5.2 · Digital currency

5.2 · 数字货币

Digital currency

数字货币

What a digital currency is and how it is used, and how blockchain, a time-stamped digital ledger that cannot be altered, keeps a permanent record of digital currency payments.

什么是数字货币、它如何被使用,以及区块链(一种带时间戳、无法被更改的数字账本)如何为数字货币付款保留一份永久记录。

Core for all candidates 所有考生均需掌握的核心内容 Covers 5.2.1 and 5.2.2 涵盖 5.2.1 和 5.2.2 The transaction process and the "cannot be altered" property are marked 交易过程与"无法被更改"这一特性都是评分要点

Explainer · 5.2.1

讲解 · 5.2.1

A currency with no physical form

一种没有实物形态的货币

Notes and coins are physical money. The balance in a bank account is a record of that physical money. A digital currency is different: there are no notes or coins for it at all, and there never were.

纸币和硬币是实物货币。银行账户里的余额是这些实物货币的一份记录。数字货币不一样:它根本没有纸币或硬币,从来就没有过。

A digital currency is a currency that only exists electronically. There is no physical version of it. People use it to pay for goods and services, or to send value to each other over a network.

数字货币是一种只以电子形式存在的货币。它没有任何实物版本。人们用它来支付商品和服务,或在网络上彼此转移价值。

Feature	特征	What it means	含义
Only electronic	只有电子形式	it exists only as data; it cannot be held, printed or minted as a physical object	它只以数据形式存在;不能被拿在手里,也不能被印制或铸造成实物
Centralised or decentralised	中心化或去中心化	some are controlled by one central organisation; others are decentralised, with no single body in control	有些由一个中心机构控制;有些是去中心化的,没有任何单一机构在控制
Usually encrypted	通常经过加密	transactions and holdings are protected by encryption so they cannot be read or changed by others	交易和持有量受加密保护,他人无法读取或篡改

"Digital currency" is not the same as money in an ordinary bank account. A bank balance stands for physical currency the bank holds. A digital currency has no physical version at any point.

"数字货币"和普通银行账户里的钱不是一回事。银行余额代表银行持有的实物货币。数字货币在任何环节都没有实物版本。

Try it yourself

动手试试

Digital currency: true or not?

数字货币:对还是不对?

Tap each statement to tag it as true of a digital currency or not true, then check.

点击每条陈述,把它标记为数字货币的正确描述还是错误描述,然后检查。

Explainer · 5.2.1

讲解 · 5.2.1

How digital currencies are used

数字货币如何使用

A digital currency does the jobs ordinary money does, but every step happens as a message on a network rather than by handing over cash.

数字货币做的事和普通货币一样,但每一步都是通过网络上的一条消息完成的,而不是把现金递过去。

paying for goods and services from a seller that accepts it
sending value directly to another person, often without going through a bank
holding value in a digital wallet, identified by a key rather than a name

向接受该货币的卖家支付商品和服务的费用
直接把价值转给另一个人,通常无需经过银行
把价值存放在数字钱包里,用一个密钥而不是姓名来标识

Because the money is only data, a currency needs a trusted way to record who paid whom, so that the same units cannot be spent twice. Many digital currencies solve this with blockchain, covered next.

因为这些钱只是数据,货币需要一种可信的方式来记录谁付给了谁,这样同一笔单位就不会被花两次。许多数字货币用区块链来解决这个问题,下面就讲。

Explainer · 5.2.2

讲解 · 5.2.2

Blockchain: a ledger that cannot be edited

区块链:一份无法编辑的账本

A ledger is a record of transactions. A paper ledger can be crossed out and rewritten. A blockchain is built so that, once a record is in, it cannot be changed.

账本是交易的记录。纸质账本可以被划掉重写。区块链的设计使得记录一旦写入,就无法被更改。

A blockchain is a digital ledger: a time-stamped series of records that cannot be altered. New records can be added, but existing ones can never be edited or removed.

区块链是一份数字账本:一系列带时间戳、无法被更改的记录。可以添加新记录,但已有记录永远不能被编辑或删除。

The records are grouped into blocks. Each block is joined to the one before it, so the blocks form a chain in the order they were added.

这些记录被分组放进一个个区块。每个区块都与它前面的那个相连,于是这些区块按照添加的顺序连成一条链。

Idea	概念	What it does	作用
Time-stamp	时间戳	every block records the date and time it was created, fixing its place in the order	每个区块都记录它被创建的日期和时间,从而固定它在顺序中的位置
Block hash	区块哈希值	a short unique identifier calculated from the block's contents; change one detail and the hash changes	根据区块内容计算出的一个简短、唯一的标识符;只要改动一处细节,哈希值就会改变
Link to the previous block	指向前一区块的链接	each block stores the previous block's hash, so the blocks are chained in a fixed order	每个区块都保存前一个区块的哈希值,于是这些区块以固定顺序串联
Decentralised copies	去中心化的副本	a full copy of the chain is held on every device in the network, not in one central place	网络中每一台设备都保存整条链的完整副本,而不是放在某个中心位置

Try it yourself

动手试试

Inside one block

一个区块的内部

Click each part of a block to see what it holds and why.

