Base64 coding can be understood this way

Worked as a programmer for four years , Frequently used Base64 code , But why use , And how it works , It has always been without understanding . I saw it in a book recently Base64 The coding principle of , It turned out to be so simple .

Base64 What problems have been solved

If we want to transmit the following problems in the network

 Hello    Children   I'm brick family   who are you ？ 

This text contains spaces 、 Line break 、 Invisible characters such as carriage return , In network transmission , Each device may have different processing mechanisms for invisible characters , There will be information transmission errors . At this point, we need a coding mechanism , Turn all invisible characters into visible characters .

Base64 Coding principle

Next, we will pass  abcd Two words turn into Base64 code , To understand its principle .

1. Group the characters into three groups , Not enough time to pass 0 A filling . such as  abc Three characters in a group ,d  Not enough for three , adopt  0  Complete as  d00

1. 2. Convert characters into binary ASCII code

1. 3. Convert the converted binary , Separate every six digits

Q： Why does the first step need to be divided into three characters ？

A： because ASCII Code each character is 8 Bit binary ,3 * 8 = 24. It can be divided into 4 individual 6 Bit binary ,4 * 6 = 24.

1. 6 Bit binary can represent  0-63, We have a rainbow watch , Can be 0-63 Each corresponds to a character , The rainbow table is as follows ：

Through the rainbow table , We can put every 6 The binary after bit division is converted

It should be noted that , Where filling occurs  0, Need to use  =  To express . So the last two are  =

Last  abcd  Convert to Base64 After coding is  YWJjZA==, The overall principle is relatively simple , It doesn't involve sophisticated algorithms .

Base64 periphery

1. because  Base64  Transcoding will include  +/= character , stay URL Unable to transmit normally . So there is a kind of URL Friendly Base64 code , It exists and is used  _- Instead of  +/, And do not add  =

2. Base32、Base16 Principle and Base64 Almost the same

3. Base64 Not suitable for encryption , Because decryption is too simple

4. Chinese characters pass  gb2312、utf-8、gbk After the coding , It can be converted to binary processing . Here is a picture description on the Internet ：

   

Base58 And Base58Check

Base58 It is a coding form used by bitcoin when generating wallet address . It and Base64 The main difference is to remove the characters that are easy to be mistaken by the naked eye 0（ zero ）、O（ Capital O）、I（ Capital i）、l（ Lowercase letters L） And several characters that affect the double-click selection ：/ and + The purpose of this coding is relatively simple , Is to prevent transfer , Read the wrong account , Transfer to wrong account .Base58 The principle of is simpler , It only involves the conversion of Radix , The general steps are as follows ：

1. Convert characters to ASCII code

2. take ASCII Code to 58 Base number

3. Through rainbow table mapping

such as  abcd transformation ：

1. Turn into ASCII code 97-98-99-100

2. convert to 58 Base number 3-28-21-49-5-22

3. Map to 3VNr6P

Base58Check code , As the name suggests, it can be right Base58 Code to check . For example, I am transmitting  qH912cvztx When coding , If the network is abnormal and other reasons , Cause data disorder or loss , The receiver should be able to recognize that there is a problem with the data .Base58Check The basic principle of coding is as follows ：

1. stay data Add a version ID in front prefix, Used to identify the encoded data type , For example, the prefix of bitcoin address is 0（ Hex is 0x00）

2. adopt hash Algorithm calculation  prefix + data Of hash value ：SHA256(prefix + data)

3. The generated hash The value is truncated to the first four digits , Splice back  prefix + data + 4 position hash

4. Carry out the result generated in the previous step Base58 Coding calculation , Get the final result