bash base64产生不一致的输出？(bash base64 producing inconsistent output?)

bash base64产生不一致的输出？(bash base64 producing inconsistent output?)

有谁能解释一下？

[vagrant@centos ~]$ echo "10IXydrdsc4DVAgxzrXldNw5GMeVAHKG:TAO04JuWz4PBVWYm" | base64 MTBJWHlkcmRzYzREVkFneHpyWGxkTnc1R01lVkFIS0c6VEFPMDRKdVd6NFBCVldZbQo= [vagrant@centos ~]$ echo "MTBJWHlkcmRzYzREVkFneHpyWGxkTnc1R01lVkFIS0c6VEFPMDRKdVd6NFBCVldZbQ==" | base64 -d 10IXydrdsc4DVAgxzrXldNw5GMeVAHKG:TAO04JuWz4PBVWYm

第一个字符串在末尾用o=编码，但最后在末尾用==编码的字符串，解码为相同的原始字符串......

GNU bash，版本4.1.2（1）-release（x86_64-redhat-linux-gnu）

Can anyone explain this?

[vagrant@centos ~]$ echo "10IXydrdsc4DVAgxzrXldNw5GMeVAHKG:TAO04JuWz4PBVWYm" | base64 MTBJWHlkcmRzYzREVkFneHpyWGxkTnc1R01lVkFIS0c6VEFPMDRKdVd6NFBCVldZbQo= [vagrant@centos ~]$ echo "MTBJWHlkcmRzYzREVkFneHpyWGxkTnc1R01lVkFIS0c6VEFPMDRKdVd6NFBCVldZbQ==" | base64 -d 10IXydrdsc4DVAgxzrXldNw5GMeVAHKG:TAO04JuWz4PBVWYm

The first string encodes with o= at the end, but the encoded string with == at the end instead, decodes to the same original string...

GNU bash, version 4.1.2(1)-release (x86_64-redhat-linux-gnu)

最满意答案

比较这些

echo "10IXydrdsc4DVAgxzrXldNw5GMeVAHKG:TAO04JuWz4PBVWYm" | base64 | od -c echo "MTBJWHlkcmRzYzREVkFneHpyWGxkTnc1R01lVkFIS0c6VEFPMDRKdVd6NFBCVldZbQ==" | base64 -D | od -c echo "MTBJWHlkcmRzYzREVkFneHpyWGxkTnc1R01lVkFIS0c6VEFPMDRKdVd6NFBCVldZbQo=" | base64 -D | od -c

如果我们在使用echo时没有发送换行符o缺少o ，请看看这个...

echo -n "10IXydrdsc4DVAgxzrXldNw5GMeVAHKG:TAO04JuWz4PBVWYm" | base64

这是被编码的换行符，它给出o=

=是填充，它可能并不总是在那里。 看看这里..

https://en.wikipedia.org/wiki/Base64#Padding

不同的实现也可以使用不同的填充字符。 你可以在这里看到一些不同之处

https://en.wikipedia.org/wiki/Base64#Variants_summary_table

来自RFC

3.2。 填充编码数据

在某些情况下，不需要或使用在基本编码数据中使用填充（“=”）。 在一般情况下，当不能进行关于传输数据大小的假设时，需要填充以产生正确的解码数据。

实现必须在编码数据的末尾包括适当的填充字符，除非引用本文档的规范另有明确说明。

base64和base32字母表使用填充，如下面第4和第6节所述，但base16字母表不需要它; 看到 第8节。

Compare these

echo "10IXydrdsc4DVAgxzrXldNw5GMeVAHKG:TAO04JuWz4PBVWYm" | base64 | od -c echo "MTBJWHlkcmRzYzREVkFneHpyWGxkTnc1R01lVkFIS0c6VEFPMDRKdVd6NFBCVldZbQ==" | base64 -D | od -c echo "MTBJWHlkcmRzYzREVkFneHpyWGxkTnc1R01lVkFIS0c6VEFPMDRKdVd6NFBCVldZbQo=" | base64 -D | od -c

If we don't send the newline when using echo the o is missing, have a look at this...

echo -n "10IXydrdsc4DVAgxzrXldNw5GMeVAHKG:TAO04JuWz4PBVWYm" | base64

It's the newline that's being encoded that gives the o in o=

The = is padding and it might not always be there. Have a look here..

https://en.wikipedia.org/wiki/Base64#Padding

Different implementations may also use different padding characters. You can see some of the differences here

https://en.wikipedia.org/wiki/Base64#Variants_summary_table

From the RFC

3.2. Padding of Encoded Data

In some circumstances, the use of padding ("=") in base-encoded data is not required or used. In the general case, when assumptions about the size of transported data cannot be made, padding is required to yield correct decoded data.

Implementations MUST include appropriate pad characters at the end of encoded data unless the specification referring to this document explicitly states otherwise.

The base64 and base32 alphabets use padding, as described below in sections 4 and 6, but the base16 alphabet does not need it; see section 8.