that all nodes are eventually recorded with the same correct data, i.e., consensus? In traditional central systems, where there is an authoritative central node endorsement, other nodes can simply reproduce central node data. Not to mention the fact that the identity of the nodes involved in the node chain is difficult to control, and there may be malicious nodes deliberately obstructing the transmission of information or sending inconsistent information to different nodes in order to disrupt the consistency of the entire system in order to benefit from it, given that the transmission of information is unreliable?

有哪些共识算法？

当前区块链系统的共识算法有许多种，主要可以归类为如下四大类：

There are many kinds of consensus algorithms for the current block chain system, which can be grouped mainly into the following four main categories:

1. 工作量证明(Proof of Work, PoW)类的共识算法；
2. Po*的凭证类共识算法；
3. 拜占庭容错(Byzantine Fault Tolerance, BFT)类算法；
4. 结合可信执行环境的共识算法。

POW共识算法

类的共识算法主要包括区块链鼻祖比特币所采用的 共识及一些类似项目(如莱特币等)的变种 ，即为大家所熟知的 挖矿 类算法。这类共识算法的核心思想实际是所有节点竞争记账权，而对于每一批次的记账(或者说，挖出一个区块)都赋予一个 难题，要求只有能够解出这个难题的节点挖出的区块才是有效的。同时，所有节点都不断地通过试图解决难题来产生自己的区块并将自己的区块追加在现有的区块链之后，但全网络中只有最长的链才被认为是合法且正确的。

The consensus algorithm of the class consists mainly of the consensus adopted in the block chain and some variants of similar projects (e.g., Letco) known as the mining algorithm. The core idea of such consensus algorithms is that all nodes actually compete for the right to account, while for each batch (or, for example, to excavate a block) a difficulty requires that only the blocks that can be dug out of the node that solves the problem is valid. At the same time, all nodes constantly try to create their own blocks by resolving them and add their own blocks after the existing chain of blocks, but only the longest of the entire network is considered legitimate and correct.

The trick of adopting this consensus algorithm for the Bitcoin block chain system is two: first, it uses the difficulty , which is difficult to answer, but which can easily verify the correctness of the answer, while the difficulty of /strung >, or the average amount of time it takes to solve a problem, can easily be controlled by adjusting some of the parameters in the puzzle. At the same time, the growth of the chain can be well controlled. At the same time, if one node succeeds in resolving the problem , the node can spread faster than the node , and the node can spread faster than the other node >, which, in conjunction with the assessment mechanism, will continue to generate the node at most of the node.

类的共识算法所设计的 难题 一般都是需要节点通过进行大量的计算才能够解答的，为了保证节点愿意进行如此多的计算从而延续区块链的生长，这类系统都会给每个有效区块的生成者以一定的奖励。比特币中解决的难题即寻找一个符合要求的随机数。然而不得不承认的是， 类算法给参与节点带来的计算开销，除了延续区块链生长外无任何其他意义，却需要耗费巨大的能源，并且该开销会随着参与的节点数目的上升而上升，是对能源的巨大浪费。

In order to ensure that nodes are willing to make so many calculations to continue the growth of the block chain, such systems offer a certain incentive to the generator of each effective block. The solution in Bitcoin is to find a random number that meets the requirements. It must be acknowledged, however, that the calculation cost of the node of the node of the node of the node of the node of the node of the node of the node of participation, which has no other meaning than to continue the node of the node, is costly of energy, and that it increases as the number of nodes in the node of the node of participation rises and is a great waste of energy.

