NSDATA+Base64 wrapper UTF8 issue

gistfile1.txt

class Base64
  def self.encode64(string)
    NSData.alloc.initWithData(string).base64EncodedString
  end

  def self.decode64(string)
    data = NSData.dataFromBase64String(string)
    NSString.alloc.initWithData(data, encoding:NSUTF8StringEncoding)
  end
end

This does not work as https://github.com/mattgemmell/MGTwitterEngine/blob/master/NSData+Base64.m expects and returns dataUsingEncoding:NSASCIIStringEncoding .