使用先生成一个密码a（数据少），再用自己私钥对a进行非对称加密，

加密后，用对方的公钥对加密后的数据进行非对称加密。生成密文b

然后，用密码a对大文档进行对称加密。生成密文c

把b、c发给对方。

对方收到b、c后，解密。

解密过程正好相反。

将b用自己的私钥解密，再用对方的公钥解密，解出密码d，

再用密码d对c解密。OK

这样可以保证，自己的合法性，只有自己有自己的私钥，

对方，用对方的公钥加密后，只有对方用他的私钥才解得开。-Mr. into a password to use a (insufficient data), and then a right to conduct its own private key asymmetric cryptography, encryption, you use each other' s public key to the encrypted data, the non-symmetric encryption. Generating ciphertext b then a large document with a password for symmetric encryption. Generating ciphertext c to b, c distributed to the other side. The other received b, c, after decryption. Decryption process just the opposite. Will b with their own private key to decrypt, and then each other' s public key to decrypt, solve the PIN d, then d for c decryption password. OK This will guarantee the legitimacy of their own, only that they have their own private key, the other party, using each other' s public key encryption, only the other side with his private key only solution was to open.