Many people have heard of Bitcoin that

很多人都聽說過比特幣

it's a fully digital currency with no government to issue it;

它是一種完全數字化的貨幣，沒有政府來發行它。

and that no banks need to manage accounts and verify transactions;

而銀行不需要管理賬戶和核實交易。

and also that no one really knows who invented it.

也沒有人真正知道是誰發明的。

And yet, many people don't know the answer to this question, at least not in full.

然而，很多人都不知道這個問題的答案，至少不知道完整的答案。

To get there,

為了達到目的。

and to make sure that the technical details underlying the answer actually feel motivated,

並確保回答的基礎技術細節實際感受到動力。

what we're going to do is walk through step by step

我們要做的是通過一步步走過。

how you might have invented your own version of Bitcoin.

你是如何發明你自己版本的比特幣的。

We'll start with you keeping track of payments with your friends using a communal ledger.

我們將從您使用公共賬本與您的朋友一起跟蹤付款開始。

And then, as you start to trust your friends and the world around you less and less,

然後，當你開始越來越不信任你的朋友和周圍的世界。

and if you're clever enough to bring in a few ideas from cryptography

如果你足夠聰明，可以從密碼學中引入一些想法

to help circumvent the need for trust,

以幫助規避信任需求。

what you end up with is what's called a "cryptocurrency".

你最終得到的是所謂的 "加密貨幣"。

You see, Bitcoin is just the first implemented example of a cryptocurrency.

你看，比特幣只是加密貨幣的第一個實施例。

And now, there are thousands more on exchanges with traditional currencies.

而現在，在與傳統貨幣的交流中，還有成千上萬的人。

Walking the path of inventing your own can help to set the foundations

走自己的發明之路，可以幫助打下基礎

for understanding some of the more recent players in the game

用於瞭解一些最近在遊戲中的玩家。

and recognizing when and why there's room for different design choices.

並認識到何時和為何有不同的設計選擇空間。

In fact, one of the reasons I chose this topic is that

事實上，我選擇這個題目的原因之一是

in the last year, there's been a huge amount of attention and investment

在過去的一年裡，有大量的關注和投資。

and, well, honestly hype directed at these currencies.

以及，說實話，針對這些貨幣的炒作。

And I'm not going to comment or speculate on the current or future exchange rates,

而我也不會去評論或猜測當前或未來的匯率。

but I think we'd all agree that

但我想我們都會同意

anyone looking to buy a cryptocurrency should really know what it is.

任何想買加密貨幣的人都應該真正知道它是什麼。

And I don't just mean in terms of analogies with vague connections to gold mining,

我不僅僅是指與金礦開採有模糊聯繫的類比。

I mean an actual direct description of what the computers are doing

我的意思是直接描述計算機正在做的事情。

when we send, receive and create cryptocurrencies.

當我們發送、接收和創建加密貨幣時。

One thing worth stressing, by the way, is that

順便說一句，有一點值得強調，那就是......。

even though you and I are going to dig into the details here,

即使你我要在這裡挖掘細節。

and that takes meaningful time,

而這需要有意義的時間。

you don't actually need to know those details if you just want to use the cryptocurrency,

如果你只是想使用加密貨幣，你其實並不需要知道這些細節。

just like you don't need to know the details of what happens under the hood when you swipe a credit card.

就像你不需要知道刷卡時的細節一樣。

Like any digital payment, there're lots of user-friendly applications that

就像任何數字支付一樣，有很多用戶友好的應用程序，這

let you just send and receive the currencies without thinking about what's going on.

讓您只需發送和接收貨幣，而無需考慮發生了什麼。

The difference is that the backbone underlying this

所不同的是，這個基礎的骨幹。

is not a bank that verifies transactions.

不是一家核實交易的銀行。

Instead, it's a clever system of decentralized trust-less verification

相反，它是一個聰明的去中心化的無信任驗證系統。

based on some of the math born in cryptography.

基於密碼學中誕生的一些數學。

But to start,

但要開始。

I want you to actually set aside the thought of cryptocurrencies and all that just for a few minutes.

