+ (NSData *) dataWithBase32String:(NSString *)base32;
- (NSString *) base32String;
Do these methods exist in the Apple frameworks? They do exist in some third party extensions, see other answers, if you have another pre-packaged solution can you post a reference?
A quick google search reveals that CocoaDev has nice implementations of both of these methods. cocoadev.com/index.pl?NSDataCategory (it was also mentioned in the first answer)