What is Block chain?

A blockchain, originally block chain, is a continuously growing list of records, called blocks, which are linked and secured using cryptography. Each block typically contains a cryptographic hash of the previous block, a timestamp and transaction data. By design, a blockchain is inherently resistant to modification of the data. It is "an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way". For use as a distributed ledger, a blockchain is typically managed by a peer-to-peer network collectively adhering to a protocol for validating new blocks. Once recorded, the data in any given block cannot be altered retroactively without the alteration of all subsequent blocks, which requires collusion of the network majority.

区块链是一个持续增长的记录链表。里面的每个记录称为区块。区块链通过加密技术链接各个区块并施加保护。每个区块一般包含前一区块的加密(cryptographic)哈希值、时间戳和当次交易数据。区块链被设计为反后续修改的(inherently resistant to modification)。它是一个开放的分布式的账本(ledger)。这个账本上以一种永久留存的(permanent)可验证的(verifiable)方式高效记录着双方的交易内容。作为一个分布式账本，区块链一般被对等网络(peer-to-peer network)中的各个节点共同(collectively)管理，并且遵守(adhering to)某种可验证(validate)新加入区块的协议。一旦区块被记入账本，如果要回滚(be altered retroactively)某个区块中的数据，就必须把它后继的所有区块都重新修改，并且整个对等网络中的节点要协力操作(collusion of the network majority)才能同步这次修改。

Blockchains are secure by design and exemplify a distributed computing system with high Byzantine fault tolerance. Decentralized consensus has therefore been achieved with a blockchain. This makes blockchains potentially suitable for the recording of events, medical records, and other records management activities, such as identity management, transaction processing, documenting provenance, food traceability or voting.

区块链具备设计上的安全性，这在高容错性(Byzantine fault tolerance)的分布式系统中得到很好证明(exemplify)。通过区块链可以获得去中心化的一致性(decentralized consensus)。这使得区块链适用于(suitable for)纪事，记录病历(medical records)，以及其他一些记录管理，例如身份信息管理、交易处理流程、记录来源(documenting provenance)、食品货运路径监控(food traceability)、还有投票 。

Blockchain was invented by Satoshi Nakamoto in 2008 for use in the cryptocurrency bitcoin, as its public transaction ledger. The invention of the blockchain for bitcoin made it the first digital currency to solve the double spending problem without the need of a trusted authority or central server. The bitcoin design has been the inspiration for other applications.

区块链是由中本聪于2008年发明的，作为加密数字货币比特币的公共交易账本。这项发明使得比特币成为世界上第一款不需要使用认证机构(trusted authority)和中央服务器(central server)来解决重复支付问题(double spending problem)的数字货币(digital currency)。比特币的产生启发(inspire)了不少其他应用。

History

The first work on a cryptographically secured chain of blocks was described in 1991 by Stuart Haber and W. Scott Stornetta. In 1992, Bayer, Haber and Stornetta incorporated Merkle trees to the design, which improved its efficiency by allowing several documents to be collected into one block.

加密安全区块链的原型最早是由 Stuart Haber 和 W. Scott Stornetta 于1991年提出的。1992年，Bayer，Haber 和 Stornetta 在设计中加入了默克尔树(Merkle trees)。通过默克尔树可以把多个文件纳入(collect into)区块中，从而提升了区块链的工作效率。

Merkle tree

In cryptography and computer science, a hash tree or Merkle tree is a tree in which every leaf node is labelled with the hash of a data block and every non-leaf node is labelled with the cryptographic hash of the labels of its child nodes. Hash trees allow efficient and secure verification of the contents of large data structures. Hash trees are a generalization of hash lists and hash chains.

在加密和计算机科学领域，一个哈希树，也叫默克尔树，的每个叶节点的标签内容是(is labelled with)数据块的哈希值，而每个非叶节点的标签内容是其孩子节点的标签内容总和的哈希值。哈希树可以完成对大数据块的高效安全验证。哈希树是一个哈希队列和哈希链表的一种抽象(generalization)。

Demonstrating that a leaf node is a part of a given binary hash tree requires computing a number of hashes proportional to the logarithm of the number of leaf nodes of the tree; this contrasts with hash lists, where the number is proportional to the number of leaf nodes itself.

