256位加密到底有多安全？：英语精读讲义

In the main video on cryptocurrencies,

在关于加密货币的主视频中，

I made two references to situations

我两次提到了某些情况：

where, in order to break a given piece of security, 語法

为了破解某项安全机制，

you would have to guess a specific string of 256 bits. 語法

你必须猜出一串特定的 256 位字符串。

One of these was in the context of digital signatures 短語搭配

其中一次是在数字签名的背景下提到的，

and the other in the context of a cryptographic hash function.

另一次则是在密码学哈希函数的背景下。

For example, if you want to find a message 語法

举个例子，如果你想找一条消息，

whose SHA-256 hash is some specific string of 256 bits,

它的 SHA-256 哈希值是某串特定的 256 位字符串，

you have no better method than to just guess and check random messages. 語法

除了随机盲猜并验证消息之外，你没有更好的方法。

And this would require, on average, 短語搭配

这平均需要进行

2 to the 256 guesses.

2 的 256 次方次猜测。

Now, this is a number so far removed from anything 語法

那么，这个数字与我们

that we ever deal with that it can be hard to appreciate its size.

平时接触的任何事物都相差甚远，以至于很难体会它有多大。

But let's give it a try. 短語搭配

但我们不妨试一试。

2 to the 256 is the same as 2 to the 32

2 的 256 次方等于 2 的 32 次方

multiplied by itself eight times.

连续自乘八次。

Now, what's nice about that split is that 2 to the 32 is 4 billion, 語法

这种拆分的好处在于，2 的 32 次方大约是 40 亿，

which is at least a number we can think about,

这至少是一个我们能想象出的数字，

right? It's the kind of thing you might see in a headline.

对吧？这是你可能会在新闻标题里看到的那种数字。

So, all we need to do is appreciate what 語法

所以，我们只需要去体会

multiplying 4 billion times itself

将 40 亿与自身相乘

eight successive times really feels like.

连续乘八次到底是什么感觉。

As many of you know,

你们中的许多人都知道，

the GPU on your computer can let you run a whole bunch of computations 用詞

你电脑里的 GPU 可以让你

in parallel, incredibly quickly.

以极快的速度并行执行大量的计算。

So, if you were to specially program a GPU to run a cryptographic hash function over and over, 講解

因此，如果你专门为 GPU 编程，让它不断运行某个密码学哈希函数，

a really good one might be able to do a little less than a billion hashes per second.

一块非常好的 GPU 每秒大概能进行略少于 10 亿次的哈希运算。

And let's say that you just take a bunch of those and 表達脈絡

假设你弄来一大堆这样的 GPU，然后

cram your computer full of extra GPUs 短語搭配

把你的电脑塞满额外的 GPU，

so that your computer can run 4 billion hashes per second.

让你的电脑每秒能运行 40 亿次哈希运算。

So, the first 4 billion here is going to represent

那么，这里的第一个 40 亿代表着

the number of hashes per second per computer.

每台电脑每秒钟进行哈希运算的次数。

Now, picture 4 billion of these GPU-packed computers.

现在，想象有 40 亿台这种装满 GPU 的电脑。

For comparison, 表達脈絡

作为对比，

even though Google does not at all make their number of servers public,

尽管 Google 完全没有公开他们的服务器数量，

estimates have it somewhere in the single-digit millions. 語法

但据估计大约在几百万台左右。

In reality, most of those servers are going to be much less powerful than our imagined GPU-packed machine.

实际上，大部分服务器的性能远不及我们想象中装满 GPU 的机器。

But let's say that Google replaced all of its millions of servers with a machine like this, 短語搭配

但假设 Google 把其数以百万计的服务器全换成这样的机器，

then 4 billion machines would mean about a thousand copies of this souped-up Google. 用詞

那么 40 亿台机器就相当于大约 1000 个这样升级版 Google 的规模。

Let's call that 1 kilo-Google worth of computing power. 講解

让我们把这种算力称为 1 kilo-Google（千个谷歌）。

There's about 7.3 billion people on Earth.

地球上大约有 73 亿人口。

So, next, imagine giving a little over half of every individual on Earth

接下来，想象一下，把这种算力分给地球上一半多一点的人，

their own personal kilo-Google.

让他们每个人都拥有自己的个人 kilo-Google。

Now, imagine 4 billion copies of this Earth.

