Asymmetric encryption
Cyber security Lesson 10 2:08 English narration · English + 中文 subtitles burned in
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Transcript
Last lesson ended on a problem: you must share the secret key first.
上一课停在一个问题上：你必须先把密钥交出去。
Asymmetric encryption answers it by using two keys instead of one.
非对称加密的回答，是用两把密钥而不是一把。
There is a public key, which you hand to anyone, and it only locks.
有一把公钥，你可以给任何人，它只能上锁。
And there is a private key, which stays with you, and it is the only thing that unlocks.
还有一把私钥，它留在你手上，而且它是唯一能开锁的东西。
Symmetric encryption needed you to share a secret first; this pair does not.
对称加密要求你先共享一个秘密；这一对密钥不需要。
Picture the public key as an open padlock.
把公钥想象成一把开着的挂锁。
You hand it out — there it goes, to anyone who wants one.
你把它发出去——它就这样递到了任何想要的人手上。
Now anyone can lock a message shut with it and send it back to you, and only your private key, which never moved, can open it.
现在谁都能用它把一条消息锁死再寄回给你， 而只有你那把从未动过的私钥能打开它。
Nothing secret ever travelled.
没有任何秘密曾经上路。
That is the breakthrough.
这就是那个突破。
R S A is real asymmetric encryption, and with tiny numbers you can watch it work.
RSA 是真实的非对称加密，用很小的数字你就能看着它跑一遍。
The public key is three and thirty-three; the private key is seven and thirty-three.
公钥是 3 和 33；私钥是 7 和 33。
Lock the number seven with the public key, then unlock the result with the private one.
用公钥把数字 7 锁起来，再用私钥把结果解开。
Two different numbers were used, and the seven comes back.
用的是两个不同的数字，而 7 回来了。
And you rely on this constantly without noticing.
而你一直在依赖它，只是没注意。
Every time you see H T T P S, asymmetric encryption is quietly setting up a secure connection.
每次你看到 HTTPS，非对称加密都在悄悄地建立一条安全连接。
It also runs in reverse, to prove who sent something — that is a digital signature.
它还能反过来用，去证明某样东西是谁发的——那就是数字签名。
Your phone uses the same idea to check that an update really came from its maker.
你的手机用同样的想法，来核实一个更新真的来自厂商。
The next lesson builds signatures out of hashing and this key pair.
下一课会用哈希和这一对密钥，把签名搭出来。
Four things to take with you.
带走四点。
One: asymmetric encryption uses a pair of keys.
第一：非对称加密用的是一对密钥。
Two: the public key locks, so give it to everyone.
第二：公钥负责上锁，所以尽管发给所有人。
Three: only the private key unlocks, so never share it.
第三：只有私钥能解锁，所以绝不要外传。
Four: this is how H T T P S avoids sharing a secret first.
第四：HTTPS 就是这样避开"先共享一个秘密"的。
Now run the tiny R S A in the task below.
现在去下面的题里把那个小小的 RSA 跑一遍。