我希望你能真正放下對加密貨幣和所有這些的想法，就幾分鐘。

We're going to begin the story with something more down-to-earth: ledgers and digital signatures.

我們要從更平實的東西開始講起：賬本和數字簽名。

If you and your friends exchange money pretty frequently,

如果你和你的朋友經常交換錢。

you know, paying your share of the dinner bill and such,

你知道，支付你的晚餐賬單等份額。

it can be inconvenient to exchange cash all the time.

一直兌換現金會很不方便。

So you might keep a communal ledger

所以，你可以保留一個公共賬本

that records all of the payments that you intend to make some point in the future.

它記錄了你在未來某個時間點上打算支付的所有款項。

You know, Alice pays Bob $20,

你知道，愛麗絲付給鮑勃20美元。

Bob pays Charlie $40, things like that.

鮑勃付給查理40美元，這樣的事情。

This ledger is going to be something public and accessible to everyone,

這個賬本將是公開的東西，每個人都可以使用。

like a website, where anyone can go and just add newlines.

就像一個網站，任何人都可以去那裡，只需添加新行。

And let's say that at the end of every month,

就說每個月月底的時候。

you all go together, look at the list of transactions and settle up.

你們一起去，看看交易清單，然後結算。

If you spent more than you received, you put that money in the pot;

如果你花的錢比你收到的多，你就把這些錢放進鍋裡。

and if you received more than you spent, you take that money out.

如果你收到的錢比你花的多，你就把這些錢拿出來。

So the protocol for being part of this very simple system might look like this:

是以，成為這個非常簡單的系統的一部分的協議可能是這樣的。

anyone can add lines to the ledger;

任何人都可以在賬本上加線。

and at the end of every month you all get together and settle up.

每個月末，你們都會聚在一起解決。

Now, one problem with a public ledger like this is that anyone can add a line,

現在，這樣的公共賬本有一個問題，就是任何人都可以增加一行。

so what's to prevent Bob from going in writing "Alice pays Bob $100" without Alice approving?

所以，什麼是防止鮑勃去寫 "愛麗絲支付鮑勃100美元 "沒有愛麗絲準許？

How are we supposed to trust that all of these transactions

我們怎麼能相信所有這些交易

are what the sender meant them to be?

是發件人的意思嗎？

Well, this is where the first bit of cryptography comes in: digital signatures.

好吧，這就是密碼學的第一點：數字簽名。

Like handwritten signatures,

像手寫的簽名。

the idea here is that Alice should be able to add something next to that transaction

這裡的想法是，Alice應該能夠在該事務旁邊添加一些東西。

that proves that she has seen it and that she's approved of it.

這證明她已經看過了，而且她也認可了。

And it should be infeasible for anyone else to forge that signature.

而其他人要偽造這個簽名應該是不可能的。

At first, it might seem like a digital signature shouldn't even be possible.

乍一看，似乎數字簽名根本就不應該存在。

I mean, whatever data makes up that signature can just be read and copied by a computer,

我的意思是，不管是什麼數據組成的簽名，都可以被電腦讀取和複製。

so how do you prevent forgeries?

那麼如何防止偽造呢？

Well, the way this works is that everyone generates what's called a "public key - private key pair",

好吧，工作方式是每個人都會生成一個所謂的 "公鑰-私鑰對"。

each of which looks like some string of bits.

每一個看起來都像一些比特的字符串。

The "private key" is sometimes also called a "secret key",

"私鑰 "有時也被稱為 "祕鑰"。

so that we can abbreviate it as "sk", while abbreviating the public key is "pk".

這樣我們就可以將其縮寫為 "sk"，而將公鑰縮寫為 "pk"。

Now as the name suggests, this secret key is something you want to keep to yourself.

現在顧名思義，這把祕鑰是你想留給自己的東西。

In the real world, your handwritten signature looks the same no matter what document you're signing.

在現實世界中，無論你簽署什麼文件，你的手寫簽名看起來都是一樣的。

But a digital signature is actually much stronger,

但數字簽名其實要強得多。

because it changes for different messages.

