  Physical-layer group secret-key (GSK) generation is an effective way of
generating secret keys in wireless networks, wherein the nodes exploit inherent
randomness in the wireless channels to generate group keys, which are
subsequently applied to secure messages while broadcasting, relaying, and other
network-level communications. While existing GSK protocols focus on securing
the common source of randomness from external eavesdroppers, they assume that
the legitimate nodes of the group are trusted. In this paper, we address
insider attacks from the legitimate participants of the wireless network during
the key generation process. Instead of addressing conspicuous attacks such as
switching-off communication, injecting noise, or denying consensus on group
keys, we introduce stealth attacks that can go undetected against
state-of-the-art GSK schemes. We propose two forms of attacks, namely: (i)
different-key attacks, wherein an insider attempts to generate different keys
at different nodes, especially across nodes that are out of range so that they
fail to recover group messages despite possessing the group key, and (ii)
low-rate key attacks, wherein an insider alters the common source of randomness
so as to reduce the key-rate. We also discuss various detection techniques,
which are based on detecting anomalies and inconsistencies on the channel
measurements at the legitimate nodes. Through simulations we show that GSK
generation schemes are vulnerable to insider-threats, especially on topologies
that cannot support additional secure links between neighbouring nodes to
verify the attacks.
