PHP で OpenSSL を使用してファイルを暗号化および復号化するにはどうすればよいですか?

// ENCRYPT FILE
function encryptFile() {
    $key = generateKey(); // Function to generate a secure encryption key
    $iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length('aes-128-cbc')); // Generate a random initialization vector

    $plaintext = file_get_contents(PATH . '/ftpd/' . $file);
    $encrypted = openssl_encrypt($plaintext, 'aes-128-cbc', $key, OPENSSL_RAW_DATA, $iv);

    $encryptedFile = fopen(PATH . '/encrypted/' . $file . '.txt', 'w');
    fwrite($encryptedFile, $iv . $encrypted);
    fclose($encryptedFile);

    unlink(PATH . '/ftpd/' . $file);
}

// DECRYPT FILE
function decryptFile() {
    $key = generateKey(); // Function to generate the same encryption key used in encryption

    if ($handle = opendir(PATH . '/encrypted')) {
        while (false !== ($file = readdir($handle))) {
            if ($file != "." && $file != "..") {
                $encryptedFile = fopen(PATH . '/encrypted/' . $file, 'r');
                $encryptedData = fread($encryptedFile, filesize(PATH . '/encrypted/' . $file));

                $iv = substr($encryptedData, 0, openssl_cipher_iv_length('aes-128-cbc'));
                $decrypted = openssl_decrypt(substr($encryptedData, openssl_cipher_iv_length('aes-128-cbc')), 'aes-128-cbc', $key, OPENSSL_RAW_DATA, $iv);

                $decryptedFile = fopen(PATH . '/decrypted/' . $file, 'w');
                fwrite($decryptedFile, $decrypted);
                fclose($decryptedFile);

                // unlink(PATH . '/encrypted/' . $file);
            }
        }
        closedir($handle);
    }
}