Po*的凭证类共识算法

鉴于的缺陷，人们提出了一些的替代者—— 。这类算法引入了 凭证 的概念(即 中的 ，代表各种算法所引入的凭证类型)：根据每个节点的某些属性(拥有的币数、持币时间、可贡献的计算资源、声誉等)，定义每个节点进行出块的难度或优先级，并且取凭证排序最优的节点，或是取凭证最高的小部分节点进行加权随机抽取某一节点，进行下一段时间的记账出块。这种类型的共识算法在一定程度上降低了整体的出块开销，同时能够有选择地分配出块资源，即可根据应用场景选择 凭证 的获取来源，是一个较大的改进。然而，凭证的引入提高了算法的中心化程度，一定程度上有悖于区块链 去中心化 的思想，且多数该类型的算法都未经过大规模的正确性验证实验，部分该类算法的矿工激励不够明确，节点缺乏参与该类共识的动力。

Given the shortcomings, a number of alternatives have been proposed. Such algorithms have introduced the concept of vouchers (i.e., they represent the type of vouchers introduced by various algorithms): a weighted random selection of a number of points based on certain attributes of each node ( holding , , , reputations etc.), a larger improvement has been made in the selection of the difficulty or priority of blocks for each node, and the selection of the best-sortted node of certificates, or the sub-node of the highest number of certificates, which has resulted in a period of account-taking.

BFT类算法

无论是 类算法还是 类算法，其中心思想都是将所有节点视作竞争对手，每个节点都需要进行一些计算或提供一些凭证来竞争出块的权利(以获取相应的出块好处)。 类算法则采取了不同的思路，它希望所有节点协同工作，通过协商的方式来产生能被所有(诚实)节点认可的区块

Whether algorithms or algorithms, the central idea is to treat all nodes as competitors and each node requires some calculation or some proof of the right to compete for blocks (in order to obtain the corresponding yield). The algorithm takes a different approach, and it wants all nodes to work together to produce, through consultation, blocks that are acceptable to all (honestly) nodes.

具体地， 类共识算法一般都会定期选出一个领导者，由领导者来接收并排序区块链系统中的交易，领导者产生区块并递交给所有其他节点对区块进行验证，进而其他节点“举手”表决时接受或拒绝该领导者的提议。如果大部分节点认为当前领导者存在问题，这些节点也可以通过多轮的投票协商过程将现有领导者推翻，再以某种预先定好的协议协商产生出新的领导者节点。

Specifically, consensus algorithms typically select, on a regular basis, a leader to receive and sort transactions in the block chain system, who generates blocks and transmits them to all other nodes for validation, and then accepts or rejects the leader's proposal when the other nodes “rise their hands” vote. If most nodes believe that there is a problem with the current leader, these nodes can also overturn the existing leader through a multi-round process of voting consultations, and produce a new leader node with some sort of predetermined agreement.

类算法一般都有完备的安全性证明，能在算法流程上保证在群体中恶意节点数量不超过三分之一时，诚实节点的账本保持一致。然而，这类算法的协商轮次也很多，协商的通信开销也比较大，导致这类算法普遍不适用于节点数目较大的系统。业界普遍认为， 算法所能承受的最大节点数目不超过100

Arithmeticals generally have adequate proof of security to ensure consistency in the books of honest nodes when the number of malicious nodes in the group does not exceed one third in the algorithmic process. However, there are many rounds of consultation for such algorithms, and the cost of the negotiated communications is larger, resulting in the fact that such algorithms are generally not suitable for systems with larger nodes.

结合可信执行环境的共识算法

上述三类共识算法均为纯软件的共识算法。除此之外，还有一些共识算法对硬件进行了利用，如一些利用可信执行环境(Trusted Execution Environment, TEE)的软硬件结合的共识算法。

All three types of consensus algorithms are purely software consensus algorithms. In addition, there are consensus algorithms that use hardware, such as some that combines software and hardware using the credible implementation environment (Trusted Exchange Environment, TEE)

可信执行环境是一类能够保证在该类环境中执行的操作绝对安全可信、无法被外界干预修改的运行环境，它与设备上的普通操作系统(Rich OS)并存，并且能给提供安全服务。

A credible enforcement environment is one in which operations performed in that environment are absolutely safe and credible and cannot be modified by outside intervention, coexisting with the general operating system on equipment (Rich OS) and providing security services.

