public ByteString fileKey(KeyBag keyBag,ICloud.MBSFile file){
  return fileKey(keyBag,file,aesWraps.get(),sha256s.get());
}

public ByteString fileKey ( KeyBag keyBag , ICloud . MBSFile file ) { return fileKey ( keyBag , file , aesWraps . get ( ) , sha256s . get ( ) ) ; }
returns the file key for the given file or null if unavailable .
