Abstract: This work investigates the group key agreement protocols，and points out that Wang et al’s key agreement protocol （Tree and Threshold Scheme，TST） is not only non-contributory，but also vulnerable to key control i.e.the sponsor of the key agreement can predetermine the group key.To over come the security flaws，this paper presents an improve scheme （I-TTS）.Security analysis indicate that I-TTS scheme is contributory，and no one can predetermine the negotiated group key.Further more，the I-TTS scheme is perfect forward secrecy.

摘要： 针对动态对等通信中的组密钥协商协议进行了分析和研究，指出王志伟等人提出的基于树结构和门限思想的组密钥协商协议（TTS）存在密钥控制和不等献性等缺陷，进而给出了一个改进的方案（I-TTS）。安全性分析表明，I-TTS协议不仅克服了TTS协议中的前向安全性和密钥控制缺陷，还满足等献性。