因為不同的資訊，它的變化。

It looks like some string of ones and zeros, commonly something like 256 bits;

它看起來像一些1和0的字符串，通常是256位的東西。

and altering the message even slightly

並稍加改變資訊

completely changes what the signature on that message should look like.

完全改變了該消息上的簽名應該是什麼樣子。

Speaking a little more formally,

說得更正式一點。

producing a signature involves a function that depends both on the message itself and on your private key.

產生簽名涉及到一個函數，這個函數既取決於資訊本身，也取決於你的私鑰。

The private key ensures that only you can produce that signature,

私鑰可以確保只有你能產生該簽名。

and the fact that it depends on the message

以及它取決於資訊的事實

means that no one can just copy one of your signatures and then forge it on another message.

意味著沒有人可以複製你的一個簽名，然後在另一條資訊上偽造。

Hand-in-hand with this is a second function used to verify that a signature is valid.

與此相配合的是第二個用於驗證簽名是否有效的函數。

And this is where the public key comes into play.

而這就是公鑰的作用。

All it does is output "true" or "false"

它所做的就是輸出 "真 "或 "假"

to indicate if this was a signature produced by the private key

來表明這是否是由私鑰產生的簽名

associated with the public key that you're using for verification.

與你用於驗證的公鑰相關聯。

I won't go into the details of how exactly both these functions work,

這兩個功能的具體工作原理我就不多說了。

but the idea is that it should be completely infeasible to find a valid signature

但這個想法是，它應該是完全不可能找到一個有效的簽名。

if you don't know the secret key.

如果你不知道祕鑰。

Specifically, there's no strategy better than just guessing and checking random signatures,

具體來說，沒有什麼策略比只猜測和檢查隨機簽名更好。

which you can check using the public key that everyone knows.

你可以用大家都知道的公鑰來檢查。

Now think about how many signatures there are with a length of 256 bits,

現在想想有多少個長度為256位的簽名。

that's 2^256.

那是2^256。

This is a stupidly large number.

這是個愚蠢的數字。

To call it astronomically large would be giving way too much credit to astronomy.

如果說它是天文上的大，那就是給天文學的功勞太大了。

In fact, I made a supplemental video devoted just to illustrating what a huge number this is.

事實上，我專門做了一個補充視頻，就是為了說明這是一個多麼龐大的數字。

Right here, let's just say that

在這裡，我們只想說

when you verified that a signature against a given message is valid,

當您驗證了針對某條資訊的簽名是有效的。

you can feel extremely confident that the only way someone could have produced it

你可以非常自信地認為，唯一的辦法就是有人能製作出來

is if they knew the secret key associated with the public key you used for verification.

是如果他們知道與你用於驗證的公鑰相關的祕鑰。

Now making sure that people sign transactions on the ledger is pretty good,

現在確保人們在臺賬上籤署交易是相當不錯的。

but there's one slight loophole:

但有一個小小的漏洞。

if Alice signs a transaction, like "Alice pays Bob $100",

如果愛麗絲簽署了一項交易，比如 "愛麗絲支付鮑勃100美元"。

even though Bob can't forge Alice's signature on a new message,

即使鮑勃無法在新的資訊上偽造愛麗絲的簽名。

he could just copy that same line as many times as he wants.

他可以複製同一行，只要他願意。

I mean, that message-signature combination remains valid.

我的意思是，這個消息和簽名的組合仍然有效。

To get around this, what we do is make it so that when you sign a transaction,

為了解決這個問題，我們要做的是讓你在簽署交易時，。

the message has to also include some sort of unique ID associated with that transaction.

該消息還必須包含某種與該交易相關聯的唯一ID。

That way, if Alice pays Bob $100 multiple times,

這樣一來，如果愛麗絲多次付給鮑勃100美元。

each one of those lines on the ledger requires a completely new signature.

賬本上的每一行都需要一個全新的簽名。

All right, great!

好吧，太好了！

Digital signatures remove a huge aspect of trust in this initial protocol,

數字簽名消除了這個初始協議中信任的一個巨大方面。

but even still, if you were to really do this,

但即使如此，如果你真的要這樣做。

you would be relying on an honor system of sorts.

