VPN, or Virtual Private Network, is a technology that encrypts and tunnels Internet connections to provide users with secure connections and privacy protection on public networks. Its principles are as follows:

1. Encryption: When a user connects to a VPN, the VPN uses encryption protocols to encrypt all data to protect the security of data transmission over public networks.

2. Tunneling: The VPN establishes an encrypted channel, called a VPN tunnel, between the user and the VPN server. All network traffic from the user is transmitted through this tunnel to the VPN server instead of directly over the public network.

3. Routing: Once the user’s data arrives at the VPN server, the VPN decrypts the data and routes it to its destination. If the user wants to access certain websites on the Internet, the VPN server will perform proxy services on the user’s request to make the request appear to come from the VPN server rather than the user’s device.

4. IP address: The VPN also provides the user with a virtual IP address. This address is assigned from the VPN server instead of the user’s local ISP. This means that the user’s real IP address is hidden, thereby improving the user’s privacy and security.

In summary, VPN provides users with a secure and private network connection by using encryption, tunneling, routing, and virtual IP address technology, protecting user privacy and security when accessing public networks.