PHPを使用して安全な暗号化通信システムを構築するにはどうすればよいですか?

<?php
$message = "Hello, World!";
$key = "mysecretkey";

$encrypted = openssl_encrypt($message, "AES-128-CBC", $key);
$decrypted = openssl_decrypt($encrypted, "AES-128-CBC", $key);

echo "加密后的数据：" . $encrypted . "
";
echo "解密后的数据：" . $decrypted . "
";
?>

<?php
$config = array(
    "private_key_bits" => 2048,
    "private_key_type" => OPENSSL_KEYTYPE_RSA,
);

$privateKey = openssl_pkey_new($config);

openssl_pkey_export($privateKey, $privateKeyString);

$publicKey = openssl_pkey_get_details($privateKey);
$publicKeyString = $publicKey["key"];

echo "私钥：" . $privateKeyString . "
";
echo "公钥：" . $publicKeyString . "
";
?>

<?php
$message = "Hello, World!";
$publicKeyString = "-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDDZ99JBqIN8vqTUijnoJLVe2fE
...
-----END PUBLIC KEY-----";

openssl_public_encrypt($message, $encrypted, $publicKeyString);

echo "加密后的数据：" . base64_encode($encrypted) . "
";
?>

<?php
$encrypted = base64_decode("encrypted data");
$privateKeyString = "-----BEGIN PRIVATE KEY-----
MIICdgIBADANBgkqhkiG9w0BAQEFAASCAmAwggJcAgEAAoGBANnPwpZwQkCrA704
...
-----END PRIVATE KEY-----";

openssl_private_decrypt($encrypted, $decrypted, $privateKeyString);

echo "解密后的数据：" . $decrypted . "
";
?>