Nowadays, most of the applications are distributed and require two or more parties to establish a secure communication channel over an open network. Key management is one of the major security issues in such applications. A good security system should reduce more complex problems related to the proper key management and secure-saving of a little number of secret keys at every endpoint. So it is difficult to save one key secretly, and the difficulty will be more and more if the number of secret keys increased. In the literature, many schemes have been proposed for key distribution and management. Although, such schemes have reduced the number of secret keys stored at the users to only one key, Key Distribution Center (KDC), known here as Key Managing Center (KMC), still maintains a shared secret key with each user in the network. In this paper, we propose a method to reduce the number of secret keys stored at the KDC to only one key, regardless of the network size. In the proposed method, the KMC will store a unique stuff data for every user. The user's secret key will be generated by taking the stuff data, adding the lifetime of the secret key, and then hashing the resulting string using the manager secret key. The output digest will be used as the user's secret key. By this way, KMC will only store one key called the manager secret key. Furthermore, we will combine the proposed method with our previous work to build an efficient key management model. Analysis and experimental results indicate that the developed model is highly secure, practical and efficient.