为什么base64编码的字符串末尾有一个=符号 [英] Why does a base64 encoded string have an = sign at the end

问题描述

我知道 base64 编码是什么以及如何在 C# 中计算 base64 编码，但是我已经多次看到当我将字符串转换为 base64 时，有一个= 在最后.

I know what base64 encoding is and how to calculate base64 encoding in C#, however I have seen several times that when I convert a string into base64, there is an = at the end.

提出了几个问题:

1. base64 字符串是否总是以 = 结尾?
2. 为什么会在末尾附加 =?

1. Does a base64 string always end with =?
2. Why does an = get appended at the end?

推荐答案

Q base64字符串总是以=结尾吗?

A:没有.(USB这个词是base64编码成dXNi)

A: No. (the word USB is base64 encoded into dXNi)

Q 为什么最后会附加一个 =?

答:简短的回答:最后一个字符(="符号)仅作为补充(填充)在使用特殊字符数对消息进行编码的最终过程中添加.

A: As a short answer: The last character ("=" sign) is added only as a complement(padding) in the final process of encoding a message with a special number of characters.

如果您的字符串有 3 个字符的倍数，则不会有 '=' 符号，因为 Base64 编码需要每个 三个 字节(一个字符=1 字节) 并将它们表示为 ASCII 标准中的 四个 可打印字符.

You will not have a '=' sign if your string has a multiple of 3 characters number, because Base64 encoding takes each three bytes (a character=1 byte) and represents them as four printable characters in the ASCII standard.

示例:

(a)如果要编码

ABCDEFG <=>[ABC] [DEF] [G

ABCDEFG <=> [ABC] [DEF] [G

Base64 将处理第一个块(产生 4 个字符)和第二个块(因为它们是完整的).但是对于第三个，它将在输出中添加一个双 == 以完成所需的 4 个字符.因此，结果将是 QUJD REVG Rw==(没有空格).

Base64 will deal with the first block (producing 4 characters) and the second (as they are complete). But for the third it will add a double == in the output in order to complete the 4 needed characters. Thus, the result will be QUJD REVG Rw== (without spaces).

(b) 如果你想编码 ABCDEFGH <=>[ABC] [DEF] [GH

(b) If you want to encode ABCDEFGH <=> [ABC] [DEF] [GH

类似地，它只会在输出的末尾添加一个 = 以获得 4 个字符.

similarly, it will add just a single = in the end of the output to get 4 characters.

结果将是 QUJD REVG R0g=(不含空格).

The result will be QUJD REVG R0g= (without spaces).

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