PHP中如何进行对称和非对称加密？

$key = '123456789'; // 密钥

$data = 'Hello World'; // 待加密字符串

$iv = mcrypt_create_iv(mcrypt_get_block_size(MCRYPT_DES, MCRYPT_MODE_CBC), MCRYPT_RAND);

$cipher = mcrypt_encrypt(MCRYPT_DES, $key, $data, MCRYPT_MODE_CBC, $iv);

echo base64_encode($cipher); // 输出加密后的字符串

$cipher = base64_decode('JnFXVC9e+rzR8oUgM67Q0w=='); // 加密后的字符串

$key = '123456789'; // 密钥

$iv = mcrypt_create_iv(mcrypt_get_block_size(MCRYPT_DES, MCRYPT_MODE_CBC), MCRYPT_RAND);

$plain = mcrypt_decrypt(MCRYPT_DES, $key, $cipher, MCRYPT_MODE_CBC, $iv);

echo $plain; // 输出解密后的字符串

$data = 'Hello World'; // 待加密字符串

$res = openssl_pkey_new(); // 生成密钥对

openssl_pkey_export($res, $privateKey); // 获取私钥

$publicKey = openssl_pkey_get_details($res)["key"]; // 获取公钥

openssl_public_encrypt($data, $cipher, $publicKey); // 加密数据

echo base64_encode($cipher); // 输出加密后的字符串

$cipher = base64_decode('RvnOeNe+p8LtlpuUcq0wqFoX2yUaGXvY6FHlWpT0NQwzVQwVc

DSnkw4C6YJMvnsMH4N5JDP18RI8x7CFqUCdJg==');

// 加密后的字符串

$privateKey = '-----BEGIN PRIVATE KEY-----

...

-----END PRIVATE KEY-----'; // 私钥

openssl_private_decrypt($cipher, $plain, $privateKey); // 解密数据

echo $plain; // 输出解密后的字符串