现在，再想象有 40 亿个这样的地球。

For comparison,

作为对比，

the Milky Way has somewhere between 100 and 400 billion stars.

银河系大约有 1000 亿到 4000 亿颗恒星。

We don't really know,

我们其实并不确定，

but the estimates tend to be in that range. 短語搭配

但估计值往往都在这个范围内。

So, this would be akin to a full 1% of every star in the galaxy 用詞

所以，这就类似于银河系中整整 1% 的恒星

having a copy of Earth

都拥有一个地球的复制体，

where half the people on that Earth

而在那个地球上，有一半的人

have their own personal kilo-Google.

都拥有自己的个人 kilo-Google。

Next, try to imagine 4 billion copies of the Milky Way.

接下来，试着想象有 40 亿个银河系。

And we're going to call this

我们把这称为

your giga-galactic supercomputer running about 2 to the 160 guesses every second.

你的十亿星系级超级计算机，它每秒大约能进行 2 的 160 次方次猜测。

Now, 4 billion seconds,

接下来，是 40 亿秒，

that's about 126.8 years.

那大约是 126.8 年。

4 billion of those,

再乘上 40 亿个 126.8 年，

well, that's 507 billion years,

嗯，那是 5070 亿年，

which is about 37 times the age of the universe.

这大约是宇宙年龄的 37 倍。

So, even if you were to have your GPU-packed kilo Google per person 語法

所以，即使你拥有这种“每人一个 kilo-Google 的满载 GPU、

multi-planetary giga-galactic computer guessing numbers for 37 times the age of the universe,

跨越无数行星的十亿星系级计算机”，让它去猜数字，猜上宇宙年龄 37 倍的时间，

it would still only have a 1 in 4 billion chance 短語搭配

它仍然只有 40 亿分之一的机会

of finding the correct guess.

能得出正确的猜测。

By the way,

顺便说一下，

the state of Bitcoin hashing these days is that all of the miners put together 講解

如今比特币哈希运算的现状是，所有矿工加在一起，

guess and check at a rate of about 5 billion billion hashes per second. 短語搭配

其盲猜验证的速率大约是每秒 500 亿亿（5 billion billion）次哈希运算。

That corresponds to 1/3 of what I just described as a kilo-Google. 短語搭配

这相当于我刚才描述的一个 kilo-Google 算力的三分之一。

This is not because there are actually billions of GPU-packed machines out there, 語法

这并不是因为外面真的有几十亿台装满 GPU 的机器，

but because miners actually use something that's about a thousand times better than a GPU.

而是因为矿工们实际上使用的一种设备，比 GPU 要强上一千倍左右。

Application-specific integrated circuits. 文化背景

专用集成电路（ASIC）。

These are pieces of hardware specifically designed for Bitcoin mining,

这些是专门为挖掘比特币而设计的硬件，

for running a bunch of SHA-256 hashes and nothing else.

除了运行大量 SHA-256 哈希运算外什么也做不了。

Turns out, there's a lot of efficiency gains to be had 講解

事实证明，这能带来极大的效率提升——

when you throw out the need for general computation 短語動詞

当你抛开通用计算的需求，

and design your integrated circuits for one and only one task.

将你的集成电路设计成只专注于唯一一项任务时。

Also, on the topic of large powers of 2 表達脈絡

另外，关于这种大到

that I personally find it hard to get my mind around, 習語

我个人都觉得难以理解的 2 的大次方问题，

this channel recently surpassed 2 to the 18th subscribers.

这个频道最近订阅数突破了 2 的 18 次方。

And to engage a little more with some sub-portion of those 2 to the 18 people,

为了能和这 2 的 18 次方人中的一部分有更多互动，

I'm going to do a Q&A session.

我打算办一场 Q&A 问答环节。

I've left a link in the description to a Reddit thread

我在描述区里留了一个 Reddit 帖子的链接，

where you can post questions and upvote the ones that you want to hear answers to. 文化背景

你可以在那里发布问题，并为你想要听到回答的问题点赞。

And probably in the next video or on Twitter or something like that, 語氣意圖

大概在下一个视频里，或者在 Twitter 等平台上，

I'll announce the format in which I'd like to give answers. 語法

我会宣布我希望以何种形式来回答这些问题。

See you then.

到时候见。