# Detailed explanation of information abstract, digital signature, digital certificate, symmetric encryption and asymmetric encryption

2022-04-23 16:40:55 GokuCode

# The information in this paper, 、 digital signature 、 digital certificate 、 Symmetric encryption and asymmetric encryption

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## 1. Problem description

1. The information in this paper, 、 digital certificate 、 What is the use of symmetric encryption and asymmetric encryption , Why do you need these .

## 2. Problem solving

Let's use a small example to illustrate .
Three characters ： the Red Army 1、 the Red Army 2、 Blue army
Scenario description ： the Red Army 1 To the Red Army 2 Send a message saying to launch an attack , With the sending scenario .
scene 1： Plaintext transmission information
At first , The Red Army did not realize the importance of information security , So direct plaintext transmission of information . therefore , It was soon acquired by the Blues , Then the red army fought and lost again and again .
You can see that if the blue army intercepts intelligence , You can immediately see what the content is , Because the red army uses clear text transmission .

scene 2： Symmetric encryption
Symmetric encryption ： Use key A encryption , Decryption also uses A The key is symmetric encryption . Specific details can be searched by yourself .
Then tell the story , After the Red Army found that it was intercepted by the blue army , Prepare to use symmetric encryption . So the key is used A. As a result, the key was monitored during transmission . The blues got the key A.

scene 3: Use asymmetric encryption
Asymmetric encryption ： Use public key encryption （ In fact, it's not called encryption , Because it's a public key , So it's an open secret , So it's called signature , That is, digital signature ）, Only the private key can be decrypted , Similarly, using the private key to encrypt , Only public key decryption can be used .
Realization principle ：
the Red Army 1: Private key a1 Public key a2
the Red Army 2: Private key b1 Public key b2
The Red Army wanted to ： Even if the blues get information encrypted with a public key , It can't be cracked , Because it has no private key . The Blues... But they don't , It can do this ：
The blues know and make their own Private key w1 Public key w2. So there was a situation .
The Blues have become middlemen , There will be such a process of sending messages

`````` the Red Army 1： Use w2 Encrypted messages
Blue army ： After receiving the message, use w1 Decrypt
Use b2 The encrypted message is sent to the user 2
the Red Army 2： Received and used b1 Decrypt
The middle Red Army 12 No problem , The blue army can also get information .
``````

scene 4: Using digital certificates

The Red Army found a blue middleman , So we need to improve the encryption method , In order to let the other party know that the public key is his own , The public key cannot be tampered with , So digital certificates are used . the Red Army 1 Certificate used , Certificate information mainly includes the following contents ：

`````` Digital certificate version ：1.0
name ： the Red Army 1
Belongs to ： World War II
only id:xxxxa1
Public key ：a1
Detailed introduction ： The army is xxxx Omit here 1 swastika
Certificate size ：100M
``````

But to the Red Army 2, Not yet. , Because of this, if some part of the certificate, especially the public key, is tampered with , What if it's forged by the blue army . Still can't prove . Then you need to use encryption to ensure that the data is not tampered with . Use md5 To encrypt , If one content is changed , that md5 The value will also change .

`````` Digital certificate version ：1.0
name ： the Red Army 1
Belongs to ： World War II
only id:xxxxa1
Public key ：a1
Detailed introduction ： The army is xxxx Omit here 1 ten thousand
Certificate size ：100M
Yes 100M After data encryption ：xjajaksd89as7df89asdf67asd78a7ds
``````

For the above encryption , the Red Army 1 Find out , The encrypted content is too long , A certificate 1 More than ten thousand words , It takes half an hour to complete the encryption . Too slow , Can you put forward some important , To encrypt , Improve encryption speed . So there was The information in this paper, , We propose to use the private key to sign hundreds of words, that is, digital signature , It's like an abstract in a paper , As long as we read a few hundred word abstract, we will know what this paper is about .
So this also needs the algorithm of information summary extraction （ Interested in self searching ）
The encrypted content becomes smaller , Encryption speed is also fast . It can also ensure data integrity

`````` Digital certificate version ：1.0
name ： the Red Army 1
Belongs to ： World War II
only id:xxxxa1
Public key ：a2
Detailed introduction ： The army is xxxx Omit here 1 ten thousand
Certificate size ：100M
The information in this paper, ：1kb
the Red Army 1 Use the private key pair 1kb Data signature ：xjajaksd89as7df89asdf67asd78a7ds
``````

But to prove this certificate is the Red Army 1 Yes or no , Because if the middle is modified by the Blues , the Red Army 2 I can't find out .

`````` Digital certificate version ：1.0
name ： the Red Army 1
Belongs to ： World War II
only id:xxxxa1
The blue army modified the public key ：w2  <---------------- The blues moved their hands and feet
Detailed introduction ： The army is xxxx Omit here 1 ten thousand
Certificate size ：100M
The information in this paper, ：1kb
Blue army private key re signature ：xwwwwksd8wwdf89asdf67asd78a7ds  <---------------- The blues moved their hands and feet
``````

To the Red Army 2, the Red Army 2 I can't find out .
This is the time , The Red Army is going to find the headquarters . Everyone at headquarters has a public key , Can be obtained from the Red Army Headquarters . That is, the Red Army 2 The headquarters knows in advance z2
So the Red Army 1 Give the certificate to the headquarters , The headquarters signs with its own private key

`````` Digital certificate version ：1.0
name ： the Red Army 1
Belongs to ： World War II
only id:xxxxa1
the Red Army 1 Public key ：a2
Detailed introduction ： The army is xxxx Omit here 1 ten thousand
Certificate size ：100M
The information in this paper, ：1kb
``````

This is the time , Even if the blues get it, they can't modify it , Because the Red Army 2 There is a public key of the headquarters , If the information is modified , The Blues have no headquarters , So I can't sign , Even if you sign , Public key z2 Can't decrypt the signature , So the Red Army 2 It can be said that this is not the Red Army 1 Certificate

The general picture

## 3. reminder , See you in the comment area if you have any questions

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