假设一颗哈希树的叶节点树为n。求证一个叶节点是否在一颗哈希树上，需要计算与log(n)成比例(proportional to)个数的哈希值。与此不同的(conrast)是，在哈希队列上，则需要计算与n成比例个数的哈希值。

The concept of hash trees is named after Ralph Merkle who patented it in 1979.

哈希树的以Ralph Merkle命名(name after)的，后者于1979年申请了哈希树的专利。

The first blockchain was conceptualized by a person (or group of people) known as Satoshi Nakamoto in 2008. It was implemented the following year by Nakamoto as a core component of the cryptocurrency bitcoin, where it serves as the public ledger for all transactions on the network. Through the use of a blockchain, bitcoin became the first digital currency to solve the double spending problem without requiring a trusted authority and has been the inspiration for many additional applications.

第一个区块链概念由一个名叫中本聪的人（也可能是个组织）于2008年提出。接下来的一年(the following year)中本聪实现了区块链，并将其作为加密数字货币比特币的核心组件。区块链被用作(serve as)比特币在网络中的所有交易的公共帐本。通过区块链，比特币成为世界上第一款不需要使用认证机构(trusted authority)和中央服务器(central server)来解决重复支付问题(double spending problem)的数字货币(digital currency)。比特币的产生启发(inspire)了不少其他应用。

In August 2014, the bitcoin blockchain file size, containing records of all transactions that have occurred on the network, reached 20GB (gigabytes). In January 2015, the size had grown to almost 30GB, and from January 2016 to January 2017, the bitcoin blockchain grew from 50GB to 100GB in size. The words block and chain were used separately in Satoshi Nakamoto's original paper, but were eventually popularized as a single word, blockchain, by 2016.

比特币的区块链囊括了网络上所有已发生交易的记录。2014年8月，区块链的文件大小达到了20G。2015年1月，文件大小增至约30G。从2016年1月至2017年1月，比特币的区块链从50G增至100G大小。区块和链这俩词儿本来在中本聪的论文里是拆开(used separately)的，但是最终在2016年普及(popularized)后被融合为一个词儿——区块链。

The term blockchain 2.0 refers to new applications of the distributed blockchain database, first emerging in 2014. The Economist described one implementation of this second-generation programmable blockchain as coming with "a programming language that allows users to write more sophisticated smart contracts, thus creating invoices that pay themselves when a shipment arrives or share certificates which automatically send their owners dividends if profits reach a certain level." Blockchain 2.0 technologies go beyond transactions and enable "exchange of value without powerful intermediaries acting as arbiters of money and information." They are expected to enable excluded people to enter the global economy, protect the privacy of participants, allow people to "monetize their own information," and provide the capability to ensure creators are compensated for their intellectual property. Second-generation blockchain technology makes it possible to store an individual's "persistent digital ID and persona" and provides an avenue to help solve the problem of social inequality by "potentially changing the way wealth is distributed". As of 2016, blockchain 2.0 implementations continue to require an off-chain oracle to access any "external data or events based on time or market conditions [that need] to interact with the blockchain.

区块链2.0说的是分布式区块链数据库的投入使用。数据库的首次合并始于2014年。经济学人杂志形容这款第二代的可编程区块链可以让用户制定更精细智能的合同(sophisticated smart contracts)，这样就能做到在收货(shipments arrives)时自动付款并生成收据(invoices)，或者在收益达到一定额度时(reach a certain level)自动给证书所有者分红(send dividends)。区块链2.0技术不只是交易，更能让双方在没有中间商(intermediary)作为货币和信息的媒介(arbiter)的情况下进行交易(exchange of value)。这种技术用来使得原本的局外人(excluded people)可以参与全球经济(global economy)，可以保护参与者(participants)的隐私，可以让人们的信息变得有价值(monetize their info)，可以让知识产权(intellectual property)得到应有的报酬(compensated)。第二代区块链使得个人的永久数字身份证(persistent digital ID and persona)成为可能，并为去除“因改变潜在的财富分配方式(change the way wealth is distributed)而造成的社会不公平(social inequality)”提供了一条道路(avenue)。到2016年为止(as of 2016)， 区块链2.0需要一个链外(off-chain)的甲骨文数据库来访问按照时间或市场环境(market conditions)组织的用于与区块链交互的外部数据或事件。