An intelligent contract based on the block chain would need to include , and

图 2

对等计算机网络(Peer-to-Peer Networking，P2P网络)，是一种消除了中心化的服务节点，将所有的网络参与者视为对等者(Peer)，并在他们之间进行任务和工作负载分配。 结构打破了传统的 C/S模式 ，去除了中心服务器，是一种依靠用户群共同维护的网络结构。由于节点间的数据传输不再依赖中心服务节点， 网络具有极强的可靠性，任何单一或者少量节点故障都不会影响整个网络正常运转。同时， 网络的网络容量没有上限，因为随着节点数量的增加，整个网络的资源也在同步增加。由于每个节点可以从任意(有能力的)节点处得到服务，同时由于 网络中暗含的激励机制也会尽力向其他节点提供服务，因此，实际上 网络中节点数目越多， 网络提供的服务质量就越高。

The structure breaks the traditional , except for the centre , which is a network structure that relies on the user community.

在区块链系统中，要求所有节点共同维护账本数据，即每笔交易都需要发送给网络中的所有节点。如果按照传统的C/S这种依赖中心服务节点的模式，中心节点需要大量交易信息转发给所有节点，这几乎是不可能完成的任务。网络的这些设计思想则同区块链的理念完美契合。在区块链中，所有交易及区块的传播并不要求发送者将消息发送给所有节点。节点只需要将消息发送给一定数量的相邻节点即可，其他节点收到消息后，会按照一定的规则转发给自己的相邻节点。最终通过一传十、十传百的方式，最终将消息发送给所有节点。

In block chain systems, all nodes are required to jointly maintain book data, i.e., each transaction needs to be sent to all nodes in the network. If, according to the traditional model of C/S, which relies on the central service node, the central node requires a large amount of transaction information to be transmitted to all nodes, this is almost impossible. These ideas of the network fit perfectly with the concept of the block chain. In the node chain, all transactions and the dissemination of blocks do not require the sender to send the message to all nodes. Node only needs to send the message to a certain number of adjacent nodes, and when the other node receives the message, it is transmitted to its node in accordance with certain rules.

以传统的银行系统为例。传统银行系统均采用C/S网络架构，即以银行服务器为中心节点，各个网点、ATM为客户端。当我们需要发起转账时，首先提供银行卡、密码等信息证明身份，然后生成一笔转账交易，发送到中心服务器后，由中心服务器校验余额是否充足等信息，然后记录到中心服务器，即可完成一笔转账交易。

Take the traditional banking system as an example. The traditional banking system uses the C/S network structure, which uses a bank server as its central node, and the ATM as its client. When we need to initiate a transfer, we first provide information such as a bank card, password, and then generate a transfer transaction, and when sent to the central server, the central server verifies the sufficiency of the balance, and then records it to the central server, so that a transfer transaction can be completed.

而在区块链网络中，并不存在一个中心节点来校验并记录交易信息，校验和记录工作有网络中的所有节点共同完成。当一个节点需要发起转账时，需要指明转账目的地址、转账金额等信息，同时还需要对该笔交易进行签名。由于不存在中心服务器，该交易会随机发送到网络中的邻近节点，邻近节点收到交易消息后，对交易进行签名，确认身份合法性后，再校验余额是否充足等信息。均校验完成后，它则会将该消息转发至自己的邻近节点。以此重复，直至网络中所有节点均收到该交易。最后，矿工获得记账权后，则会将该交易打包至区块，然后再广播至整个网络。区块广播过程同交易的广播过程，仍然使用一传十、十传百的方式完成。收到区块的节点完成区块内容验证后，即会将该区块永久地保存在本地，即交易生效。

In the block chain network, there is no central node to verify and record the transaction information. Once checked, it transmits the message to its immediate node. This is repeated until all nodees in the network receive the transaction. Finally, when the miner has the right to account, the transaction is packaged to a block and then broadcast to the entire network.

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