base 64编码的有效字符范围 [英] Range of valid character for a base 64 encoding

问题描述

我对以下内容感兴趣：

是否有从不作为基本64位编码字符串的一部分出现的字符列表？

例如 * 。我不确定这是否会发生。如果原始输入实际上有 * 作为其中一部分的编码方式不同？

I am interested in the following:
Is there a list of characters that would never occur as part of a base 64 encoded string?
For example *. I am not sure if this would occur or not. If the original input actually had * as part of it would that be encoded differently?

推荐答案

以下是我可以提出的建议： RFC 4648

Here is what I could turn up: RFC 4648

它包括这个方便的表格：

It includes this convenient table:

                  Table 1: The Base 64 Alphabet

 Value Encoding  Value Encoding  Value Encoding  Value Encoding
     0 A            17 R            34 i            51 z
     1 B            18 S            35 j            52 0
     2 C            19 T            36 k            53 1
     3 D            20 U            37 l            54 2
     4 E            21 V            38 m            55 3
     5 F            22 W            39 n            56 4
     6 G            23 X            40 o            57 5
     7 H            24 Y            41 p            58 6
     8 I            25 Z            42 q            59 7
     9 J            26 a            43 r            60 8
    10 K            27 b            44 s            61 9
    11 L            28 c            45 t            62 +
    12 M            29 d            46 u            63 /
    13 N            30 e            47 v
    14 O            31 f            48 w         (pad) =
    15 P            32 g            49 x
    16 Q            33 h            50 y

因此，匹配任何应该从不出现在Base 64编码中的字符的正则表达式将是：

So a regular expression that matches any character that should never appear in Base 64 encodings would be:

[^A-Za-z0-9+/=]

然而，正如kapeps回答指出的那样，这只是建议。具体实现可能会选择一组不同的64个字符。 （事实上​​，即使链接的RFC包含URL和文件名安全编码的替代表，它将字符62和63替换为 - 和 _ 。所以我想这实际上取决于创建编码的实现。

However, as kapeps answer points out, this is only the recommendation. Specific implementations might choose a different set of 64 characters. (In fact, even the linked RFC contains an alternative table for URL and filename safe encoding, which replaces character 62 and 63 with - and _ respectively). So I guess it really depends on the implementation that created the encoding.

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