Abstract: Some narrowband IoT devices cannot use group authentication to access the core network due to resource constraints. Under the framework of 5G network access authentication， a large number of devices accessing the core network at the same time will cause the devices to wait in a queue and cause network congestion. Based on the RFC7228 standard on resource-constrained devices issued by the IETF working group， this paper proposes a group authentication scheme for 3 device types. Firstly， the security and congestion problems of 5G access authentication for narrowband IoT devices are pointed out; then， a solution group authentication scheme is proposed; finally， the access authentication methods are determined for three resource-constrained devices. Experimental results and performance and security analysis show that the proposed scheme meets the resource capabilities required for device group authentication. Compared with the 5G access authentication scheme， the proposed scheme can reduce the number of network signaling by more than 60%， and it decreases with the increase of devices in the group. In terms of security， it has the ability to resist replay attacks， man-in-the-middle attacks and Dos attacks.

Key words: NB-IoT； resource constrained devices； group authentication； 5G network authentication protocol, network congestion； IETF working group；