Base64 Encoding safe for filenames?

Question

Is Base64 encoding safe to use for filenames on Windows and Linux systems? From my research I have found that replacing all / characters of the result with - or _ should resolve any issues.

Can anyone provide more details on this?

Currently in Java I am using the following peice of code:

MessageDigest md5Digest = MessageDigest.getInstance("MD5");
md5Digest.reset();
md5Digest.update(plainText.getBytes());

byte[] digest = md5Digest.digest();

BASE64Encoder encoder = new BASE64Encoder();
hash = encoder.encode(digest);
hash.replace('/','_');

Answer 1

Modified Base64 (when /,= and + are replaced) is safe to create names but does not guarantee reverse transformation due to case insensitivity of many file systems and urls.

Base64 is case sensitive, so it will not guarantee 1-to-1 mapping in cases of case insensitive file systems (all Windows files systems, ignoring POSIX subsystem cases). Most urls also case insensitive preventing 1-to-1 mapping.

I would use Base32 in this case - you'll get names a bit longer, but Base32 encoded values are 100% safe for file/uri usage without replacing any characters and guarantees 1-to-1 mapping even in cases of insensitive environment (FAT/Win32 NTFS access).

Unfortunately there is usually no built-in support for this encoding in frameworks. On other hand code is relatively simple to write yourself or find online.

http://en.wikipedia.org/wiki/Base32.