// is more efficient than decrypting ETags sequentually.
func DecryptETags(ctx context.Context, k kms.KMS, objects []ObjectInfo) error {
	const BatchSize = 250 // We process the objects in batches - 250 is a reasonable default.
	var (
		metadata = make([]map[string]string, 0, BatchSize)
		buckets  = make([]string, 0, BatchSize)
		names    = make([]string, 0, BatchSize)
	)
	for len(objects) > 0 {