Key agreements that use only password authentication are convenient in communication networks, but these key agreement schemes often fail to resist possible attacks, and therefore provide poor security compared with some other authentication schemes. To increase security, many authentication and key agreement schemes use smartcard authentication in addition to passwords. Thus, two-factor authentication and key agreement schemes using smartcards and passwords are widely adopted in many applications. Vaidya et al. recently presented a two-factor authentication and key agreement scheme for wireless sensor networks (WSNs). Kim et al. observed that the Vaidya et al. scheme fails to resist gateway node bypassing and user impersonation attacks, and then proposed an improved scheme for WSNs. This study analyzes the weaknesses of the two-factor authentication and key agreement scheme of Kim et al., which include vulnerability to impersonation attacks, lost smartcard attacks and man-in-the-middle attacks, violation of session key security, and failure to protect user privacy. An efficient and secure authentication and key agreement scheme for WSNs based on the scheme of Kim et al. is then proposed. The proposed scheme not only solves the weaknesses of previous approaches, but also increases security requirements while maintaining low computational cost.

Group authenticated key agreements (GAKAs) for an Internet of Medical Things (IoMT) enable medical sensor devices to authenticate each other and agree upon a common session key. These medical sensor devices can then establish a secure channel using this session key and exchange information securely. Owing to hardware limitations, sensors do not have sufficient computing power, energy, and storage resources to implement burdensome protocols. Moreover, sensors are easily damaged, causing the number of members of the group to change. Therefore, a group key agreement (GKA) protocol is required to consider dynamic groups and reduce the computational cost of an IoMT. The physical unclonable function (PUF) uses the uniqueness and randomness of its circuit to perform calculations. It has message fingerprints so that the user is not necessary to store a private key. The PUF is less computationally burdensome than the more common modular exponentiation and can be applied in an IoMT environment with limited resources. This article develops lightweight anonymous dynamic GAKA (DGAKA) that uses the PUF to solve the problems of data storage, transmission security, and computing efficiency that are faced by the IoMT. The proposed protocol has higher security and efficiency in computation and storage than those previously developed.