Those following this thread may be interested in checking out RFC 3548: <http://www.faqs.org/rfcs/rfc3548.html>. It appears to address some of the concerns raised in this thread and what the recommended practices are. It is worth noting the RFC 2045 states that decoders *must* ignore invalid characters when decoding. However, I believe RFC 2045 is ambiguous about '='. If it appears in the middle of input stream, it could imply end-of-data or an invalid character if you take the approach that '=' is only a valid base64 character at the end of encoded data. The following is written in the Security Considerations of RFC 3548: 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. --ewh
