err = errors.New("Object is not encrypted")
		return
	}

	if rs == nil {
		// No range, so offsets refer to the whole object.
		return 0, o.Size, 0, 0, 0, nil
	}

	// Assemble slice of (decrypted) part sizes in `sizes`
	var sizes []int64
	var decObjSize int64 // decrypted total object size
	if o.isMultipart() {
		sizes = make([]int64, len(o.Parts))
		for i, part := range o.Parts {