你會依靠榮譽系統的種類。

Namely, you're trusting that everyone will actually follow through

也就是你相信大家會真正的貫徹執行。

and settle up in cash at the end of each month.

並在每月月底以現金結算。

What if, for example, Charlie racks up thousands of dollars in debt

比如說，查理欠了幾千塊錢的債，怎麼辦？

and just refuses to show up.

而只是拒絕出現。

The only real reason to revert back to cash to settle up

唯一真正的理由是恢復到現金來結算。

is if some people (I'm looking at you, Charlie) owe a lot of money.

是如果有些人（我看著你，查理）欠了很多錢。

So maybe, you have the clever idea that you never actually have to settle up in cash,

所以，也許，你有聰明的想法，你永遠不會真正的用現金結算。

as long as you have some way to prevent people from spending too much more than they take in.

只要你有一些方法來防止人們花的錢比他們的收入多得多。

Maybe what you do is start by having everyone pay $100 into the pot,

也許你要做的是先讓每個人都交100元錢到鍋裡。

and then have the first few lines of the ledger read

然後讓賬簿的前幾行改為

"Alice gets $100", "Bob gets $100", "Charlie gets $100", etc.

"愛麗絲得到100美元"、"鮑勃得到100美元"、"查理得到100美元 "等。

Now, just don't accept any transactions

現在，只要不接受任何交易

where someone is spending more than they already have on that ledger.

有人在該賬目上的花費超過了他們已經擁有的資金。

For example, if the first two transactions are

例如，如果前兩個交易是

"Charlie pays Alice $50" and "Charlie pays Bob $50",

"查理國愛麗絲50美元 "和 "查理國鮑勃50美元"。

if he were to try to add "Charlie pays you $20", that would be invalid,

如果他想加上 "查理付給你20美元"，那就無效了。

as invalid as if he had never signed it.

就像他從未簽署過一樣無效。

Notice, this means that verifying a transaction

注意，這意味著驗證一個交易

requires knowing the full history of transactions up to that point.

需要知道截至該點的全部交易歷史。

And this is more or less also going to be true in cryptocurrencies,

而這一點在加密貨幣中或多或少也會出現。

though there is a little room for optimization.

雖然還有一點優化空間。

What's interesting here is that

有趣的是

this step removes the connection between the ledger and actual physical US Dollars.

這一步消除了分類賬和實際實物美元之間的聯繫。

In theory, if everyone in the world was using this ledger,

理論上，如果世界上每個人都在使用這個賬本。

you could live your whole life just sending and receiving money on this ledger

你可以用這個賬本收發錢財過一輩子

without ever having to convert to real US Dollars.

無需兌換成真正的美元。

In fact, to emphasize this point,

其實，為了強調這一點。

let's start referring to the quantities on the ledger as "ledger dollars", or "LD" for short.

讓我們開始把分類賬上的數量稱為 "分類賬美元"，簡稱 "LD"。

You are, of course, free to exchange ledger dollars for real US Dollars.

當然，你可以自由地把賬本上的美元換成真正的美元。

For example, maybe Alice gives Bob a $10 bill in the real world

例如，也許愛麗絲在現實世界中給了鮑勃一張10美元的鈔票。

in exchange for him adding and signing the transaction

作為交換，他增加和簽署交易

"Bob pays Alice 10 LD" to this communal ledger.

"鮑勃向愛麗絲支付了10 LD "到這個公共賬本。

But exchanges like that, they're not going to be guaranteed by the protocol.

但像這樣的交流，是不會有協議保證的。

It's now more analogous to how you might exchange dollars for Euros,

現在更類似於你用美元兌換歐元的方式。

or any other currency on the open market,

或公開市場上的任何其他貨幣。

it's just its own independent thing.

它只是它自己獨立的東西。

This is the first important thing to understand about Bitcoin or any other cryptocurrency:

這是瞭解比特幣或其他加密貨幣的第一件重要事情。

what it is is a ledger, the history of transactions is the currency.