点击区块的每一部分,看看它保存了什么、为什么。

Explainer · 5.2.2

讲解 · 5.2.2

How a transaction is added to the blockchain

一笔交易如何被添加到区块链

This is the sequence markers ask candidates to describe, or to set out as a labelled diagram. Follow one payment from the payer's device to a permanent record on every copy of the chain.

这就是考官要求考生描述、或者画图并标注的那段流程。跟着一笔付款,从付款人的设备一直走到链的每一份副本上的永久记录。

Step	步骤	What happens	发生了什么
1	1	the payer's device encrypts the payment data (payer, recipient, amount)	付款人的设备把付款数据(付款人、收款人、金额)加密
2	2	the device sends the transaction out to the network that holds the digital ledger	该设备把这笔交易发送到保存数字账本的网络
3	3	the transaction is checked, then placed into a new block together with other recent transactions	这笔交易经过检查,然后与其他近期交易一起放入一个新区块
4	4	the block is given a time-stamp and a block hash, and it stores the previous block's hash	这个区块被赋予一个时间戳和一个区块哈希值,并保存前一个区块的哈希值
5	5	once a block has no more room, it is placed on the end of the chain	当这个区块装满时,它被添加到区块链的末尾
6	6	the updated chain is copied to every device in the network, so all copies match	更新后的链被复制到网络中的每一台设备,于是所有副本都保持一致

Name the terms in order: encrypt, send to the ledger, into a block, time-stamp and hash, added to the chain, copied to every device. A drawn answer should label each arrow with what is being sent.

按顺序说出这些术语:加密、发送到账本、放入一个区块、时间戳和哈希、添加到链上、复制到每一台设备。画图作答时,应在每个箭头上标注传输的内容。

Try it yourself

动手试试

Follow a transaction

跟踪一笔交易

Mia buys a second-hand mountain bike from Lachlan for 30 units of a digital currency. Step through what happens to her payment.

Mia 用 30 单位的某种数字货币向 Lachlan 买了一辆二手山地自行车。逐步走一遍她这笔付款的经过。

Explainer · 5.2.2

讲解 · 5.2.2

Why a recorded transaction cannot be altered

为何已记录的交易无法被更改

Two features work together to make the ledger tamper-evident.

两个特性共同作用,让这份账本任何改动都会被发现。

The blocks are chained by hash. Editing a transaction in an old block changes that block's hash, so it no longer matches the "previous hash" stored in the next block. The chain breaks at that point, and the change is obvious.

区块通过哈希值串联。修改旧区块里的一笔交易会改变该区块的哈希值,于是它与下一个区块中保存的"前一哈希值"对不上了。链在那个位置断开,改动一目了然。

Every device holds a copy. A changed copy no longer agrees with all the others on the network, so the network rejects it. To force a change through, someone would have to alter the majority of copies at the same time.

每一台设备都保存一份副本。被改动的副本与网络上其他所有副本不再一致,于是网络拒绝它。要强行让改动生效,就得同时改掉大多数副本。

So the ledger is append-only: new transactions can be added as new blocks, but nothing already recorded can be edited or deleted. This also means any transaction can be traced by following the chain back through the blocks.

因此这份账本是只能追加的:可以把新交易作为新区块添加进去,但已经记录的任何内容都不能被编辑或删除。这也意味着,沿着链在各区块间往回追,可以追踪任何一笔交易。

Try it yourself

动手试试

Allowed or not allowed?

允许还是不允许?

Tap each action to tag it as something a blockchain allows or does not allow, then check.

点击每个操作,把它标记为区块链允许还是不允许的事,然后检查。

Check your understanding

自测

What does it mean that a digital currency only exists electronically?

数字货币只以电子形式存在是什么意思?

Check your understanding

自测

Why can a transaction already recorded on a blockchain not be altered?

为什么已经记录在区块链上的一笔交易无法被更改?

Check your understanding

自测

What happens once a block has no more room?

当一个区块再也放不下时会发生什么?

Common mistakes

常见错误

Markers reported these patterns for 5.2.1 and 5.2.2 考官针对 5.2.1 和 5.2.2 报告了以下模式

RecurringAsked to show how a digital currency payment is recorded with blockchain, very few candidates can give the process in order. The steps to name are: encrypt the payment data, send it to the ledger, place it in a block, give the block a time-stamp and hash, add the full block to the chain, copy the chain to every device.

