Recently, Tseng and Wu pointed out that the second protocol of Biswas's two-party keys scheme based on the Diffie-Hellman technique has a security weakness and proposed a new protocol to remedy the weakness. In this article, we point out that Tseng-Wu's protocol is vulnerable to a man-in-the-middle attack. An attacker could intercept, delete, or modify the communicated messages between two communicating party or among the group members. Keywords: Diffie-Hellman key-exchange, group key, man-in-the-middle attack, multiple two-party keys
