base64 - Base64 编码时删除尾随 "="

Question

我注意到每当我对字符串进行 Base64 编码时，都会在末尾附加一个“=”。我可以删除这个字符，然后通过将其添加回去来可靠地解码它吗？或者这很危险吗？换句话说，“=”总是附加，还是仅在某些情况下附加？

我希望编码的字符串尽可能短，这就是为什么我想知道是否可以删除“=”字符并在解码之前将其添加回来。

Answer 1

= 是填充。 <!------------>

Wikipedia说

An additional pad character is allocated which may be used to force the encoded output into an integer multiple of 4 characters (or equivalently when the unencoded binary text is not a multiple of 3 bytes) ; these padding characters must then be discarded when decoding but still allow the calculation of the effective length of the unencoded text, when its input binary length would not be a multiple of 3 bytes (the last non-pad character is normally encoded so that the last 6-bit block it represents will be zero-padded on its least significant bits, at most two pad characters may occur at the end of the encoded stream).

如果您控制另一端，则可以在传输时将其移除，然后在解码之前重新插入(通过检查字符串长度)。
请注意，数据在传输中不会是有效的 Base64。

另外，另一位用户指出(与 PHP 用户相关):

Note that in PHP base64_decode will accept strings without padding, hence if you remove it to process it later in PHP it's not necessary to add it back. – Mahn Oct 16 '14 at 16:33

因此，如果您的目标是 PHP，您可以安全地去除填充并进行解码，而无需进行复杂的计算。