無線電叫人系統是一單向通信系統，目前台灣所通用的系統共
有二種，分別是低速率之POSAG (Post Office Code Standardization
Advisory Group)系統與高速率之FLEX系統，而此二系統對空中介
面所傳送的資料並無保密安全措施，任何人只要有類似信號截取分
析器之相關設備，對準相同之頻率，即可截取用戶之相關資料。本
論文針對現行無線電叫人系統安全機制之缺失，提出以祕密金鑰密
碼系統為基礎之安全機制，做為系統改進研究之參考。
為使密文達到混淆及散佈的效果並防禦窮舉式攻擊法的攻擊，
本研究結合隨機亂數與IDEA祕密金鑰密碼系統建構本系統之安全
機制，經由模擬結果顯示其速度與效能符合無線電叫人系統之需求。
同時為系統之週延與完整，本研究並就系統管理之運作，提出一可
供遵循之準則，以提高系統的強健性。

Current radio paging system utilized in Taiwan is a one-way communication system without security protection. It is known that people can do multiple reproduction of any code for fraud. There is a great need to develop a security protection algorithm for avoiding illegal application. The carrier frequencies of POSAG ( Post Office Code Standardization Advisory Group) system and FLEX system can be scanned and grabbed with signaling analyzer and applied by an unlawful user.
In order to develop an applicable security algorithm for above two communication systems With secret key concept. The technique of random number and the secret key cryptography of IDEA are organized in this study to encode the transmitted signal and lessen the attack of exhausted method used by unlawful user. The results of simulation show that the speed and security of encryption and decryption are better than current communication system. The robustness of randomized cryptography of IDEA has been improved to applicable level. The recommended security management system can be used in the current communication system.