In 2016, the central securities depository of the Russian Federation (NSD) announced a pilot project, based on the Nxt blockchain 2.0 platform, that would explore the use of blockchain-based automated voting systems. IBM opened a blockchain innovation research center in Singapore in July 2016. A working group for the World Economic Forum met in November 2016 to discuss the development of governance models related to blockchain. According to Accenture, an application of the diffusion of innovations theory suggests that blockchains attained a 13.5% adoption rate within financial services in 2016, therefore reaching the early adopters phase. Industry trade groups joined to create the Global Blockchain Forum in 2016, an initiative of the Chamber of Digital Commerce.

2016年，俄罗斯联邦的中央证券存管机构(central securities depository)宣布启动一个试点项目(pilot project)，基于下一代的未来币区块链2.0平台。这将开发基于区块链的自动投票系统。2016年7月，IBM在新加坡开设了一个区块链创新研究中心。世界经济论坛的一个工作小组在2016年11月会面商讨基于区块链的治理模型(governance models)的研发。一个名为Accenture的致力于传播创新理论的应用表示，2016年在金融服务领域区块链使用率(adoption rate)占到(attain)13.5%。2016年，多家工业贸易组织(Industry Trade Groups)聚在一块成立了全球区块链论坛，这是数字化商会(Chamber of Digital Commerce)的前身(initiative)。

Central securities depository

A central securities depository (CSD) is a specialist financial organization holding securities such as shares either in certificated or uncertificated (dematerialized) form so that ownership can be easily transferred through a book entry rather than the transfer of physical certificates. This allows brokers and financial companies to hold their securities at one location where they can be available for clearing and settlement. This is usually done electronically, making it much faster and easier than was traditionally the case where physical certificates had to be exchanged after a trade had been completed.

中央证券存管机构是一家专业的金融组织。它负责持有受认证的或未受认证的（无形的/dematerialized）有价证券（例如股份/shares），并可以通过简单地记账(through a book entry)而非转移实体证书(transfer physical certificates)的方式来更替证券所有权(ownership)。这使得证券经纪人和金融公司存于中央证券存管机构的有价证券可以随时清理和结算(clearing and settlement)。这常常是在电子设备上完成的(electronically)，速度快而且操作简便。而传统的方式往往还要在交易结束后互相验证实体证书。

In some cases these organizations also carry out centralized comparison, and transaction processing such as clearing and settlement of securities.

在一些场景中，这些组织也能执行一些中心化的比较和交易处理例如清理和结算证券。

NXT

Nxt is an open source cryptocurrency and payment network launched in November 2013 by anonymous software developer BCNext. It uses proof-of-stake to reach consensus for transactions—as such there is a static money supply and, unlike bitcoin, no mining. Nxt was specifically conceived as a flexible platform around which to build applications and financial services. It has an integrated Asset Exchange (comparable to shares), messaging system and marketplace. Users can also create new currencies within the system. The last major release enabled Multisignature capabilities and a plugin-system for the client.

未来币是一种开源数字货币和支付网络。它是在2013年11月由一位匿名软件开发者BCNext所发起的项目。未来币使用权益证明(proof-of-stake)算法来实现交易一致性(transaction consensus)——这样就能产生恒定的货币供给(static money supply)，并且不像比特币那样需要挖矿(mining)。未来币被设计为一种可搭建应用和金融服务的灵活平台。它拥有一套完整的资产（例如/comparable to/股份）交易(asset exchange)和信息处理系统，也有对应的市场(marketplace)。用户可以通过这套系统创建新型货币。未来币的最新版支持了多签名功能和客户端的插件系统。

Nxt has been covered extensively in the "Call for Evidence" report by ESMA, to which the Nxt community responded in July 2015.

