现在 有一种价值数百美元的货币 但它不是
Say there’s a coin that’s currently worth hundreds of U.S. dollars, but it’s not made
of gold, or platinum, or any precious metal.
In fact, it’s not the kind of coin you can hold in your hand or stick in a piggy bank.
It’s a digital currency, which means it only exists electronically.
I’m talking about bitcoin.
Bitcoin doesn’t work like most money.
It isn’t attached to a state or government, so it doesn’t have a central issuing authority
or regulatory body.
Basically, that means there’s no organization deciding when to make more bitcoins, figuring
制造多少 记录它们在哪儿 或是调查诈骗
out how many to produce, keeping track of where they are, or investigating fraud.
So how does bitcoin work as a currency, or have any value at all?
Well, bitcoin wouldn’t exist without a whole network of people and a little thing called
In fact, it’s sometimes described as the world’s first cryptocurrency.
And here’s how it works.
Bitcoin is a fully digital currency, and you can exchange bitcoins between computers in
a worldwide peer-to-peer network.
The whole point of most peer-to-peer networks is sharing stuff, like letting people make
copies of super legal music or movies to download.
If bitcoin is a digital currency, what’s stopping you from making a bunch of counterfeit
copies and becoming fabulously wealthy?
Well, unlike a mp3 or a video file, a bitcoin isn’t a string of data that can be duplicated.
A bitcoin is actually an entry on a huge, global ledger called the blockchain, for reasons
we’ll get to in a minute.
The blockchain records every bitcoin transaction that has ever happened.
And, as of late 2016, the complete ledger is about 107 gigabytes of data.
So when you send someone bitcoins, it’s not like you’re sending them a bunch of
Instead, you’re basically writing the exchange down on that big ledger – something like,
“Michael sends Hank 5 bitcoins.”
现在 也许你正在想 “但是 等等
Now, maybe you’re thinking, “But, wait.
You said bitcoin doesn’t have a central authority to keep track of everything!”
Even though the blockchain is a central record, there’s no official group of people who
update the ledger and keep track of everybody’s money like a bank does – it’s decentralized.
In fact, anybody can volunteer to keep the blockchain up to date with all the new transactions.
And a ton of people do.
It all works because there are lots of people keeping track of the same thing, to make sure
all transactions are accurate.
比如 想象你正在和朋友们玩扑克 但是没有人有筹码
Like, imagine you’re playing a game of poker with some pals, but none of you have poker
chips, and you left your cash at home.
There’s no money on the table, so a few of you get out some notebooks, and start writing
开始写下谁下了多少赌注 谁赢了 谁输了
down who bets how much, who wins, and who loses.
You don’t completely trust anyone else, so everyone keeps their ledgers separately.
And at the end of every hand, you all compare what you’ve written down.
这样的话 如果有人犯错 或是试图作弊得到额外的钱
That way, if someone makes a mistake, or tries to cheat and snag some extra money for themselves,
that discrepancy is caught.
几局之后 关于资金流动的记录 你也许写满了
After a couple hands, you might fill up a page of your notebook with notes about the
You can think of each page as a “block of transactions.”
Eventually, your notebook will have pages and pages of information – a chain of those
Now, if thousands of people are separately maintaining the bitcoin blockchain, how are
all the ledgers kept in sync?
To stick with our poker analogy: think of the entire bitcoin peer-to-peer network as
a really huge poker table with millions of people.
Some are just exchanging money, but lots of volunteers are keeping ledgers.
So when you want to send or receive money, you have to announce it to everyone at the
table, so the people keeping track can update their ledgers.
So for every transaction, you’re announcing a couple of things to the bitcoin network:
你的账号 交易对象的账号 以及
your account number, the account number of the person you’re sending bitcoins to, and
how many bitcoins you want to send.
And all of the users who are keeping copies of the blockchain will add your transaction
to the current block.
Having a bunch of people keep track of transactions seems like a pretty good security measure.
But if all it takes to send bitcoins is a couple of account numbers, that seems like
it might be a security problem.
It’s a huge problem with regular money – just think about all the ways criminals try to
steal other people’s credit card information.
And with bitcoin, there’s no central bank to notice anything weird going on to shut
down fraud, like if it looked like suddenly you spent your entire life savings on beef
So what’s stopping Hank from pretending he’s me and just sending himself all of
因为密码学 比特币是相当安全的 这也是为什么它被认为是一种加密货币
Bitcoins are kept pretty safe thanks to cryptography, which is why it’s considered a cryptocurrency.
Specifically, bitcoin stays secure because of keys, which are basically chunks of information
能被用来加密消息 如“嘿 这真的
that can be used to make mathematical guarantees about messages, like “hey, this is really
When you create an account on the bitcoin network, which you might have heard called
“钱包” 那个账户链接两个独特的密钥：一个是私钥 一个
a “wallet,” that account is linked to two unique keys: a private key, and a public
In this case, the private key can take some data and basically mark it, also known as
signing it, so that other people can verify those signatures later if they want.
So let’s say I want to send a message to the network that says, “Michael sends 3
bitcoins to Olivia.”
I sign that message using my private key, which only I have access to, and nobody else
Then, I send that signed message out to the bitcoin network, and everyone can use my public
key to make sure my signature checks out.
That way, everyone keeping track of all the bitcoin trading knows to add my transaction
to their copy of the blockchain.
