随着互联网和移动增值业务的迅猛发展，用户规模与市场规模不断扩大，以及国内 3G时代的到来，移动增值业务必将成为拉动整个通信行业的新亮点。考虑到消息在空中传输的安全性，设计并实现了空中下载技术（OTA）系统的密钥管理，加入MAC（消息验证码）保证数据的安全性，从而保证了数据在服务器端和USIM卡端传输的安全性和完整性，为开展移动增值业务提供了安全保障。

With the rapid development of the Internet and the mobile value added services, the increasingly expansion of users and markets and the coming of Chinas 3G Time, the mobile value added services will be a bright spot to uplift the mobile communication industry. In this paper, the writer studied the security issue of transferring messages with mobile devices, and planned and realized the key management of OTA system by adding MAC (message authentication code) to ensure data security. It ensures the safety and completeness of the data transformation between the server and the USIM card; therefore it provides the guarantee to the launch of the mobile value added services.