未来币在欧洲证券市场管理局(European Securities & Market Authority)发布的报告《求证》(call for evidence)中被广泛引用(covered extensively)，未来币社区也对此做出了回应。

Structure

A blockchain is a decentralized, distributed and public digital ledger that is used to record transactions across many computers so that the record cannot be altered retroactively without the alteration of all subsequent blocks and the collusion of the network. This allows the participants to verify and audit transactions inexpensively. A blockchain database is managed autonomously using a peer-to-peer network and a distributed timestamping server. They are authenticated by mass collaboration powered by collective self-interests. The result is a robust workflow where participants' uncertainty regarding data security is marginal. The use of a blockchain removes the characteristic of infinite reproducibility from a digital asset. It confirms that each unit of value was transferred only once, solving the long-standing problem of double spending. Blockchains have been described as a value-exchange protocol. This blockchain-based exchange of value can be completed more quickly, more safely and more cheaply than with traditional systems. A blockchain can assign title rights because it provides a record that compels offer and acceptance.

区块链是去中心化的分布式的公共数字账本。这个账本可用于记录电脑之间的交易信息，这样一条记录就不能在不修改后继区块以及脱离全网协作的情况下回滚。这使得参与者可以极小的成本对交易进行验证和审计。区块链的数据库是通过对等网络和分布式时间戳服务器自管理的(managed autonomously)。他们得到了网络中所有对等实体终端(mass collaboration)的集体授权(authenticated)。而这种集体授权是基于每个个体的共同利益(collective self-interests)。这样就形成了一条健壮的工作流，在其中的参与者所面临的数据安全的不确定性(uncertainty)大大降低(marginal)。区块链去除了数字资产的无限重放(infinite reproducibility)的缺陷(characteristic)。也就是说，它保证每笔交易只执行一次，解决了长期存在的(long-standing)重复支付的问题。区块链被认为是一种价值交换协议。基于区块链的价值交换体系将比老式系统更加快捷更加安全并且更加经济。可以使用区块链来分配产权(title rights)，因为它能产生一个强制的支出和收入证明(compels offer and acceptance)。

Blocks

Blocks hold batches of valid transactions that are hashed and encoded into a Merkle tree. Each block includes the cryptographic hash of the prior block in the blockchain, linking the two. The linked blocks form a chain. This iterative process confirms the integrity of the previous block, all the way back to the original genesis block.

区块存储了带有哈希值的多个真实交易信息，这些交易信息被编码为一棵哈希树。每个区块包含了区块链中前一个区块的哈希值，其后还链接这两个子区块。彼此相连的区块构成了整个链条。这种迭代过程保证了前一区块的完整性，并且可以一直追溯到源头区块(genesis block)。

Sometimes separate blocks can be produced concurrently, creating a temporary fork. In addition to a secure hash-based history, any blockchain has a specified algorithm for scoring different versions of the history so that one with a higher value can be selected over others. Blocks not selected for inclusion in the chain are called orphan blocks. Peers supporting the database have different versions of the history from time to time. They only keep the highest-scoring version of the database known to them. Whenever a peer receives a higher-scoring version (usually the old version with a single new block added) they extend or overwrite their own database and retransmit the improvement to their peers. There is never an absolute guarantee that any particular entry will remain in the best version of the history forever. Because blockchains are typically built to add the score of new blocks onto old blocks and because there are incentives to work only on extending with new blocks rather than overwriting old blocks, the probability of an entry becoming superseded goes down exponentially as more blocks are built on top of it, eventually becoming very low. For example, in a blockchain using the proof-of-work system, the chain with the most cumulative proof-of-work is always considered the valid one by the network. There are a number of methods that can be used to demonstrate a sufficient level of computation. Within a blockchain the computation is carried out redundantly rather than in the traditional segregated and parallel manner.

