Secure communication system, method, and device

A secure communication method, comprising: a first communication party sends a multilevel-encrypted key data packet to a second communication party to execute security authentication between the first communication party and the second communication party; and the first communication party sends a multilevel-encrypted instruction data packet to the second communication party to send instruction data to the second communication party. The present invention also provides a secure communication system and device. The present invention is able to prevent replay attacks in a communication system.