}
		key, err := decryptObjectMeta(key, o.Bucket, o.Name, o.UserDefined)
		if err != nil {
			return nil, err
		}
		mac := hmac.New(sha256.New, key)
		mac.Write([]byte(baseKey))
		return sio.DecryptBuffer(nil, input, sio.Config{Key: mac.Sum(nil)})
	}
}

// decryptPartsChecksums will attempt to decrypt and decode part checksums, and save
// only the decrypted part checksum values on ObjectInfo directly.