反复出现被要求画出或描述如何用数字货币和区块链完成一笔付款时,很少有考生能按顺序说出这个过程。要说出的步骤是:加密付款数据、发送到账本、放入一个区块、给区块加时间戳和哈希值、把装满的区块添加到链上、把链复制到每一台设备。

Markers also note that responses need more technical terminology, and that candidates should use the key terms given in the question and stay in its context. "It is stored safely on computers" earns little; naming the ledger, blocks, the time-stamp and the hash earns the marks.

考官还指出,作答需要更多技术术语,考生应使用题目中给出的关键术语并贴合题目的情境。"它被安全地存储在计算机上"几乎得不到分;说出账本、区块、时间戳和哈希值才能得分。

On digital currency, candidates describe online banking or a card payment instead. The point of a digital currency is that it has no physical form at all; a card or a bank balance still represents physical money.

关于数字货币,考生转而去描述网上银行或刷卡支付。数字货币的关键在于它完全没有实物形态;银行卡或银行余额仍然代表着实物货币。

On blockchain, candidates say only that "it stores transactions" and stop. That is true of any database. What makes it a blockchain is that the records are time-stamped, linked to the previous record, cannot be altered, and are copied to every device.

关于区块链,考生只说"它存储交易"就停下了。任何数据库都能做到这一点。让它成为区块链的,是这些记录带时间戳、与前一条记录相连、无法被更改,并且被复制到每一台设备。

Too vague: "A digital currency is money you keep on your phone instead of in your pocket."

太含糊:"数字货币就是你放在手机里而不是口袋里的钱。"

✓

Right: "A digital currency is a currency that only exists electronically. It has no physical notes or coins, and it is used to pay for goods and services or to transfer value between people."

正确:"数字货币是一种只以电子形式存在的货币。它没有实物纸币或硬币,用于支付商品和服务,或在人与人之间转移价值。"

Any database does this: "Blockchain is a place where all the transactions are stored."

任何数据库都能做到:"区块链就是一个存储所有交易的地方。"

✓

Right: "Blockchain is a digital ledger, a time-stamped series of records that cannot be altered. Each block is linked to the previous one, and a copy of the whole chain is held on every device, so new transactions can be added but existing ones cannot be changed."

正确:"区块链是一份数字账本,是一系列带时间戳、无法被更改的记录。每个区块都与前一个相连,整条链的一份副本保存在每一台设备上,因此可以添加新交易,但已有的交易无法被更改。"

Go deeper

深入练习

Paper 1

Draw the blockchain transaction process from memory

凭记忆画出区块链交易过程

From memory, sketch the six steps from the payer's device to a record on every copy of the chain, labelling each arrow with what is sent, and naming the ledger, the block, the time-stamp and the hash. Check the order against 5.2.2.

凭记忆勾画从付款人设备到链的每一份副本上留下记录的六个步骤,在每个箭头上标注传输的内容,并说出账本、区块、时间戳和哈希值。对照 5.2.2 核对顺序。

Try the revision questions 做一做复习题

Revision questions

复习题

Past-paper style. Write an answer, then reveal the marking points and mark yourself.

采用历年真题风格。写下答案,然后展开评分要点给自己打分。

Question 1 · 1 mark 第 1 题 · 1 分

[1]State what is meant by the term digital currency.

[1]陈述数字货币一词的含义。

Question 2 · 2 marks 第 2 题 · 2 分

[2]State two features of a digital currency.

[2]陈述数字货币的两个特征。

Question 3 · 2 marks 第 3 题 · 2 分

[2]Describe what is meant by blockchain.

[2]描述区块链的含义。

Question 4 · 4 marks 第 4 题 · 4 分

[4]Sketch a labelled diagram of the steps that take place when a person pays for an item with a digital currency that uses blockchain.

[4]勾画一张带标注的图,展示当一个人用采用区块链的数字货币购买一件物品时所经历的步骤。

Question 5 · 3 marks 第 5 题 · 3 分

[3]Explain why a transaction recorded on a blockchain cannot later be altered.

[3]解释为什么记录在区块链上的一笔交易之后无法被更改。

Flashcards

记忆卡片

Active recall for this subtopic’s key terms.

针对本子主题关键术语的主动回忆练习。

Keep this subtopic’s practice with you

把这个子主题的练习保存下来

Free account: unlock every revision question and flashcard for 5.2, and every other IGCSE 0478 statement.

免费账户:解锁 5.2 以及所有其他 IGCSE 0478 考纲陈述的全部复习题和记忆卡片。