有时候一些区块可以并行生成(produced concurrently)并分别创建区块链的临时分支(temporary fork)。在拥有一个基于安全哈希算法的history值的基础上，任何区块链拥有自己专门的算法生成(score)不同版本history值。这样具有更大history值的区块链分支可以被选择并覆盖(be selected over)其他区块链分支。未被选中(not selected for inclusion)的区块被称为独孤区块(orphan blocks)。网络中支持区块链数据库的终端不时(from time to time)会产生具有不同版本的history值的区块链数据库分支。他们只是保留当前最高分的数据库版本。每当终端收到一个更高分的版本（通常是旧的版本链入了一个新的区块），它们扩展或重写当前数据库并发送这份修改后的数据库给网络中的其他终端。无法保证任何区块都能保存在最好版本（即history值最高的区块链数据库）之中。因为一般创建区块链是为了叠加区块使得区块链的得分更高，并且只有扩展新的区块才会产生动力(incentives)而非重写旧的区块。一个区块被替换(superseded)的概率随着越来越多的新区块叠加在其上而呈指数级下降，直至最后变得微乎其微。举个例子，在一个使用工作量证明系统(proof-of-work system)的区块链中，累积最多工作量的区块链始终被对等网络视作那个真正有效的区块链。有一些(a number of)方法可以用来展示充足的算力(level of computation)。在区块链中，运算策略一般是冗余式(redundantly)的而非以往的分布并行(segregated and parallel)。

Block time

The block time is the average time it takes for the network to generate one extra block in the blockchain. Some blockchains create a new block as frequently as every five seconds. By the time of block completion, the included data becomes verifiable. In cryptocurrency, this is practically when the money transaction takes place, so a shorter block time means faster transactions. The block time for Ethereum is set to between 14 and 15 seconds, while for bitcoin it is 10 minutes.

区块时间是对等网络在区块链中生成一枚新的区块所需的平均时间。一些区块链每5秒就能创建一个新的区块。当区块生成完毕，其内部的数据处于可验证状态。在加密数字货币领域，一般当货币交易发生(take place)时才会创建新区块。所以较短的区块时间意味着更快的交易速度。以太坊的区块时间被设定为14-15秒，而比特币的相应时间则是10分钟。

Ethereum

Ethereum is an open-source, public, blockchain-based distributed computing platform and operating system featuring smart contract (scripting) functionality. It supports a modified version of Nakamoto consensus via transaction based state transitions. In popular discourse, the term Ethereum is often used interchangeably with Ether to refer to the cryptocurrency that is generated on the Ethereum platform.

以太坊是一个开源公共的基于区块链的分布式计算平台。它的操作系统的主打功能是智能合同。它通过基于交易的状态转换支持改进后的中本聪交易一致性。在一些流行的说法中，Ethereum 也常被用来代替(used interchangeably) Ether 来指代以太坊平台上发行的加密数字货币。

Ether is a cryptocurrency whose blockchain is generated by the Ethereum platform. Ether can be transferred between accounts and used to compensate participant mining nodes for computations performed. Ethereum provides a decentralized Turing-complete virtual machine, the Ethereum Virtual Machine (EVM), which can execute scripts using an international network of public nodes. "Gas", an internal transaction pricing mechanism, is used to mitigate spam and allocate resources on the network.

以太币是一种加密数字货币。它的区块链由以太坊生成。以太币可以在账户之间流通，也可为矿工的算力支付报酬(compensate)。以太坊提供了一种去中心化的图灵完备(Turing-complete)虚拟机——以太坊虚拟机(EVM)。这种虚拟机可以在公共节点组成的对等网络中执行脚本。“瓦斯”是以太坊内部的一种交易定价机制。它被用于防御垃圾邮件和在网络中分配资源。

Turing Complete

In computability theory, a system of data-manipulation rules (such as a computer's instruction set, a programming language, or a cellular automaton) is said to be Turing complete or computationally universal if it can be used to simulate any Turing machine. The concept is named after English mathematician and computer scientist Alan Turing.

在计算机领域，如果一个数据操作规则的系统（例如一份计算机指令集、一门编程语言、或者元胞自动机/cellular automation）可用于模拟任何图灵机，那么我们说它是图灵完备或计算通用的。这个概念是以英国数学家、计算机科学家阿兰·图灵命名的。

Ethereum was proposed in late 2013 by Vitalik Buterin, a cryptocurrency researcher and programmer. Development was funded by an online crowdsale that took place between July and August 2014. The system went live on 30 July 2015, with 11.9 million coins "premined" for the crowdsale. This accounts for approximately 13 percent of the total circulating supply.

