I wrote this little program not too long ago when I was implementing IMAP protocol. Often, email handling software use MIME defined rules to deal with attachements. Base64 encoding is one of the encoding methods that is used to encode email. Why do you need to encode? Well as RFC1341 states, encoding is "applied to the data in order to allow it to pass through mail transport mechanisms which may have data or character set limitations.". The program is not too complicated and the algorithm is rather simple. I implemented the algorithm just for fun, and I post this information just for fun.

The current version of the code is the iteration number 6. The last three were posted here as I thought they were complete. I was very wrong as the first one was just bad in terms of performance (encoding 6 times slower than MS version), second version was a bit buggy (encoding slower just 2 times, but decoding 2 faster <-- none matter as the results were not always correct). I think now I have arrived at the final solution (with maybe one more mod to the decode routine) which produces correct results and runs fast (exact measurements will be posted soon). The component was tested with my helper random string generating utility and test harness which compared the MS and my generated base64 encodings and decodings.

You can get source. I am thinking to post the whole C# project.

Sample input (excerpt from RFC1341):

These values are not case sensitive.  That  is,  Base64  and
BASE64  and  bAsE64 are all equivalent.  An encoding type of
7BIT requires that the body is already in a seven-bit  mail-
ready representation.

Resulting output:

VGhlc2UgdmFsdWVzIGFyZSBub3QgY2FzZSBzZW5zaXRpdmUuICBUaGF0ICBpcywgIEJhc2U2
NCAgYW5kIEJBU0U2NCAgYW5kICBiQXNFNjQgYXJlIGFsbCBlcXVpdmFsZW50LiAgQW4gZW5j
b2RpbmcgdHlwZSBvZiA3QklUIHJlcXVpcmVzIHRoYXQgdGhlIGJvZHkgaXMgYWxyZWFkeSBp
biBhIHNldmVuLWJpdCAgbWFpbC1yZWFkeSByZXByZXNlbnRhdGlvbi4=

Like I said, the algorithm is pretty simple, just take 3 bytes of existing data, then make 4 6-bit pieces and use that to obtain the encoding. Read some RFCs or look at the source code that I will put up soon.

.NET frameworks offers the same functionality with Convert class that belongs to System namespace. I still like using my own version though :)