func newAesDecryptReader(r io.Reader, key, iv []byte) *cipherBlockReader {
	block, err := aes.NewCipher(key)
	if err != nil {
		panic(err)
	}
	mode := cipher.NewCBCDecrypter(block, iv)

	return newCipherBlockReader(r, mode)
}
func newAesDecryptReader(r io.Reader, key, iv []byte) *cipherBlockReader {
	block, err := aes.NewCipher(key)
	if err != nil {
		panic(err)
	}
	mode := cipher.NewCBCDecrypter(block, iv)

	return newCipherBlockReader(r, mode)
}
// newAesDecryptReader returns a cipherBlockReader that decrypts input from a given io.Reader using AES.
// It will panic if the provided key is invalid.