Client side, server and data transmission method and system

The invention discloses a client side, a server and a data transmission method and system. The client side requests to be connected with the server, the server calculates a first public key and a matched first private key and sends the first public key to the client side, and the client side calculates a second public key and a second private key matched with the second public key and sends the second public key to the server. When the client side requests data from the server, the server encrypts the data through the second public key, the encrypted data is sent to the client side, the client side decrypts the data through the second private key matched with the second public key, and therefore the data is obtained. When the data is sent to the server through the client side, the client side encrypts the data to be sent through the first public key, the encrypted data is sent to the server, the server decrypts the data through the first private key matched with the first public key, and therefore the data is obtained. The public keys of the server and the client side are shared to encrypt information, only the respective private keys can be used for decryption, and therefore the safety of data transmission can be effectively improved.