也就是说 如果公钥生效了 就证明那条消息用我的私钥签名的
In other words, if the public key works, that’s proof that the message was signed by my private
key and is something I wanted to send.
不像手写的签名 或是信用卡卡号 这个身份证明不能
Unlike a handwritten signature, or a credit card number, this proof of identity isn’t
something that can be faked by a scam artist.
The “who” part of each transaction is obviously important, to make sure the right
people are swapping bitcoins.
But the “when” matters, as well.
举个例子 如果你的银行账户里有一千美元 然后想要买两个
If you had a thousand dollars in your bank account, for example, and tried to buy two
things for a thousand dollars each, the bank would honor the first purchase and deny the
If the bank didn’t do that, you’d be able to spend the same money multiple times.
Which … might sound awesome, but it’s also terrible.
A financial system can’t work like that, because no one would get paid.
So if I only have enough money to pay Olivia or Hank, but I try to pay them both, there’s
a check built into the bitcoin system.
Both the bitcoin network and your wallet automatically check your previous transactions to make sure
you have enough bitcoins to send in the first place.
But there’s another problem that might happen with timing:
Because lots of people are keeping copies of the blockchain all over the world, network
delays mean that you won’t always receive the transaction requests in the same order.
So now you’ve got a bunch of people with a bunch of slightly different blocks to pick
from, but none of them are necessarily wrong.
How do you solve that problem?
Turns out, it’s by actually solving problems.
To add a block of transactions to the chain, each person maintaining a ledger has to solve
a special kind of math problem created by a cryptographic hash function.
A hash function is an algorithm that takes an input of any size, and turns it into an
output with a fixed size.
For example, let’s say you had this string of numbers as your input
And our example hash function says to add all of the numbers together.
所以 这样的话 输出结果就是10
So, in this case, the output would be 10.
What makes hash functions really good for cryptography is that when you’re given an
input, it’s really easy to find the output.
But it’s really hard to take an output and figure out the original input.
Even in this super simple example, there are lots of strings of numbers that add up to
The only way to figure out that the input was ‘1-2-3-4’ is to just guess until you
get it right.
如今 比特币使用的哈希函数被叫做SHA256 代表
Now, the hash function that bitcoin uses is called SHA256, which stands for Secure Hash
And it was originally developed by the United States National Security Agency.
Computers that were specifically designed to solve SHA256 hash problems take, on average,
about ten minutes to guess the solution to each one.
That means they’re churning through billions and billions of guesses before they get it
Whoever solves the hash first gets to add the next block of transactions to the blockchain,
which then generates a new math problem that needs to be solved.
If multiple people make blocks at roughly the same time, then the network picks one
to keep building upon, which becomes the longest, and most trusted chain.
And any transactions in those alternate branches of the chain get put back into a pool to be
added onto later blocks.
These volunteers spend thousands of dollars on special computers built to solve SHA256
problems, and run their electricity bills up sky high to keep those machines running.
What do they get out of maintaining the blockchain?
Is it just community service?
Well, bitcoin actually has a built-in system to reward them.
现在 每次你成功把一个区块加到区块链中 就会凭空产生12.5个新比特币
Today, every time you win the race to add a block to the blockchain, 12 and a half new
bitcoins are created out of thin air, and awarded to your account.
In fact, you might know the bitcoin ledger-keepers by another name: miners.
That’s because keeping the blockchain updated is like swinging a proverbial pickaxe at those
hash problems, hoping to strike it rich.
When bitcoins were first created in 2009, they didn’t really have any perceived value.
Tens of bitcoins would have been worth the same as a bunch of pennies.
As of November 10th, 2016, though, one bitcoin is worth 708 US dollars.
So 12 and a half bitcoins are worth 8,850 dollars.
That’s a nice chunk of change!
Every single bitcoin that exists was created to reward a bitcoin miner.
除了巨额支出 当他们增加新区块的交易 矿工们基本上
Besides the big payout when they add a new block of transactions, miners are also essentially
tipped a very small amount for each transaction they add to the ledger.
值得注意的是每产生21万区块后 增加一个新的区块 比特币的数目
It’s also worth noting that every 210,000 blocks, the number of coins generated when
a new block is added goes down by half.
所以一开始奖励50比特币 然后降到25 然后降到12.5
So what started as a reward of 50 bitcoins decreased to 25, then 12 and a half.
It’ll only be around 6 bitcoins in a couple more years, and keep decreasing.
最终 一个区块里有足够多的交易 仍然值得矿工们
Eventually, there will be so many transactions in a block, that it’ll still be worthwhile
for miners to mostly be paid in tips.
According to current projections, the last bitcoin – probably around the 21 millionth
coin – will be mined in the year 2140.
This decreasing number of bitcoins is actually modelled off the rate at which things like
gold are dug out of the earth.
And the idea is that keeping the supply of bitcoins limited will raise their value over
So, is investing in bitcoin a good idea?
Now that’s… not really a SciShow kind of question.
Bitcoin is still volatile, and experimental.
A lot of people love it, and a lot of people think it’s doomed to fail.
We just think it’s an interesting idea, and it makes us wonder what cryptography might
do for us next.
Thanks for watching this episode of SciShow, brought to you by our patrons on Patreon.
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现在 有一种价值数百美元的货币 但它不是