read.go
func NewReader(f io.ReaderAt, size int64) (*Reader, error) {
	return NewReaderEncrypted(f, size, nil)
}
func NewReader(f io.ReaderAt, size int64) (*Reader, error) {
	return NewReaderEncrypted(f, size, nil)
}
// NewReader opens a file for reading, using the data in f with the given total size.