Method for protecting the first message of security protocol

A method for protecting a fist message of a security protocol, comprising the steps of:

• 1) initializing
• pre-sharing, by an initiating device and a responding device, private information of a Pre-Shared Master Key, wherein the initiating device and the responding device possess the same Master Key Identifier identifying the Pre-Shared Master Key and support the same function of calculating a Message Integrity Code or a Message Authentication Code;
• 2) transmitting a first message by the initiating device
• calculating, by the initiating device, a Message Integrity Code or a Message Authentication Code on security parameters to be transmitted in the first message and the Pre-Shared Master Key with the function of calculating a Message Integrity Code or a Message Authentication Code, and transmitting to the responding device the first message comprising a non-security parameter, the security parameters, the Master Key Identifier and the Message Integrity Code or the Message Authentication Code;
• 3) receiving the first message by the responding device
• verifying, by the responding device, the non-security parameter in the first message for legality upon reception of the first message;
• and
• if the non-security parameter is illegal, discarding the first message and setting a status code to notify the initiating device or disconnecting a link;
• or if the non-security parameter is legal, calculating a Message Integrity Code or a Message Authentication Code on the security parameters in the first message and the locally stored Pre-Shared Master Key and comparing the calculated Message Integrity Code or Message Authentication Code with the received Message Integrity Code or Message Authentication Code;
• and
• if the calculated Message Integrity Code or Message Authentication Code is different from the received Message Integrity Code or Message Authentication Code, discarding the first message and setting a status code to notify the initiating device or disconnecting the link;
• otherwise, further verifying the security parameters in the first message for legality;
• and
• if there is an illegal value in the security parameters, discarding the first message and setting a status code to notify the initiating device or disconnecting the link.