2013年下半年，Vitalik Buterin提出以太坊的概念。他是一名加密数字货币研究人员，同时也是一位程序员。2014年7月至8月间，以太坊的开发过程得到了在线众筹(online crowdsale)的资金支持。系统于2015年7月30日正式上线，1190万提前挖好的以太币献给了众筹支持者。这些币占(account for)总流通量(circulating supply)的13%。

In 2016, as a result of the collapse of The DAO project, Ethereum was split into two separate blockchains – the new separate version became Ethereum (ETH), and the original continued as Ethereum Classic (ETC). The value of the Ethereum currency grew over 13,000 percent in 2017.

2016年，DAO项目因为被黑客攻击而崩溃，以太坊也不得不分裂出两条不同的区块链——新版本为ETH，旧版本为ETC。2017年，以太币的市值增长了13000%。

Hard forks

A hard fork is a rule change such that the software enforcing the old rules will see the blocks adhering to the new rules as invalid. To prevent a blockchain split, all nodes running the old software shall upgrade to new rules. Alternatively, all nodes using the new software shall return to the old rules as was the case of bitcoin split on 12 March 2013.
Ethereum has hard-forked to "make whole" the investors in The DAO, which had been hacked by exploiting a vulnerability in its code. In this case, the fork resulted in a split creating Ethereum and Ethereum Classic chains. In 2014 the Nxt community was asked to consider a hard fork that would have led to a rollback of the blockchain records to mitigate the effects of a theft of 50 million NXT from a major cryptocurrency exchange. The hard fork proposal was rejected, and some of the funds were recovered after negotiations and ransom payment.

硬分支是一个规则交换算法。这个算法使得执行失效旧规则的软件能够查看到遵守(adhering to)新规则的区块。为了避免区块链分产生永久分支，所有运行于旧版软件的终端都应该升级新规则。否则(alternatively)，所有使用新规则的终端都应该回滚为比特币在2013年3月12日产生永久分支前的样子。以太坊有硬分支可以在去中心化自治组织(The DAO)里为投资人复原(make whole)区块链（但不幸的是，这个组织的系统已经被黑客入侵了）。这个硬分支操作中创建了两个分支，一个是旧的以太坊区块链，另一个是新的。在2014年，Nxt社区被要求执行一个硬分支操作。一旦得到执行，将会引发区块链的回滚。这样做的目的是为了减轻(mitigate)一次重大(major)的加密数字货币交易中发生的5000万未来币被盗事件的影响。最终硬分支操作的提议(proposal)被否决(rejected)，但在与黑客的一系列谈判并交付赎金后(ransom payment)，一些资金被退回(recovered)。

Decentralization

By storing data across its network, the blockchain eliminates the risks that come with data being held centrally. The decentralized blockchain may use ad-hoc message passing and distributed networking.

通过把数据存储在网络的各个对等终端上，区块链消除(eliminate)了数据存储中心化的风险。去中心化的区块链使用对等消息传递和分布式网络。

Its network lacks centralized points of vulnerability that computer crackers can exploit; likewise, it has no central point of failure. Blockchain security methods include the use of public-key cryptography. A public key (a long, random-looking string of numbers) is an address on the blockchain. Value tokens sent across the network are recorded as belonging to that address. A private key is like a password that gives its owner access to their digital assets or the means to otherwise interact with the various capabilities that blockchains now support. Data stored on the blockchain is generally considered incorruptible.

它的网络没有脆弱的中心点，这样就不会被电脑黑客利用。同样地(likewise)，他也不需要担心中心点失灵损坏的问题。区块链完全方法包括使用公钥加密系统。公钥（长长的长得像随机数的一串数字）是区块链中的一个地址。在网络中传输的价值令牌（意指区块）被登记在相应的地址名下。私钥是则像是一个密码。这个密码让它的拥有者可以访问他的数字资产。它也像是一个工具使得它的拥有者可以使用区块链所支持的各种功能。存储在区块链上的数据一般认为是不会腐坏的。

