Due to the rapid growth of the Internet of Things (IoT), secure communication is becoming a significant concern. Nodes that compose such a dynamic network need to exchange sensitive and valuable data. The data must be kept safe against attacks. This protection requires the development of efficient key management protocols. However, this task is challenging because of the high resource constraints of most IoT devices in terms of storage, communication, processing, and energy capabilities. Some existing key management techniques have certain weaknesses since sensitive parameters are not protected during transmission, and cryptographic keys are stored in plain text and usually renewed at a fixed period of time. This paper proposes a new key management protocol aiming to secure communications before and after key establishment. Our scheme uses hash and one–one functions to achieve security during the key establishment process. The symmetrical character of the invertible functions is thus exploited to conceal critical data and pairwise keys stored in nodes’ memories. Moreover, the key refresh period is variable, which can be adjusted according to the number of occurred attacks in the network. BAN (Burrows Abadi Needham) logic is employed to assess the correctness of the proposed scheme. The results show that our scheme operates correctly and does not have redundancies or security flaws. Furthermore, the security and performance analysis point out that the proposed scheme is resilient against well-known attacks, and efficient in terms of storage, communication, computation overhead, and energy consumption.