  Authentication is the first defence mechanism in many electronic systems,
including Internet of Things (IoT) applications, as it is essential for other
security services such as intrusion detection. As existing authentication
solutions proposed for IoT environments do not provide multi-level
authentication assurance, particularly for device-to-device authentication
scenarios, we recently proposed the M2I (Multi-Factor Multi-Level and
Interaction based Authentication) framework to facilitate multi-factor
authentication of devices in device-to-device and device-to-multiDevice
interactions. In this paper, we extend the framework to address group
authentication. Two Many-to-One (M2O) protocols are proposed, the Hybrid Group
Authentication and Key Acquisition (HGAKA) protocol and the Hybrid Group Access
(HGA) protocol. The protocols use a combination of symmetric and asymmetric
cryptographic primitives to facilitate multifactor group authentication. The
informal analysis and formal security verification show that the protocols
satisfy the desirable security requirements and are secure against
authentication attacks.
