}

func (d *DecryptBlocksReader) buildDecrypter(partID int) error {
	var partIDbin [4]byte
	binary.LittleEndian.PutUint32(partIDbin[:], uint32(partID)) // marshal part ID

	mac := hmac.New(sha256.New, d.objectEncryptionKey) // derive part encryption key from part ID and object key
	mac.Write(partIDbin[:])
	partEncryptionKey := mac.Sum(nil)

	// Limit the reader, so the decryptor doesn't receive bytes