它是什麼是一個賬本，交易的歷史是貨幣。

Of course, with Bitcoin,

當然，隨著比特幣。

money doesn't enter the ledger with people buying in using cash.

人們用現金買進的錢是不會進入賬本的。

I'll get to how new money enters the ledger in just a few minutes,

我一會兒就會講到新的錢是如何進入賬本的。

but before that, there's actually an even more significant difference

但在這之前，其實還有一個更顯著的區別就是

between our current system of ledger dollars and how cryptocurrencies work.

我們目前的賬本美元系統和加密貨幣的工作方式之間。

So far, I've said that this ledger is in some public place,

到目前為止，我已經說過，這個賬本是在某個公共場所。

like a website, where anyone can add newlines.

就像一個網站，任何人都可以添加新行。

But that would require trusting a central location,

但這就需要相信一箇中心位置。

namely "who hosts the website?",

即 "誰來主持網站？"。

"who controls the rules of adding new lines?".

"誰來控制增加新線路的規則？"。

To remove that bit of trust, we'll have everybody keep their own copy of the ledger.

為了消除這一點信任，我們會讓每個人都保留自己的賬本。

Then when you want to make a transaction, like Alice pays Bob 100 LD,

然後當你想進行交易時，比如愛麗絲支付給鮑勃100LD。

what you do is broadcast that out into the world

你要做的是把它廣播到世界上

for people to hear and to record on their own private ledgers.

讓人們聽到，並記錄在自己的私人賬本上。

But, unless you do something more, this system is absurdly bad.

但是，除非你再做一些事情，否則這個制度是荒謬的壞事。

How could you get everyone to agree on what the right ledger is?

你怎麼能讓大家都同意什麼是正確的賬本呢？

When Bob receives a transaction, like Alice pays Bob 10 LD,

當鮑勃收到一筆交易時，比如愛麗絲支付給鮑勃10LD。

how can he be sure that everyone else received and believes that same transaction

他怎麼能確定其他人都收到了同樣的交易，並且相信了同樣的交易

that he'll be able to later on go to Charlie and use those same 10 LD to make a transaction?

他以後就可以去找查理，用那10個LD做交易？

Really, imagine yourself just listening to transactions being broadcast,

真的，想象一下自己只是在聽交易的廣播。

how can you be sure that everyone else is recording the same transactions and in the same order?

你怎麼能確定其他人都是以同樣的順序記錄同樣的交易呢？

This is really the heart of the issue.

這確實是問題的核心。

This is an interesting puzzle.

這是個有趣的謎題。

Can you come up with a protocol for how to accept or reject transactions

你能不能想出一個接受或拒絕交易的協議？

and in what order so that you can feel confident that

順序是怎樣的，這樣你就可以放心了。

anyone else in the world who's following that same protocol

世上還有誰在遵循同樣的協議？

has a personal ledger that looks the same as yours?

有一個個人賬本，看起來和你的一樣嗎？

This is the problem addressed in the original Bitcoin paper.

這就是比特幣原論文中解決的問題。

At a high level, the solution that Bitcoin offers is

在高層次上，比特幣提供的解決方案是

to trust whichever ledger has the most computational work put into it.

相信哪一個賬本的計算量最大。

I'll take a moment to explain exactly what that means,

我花點時間解釋一下這到底是什麼意思。

it involves this thing called a "cryptographic hash function".

這涉及到一個叫做 "加密哈希函數 "的東西。

The general idea that we'll build to

總的思路是，我們將建立到

is that if you use computational work as a basis for what to trust,

是，如果你把計算工作作為信任的基礎。

you can make it so that fraudulent transactions and conflicting ledgers

你可以使它，以便欺詐性交易和衝突的分類帳。

would require an infeasible amount of computation to bring about.

這將需要不可估量的計算量才能實現。

Again, I'll remind you that this is getting well into the weeds

我再次提醒你，這已經進入了雜草叢生的階段

beyond what anyone would need to know just to use a currency like this,

超越了任何人需要知道的只是使用這樣的貨幣。

but it's a really cool idea!