RSA简洁幽雅，但计算速度比较慢，通常加密中并不是直接使用RSA 来对所有的信息进行加密， 最常见的情况是随机产生一个对称加密的密钥，然后使用对称加密算法对信息加密，之后用 RSA对刚才的加密密钥进行加密。-RSA elegant simplicity, but the computing speed is relatively slow, usually not direct the use of encryption in the RSA to encrypt all the information, the most common situation is a random symmetric encryption key, and then use symmetric encryption algorithm for encryption of information, just after the use of RSA encryption keys for encryption.