base64 что это

Ответ от Super Light[гуру]
В спецификации все четко написано!! !
8. Security Considerations
When implementing Base encoding and decoding, care should be taken
not to introduce vulnerabilities to buffer overflow attacks, or other
attacks on the implementation. A decoder should not break on invalid
input including, e.g., embedded NUL characters (ASCII 0).
If non-alphabet characters are ignored, instead of causing rejection
of the entire encoding (as recommended), a covert channel that can be
used to "leak" information is made possible. The implications of
this should be understood in applications that do not follow the
recommended practice. Similarly, when the base 16 and base 32
alphabets are handled case insensitively, alteration of case can be
used to leak information.
Base encoding visually hides otherwise easily recognized information,
such as passwords, but does not provide any computational
confidentiality. This has been known to cause security incidents
when, e.g., a user reports details of a network protocol exchange
(perhaps to illustrate some other problem) and accidentally reveals
the password because she is unaware that the base encoding does not
protect the password.
Super Light
Просветленный
(23894)
там написано, что декодирование недолжно прекращаться, неверные символы просто выкидываюся всей 4-ой.
а третий я не понял вопрос вообще.