This is where blockchain has its advantage. While centralized data is more controllable, information and data manipulation are common. By decentralizing it, blockchain makes data transparent to everyone involved.
Every node in a decentralized system has a copy of the blockchain. Data quality is maintained by massive database replication and computational trust. No centralized "official" copy exists and no user is "trusted" more than any other. Transactions are broadcast to the network using software. Messages are delivered on a best-effort basis. Mining nodes validate transactions, add them to the block they are building, and then broadcast the completed block to other nodes. Blockchains use various time-stamping schemes, such as proof-of-work, to serialize changes. Alternate consensus methods include proof-of-stake. Growth of a decentralized blockchain is accompanied by the risk of node centralization because the computer resources required to process larger amounts of data become more expensive.

这是区块链所具备的优势。虽然中心化数据更容易掌控，但是信息和数据操作则更为普遍。通过去中心化，区块链使得数据对于网络中的每个人来说都是透明的。每个去中心化网络中的终端都有一份区块链的拷贝。通过大量的数据库复制品(replication)和运算证书(computational trust)可以维护数据。没有中心的管理员副本存在，也没有一个用户比其他用户具备更高的可信度。通过软件把交易广播到网络中。消息被尽最大努力(on a best-effort basis)投递。挖矿终端验证交易，把它们添加到新区块中，然后把创建好的新区块广播给网络中的其他终端。区块链使用多种时间戳方案，如工作量证明算法，来记录(serialize)内部的变化。其他的一致性算法还有权益证明算法。去心化的区块链不断增长伴随着终端中心化的风险。因为用于处理更大量数据的计算机资源会越来越贵。

Openness

Open blockchains are more user-friendly than some traditional ownership records, which, while open to the public, still require physical access to view. Because all early blockchains were permissionless, controversy has arisen over the blockchain definition. An issue in this ongoing debate is whether a private system with verifiers tasked and authorized (permissioned) by a central authority should be considered a blockchain. Proponents of permissioned or private chains argue that the term "blockchain" may be applied to any data structure that batches data into time-stamped blocks. These blockchains serve as a distributed version of multiversion concurrency control (MVCC) in databases. Just as MVCC prevents two transactions from concurrently modifying a single object in a database, blockchains prevent two transactions from spending the same single output in a blockchain. Opponents say that permissioned systems resemble traditional corporate databases, not supporting decentralized data verification, and that such systems are not hardened against operator tampering and revision. Nikolai Hampton of Computerworld said that "many in-house blockchain solutions will be nothing more than cumbersome databases." Business analysts Don Tapscott and Alex Tapscott define blockchain as a distributed ledger or database open to anyone.

开放式区块链对用户更加友好。而传统的所有权记录虽然对大众开放，但始终需要实体才能访问查看。所有早期的区块链都是不需要许可证的，后来针对区块链定义的论战(controversy)逐渐甚嚣尘上。这场旷日持久的辩论中的一个焦点问题就是：一个被中心管理员分配任务并授权的私有系统是否可以视为区块链。被授权链或者说私有链的支持者认为(argue)区块链这个名词可以被运用到任何数据结构上，只要这个数据结构可以把数据打包到带有时间戳的区块内。这些区块链是(serve as)一种多版本并发控制(Multiversion concurrency control)的分布式数据库。正如多版本并发控制系统会阻止两个并发事务同时修改同一数据库对象一样，区块链也会阻止连个交易占用(spending)链中同一个区块。反对者则认为授权系统很像(resemble)传统的企业级(corporate)数据库，并不支持去中心化的数据验证。并且这些系统无法抵御(harden against)操作者篡改和修订数据(operator tampering and revision)。出版网站“电脑世界”的Nikolai Hampton说，许多私有(in-house)区块链解决方案简直就是(will be nothing more than)笨重的(cumbersome)数据库。商业分析师(Business analysis) Don Tapscott 和Alex Tapscott 把区块链定义为一个向所有人开放的分布式的账本数据库 。

Permissionless

The great advantage to an open, permissionless, or public, blockchain network is that guarding against bad actors is not required and no access control is needed. This means that applications can be added to the network without the approval or trust of others, using the blockchain as a transport layer.

