Cifrado de datos en PHP

<?php
$plaintext = "test@test.com";
$key = "secret";

$method = "AES-256-CBC";

$iv_length = openssl_cipher_iv_length($method);
$iv = openssl_random_pseudo_bytes($iv_length);
$ciphertext = openssl_encrypt($plaintext, $method, $key, OPENSSL_RAW_DATA, $iv);
$ciphertext = base64_encode($iv . $ciphertext);
echo "cifrado: " . $ciphertext . "\n";

$ciphertext = base64_decode($ciphertext);
$iv_decoded = substr($ciphertext, 0, $iv_length);
$ciphertext_decoded = substr($ciphertext, $iv_length);
$plaintext_decoded = openssl_decrypt($ciphertext_decoded, $method, $key, OPENSSL_RAW_DATA, $iv_decoded);
echo "descifrado: " . $plaintext_decoded . "\n";