公共开放式非授权区块链网络的巨大优势是不需要专门的针对恶意参与者的防御(guarding against bad actor)也不需要对网络的访问控制系统。这意味着使用区块链作为一个透明传输层时，应用不需要他人的批准或信任即可加载到网络中。

Bitcoin and other cryptocurrencies currently secure their blockchain by requiring new entries to include a proof of work. To prolong the blockchain, bitcoin uses Hashcash puzzles developed by Adam Back in the 1990s.

比特币和其他加密数字货币当前通过要求新的区块带上一个工作量证明来维护区块链的安全。为了让区块链可以继续增长(prolong)，比特币使用了 Adam Back 1990年代发明的 Hashcash 密码(puzzles)。

Financial companies have not prioritised decentralized blockchains. In 2016, venture capital investment for blockchain related projects was weakening in the USA but increasing in China. Bitcoin and many other cryptocurrencies use open (public) blockchains. As of January 2018, bitcoin has the highest market capitalization.

金融公司并未提升去中心化区块链的优先级别(prioritize)。2016年，比特币相关的风投项目在美国逐渐式微，却在中国方兴未艾。比特币和许多其他数字加密货币使用公开区块链。截至2018年1月，比特币达到了其最大市值(market capitalization)。

Permissioned (private) blockchain

Permissioned blockchains use an access control layer to govern who has access to the network. In contrast to public blockchain networks, validators on private blockchain networks are vetted by the network owner. They do not rely on anonymous nodes to validate transactions nor do they benefit from the network effect.

授权区块链使用版本控制层来管理对网络的访问请求。对比(in contrast to)公开区块链网络，私有区块链网络的验证者们需要接受网络主的审查(vet)。它们不依赖于匿名的网络终端来验证交易，也不从网络效应(network effect，意指挖矿、升值等)中获利。

Permissioned blockchains can also go by the name of 'consortium' or 'hybrid' blockchains.

授权区块链也被命名为(go by the name of)“联盟(consortium)区块链”或者“混合(hybrid)区块链”。

The New York Times noted in both 2016 and 2017 that many corporations are using blockchain networks "with private blockchains, independent of the public system.

纽约时报写道，2016至2017年，许多公司开始使用独立于(independent of)公共区块链系统的私有区块链网络。

Disadvantages

Nikolai Hampton pointed out in Computerworld that "There is also no need for a "51 percent" attack on a private blockchain, as the private blockchain (most likely) already controls 100 percent of all block creation resources. If you could attack or damage the blockchain creation tools on a private corporate server, you could effectively control 100 percent of their network and alter transactions however you wished." This has a set of particularly profound adverse implications during a financial crisis or debt crisis like the financial crisis of 2007–08, where politically powerful actors may make decisions that favor some groups at the expense of others. and "the bitcoin blockchain is protected by the massive group mining effort. It's unlikely that any private blockchain will try to protect records using gigawatts of computing power — it's time consuming and expensive." He also said, "Within a private blockchain there is also no 'race'; there's no incentive to use more power or discover blocks faster than competitors. This means that many in-house blockchain solutions will be nothing more than cumbersome databases."

在“电脑世界网”上 Nikolai Hampton 指出：“对与一个私有区块链，并不存在51%的黑客攻击，因为私有区块链大部分都已经掌控了100%的区块创建资源(block creation resources)。如果你可以在一个私有公司服务器上攻击或者毁坏区块链的创建工具，你便能有效地完全控制它们的网络并随心所欲地修改交易数据。” 这在类似2007-2008年的金融危机(financial crisis)或者债务危机(debt crisis)中将会造成一系列不利而深远的影响(a set of particularly profound adverse implications)。具备政治势力的参与者可能会做出一些取悦(favor)某些组织从而损害他方利益的(at the expense of others)决定。“而比特币区块链则受到广大“矿工”组织的保护。私有区块链不太可能会为了保护记录而花费数十亿瓦的算力——这成本可太高昂(consuming and expensive)了。”他同时说道，“在一个私有区块链中也不存在竞争，并没有任何动机能让你想要使出更多力气去挖掘出更多区块从而超越竞争者。这意味着许多私有区块链解决方案只能是一个尾大不掉的数据库。”